Quantum Computing Research Archive

Guest Post by Edwin Mata, Co-Founder and CEO of Brickken Building financial infrastructure is strange: you have to make decisions today for assets that may still exist long after the underlying technology has changed. That is especially true in tokenization because a bond issued on-chain today might mature in twenty years. An interest in a private company could sit on a cap table for decades. Real estate, private credit, funds and other assets being brought on-chain involve legal rights and economic relationships that can persist for a very long time. So when we talk about quantum computing and finance, I think the useful question is not when a sufficiently powerful quantum computer will arrive. I do not know, and I am skeptical of anyone who gives you a precise date. The alternative question is much more practical: are we building tokenized financial infrastructure that can evolve when the cryptography securing it needs to evolve? I think we can, but only if we build adaptability into the architecture now. An asset may need to outlive the technology supporting it. We have already seen this problem, on a smaller scale, throughout the history of technology: protocols change, security assumptions evolve and networks are upgraded. Software that looked perfectly adequate ten years ago becomes obsolete. Financial assets are different because you cannot simply treat them as old software and replace them. Consider an investment administered through a digital asset. There is an issuer. There are ownership records. Restrictions may limit who can hold or receive the investment. There are compliance obligations, contractual rights, reporting requirements and potentially several intermediaries interacting with it. The applicable law and governing documents determine the investor’s rights. Now imagine that the cryptographic environment changes and the asset needs to move to new infrastructure. What exactly are we migrating? Moving the token is only one part of the problem.

Insider Brief Fujitsu developed what it describes as the world’s first working diamond-spin quantum computer prototype integrating tin-vacancy centers with photonic circuits. The prototype operates at minus 271.6 degrees Celsius and can be accessed through Fujitsu ’s Hybrid Quantum Computing Platform. Fujitsu plans to develop a multi-module prototype by 2027 and is exploring integration with superconducting quantum computers. Image: The diamond-spin quantum computer prototype. ( Fujitsu ) PRESS RELEASE — Fujitsu today announced that it has developed the world’s first working prototype of a diamond-spin quantum computer incorporating tin-vacancy (SnV) centers into photonic integrated circuits [1] [2]. The prototype can be operated at -271.6°C, higher than the typical operating temperature of superconducting quantum computers (-273.13°C) and Fujitsu has demonstrated in a test environment that it can be utilized via the Fujitsu Hybrid Quantum Computing Platform without any additional specialist knowledge. This development represents an important milestone toward realizing a modular architecture, one of the most promising approaches for scaling quantum computers, due to its high fidelity and efficient optical connectivity. The prototype is based on the results of joint research started in 2020 by Fujitsu , Delft University of Technology , and QuTech , a world-leading quantum technology research institute and part of TU Delft . Fujitsu is set to develop a prototype of a multi-module diamond-spin quantum computer by 2027. In addition, Fujitsu will begin developing of technologies to integrate diamond-spin approach with superconducting approach, driving progress toward achieving large-scale quantum computers. This initiative comes as part of Fujitsu’s quantum roadmap, which outlines company’s aim to realize practical quantum computing by 2030. Comment from Vivek Mahajan, Corporate Executive Officer, Corporate Vice President, CTO, in charge of System Platform, Fujitsu

Insider Brief Singapore and Luxembourg plan to deepen cooperation in quantum computing, artificial intelligence, space technology and satellite communications. The countries are major financial hubs with strong investment ties and limited domestic markets. Their leaders also discussed closer ASEAN-EU relations and support for international stability, trade and the rule of law. Singapore and Luxembourg plan to deepen cooperation in quantum computing, artificial intelligence, space technology and satellite communications as the two small, trade-dependent nations seek closer economic and strategic ties. Singapore Prime Minister Lawrence Wong identified the technologies as emerging and critical areas for collaboration during an official lunch for Luxembourg Prime Minister Luc Frieden on Sept. 7, according to Asia News Network . Frieden was visiting Singapore from Sept. 6 to 8, his first official trip to the country since becoming prime minister. The visit also followed Luxembourg’s opening of its first resident embassy in Singapore, a step Wong described as a “strong signal” of Luxembourg’s commitment to greater engagement with Singapore and Southeast Asia. The proposed technology cooperation builds on extensive financial and commercial ties between the countries. Luxembourg is the largest European Union investor in Singapore, while Singapore ranks as Luxembourg’s second-largest investment destination within the bloc, Wong said. Although no specific projects, funding commitments or timelines were announced, the focus on quantum computing, AI and satellite communications points toward industries with both commercial and national-security importance. Quantum computers are designed to use quantum physics to perform certain calculations that could prove difficult for conventional machines. AI is becoming central to finance, manufacturing and government services, while satellites support communications, navigation and Earth observation. Shared Ambitions Wong, who also serves

Physicists at the BESIII Collaboration have breathed new life into a decades-old test of one of the Standard Model's most important ideas, using a technique that had gone almost untouched by experimenters for 35 years.

Insider Brief India’s Global Fintech Fest 2026 is set to open in Mumbai on September 8, with quantum technology, agentic AI and tokenization among the main topics on the agenda. The four-day event will bring together regulators, financial institutions, technology companies, investors and academics to discuss emerging technologies and financial systems. Maharashtra officials are positioning Mumbai as a fintech hub, citing the state’s startup and investment activity, data-center capacity and fintech-specific policies. Photo from Unsplash by Rahul Sapra . Prime Minister Narendra Modi is set to open the seventh Global Fintech Fest (GFF) in Mumbai on Tuesday, kicking off a four-day programme running September 8 through 11 that brings together regulators, financial institutions, technology firms, investors, and academics, the Free Press Journal reported . The event, which has run annually since 2020, carries the theme “Potential to Impact: Agentic AI, Tokenisation, Quantum – Trusted, Connected, Global Systems for Inclusive Finance.” Organizers said sessions will focus on how agentic AI, programmable finance, quantum technologies, and other emerging fields can produce measurable outcomes for citizens, enterprises, and economies globally, according to a government statement cited by the publication. Maharashtra Chief Minister Devendra Fadnavis has also sought to position Mumbai as India’s fintech capital, rather than solely as a financial center. He said the city has historically underused its position as a banking and capital markets hub, and argued that combining that financial base with digital infrastructure is helping Mumbai develop into a broader fintech hub. Responding to comparisons with Bengaluru and Hyderabad, the chief minister said Maharashtra leads India in total startups, venture funding, and unicorns, with fintech companies driving much of that activity. He added that the state hosts more than 60% of India’s total data center capacity,

NEC Corporation has ceased its research and development into superconducting quantum computers, shifting focus to quantum-inspired annealing and classical emulation due to long commercialization timelines and high capital investment. This move, reported by Nikkei Asia, means NEC will now concentrate on software and optimization services, leaving Fujitsu as the main domestic corporate developer of superconducting hardware in Japan. The post NEC Discontinues Superconducting Quantum Computer Development to Focus on Annealing and Classical Emulation appeared first on Quantum Computing Report .

Guest Post by Somtochukwu Igwegbe, African Quantum Consortium Correspondent, Research & Development, Quantum Africa. Quantum computing hardware is being built almost entirely outside Africa, in laboratories across North America, Europe, and Asia. That fact has shaped how the continent is usually written into the story: as a market to eventually reach, not a place doing the research. The second edition of the Quantum Machine Learning for Africa (QML4Africa) workshop, organized by Quantum Africa and held in August as part of Deep Learning Indaba 2026 in Lagos, Nigeria, was built around a different premise: that African researchers should be building with quantum tools now, while the field is still taking shape, rather than waiting to be introduced to it later. I attended the workshop as part of its organizing team, moving between sessions and conversations over the course of the day. From Kigali to Lagos QML4Africa began a year earlier in Kigali, Rwanda, as part of Deep Learning Indaba 2025. Organizers billed it at the time as the first QML workshop dedicated to the African continent , organized by Quantum Africa, with instruction led by researchers from IBM Research Africa and New York University Abu Dhabi . That inaugural edition was structured as a half-day, hands-on programme built around IBM’s Qiskit programming framework, with that year’s focus on using quantum machine learning models for cancer classification from histopathology images. The Lagos edition kept that hands-on structure while widening the material. Sessions covered quantum machine learning , quantum data preprocessing, quantum natural language processing, quantum optimization, and quantum error mitigation, alongside discussions of potential applications in healthcare and finance. Rather than treating quantum computing as a subject reserved for specialists, organizers built the day around students, researchers, educators, and AI practitioners working through the material together on

Superconductors are materials that conduct electricity without electrical resistance when cooled below a specific critical temperature. These materials have proved promising for the development of various technologies, including medical imaging instruments, particle accelerators, ultrasensitive detectors and quantum processors.

Insider Brief Sparrow Quantum and Ruhr University Bochum developed a deterministic source that delivers more than 500 million usable photons per second into optical fiber. The source operates at 1 gigahertz with more than 50% fiber efficiency while maintaining high photon purity and indistinguishability without spectral filtering. The increased photon supply could enable experiments involving 10 to 20 photons and support applications in quantum computing, networking, communications and metrology. PRESS RELEASE — Quantum computers are being built in several ways: superconducting circuits, trapped ions, neutral atoms, semiconductor spins and photonics. Photonic quantum systems have one fundamental advantage: their information carriers can travel through optical fibre, making the same technology relevant to both quantum processors and quantum networks. What photonic quantum systems need in exchange is a supply of photons that behaves: each one identical to the last, each arriving when the machine asks rather than when physics happens to oblige. For much of the field’s history, that has meant probabilistic sources: excite a material, wait for the photon-generation event to occur, and discard the occasions when it does not. A lottery is survivable when you need one photon and punishing when you need many. Every photon has to arrive together with all the others, so losses multiply rather than add: a source that works well enough for one photon can be hopeless for ten. That is why the source sets the ceiling for everything built on top of it. Improve it once, at the point of generation, and the improvement carries through the whole system. In work carried out with Ruhr-Universität Bochum , Sparrow Quantum ‘s deterministic source now operates at 1 GHz, delivering more than 500 million usable photons per second into a single-mode fibre — the highest single-photon flux reported to date. The significance is not speed alone: the source combines gigahertz repet

Insider Brief NEC has halted development of quantum computer hardware after determining that commercialization would take too long to produce an adequate return on investment. The company will continue developing quantum annealing, quantum-inspired computing and related services using conventional computer systems. The decision ends a hardware effort that included the world’s first demonstration of a superconducting solid-state qubit in 1999 and an eight-qubit annealing prototype unveiled in 2023. Image: NEC NEC has ended its effort to build a working quantum computer, pulling back from a field that the company helped pioneer. The company discontinued development of a physical quantum computing system at the end of March, Nikkei Asia reported . NEC apparently concluded that bringing the technology to market would take too long to produce an adequate return on its investment. NEC will continue working on related technologies and services, including quantum annealing — which is an approach designed to find efficient answers to problems involving a large number of possible combinations, such as optimizing delivery routes, production schedules or investment portfolios. The company also plans to expand services that use conventional computers to imitate some of the problem-solving methods associated with quantum machines. These so-called quantum-inspired systems do not require quantum hardware and can be deployed using existing computing infrastructure. A Long Record in Quantum Research NEC ’s played an early role in superconducting quantum computing. In 1999, NEC researchers became the first to demonstrate the operation of a superconducting solid-state qubit , the basic unit of information used in many quantum computers. NEC had pursued quantum annealing hardware alongside Japan’s National Institute of Advanced Industrial Science and Technology. In 2023, NEC and Tohoku University began j oint research using an eight-qubit annealing machine developed by NEC and the

Cécile Perrault is the new Executive Director of QuIC, Kevin Messerle is the new CFO of Atom Computing, and Albert Solana is the new Chief of Staff at Qilimanjaro Quantum Tech, all bringing their expertise to advance quantum technologies. The post Who’s News: Strategic Appointments at QuIC, Atom Computing, and Qilimanjaro Quantum Tech appeared first on Quantum Computing Report .

Yuval Boger interviews Brian Gaucher, an experienced engineer and IBM veteran who co-chaired ERVA’s report Engineering Research to Advance Quantum Technologies. Brian explains that while U.S. quantum science remains strong, global competition is accelerating and the key limiter is no longer physics discovery but engineering the path from “lab to fab”—scalable, manufacturable, reliable systems. They discuss why the U.S. should pursue a coordinated, semiconductor-like national strategy with shared pilot lines, standards, metrology, public-private investment, and a broader workforce—not just physicists. They also cover the report’s four pillars (materials, biology, computing, AI), the importance of domestic fabrication, and why biology and quantum sensing may deliver surprisingly near-term impact. Transcript ​​Yuval: Hello, Brian, and thank you for joining me today. Brian:  My pleasure. Yuval:  So Brian, who are you and what do you do? Brian:  Oh, good question. It’s a long sordid story. I started off as an electrical engineer and hardware designer by background. And I spent probably 10 or 12 years at an aerospace and defense company doing military R&D for satellite and radar communications systems, and then moved to IBM where they wanted me to translate a million dollar communication system to something that would be cost effective in a laptop. That was fun. And that was back in the mid 90s. And I spent a long part of my career in what we call millimeter wave design and CMOS technologies. Eventually I managed a group of folks doing profit and loss on some of our chips up in Poughkeepsie and Fishkill, and then got a chance to come back to research and do a little bit of AI. When the quantum chance came around, it just seemed like a really good opportunity to look at a hard problem, both from a physics perspective, and by then in my career, looking at it from more of a systems and architectural perspective and seeing the challenges that are comi

Insider Brief Forschungszentrum Jülich has inaugurated JION, a trapped-ion quantum computer intended to help researchers and companies test quantum computing alongside conventional supercomputers. Developed with eleQtron through a partnership receiving about 21 million euros in state funding, JION uses microwaves and magnetic fields to control charged ytterbium atoms. Two additional projects will each receive up to about 25 million euros to develop scalable trapped-ion technology and integrate a semiconductor quantum computer with up to 200 qubits into Jülich’s infrastructure. Official Launch of JION Quantum Computer at Jülich: Dr Michael Johanning, CTO of eleQtron, Jan Leisse, CEO of eleQtron, Minister-President Hendrik Wüst, Minister Ina Brandes, Prof. Dr Kristel Michielsen, Director of JSC, Prof. Dr Astrid Lambrecht, Chair of the Board of Directors of Forschungszentrum Jülich, and Prof. Dr Dr Thomas Lippert, Director of JSC. (Land NRW / Marius Becker) Germany’s Forschungszentrum Jülich has inaugurated a quantum computer intended to help researchers and companies test how quantum processors can work alongside conventional supercomputers. The system, called JION, is operational at the Jülich Supercomputing Centre , according to t he research center . Its first public calculation was performed during the inauguration ceremony. JION will be integrated into the Jülich Unified Infrastructure for Quantum Computing, or JUNIQ , which provides access to different quantum systems and connects them with the center’s high-performance computers. The arrangement allows selected computing operations to be assigned to quantum processors as part of a larger calculation. Researchers and companies are expected to use JION to develop and test these combined computing methods. Potential applications include logistics, materials research, chemistry and machine learning, the center said. JION, short for Jülich trapped-ion quantum computer, stores quantum information in electrically char

Insider Brief RIKEN has adopted QunaSys ’s QURI SDK Enterprise for the JHPC-quantum project, enabling users to access quantum computing resources from the Fugaku supercomputer environment. QURI SDK Enterprise supports IBM Quantum System Two and Quantinuum System Model H2, along with Fugaku and the ROQUO GPU supercomputer for quantum-HPC hybrid workflows. The SDK provides quantum-HPC algorithms including QSCI and ADAPT-QSCI, with applications spanning quantum chemistry, materials science and computer-aided engineering. PRESS RELEASE — QunaSys Inc. (headquartered in Bunkyo-ku, Tokyo; Representative Director and CEO: Tennin Yan; hereinafter “QunaSys”), a company specializing in the development of quantum computing algorithms and software, announced that its quantum software development kit “QURI SDK Enterprise” has been officially adopted for RIKEN ’s Quantum-HPC Hybrid Platform as part of the “JHPC-quantum” project. JHPC-quantum is a project commissioned by NEDO (New Energy and Industrial Technology Development Organization) under the jurisdiction of the Ministry of Economy, Trade and Industry (METI). The project has developed JHPC-quantum platform for quantum-HPC hybrid applications by linking the supercomputer Fugaku and the IBM Quantum System Two “ibm_kobe” at the RIKEN Center for Computational Science (R-CCS) in Kobe with the trapped-ion quantum computer “Reimei” (Quantinuum System Model H2) at RIKEN’s Wako campus in Saitama. With this adoption, JHPC-quantum users will be able to access quantum devices from Fugaku’s compute and pre/post nodes through QURI SDK Enterprise. The SDK incorporates state-of-the-art quantum-HPC hybrid algorithm libraries, including QSCI (Quantum Selected Configuration Interaction) and ADAPT-QSCI, supporting computation in fields such as quantum chemistry, materials science, and CAE (Computer-Aided Engineering), with a view to future practical applications. Comprehensive documentation, sample code, and toolchains allow researchers to

Insider Brief Scientek and Classiq have signed a go-to-market agreement to expand access to Classiq’s hardware-agnostic quantum software platform across Taiwan’s semiconductor, research and academic sectors. Scientek will introduce Classiq’s platform to companies, research institutes, universities and government organizations while supporting training, customer engagement and potential joint R&D programs. The partnership will initially target quantum applications in semiconductor research, materials and chemical simulation, optimization and hybrid quantum-classical computing. PRESS RELEASE – Scientek Corporation (科榮股份有限公司)  and  Classiq , the leading quantum computing software company, today announced a go-to-market agreement to expand access to Classiq’s  hardware-agnostic quantum software platform  across Taiwan’s semiconductor, research and academic communities. Under the partnership agreement, Scientek will introduce Classiq’s platform to semiconductor companies, research institutes, universities, government organizations and other customers within its established network. The companies also plan to offer enablement and training and explore joint research and development programs involving quantum computing applications. Scientek distributes semiconductor equipment, scientific and analytical instruments and advanced technology systems to Taiwan’s industrial and research communities. Its experience supporting advanced technology infrastructure, including quantum hardware, positions the company to help customers connect their computing investments with the software required to design, optimize and execute quantum algorithms. Classiq’s platform allows researchers and technical teams to describe quantum algorithms as high-level functional models. The platform then automatically creates optimized quantum circuits for the selected hardware or execution environment. This hardware-agnostic approach allows organizations to develop software w

Insider Brief Quantum computing still faces major hardware, error correction, scaling, software and workforce challenges before it can support commercially valuable applications. High error rates and decoherence limit current quantum processors, while fault-tolerant systems require large numbers of physical qubits and significant advances in control, cooling, wiring and manufacturing. Limited quantum algorithms, immature software tools and a shortage of specialized workers add further constraints as the industry moves toward fault-tolerant quantum computing. Quantum computing has attracted billions in investment, sustained media attention, and some of the most concentrated scientific talent on a single engineering problem. Progress has been significant, but the results so far have yet to match the scale of investment and research behind the field. To date, no quantum computer has outperformed a classical computer on a commercially valuable problem. Current systems operate in what researchers call the Noisy Intermediate-Scale Quantum (NISQ) era, characterized by devices with enough qubits to demonstrate quantum behavior but too much noise to run useful algorithms reliably. The gap between where the hardware is and where it needs to be is not a matter of incremental improvement. It involves solving several distinct problems, each of which is difficult on its own and harder in combination. This article covers what those problems are, how serious each one is, and what it would take to solve them. What Decoherence is and Why it Limits Everything Else A qubit stores information in a quantum state, a superposition of 0 and 1 that allows quantum computers to process information differently from classical machines. That state is fragile. Any interaction with the surrounding environment can collapse the superposition into a definite 0 or 1, ultimately, destroying the quantum information it held. This process is known as decoherence. It sets a hard time limit on every quantum

Insider Brief Quantum Foundry Copenhagen plans to open a 5,300-square-meter quantum chip fabrication facility in Copenhagen in 2027 to support commercial-scale manufacturing. The facility will combine nanofabrication, characterization, testing, chip assembly, packaging and ultra-high-vacuum manufacturing capabilities. The Novo Nordisk Foundation has committed more than DKK 2.9 billion (€390 million) to quantum technologies, including a program targeting a fault-tolerant quantum computer before 2034. PRESS RELEASE — Today, Quantum Foundry Copenhagen and the Novo Nordisk Foundation announce plans to establish a new 5,300 m² quantum chip fabrication facility in Copenhagen. The facility will develop and scale the advanced manufacturing equipment needed to produce the next generation of quantum chips and strengthen Europe’s position in an increasingly competitive global quantum landscape. While Europe has built one of the world’s strongest research environments in quantum science, global leadership in quantum technologies will ultimately depend not only on scientific breakthroughs, but also on the ability to turn these breakthroughs into commercial products at scale. The fabrication of high-quality quantum chips, the specialised core processing units inside a quantum computer, is a crucial part of that process. Quantum technologies have the potential to solve problems that are beyond the reach of today’s most powerful computers. In the future, they could help researchers develop new medicines faster, design more sustainable materials, optimise energy systems, and strengthen cybersecurity. Owned by the Novo Nordisk Foundation , Quantum Foundry Copenhagen is a specialised technology company developing proprietary tools, materials and processes for quantum chip manufacturing. The company’s new facility will uniquely combine laboratory space for nanofabrication of quantum materials, advanced characterisation, testing, chip assembly and packaging with ultra-high vacuum

Research center Forschungszentrum Jülich and University of Siegen spin-off eleQtron GmbH have officially brought the JION (Jülich trapped-ION) quantum computer into operation at the Jülich Supercomputing Centre (JSC). Integrated into the JUNIQ (Jülich UNified Infrastructure for Quantum computing) platform, the gate-based trapped-ion processor is linked directly to JSC's High-Performance Computing (HPC) supercomputing cluster—including the JUPITER [...] The post Forschungszentrum Jülich Operates eleQtron’s JION Trapped-Ion QPU via JUNIQ Infrastructure appeared first on Quantum Computing Report .

Technology firm Quantum Foundry Copenhagen and the Novo Nordisk Foundation have announced plans to construct a 5,300 m² commercial quantum chip fabrication facility in Copenhagen, Denmark. Operational by 2027, the infrastructure is engineered to bridge academic research with industrial manufacturing, offering commercial wafer fabrication, characterization, assembly, and packaging services to global quantum technology vendors. [ [...] The post Quantum Foundry Copenhagen and Novo Nordisk Foundation Announce 5,300 m² Fabrication Facility for Quantum Chips appeared first on Quantum Computing Report .

The RIKEN Center for Computational Science (R-CCS) has officially adopted the enterprise quantum software development kit QURI SDK Enterprise from Tokyo-based algorithm developer QunaSys Inc. as the primary software layer for Japan’s national JHPC-quantum project. Funded by the New Energy and Industrial Technology Development Organization (NEDO) under the Ministry of Economy, Trade and Industry (METI), [...] The post RIKEN Integrates QunaSys QURI SDK Enterprise into Japan’s JHPC-quantum Platform appeared first on Quantum Computing Report .

Insider Brief MIT researchers designed a qubit architecture that simulations suggest could speed quantum operations while preserving stored information, potentially supporting more reliable quantum computers. The “arm qubit” separates information storage from interactions with other components, using a specialized coupler to connect the two functions while reducing unwanted interference. The researchers plan to fabricate the qubit to test whether its predicted performance holds up in hardware and could support quantum error correction. MIT researchers have designed a quantum computing component that simulations suggest could perform faster operations while preserving stored information. It’s an advance that potentially could help future machines complete longer, more reliable calculations, according to the researchers. The architecture separates two jobs within a quantum bit, or qubit. One component stores information, while another connects with other qubits and electronics. According to MIT News , the design could address a central engineering challenge in quantum computing — allowing qubits to interact strongly enough to perform calculations without quickly losing the information they hold. The researchers call the design an “arm qubit” because its interaction component reaches out to other parts of the system. Their simulations indicate that it could combine long information-storage times with faster operations and faster measurement than existing superconducting qubit designs. The findings, published in Physical Review Applied , remain a modeling result. The team has yet to fabricate the qubit and establish whether its predicted advantages hold up in hardware. If those results translate to a working device, the architecture could support quantum error correction, the process of detecting and correcting errors that otherwise derail calculations. That capability is essential to building quantum computers that can reliably run long, complex algorithms.

Researchers have completely suppressed superconductivity in magic-angle graphene by screening interactions between electrons, helping resolve a long-running debate about the origin of the phenomenon.

Insider Brief European quantum leaders called for coordinated action to turn the region’s scientific expertise into industrial capacity, competitive companies and strategic strength. The proposed EU Quantum Act is expected to promote cooperation, market consolidation, supply-chain resilience and links with sectors such as semiconductors, photonics and cloud computing. Speakers identified fragmented investment, limited coordination and competition for skilled workers as major obstacles to building a unified European quantum market. PRESS RELEASE — Europe’s quantum community gathered yesterday at the European Parliament for “ Europe’s Quantum Moment: From Lab to Leadership”, an event hosted by MEP Dr. Sergey Lagodinskythat brought together representatives from the European Commission, European Council and European Parliament, as well as quantum researchers, business leaders and investors. The goal of this high-level discussion was to explore how the EU could transform its indisputable scientific expertise into lasting industrial and strategic strength. But the discussion, organized into two panels, quickly developed into a thrilling debate on the geopolitical and economic challenges Europe faces to consolidate its market, maintain its technological sovereignty and become a global leader in quantum technologies. The three-hour session was packed with specific proposals and overarching political and economic strategies that might help shape the upcoming Quantum Act, the new legislation on quantum technologies that the European Commission is expected to announce by the end of 2026. But the ambition went beyond technical aspects of the policy as well: “ It’s not just a competition between business models, it’s a competition between societal models, and, in this competition, technology and leadership in the realm of innovation plays the role ”, explained the MEP during his opening remarks. “ If we are not capable to keep the leadership, then we are lost i

Insider Brief QuFi Network has launched the QuFi Platform, a post-quantum verification layer designed to validate digital assets and financial transactions without requiring changes to existing settlement networks. The platform uses a hybrid architecture combining ML-DSA-65, SLH-DSA and ML-KEM-1024 for post-quantum signatures and key encapsulation. QuFi has also introduced uBTC as a proof-of-concept on Bitcoin Testnet4 and opened applications for its Genesis Node Program to expand decentralized verification capacity. PRESS RELEASE — As the digital asset industry transitions toward post-quantum security, blockchain networks face an emerging infrastructure challenge. Depending on the cryptographic scheme and implementation, post-quantum signatures can be more than 100 times larger than the elliptic-curve signatures widely used today. This can drive substantial increases in storage, bandwidth, and computational requirements. As a result, every blockchain that adopts these new cryptographic standards must absorb those costs independently, creating scalability and efficiency constraints that compound across the broader digital asset ecosystem. QuFi Network Limited (“QuFi”) today announced the launch of the QuFi Platform, a post-quantum verification platform that enables quantum-resistant validation across digital assets, financial infrastructure, digital ownership, and tokenized forms of economic value without requiring changes to existing settlement networks. Just as traditional financial markets evolved specialized infrastructure to separate trading, clearing, and settlement, the digital asset economy increasingly requires a dedicated layer for post-quantum verification. The launch introduces a new infrastructure approach that separates verification from settlement, allowing cryptographic validation to occur before value moves. “Digital finance has spent the last decade building settlement infrastructure. The next decade will require verification infrastructure.

Trapped-ion quantum hardware developer Quantinuum (NASDAQ: QNT) and integrated energy firm Aramco have executed a non-binding Memorandum of Understanding (MoU) during the LEAP technology conference in Riyadh. The agreement establishes a framework for preliminary technical onboarding, knowledge exchange, and benchmarking quantum modalities to identify industrial use cases across energy production and digital transformation workflows. [ [...] The post Quantinuum and Aramco Execute Non-Binding MoU for Energy Sector Quantum R&D appeared first on Quantum Computing Report .

Abstract We translate the one-mode unitary-dilation framework for nonunitary linear dynamics into a gate-level hybrid oscillator--qubit architecture. An ancillary oscillator encodes the integral kernel through state preparation and postselection. A qubit register represents and simulates the discretized system operator. The construction applies to time-independent dynamics \(\dot u=-(L+iH)u\), including discretized partial differential equations, and removes the \(\mathcal{O}(\log M_a)\) ancilla-qubit overhead of a discrete-variable (DV) \(M_a\)-term quadrature register. We bound the squeezed-Fock coefficient-projection error of the ideal kernel state. It decays superalgebraically with cutoff \(N\) for Schwartz-class kernels and at a stretched-exponential rate under stronger joint decay and smoothness assumptions. The finite squeezed-Fock kernel state generically has stellar rank \(N-1\), making \(N\) a discrete measure of the oracle's non-Gaussian resource. For hybrid oscillator--qubit evolution, a \(p\)th-order product formula requires \(\mathcal{O}(t^{1+1/p}N_{\mathrm{Fock}}^{(p+1)/(2p)}\epsilon_t^{-1/p})\) Trotter steps in the worst case, up to generator-dependent commutator factors, to reach error \(\epsilon_t\), where \(N_{\mathrm{Fock}}\) is the oscillator dimension. A perturbation bound separates the total scaled-map error from the physical postselection probability. We benchmark Law--Eberly synthesis and assess a variational SNAP+\(\mathcal D\) route at the state-preparation level on discretized heat-equation instances. For full circuit-level maps of one-dimensional heat and non-normal advection--diffusion instances up to \(D=32\), the fixed-scale map error is at most \(1.48\%\) and the conditional infidelity at most \(4.68\times10^{-4}\) over all computational-basis inputs. At kernel parameters selected on the one-dimensional family, a \(4\times4\) two-dimensional stress case reaches \(7.40\%\) fixed-scale error under a reference norm shrunk by the stronger two-dimensional damping, with worst-input conditional infidelity \(6.20\times10^{-3}\). At the prescribed DV sizing, the hybrid CV--DV route has smaller fixed-scale error in all ten instances. The DV route accepts with fewer repetitions in every instance. These results provide a block-by-block finite-size resource account of when a single continuous qumode can replace a discretized ancilla register.

Abstract Tuning gate-defined quantum dots for qubit operation is an often frustrating and time-consuming activity in spin qubit research due to inherent device variability and the complex interactions between dots. Furthermore, tuning these devices grows more complicated as quantum computers grow to utility-scale. Computer-automated and machine learning techniques are popular approaches to accelerate the tuning process. However, these techniques need to become much faster and more accurate to address the tuning of millions of qubits in utility-scale quantum computing. We examine the literature of computer-automated and machine learning spin qubit tuning algorithms, grouping the algorithms by similar tasks and analyzing them from a computer science perspective to keep necessary background knowledge of quantum computing/physics at a minimum. We look at which approaches seem propitious for scaling up to utility-scale systems and where computer scientists could potentially have the most impact.

Abstract Multi-controlled gates are essential primitives in quantum algorithms, yet implementing them via standard gate-level decompositions remains resource-intensive. We develop efficient pulse-level implementations of multi-controlled gates in trapped-ion systems using the Cirac–Zoller scheme. We first show that the Cirac–Zoller construction admits a freedom in the sign choice of red-sideband (RSB) pulses, which leaves the logical operation invariant up to a local Pauli-Z correction. By exploiting this freedom, we construct equivalent realizations of multi-controlled gates and develop pulse cancellation for more efficient implementations of successive gates. We perform numerical simulations and show that pulse cancellation reduces the gate time and improves the state fidelity. Furthermore, we propose ancilla-free circuits for general N-controlled gates that use a single-controlled gate primitive and O(N) RSB pulses. As a key application, we apply our pulse cancellation to the linear combination of unitaries (LCU) method for block encoding. We show that the RSB-pulse cost of the select operator over L unitaries can be reduced from O(L log L) to O(L), which improves the efficiency and scalability of LCU-based quantum circuits.

Abstract Gravitational time dilation implies that clocks held at different heights accumulate different proper times. We analyze a memory-assisted photonic clock interferometer in which a two-frequency (frequency-bin) optical clock is stored in two vertically separated quantum memories for a controllable duration, such that the joint state evolves in a quantum superposition of two proper times. After retrieval, the photonic modes interfere in a Hong–Ou–Mandel (HOM) interferometer, for which we derive analytic expressions for the resulting multiphoton detection statistics. Extending this HOM-based scheme from entangled photon pairs to frequency-entangled 2N-photon inputs, we show that the proper-time dependent phase is amplified by a factor N, leading to an N-times faster collapse and revival of the interference signal compared with the two-photon case. Incorporating finite memory efficiency and lifetime, we identify regimes where this modulation remains observable. For parameters compatible with demonstrated Rb and Cs memories and achievable optical frequency separations, the first collapse occurs for height differences in the order of 10–100 m with subsecond to few-second storage times, while suitable rare-earth ion and alkali memory combinations can reduce the required height to the few-metre scale. These results establish near-term laboratory conditions for observing entanglement dynamics driven by gravitational time dilation in a photonic platform.

Abstract We investigate a microwave-cavity-based displacement readout employing a split-post geometry to measure the motion of a dielectric membrane. Due to symmetry, the cavity response to membrane displacement is inherently quadratic when the membrane is positioned at the centre of the posts. We characterise this behaviour by driving the membrane with a piezoelectric actuator at both central and off-centre positions and we estimate the drive-to-displacement transfer function using the independently calibrated frequency-to-voltage response of the interferometric readout. When the membrane is located at the centre of the cavity and driven, the system exhibits the largest quadratic output, measured at the second harmonic of the membrane acoustic frequency. As the membrane is moved away from the centre, the response transitions from predominantly quadratic to predominantly a linear response at the membrane acoustic frequency. Quadratic optomechanical coupling is a key requirement for displacement - squared readout and, in the quantum regime, for measurements sensitive to mechanical energy or phonon number. The present work therefore establishes the split-post geometry as a promising platform for microwave-mechanical transduction, providing a practical route toward future experiments aimed at probing quantised mechanical motion and energy-sensitive readout schemes.

Time-series foundation models produce rich embeddings, but whether quantum models can exploit them, and how far hybrid classical-quantum architectures scale, remains unclear. We address this by fine-tuning Chronos for power-grid event classification (PSML-5) with a quantum head on the model's embeddings. Grouping embeddings by physical sensor type before summarization already surpasses the best published baseline built for this benchmark, and with finer-grained features the quantum head outperforms a larger classical multilayer perceptron on identical inputs by 1.7-2.0 percentage points of balanced accuracy. Yet the gains saturate: past a point, feeding more information to the same fixed-width register yields no improvement. We show the bottleneck is neither the supply of information nor circuit expressiveness, but the bandwidth of the data intake. To overcome this limitation, we introduce the wing module, a self-contained few-qubit circuit that feeds additional information into the core circuit through a sparse, one-way coupling. Under a preregistered four-seed protocol, we attach wings to a fixed 12-qubit core with fixed features. Balanced accuracy increases with each added wing, from 83.6% with no wings (13 qubits, including a post-selection qubit) to 85.2% with two (19 qubits). Ablations establish that a circuit enlarged without new information gains nothing, while a wing fed information from the wrong sample harms accuracy. These results reframe scaling for quantum fine-tuning: added qubits help when they carry added inputs, not merely more parameters. Wings offer a modular and stable route to widening that bandwidth.

Multiparameter quantum estimation in open optomechanical systems is fundamentally constrained by dissipation, thermal fluctuations, and measurement incompatibility. In this work, we investigate a coupled-cavity optomechanical platform in which two mechanical modes interact with driven optical cavities, two-mode squeezed vacuum, intracavity degenerate parametric amplification, and coherent optical feedback. Using the continuous-variable Gaussian-state formalism, we derive the linearized quantum Langevin dynamics and steady-state covariance matrix and evaluate the quantum Fisher information matrices associated with simultaneous estimation of the optomechanical coupling strength and cavity dissipation rate. We characterize the precision bounds using the symmetric and right logarithmic derivative formalisms and employ $\mathcal{B}_{\rm MI}=\max\{\mathcal{B}_S,\mathcal{B}_R\}$ as a comparative figure of merit within the SLD/RLD framework. We find that parametric amplification can substantially reduce , demonstrating an enhancement of multiparameter sensitivity over a broad range of operating conditions. In contrast, coherent feedback produces a nonmonotonic modification of the estimation precision, with its effect depending sensitively on the feedback reflectivity, phase, squeezing strength, and thermal occupation. This behavior reveals that coherent feedback acts not simply as an enhancing or degrading mechanism, but as a tunable resource for engineering the quantum fluctuations and parameter-dependent correlations of the optomechanical state. We further analyze the transient and steady-state regimes and identify parameter regions in which squeezing and parametric amplification provide the largest metrological gain.

Non-reciprocal interactions are ubiquitous in active, biological, and disordered systems, generically driving them out of equilibrium. Here, we introduce a hierarchy of non-reciprocally interacting Ornstein-Uhlenbeck (NROU) models governed by a tunable non-reciprocity parameter $g$. At a special point $g=g^*$, the drift matrix becomes non-diagonalizable, realizing exceptional points (EP's) of different orders, where eigenvalues and eigenvectors simultaneously coalesce. The hierarchy encompasses non-reciprocally coupled dimers, their disordered counterparts, and a many-body chain exactly mapping onto the paradigmatic Hatano-Nelson model in the arena of non-Hermitian quantum systems. For the disordered model, we show that the distribution of the EP location $g^*$ across disorder realizations develops a universal edge singularity precisely at the clean-system EP, and is manifestly non-self-averaging. Across all models, we find that at the EP, the usual exponential relaxation of the autocorrelation and covariance functions is dressed by a polynomial-in-time prefactor whose degree is set by the order of the EP and whose detailed structure encodes the spatial architecture of the chain. At complete asymmetry, the many-body chain exhibits ``pseudo-equilibrium'': its steady-state distribution factorizes into equilibrium-like single-particle measures despite a nonzero steady-state current. Moreover, the $N$-particle interacting system decomposes into $N/2$ independent complex OU processes. Finally, using the Harada-Sasa relation, we obtain a closed-form expression for the total steady-state heat dissipation and uncover a boundary refrigeration effect, in which the boundary particles switch from acting as a hot to a cold reservoir as the non-reciprocity is tuned.

Advanced optical quantum technologies demands high quality quantum light generation at very high rates. Here, we report on a deterministic single-photon source that simultaneously combines high excitation rates with high system efficiency to reach over 500 MHz of in-fibre single-photon flux. The source delivers optical power of over 100 pW, as is measured with an off-the-shelf powermeter, enabling a simple and direct way of determining the single-photon source fiber efficiency.

Three-photon states generated via cascaded spontaneous parametric downconversion provide a direct route to multipartite entanglement. However, current implementations require careful spectral matching between successive nonlinear stages, which constrains the choice of downconversion sources. In this work, we show that coincidence-based spectral filtering relaxes this requirement by conditionally tailoring the spectrum of the pump photon entering the second stage. By filtering the herald photon, we conditionally tailor the spectrum of its partner to match the acceptance bandwidth of the secondary nonlinear process, enabling efficient coupling between broadband and narrowband stages without altering the sources themselves. Using an electro-optically gated spectrometer, we directly measure the conditional spectra that govern the cascaded process, allowing us to quantitatively predict the enhancement in second-stage conversion probability per detected herald. We then verify this prediction through photon-triplet measurements, demonstrating improved performance at fixed heralding rates. Our results establish coincidence-based spectral engineering as a practical tool for optimizing cascaded downconversion, particularly in regimes limited by detector saturation or spectral incompatibility.

Quantum metrology with indefinite causal order (ICO) has attracted intense interest due to its potential to surpass the limitations of conventional fixed-order strategies. A key open question is whether ICO can fundamentally enhance asymptotic precision scaling. In this work, we bridge this gap for the estimation of a single parameter encoded in $N$ identical uses of a finite-dimensional quantum channel. We first establish a universal Heisenberg-scaling upper bound for the full general ICO process-matrix class and show that for unitary channels its optimal quantum Fisher information (QFI) coincides exactly with that of parallel strategies. For noisy channels, a structurally refined bound shows that channels restricted to the standard quantum limit (SQL) under parallel strategies remain SQL-limited under general ICO strategies. Most significantly, an asymptotically tight (AT) bound is derived to close the remaining possibility of an asymptotic ICO advantage by showing that general ICO and optimal parallel strategies have exactly the same leading QFI coefficient in both the SQL and Heisenberg regimes. For the operationally motivated class of quantum circuits with quantum control of causal order, we further obtain an iterative constraint on finite-query precision whose asymptotic limit agrees with that of the AT bound. Our results clarify the ultimate role of indefinite causality as a metrological resource for quantum channel estimation.

We investigate how dipolar interactions between microwave-shielded polar molecules structure the self-bound droplets formed under variation of the interaction strength. We identify the transition from droplets to crystals as a finite-size first order transition. With droplet-ring states and transitional supersolid states we predict additional structure in the crystal and droplet phases, respectively. To describe this strongly correlated regime, and in particular the reconfiguration of quantum ground states, we design a variational Monte Carlo framework based on neural quantum states. It is especially suitable to describe ground states and almost degenerate states with very different configurations. Moreover, one can easily determine the superfluid fraction. Our results reveal the sequence of finite-size structures through which dipolar interactions reorganize molecular droplets into crystals.

Real-amplitude quantum theory is the subtheory of quantum theory invariant under complex conjugation, and experiments in a network of independent sources have measured correlations above the real bound. A theory can nevertheless carry the same conjugation without complete positivity and still have exactly the correlations of its own conjugation-invariant subtheory in every causal structure, the bilocality scenario included. The states of that theory are all the density matrices, and its effects are the operators every partial transpose of which is again a quantum effect. Its symmetrized subtheory simulates it once each source carries a reference frame rather than each system. One map therefore receives three different verdicts in three theories, so the symmetry alone marks no boundary at all, and what sustains the separation in quantum theory is a property of quantum theory. Quantum theory admits every effect its states permit and this theory does not. What does have a boundary is the class of theories where the correlations of a theory and of its symmetrized subtheory coincide. We show that sectorial closure, meaning invariance of the effects and the operations under the symmetry acting independently on each source, suffices for the absence of a gap under any finite group, and that it cannot be weakened on the effects. Fixing unrestricted states and conjugation makes the effects of that theory the largest the symmetry admits, and its operations the largest sectorially closed ones. Locating where sectorial closure fails, for a candidate effect set built from a fixed bound entangled state, is a finite computation on a single ray of effects.

As quantum computing enters the early fault-tolerant era, circuit compilation choices will increasingly depend on details of the underlying architecture rather than solely optimizing for generic proxies such as non-Clifford count. We present an active-volume-aware compilation of the ground-state energy estimation algorithm for the two-dimensional Fermi-Hubbard model using quantum phase estimation and Trotterized time evolution. The proposed compilation reduces the active volume across $L\times L$ square lattices with $L=4$ to $20$, achieving up to a $3.9\times$ reduction over prior work optimized for non-Clifford cost. As a by-product of these compilation improvements, the resulting circuits also achieve state-of-the-art Toffoli counts, with a ~$2\times$ reduction for the $L=20$ case. Lastly, the active volume architecture and recent execution scheduling advances provide a means of translating these reduction trends into runtime. This demonstrates the increasing importance of architecture-aware compilation for practical early fault-tolerant quantum computing.

Change detection in synthetic aperture radar (SAR) and interferometric synthetic aperture radar (InSAR) underpins disaster response, infrastructure monitoring and land-use enforcement. Detection is limited by the background estimator, which conventionally forms a conditional expectation directly from observed pixel statistics and degrades where those statistics are sparse, including the regime produced by the heavy-tailed marginals of sub-meter-resolution radars. In this work, we integrate state-of-the-art satellite imagery with quantum machine learning on IonQ trapped-ion-based quantum processors. By replacing the empirical conditional with a quantum circuit Born machine (QCBM)-sampled generative model in Copula space, we substantially improve change detection on sparse real-world images. On Capella Space satellite image acquisitions, the generative estimator matches conventional methods when the observed statistics are adequate, and substantially outperforms them when they are not. Executing the trained model on IonQ trapped-ion based hardware reproduces the results of the ideal and noisy simulations and demonstrates up to par, or even better, performance with the classical state-of-the-art methods. For a SAR dataset of an airport, QPU circuit evaluations for both training and inference achieved a maximized filtered F1 score of 0.32, compared with 0.16 and 0.24 for the two classical baselines. For an InSAR dataset of a volcanic lava flow, all three methods reached a maximum filtered F1 of approximately 0.66. These experiments demonstrate the feasibility of executing a QCBM-based background estimator on trapped-ion hardware. We further demonstrate that the QCBM method successfully extends to interferometric coherence data, achieving performance comparable to classical approaches.

In modular quantum computing architectures, communication between hardware modules is mediated by traveling qumodes sent through transmission lines. Each output qumode interacts with the emitting module only once through a beam-splitter-type interaction and becomes inaccessible to that module after emission. Information required for subsequent outputs must therefore remain in long-lived memory qumodes. For a prescribed multimode Gaussian transformation on $N$ qumodes, this work determines the minimum memory cost for any given emission order, constructs an explicit sequential protocol attaining this minimum, and develops a greedy method for identifying memory-efficient emission orders. The transformation is represented by a symplectic matrix $S$, specified either directly or through a Gaussian gate sequence. The exact minimum memory cost is obtained from the ranks of submatrices of $S$ and further reduces to a support-based counting rule whose computational cost is linear in the size of the support data. When $S$ is specified directly, a matrix-based protocol attains the minimum memory cost. If instead $S$ is specified through a gate sequence, the original gates can be reused without additional synthesis, although the resulting memory usage need not be minimal. Gaussian transformations with local support on a $D$-dimensional cubic lattice can be realized sequentially with $O(N^{(D-1)/D})$ memory qumodes. The protocols also apply to non-Gaussian inputs, including GKP and cat states, and thereby provide an explicit, resource-efficient scheme for intermodule communication in modular architectures for universal continuous-variable quantum computation.

Quantum-state texture (QST) has found applications in several fields from quantum foundations and computation to quantum criticality. However, a general theory of QST dynamics under arbitrary physical processes remains unavailable, limiting both its practical application and experimental exploration. Here, we demonstrate that the QST response to an arbitrary finite-dimensional channel is fully encoded in the dual evolution of a single reference state. This description yields necessary and sufficient conditions for texture preservation and implies exact conservation under all free-unital dynamics. Using a nuclear magnetic resonance quantum processor, we experimentally verify these predictions across distinct channel classes. Furthermore, we show that local QST measurements provide an operational signature of entangling gates in circuit layers. Our results establish quantum-state texture as a resource and a practical diagnostic tool in quantum information processing.

Protein-protein interaction (PPI) network alignment combines topological and sequence information to identify conserved modules across species, but global alignment remains challenging: heuristics sacrifice optimality, while exact methods lack scalability. We model the alignment as a weighted maximum common induced subgraph problem and reformulate it through the modular product graph to a minimum-weight vertex cover on the complement, with node weights carrying sequence similarity. To solve this problem, we develop a hybrid framework combining kernelisation, branch-and-bound, and seven Quantum Approximate Optimisation Algorithm (QAOA) formulations. These formulations differ in how the cover constraints are enforced, from penalty terms in the cost Hamiltonian to mixers confined to the feasible subspace. For single round QAOA, we derive closed-form expressions for the expected cost of four circulant mixer variants, enabling performance characterisation without circuit simulation. Applied to synthetic and real-world networks reduced to KEGG pathways, the QAOA formulations achieve high topological conservation on the aligned core while at least maintaining biological conservation comparable to leading classical aligners, at the cost of reduced node coverage. Across selected KEGG pathways, the aligned subnetworks retain disease-associated proteins, preserving biologically relevant information. Cheaper formulations leave more edges uncovered, while enforcing feasibility in the mixer raises circuit depth by one to two orders of magnitude. Together, these results highlight the potential of quantum optimisation for PPI network alignment and the resource trade-offs that will shape its scalability as quantum hardware matures.

The struggle of the hour in quantum computing research is achieving effective suppression of the error mechanisms induced by the interaction of external radiation with superconducting quantum devices. Despite the rapid advancements in quantum error correction (QEC) of recent years, radiation-induced faults are yet to be fully addressed. These events are known to be the cause of simultaneous correlated defects in qubits that lie onto a single substrate, ultimately jeopardising QEC code effectiveness. In this paper, we propose to selectively combine substrate-level phonon barriers and QEC interleaving via a planar-mesh tiling algorithm, TETRIS-Q, reaching efficient and effective suppression of radiation events. Our cross-layer solution comes at no extra cost in terms of QEC code execution or decoding time. We model and simulate radiation-induced transient faults over a plethora of barrier and QEC interleaving configurations. Through more than 51 million quantum circuit simulations, we show peak logical error reductions of more than $99.8 \%$, together with an $80\%$ reduction of the observable transient duration with permeable barriers. We find that sparser tiling can reach comparable performance to single qubit tiling, prompting cost reductions of upwards of $87 \%$ in barrier tracing. By leveraging independent QEC code interleaving, we measure up to one order of magnitude average logical error rate reductions without the use of permeable barriers, and up to three orders of magnitude with the joint usage of barriers.

One-shot information theory measures often require an optimization over states, but the form of these optimizers can be complicated or depend on the initial problem in nonlinear ways. In this note, we show that in many instances using the marginal instead of the optimal state is sufficiently good and only changes the result by a small factor. We prove that for the Petz-Rényi divergence of order $α\in[1/2,1)$, replacing the optimizing state on $B$ by the marginal $ρ_B$ results in a multiplicative overhead of at most $1/α$. We also show a similar relation for the fidelity, and in the case of pure or quantum-classical states for the sandwiched Rényi divergence.

Tunable couplers have enabled two-qubit gate fidelities in superconducting quantum processors to approach $99.9\%$, yet simultaneously suppressing residual interactions and maintaining flexible qubit-frequency allocation remain central challenges for scaling. Here, we propose a double-resonator coupler (DRC) consisting of two resonators interconnected by a single Josephson junction and a capacitor. The hybridized resonator modes provide two mediated exchange paths whose interference controls the qubit-qubit interaction. The DRC enables complete cancellation of residual $ZZ$ interaction for qubit-qubit detunings well outside the straddling regime, even in the absence of direct qubit-qubit coupling, thereby relaxing constraints on frequency allocation and qubit placement. Away from the idle point, the same circuit provides a strong $ZZ$ interaction of approximately $70\,\mathrm{MHz}$, enabling a $20\,\mathrm{ns}$ controlled-Z gate with simulated coherent infidelity below $10^{-5}$. These results establish the DRC as a flexible single-junction coupler architecture for high-fidelity superconducting quantum processors.

Weyl semimetals (WSMs), with their unique topological properties and distinct electronic structure, exhibit intriguing properties when either time-reversal or inversion symmetries are broken. In this work, we consider the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between magnetic impurities in time-reversal symmetry-breaking WSMs. We derive analytical expressions for the full RKKY exchange tensor in arbitrary two-band spinful lattice systems. Our approach reveals both Heisenberg, anisotropic Ising and Dzyaloshinsky-Moriya terms, which can be calculated by energy-integrating real-space Green's functions across the entire Brillouin zone, with the band edge acting as a natural energy cutoff. We apply this framework to study a two-band tight-binding model for a time-reversal symmetry-breaking WSM that interpolates between a Weyl phase with well-separated chiral nodes and a quadratic band-touching semimetal phase. Remarkably, the spatial profile, magnitude, and anisotropic tensor structure of the exchange couplings remain persistent across the node-annihilation transition. This topological robustness reveals that short- and intermediate-range RKKY interactions are mediated by the global, Brillouin-zone-integrated quantum metric of the full valence band rather than being strictly dictated by local low-energy Berry curvature monopoles. These findings demonstrate the necessity of full-band tight-binding formulations when predicting real-space magnetic interactions, providing key insights for electric-field tuning of magnetic anisotropy and constructing realistic models of heavy-fermion and Weyl-Kondo semimetals.

We consider the problem of establishing limitations on the power of quantum query algorithms via the completely bounded polynomial method. In particular, we prove several optimal functional inequalities involving different notions of completely bounded polynomials. These inequalities lead to limiting theorems for the power of quantum query algorithms that improve on prior works. 1. An optimal root-influence bound for block-multilinear polynomials. Prior work showed that block-multilinear polynomials $p$ of degree $t$ satisfy a root-influence bound, $\|p\|_{\text{cb}}\geq \sum_i \sqrt{\mathrm{Inf}_i[p]}/t^2$, which is stronger than the bound appearing in the Aaronson-Ambainis conjecture. We find the optimal constant in that inequality: $\|p\|_{\text{cb}}\geq \sum_i \sqrt{\mathrm{Inf}_i[p]}/t$. Since the amplitudes of quantum algorithms that query disjoint blocks of inputs-such as $t$-fold forrelation- are block-multilinear polynomials with $\|p\|_{\text{cb}}\leq 1,$ our inequality shows that they satisfy $t\geq \sum_i\sqrt{\mathrm{Inf}_i[p]}$. We prove that this inequality yields both a more efficient classical simulation than prior results based on the Aaronson-Ambainis argument, and a qualitative improvement: all classical queries are nonadaptive. 2. Optimal Fourier growth of the highest level of quantum query algorithms. We show that for every polynomial $p$ defined on $\{-1,1\}^n$ of degree $2t$, the Fourier Growth at the level $2t,$ namely $\|\widehat p_{2t}\|_{\ell_1}$, satisfies $\|\widehat p_{2t}\|_{\ell_1}\leq (en/(2t-1))^{\frac{2t-1}{2}}\|p\|_{\text{cb}}$. This is optimal up to the factor $e$, as witnessed by $2t$-fold forrelation. As quantum query algorithms that make $t$ queries (to the whole input) satisfy $\|p\|_{\text{cb}}\leq 1$, this yields a Fourier growth bound for these algorithms, partially resolving a question by Girish (STOC, 2026).

Two conventional Josephson junctions connected in series can reproduce, in the static limit in which the currents through the capacitive and resistive channels are negligible, the current-phase relation of a single effective weak link with tunable transparency. Therefore, the two-junction series can be treated as a single synthetic high-transparency element. Here, we investigate to what extent this mapping remains valid under finite-frequency drive and retaining the junctions' resistive and capacitive terms. The full resistively and capacitively shunted junction equations are compared with an effective synthetic element with tunable transparency that retains the synthetic tunable-transparency current-phase relation together with effective capacitive and dissipative terms, thus reducing the two second order degree of freedom system to a single second order degree of freedom. The resulting single-element dynamics is compared with the complete two-junction system under ac excitation. The agreement is quantified through a normalized root-mean-square error between the full and effective voltage waveforms. A broad low-error region is found at low drive frequency, while pronounced deviations emerge as the drive frequency approaches the relevant plasma-frequency scale and at larger drive amplitudes. The results provide a quantitative dynamical criterion for using the reduced single-element description of a synthetic high-transparency Josephson element in superconducting circuits.

Edge-magnetoplasmon resonators have been proposed as a powerful tool to detect anyons by introducing a quantum point contact into an isolated quantum Hall system probed via radiofrequency radiation. In this paper, we study the effect of a quantum point contact embedded within an edge-magnetoplasmon resonator and how its polarization influences the propagating magnetoplasmonic mode. Combining dc and rf measurements, we unambiguously evidence the signature of both integer ($ν= 1$ and $2$) and fractional quantum Hall states ($ν= 4/3$ and $2/3$) within the radiofrequency transmission signal. Using electrostatic gating, we determine the physical parameters characterizing the electrostatic edge of an AlGaAs/GaAs based two-dimensional electron gas. We extract the dependence of the cavity perimeter with the gate voltage of the quantum point contact and fully characterize the path followed by edge magnetoplasmons in this system. Finally, we provide a geometric model in good agreement with experimental results.

Formalizing mathematics in a proof assistant, where a machine checks every definition, statement and proof, has set a new standard of rigor. Large language models are now capable of formalizing autonomously, even at the scale of whole textbooks. We bring this standard of rigor to physics, where theoretical arguments carry idealizations that are rarely stated fully, and any logical gaps could have a cascading effect on interdependent results. Recognizing the need to evaluate autoformalization systems for physics, we release AxQM, 1,019 kernel-checkable proof-synthesis tasks over 479 items drawn from the textbook Quantum Computation and Quantum Information by Nielsen and Chuang. The tasks are stated in a custom Lean library of finite-dimensional quantum mechanics. By task count, it is the largest proof-synthesis benchmark in physics by a factor of four. AxQM is derived from a near-complete formalization of the formal portions of the textbook, so every task is guaranteed a solution, which we keep private. Grading of the benchmark is done deterministically by the Lean kernel, which checks that the proof compiles, that no sorry appears in it or in any declaration it depends on, and that it introduces no new axioms.

Whether $\mathsf{QAC}^0$ can compute $\mathtt{PARITY}_n$ remains open. Computing $\mathtt{PARITY}_n$ is equivalent to implementing $\mathtt{FANOUT}_n$ under $\mathsf{QAC}^0$ reductions. This raises a more general question: for an arbitrary symmetric Boolean function $f:\{0,1\}^n\to\{0,1\}$, what fanout size is necessary and sufficient for computing $f$ in $\mathsf{QAC}^0$? We show that the answer is exactly the transition radius $ρ(f)$: computing $f$ and implementing $\mathtt{FANOUT}_{ρ(f)}$ are equivalent under $\mathsf{QAC}^0$ reductions. In particular, if $ρ(f)\ge n^δ$ for some constant $δ>0$, then computing $f$ is $\mathsf{QAC}^0_{\mathrm{f}}$-complete. Combined with Paturi's theorem, our characterization implies that if $\mathtt{PARITY}_n \notin \mathsf{QAC}^0$, then any Boolean function in $\mathsf{QAC}^0$ of approximate degree $n^{1/2+Ω(1)}$ must be nonsymmetric.

We study steady-state transport in a one-dimensional Fermi-Hubbard chain coupled to particle reservoirs at the boundaries and to local dephasing baths at each site, using the time-evolving block decimation (TEBD) method to solve the Lindblad master equation. In the absence of dephasing, the current exhibits two well-separated maxima as a function of the boundary driving rate, reflecting the distinct charge and spin energy scales of the strongly correlated regime. Upon introducing dephasing, we find two distinct dephasing-induced transport-enhancement regimes, in contrast to the single enhancement previously reported for spinless fermions. Analysis of the non-equilibrium steady state in the Hamiltonian eigenbasis reveals that the two regimes originate from distinct dephasing-induced redistribution processes: the first involves redistribution within the uppermost Hubbard band, while the second involves transitions between Hubbard bands. Our results demonstrate how many-body correlations shape the interplay between coherent driving, dephasing, and quantum Zeno physics in strongly correlated open systems.

We study the impact of noise on the theories of quantum nonlocality and entanglement-assisted communication complexity. We consider non-local games and entanglement-assisted communication complexity in a model where Alice and Bob may share arbitrarily many noisy EPR pairs. We study four noise models: depolarizing noise, unital noise, biased reset noise, and erasure noise. Our results are as follows: 1. We upper bound the value of the CHSH game under all these noise models in terms of the noise parameter, without any assumptions on the measurements used in the strategy. 2. We prove a parallel repetition theorem for general non-local games under all noise models except biased reset noise; we prove an improved parallel repetition theorem for unique games. Our parallel repetition rate is smaller than the quantum parallel repetition rate for CHSH in a nontrivial noise regime. 3. Using our unique-game parallel repetition theorem and a relation defined by the CHSH game, we prove a separation between communication complexity with noisy vs noiseless entanglement. This implies an $Ω(n)$ two-way communication lower bound for distilling $n$ EPR pairs from noisy EPR pairs, in the same nontrivial noise regime. 4. We show that any interactive entanglement-assisted communication protocol can be simulated by an SMP communication protocol with noisy shared randomness, with an exponential blowup in communication. This generalizes a known result on the simulation of noiseless shared randomness with noisy shared randomness. 5. We show a polynomial lower bound on the number of copies of noisy EPR pairs required to compute the Equality function with constant communication, under all four noise models. The previous result gives a matching upper bound, and moreover, this answers an open question in the literature on whether logarithmically many noisy shared bits suffice for communication.

We study the operator entanglement of local operators in one-dimensional brickwork circuits whose two-site gate satisfies the braid relation; throughout this work, we call such a gate a Yang--Baxter gate. We establish upper bounds for several structured, overlapping classes of Yang--Baxter gates. We show that the operator Schmidt rank remains uniformly bounded in time for all qubit Yang--Baxter gates and, in arbitrary local dimension, for permutation gates obtained from non-degenerate Yang--Baxter maps. We also show that it grows at most polynomially for involutive dual-unitary Yang--Baxter gates and for arbitrary phase dressings of permutation gates obtained from non-degenerate Yang--Baxter maps. These results imply, respectively, constant and logarithmic upper bounds on the operator entanglement. Conversely, we construct a seven-state involutive Yang--Baxter gate without dual unitarity and a one-site operator whose exact operator Schmidt rank grows exponentially, although the corresponding operator entropies remain undetermined. Entanglement growth in the general Yang--Baxter case remains open. All proofs and selected examples were constructed by ChatGPT 5.6 Sol.

Replacing classical entropy with QRNG output does not change honest Bitcoin PoW success probability when candidate headers remain distinct. The original contribution of this paper is a reproducible benchmark that locates and measures the operational value of quantum entropy in hybrid quantum-classical mining infrastructure through two scheduler-level observables, the entropy-efficiency factor $η$ and the reboot-diversity index $ρ$. Monte Carlo and scheduler simulations with confidence intervals show parity for competent deterministic and strong-classical baselines, while QRNG value emerges in assurance-oriented scenarios involving correlated restart faults, namespace reuse, and entropy provenance. The study is therefore positioned as a simulation-based validation framework rather than as a device-level QRNG demonstration; hardware-in-the-loop validation with recorded or live QRNG streams is identified as the next experimental step.

We investigate coherent thermoelectric transport in magnetic-flux-threaded quasiperiodic Su-Schrieffer-Heeger (SSH) rings with engineered multi-site electrode couplings using the nonequilibrium Green's function formalism within the Landauer-Büttiker framework. We demonstrate that the electrode-coupling geometry serves as a powerful control parameter for tailoring quantum interference, thereby reshaping the transmission spectrum and thermoelectric response. In the absence of magnetic flux, the trivial dimerized phase ($t_1>t_2$) exhibits the highest thermoelectric efficiency, with asymmetric coupling producing a substantially larger figure of merit than the symmetric geometry. Magnetic flux further reconstructs the transmission spectrum through Aharonov-Bohm interference, driving a crossover of the optimal thermoelectric regime from the trivial to the topological dimerized phase. Under optimal flux conditions, the thermoelectric figure of merit reaches $ZT \approx 12$ for symmetric coupling and is dramatically enhanced to $ZT \approx 90$ for asymmetric coupling through enhanced energy filtering and suppressed electronic thermal transport. We further establish a clear correlation between the enhancement of thermoelectric efficiency and the violation of the Wiedemann-Franz law. Our results demonstrate that the combined interplay of quasiperiodicity, topology, magnetic flux, and electrode-coupling geometry provides a versatile strategy for engineering high-performance coherent thermoelectric devices.

As quantum hardware scales to larger devices, the classical software layers that interface with it must evolve in step. Postprocessing routines developed and tested primarily in simulator settings can encode assumptions that no longer hold on utility-scale devices, leading to data loss that can be difficult to detect from high-level model outputs alone. We present a case study of \texttt{SamplerQNN}, the sampling-based quantum neural network class in the Qiskit Machine Learning library. Here, the postprocessing method applies a filter that assumes measurement bit-strings are in virtual qubit space. On our quantum hardware runs, where bit-strings span over 100 physical qubits, this filter led to the loss of 85 to 99.6\% of valid measurement shots, depending on the transpiler's qubit placement. The resulting probability vector is unnormalised, allowing distorted prediction and loss values to propagate through the model without an API-level warning. We demonstrate the impact across five experiments on two IBM backends: for inference, accuracy drops from 0.94 to 0.39 on the same raw measurements; for training, the loss signal is compressed by 22 to 27$\times$, substantially reducing the sensitivity of the optimiser to the objective landscape. The behaviour arises in all released versions of the library (0.8.4 to 0.9.0). We implemented a layout-based marginalisation fix, merged into the GitHub codebase as Pull Request \#1041, that makes \texttt{SamplerQNN} postprocessing forward-compatible with current and upcoming hardware.

Quantum software development is iterative and error-prone. Noisy hardware and repeated re-execution make experiment tracking, provenance, and reproducibility essential, yet these practices are hard to adopt because of tooling complexity and the specialized knowledge they demand. General-purpose language models can help but tend to hallucinate and lack grounding in domain-specific tooling. We present Qlippy, a retrieval-augmented GenAI assistant embedded in the development environment that grounds its responses in a curated corpus of quantum-software-engineering knowledge. Qlippy explains reproducibility and provenance concepts in context and augments existing Qiskit programs with MLflow-based experiment tracking aligned to the QProv schema. By separating knowledge from model parameters, grounding gives explicit control over the scope and provenance of the assistant's responses and reduces reliance on model scale, which points toward low-cost, privacy-preserving local deployment.

We study the distribution of the positive sojourn time for a one-dimensional two state quantum walk, conditioned on return to the origin. Konno showed that, for the Hadamard walk, this conditional distribution is exactly uniform at times divisible by $4$. In this paper, we investigate whether this finite time exact uniformity characterizes the Hadamard coin within the family of rotation coins. For a fixed initial state, we prove that the following three conditions are equivalent for rotation coins: the conditional distribution is exactly uniform at time $8$; the conditional distribution is exactly uniform at every time $4m$ with $m\ge2$; and the coin is the Hadamard coin. Thus, the uniformity phenomenon found by Konno is characterized as a rigidity phenomenon of the Hadamard coin within the rotation coin family. The proof uses a matrix-valued generating function for paths returning to the origin. We analyze the algebraic structure arising from an absorbing process on the half line. Finally, by comparing low degree coefficients at time $8$, we show that exact uniformity forces the rotation coin to be the Hadamard coin.

ANT.UI is a Python graphical interface that automates the construction of molecular-junction geometries for NEGF-DFT quantum transport calculations. Through a real-time 3D viewer, users interactively position electrodes and molecules and generate complete, ready-to-run input files for Gaussian and ANT.Gaussian without manual scripting. Dedicated Pull, Grid, and Rotation assistants further automate electrode-pulling sequences, surface scans, and step-wise rotation studies, with optional geometry-optimisation chaining across each sequence. By replacing a process that previously demanded days of custom scripting with a point-and-click workflow, ANT.UI accelerates research in theoretical molecular electronics and lowers the barrier to entry for new users. The software also exports all constructed geometries in standard XYZ format, allowing direct reuse in molecular dynamics codes or third-party visualization tools without manual reformatting.

We introduce Lindblad Multiproduct Formulas: a quantum error mitigation technique that uses two-dimensional tensor networks contracted with loop-corrected belief propagation. The quantities required to implement the error mitigation scheme that are evaluated with tensor networks can be less computationally expensive to calculate than the expectation values themselves, thus allowing for the possibility of applying our method to certain systems for which tensor network methods may struggle to calculate the observable quantities of interest. The workflow incorporates Clifford rescaling techniques and outputs an estimated error bar. We apply our method to a model of two-dimensional discrete time crystals studied previously and implement it on $65$ qubits arranged in a $3\!\times\!3$ heavy-hexagonal topology on the quantum computer ibm_basquecountry. We show that a GPU implementation of the classical part of our workflow achieves a speedup of up to $5.6\times$.

Efficiently characterizing quantum error correcting codes is a key challenge on the path to fault-tolerant quantum computation. Stabilizer codes, a central class of such codes, are defined by a set of stabilizer generators. Here, we present an algorithm that uses random single-qubit measurements to learn the stabilizer generators of any stabilizer code from $N$ copies of stabilizer states in its codespace, requiring no prior knowledge of the code's structure. This also enables verification that a device implements its intended code. We derive a lower bound on $N$ needed to recover the stabilizer generators with high probability, together with a bound on the algorithm's overall probability of success. When applied to quantum low-density parity-check (qLDPC) codes, a leading candidate for practical fault-tolerant architectures, our approach requires a number of states that scales polylogarithmically with $n$, the number of qubits.

This work examines the physical and conceptual evolution of the light quantum from Planck's blackbody theory to the theoretical and experimental developments that led to the quantization of the electromagnetic field. The present study shows that the decisive transition occurred in Einstein's quantum theory of radiation (1916-1917). Absorption, stimulated emission, and spontaneous emission were formulated as elementary probabilistic mechanisms whose statistical balance alone reproduces the blackbody spectrum. In particular, spontaneous emission requires the emission of a light quantum, thereby implicitly proving its physical necessity before its theoretical status was clarified. At the same time, the already existing term photon began to acquire a stable usage following Lewis's 1926 proposal and became increasingly associated with Einstein's light quantum. By the mid-1920s, the central problem had shifted from whether light quanta were physically required to how radiation could be incorporated into the emerging quantum-mechanical formalism. This transition marks a key stage, illustrating how initial debates about the existence of light quanta gave way to their integration into a comprehensive theoretical structure. The resulting asymmetry between the novel quantum description of matter and the still-classical description of radiation, called into question by the phenomenon of spontaneous emission, identifies the physical problem that led to the quantization of the electromagnetic field.

We investigate the spin dynamics of excitons localized in type I (In,Al)As/AlAs quantum dots with an indirect in momentum space band structure. Polarized selective photoluminescence spectroscopy, i.e. fluorescence line narrowing, under magnetic fields up to 5 T applied in the Faraday geometry is employed. The experiment reveals a cascade spin evolution process of excitons in the indirect band-gap quantum dots: an initial short term spin dynamics associated with excited direct exciton states possessing a large oscillator strength is followed by electron relaxation into the X valley of the Brillouin zone and subsequent long term spin dynamics of indirect excitons. The two step mechanism manifests itself in the distinct features of the magnetic field dependences of photoluminescence: two component recovery of optical orientation, two component linear to circular polarization conversion and the presence of the linear polarization plane rotation. At the same time, suppression of the optical alignment shows one-component behavior governed by the spin dynamics of the indirect exciton states. Within the pseudospin formalism, we derive analytical expressions that quantitatively describe the observed dependences and yield estimates for the anisotropic exchange splitting: 210 μeV for direct excitons and 1.3 μeV for indirect excitons. Further analysis using the density matrix formalism agrees well with the pseudospin model calculations and shows that the finite optical orientation at zero magnetic field is due to comparable magnitudes of the anisotropic splitting of the indirect exciton states and the splitting of the X-valley electron states caused by the hyperfine interaction with nuclei.

Accurate temperature readings of transient events at the nanometer scale are challenging due to the low sensitivity of available sensors. Nanodiamonds containing nitrogen-vacancy (NV) centers have been used for nanoscale thermometry in complex environments, including inside living cells. However, their performance has been limited by short coherence times and low photon counts. In this work, we use isotopically-purified dual-NV nanodiamonds and a bespoke quantum sensing chip to showcase an order of magnitude improvement in temperature measurement sensitivity compared with previous reports. We demonstrate robust temperature measurements with an error of 682 $μ$K, experimental sensitivities below 50 mK/$\surd \text{Hz}$ and a shot-noise limited sensitivity of 9.6 mK/$\surd \text{Hz}$. To confirm the utility of these high-performance nanothermometers, we quantify the temperature change induced by the thermometry measurement itself, specifically the optical excitation laser used to probe the NV spin state. In addition, we observe directly at the nanometre scale the transient heating caused by the exothermic mixing of dimethyl sulfoxide in water. Sub-millikelvin resolution and millikelvin sensitivity thermometry unlock the possibility of monitoring minute thermal fluctuations in living systems and assessing catalyst performance at the nanometre scale.

Engineering the properties of a reservoir and its coupling to a quantum system is a powerful tool for simulating quantum thermodynamic processes and for generating otherwise inaccessible steady states. Yet tailoring both the reservoir and its coupling within a single platform remains challenging. Here we introduce a platform, in which an ancilla qubit mediates the coupling of a target system to a reservoir, providing independent control over the interaction form, coupling strength, and effective reservoir temperature. Our implementation uses the electron spin of a single nitrogen-vacancy center in diamond as the ancilla and a proximal $^{13}$C nuclear spin as the target. By alternating engineered unitary interactions with dissipative ancilla resets, we realize dynamics naturally described by a collision model, enabling straight-forward tracking of the work, heat, coherence, and entropy generated at every collision. We experimentally demonstrate conventional thermalization and also realize anti-thermalization: the stabilization of the target system in a temperature opposite to that of its reservoir. Finally, harnessing this steady-state engineering, we utilize the nuclear spin as a quantum battery, achieving a steady-state ergotropy exceeding $70\%$ of the theoretical maximum.

Different sets of local correlations are not equivalent: some fragments of reduced data uniquely determine a global quantum state, while others leave it ambiguous. The quantum marginal problem asks whether a collection of reduced density matrices uniquely determines a compatible global quantum state. Although generic quantum states are uniquely specified by suitable sets of marginals, different collections of marginals are not equally informative: some uniquely determine the global state, whereas others leave it ambiguous. Identifying when uniqueness holds, and reconstructing the global state from partial information, remains computationally demanding and experimentally challenging. We show that information about the multipartite entanglement class and reconstructability in four-qubit systems is compactly encoded in small sets of two- and three-qubit marginals. Using semidefinite programming, we chart the reconstructability landscape across 49 inequivalent SLOCC entanglement classes and show that uniqueness strongly depends on both entanglement structure and marginal order. Neural networks trained only on reduced density matrices learn this structure directly. They accurately classify marginal reconstructability and, when uniqueness holds, reconstruct the full four-qubit density matrix with high fidelity from two- and three-qubit marginals. We benchmark the approach on a four-qubit nuclear magnetic resonance quantum processor and demonstrate that reconstructions from experimentally measured marginals remain faithful despite phase damping and control imperfections. Our results show that neural networks can learn when local correlations uniquely specify a global quantum state, and reveal how global quantum structure is encoded in reduced data.

In the weak measurement regime, post-selection can result in the observation of anomalous weak values, seemingly contradicting the eigenvalue statistics observed when the measurement interaction is strong. Here, we investigate the dependence of meter statistics on measurement strength in a post-selected measurement. We find that the meter statistics in the intermediate regime between weak and strong measurements is nearly independent of measurement strength and show that, in this regime, the system performs a measurement of momentum on the meter. The transition between weak and strong measurements is explained by a reversal of the roles of the system and the meter, where the post-selection acts as a readout of information about the meter.

Data valuation asks how learning utility should be attributed to training data contributors. Most classical formulations begin after data have become reusable records, so the physical readout of the data is effectively fixed. Finite-copy quantum data are different: unknown states are consumable physical systems, and the same supplied states and downstream task can yield different Shapley values under different physical access models. Our framework makes this dependence explicit by treating physical access as a component of quantum data valuation itself. We establish an exact connection between physical-access advantage and contributor-level data valuation. For nested access models, we prove that the maximal downstream utility gain enabled by richer physical access exactly determines the largest symmetric Shapley ranking-reversal margin. More generally, for arbitrary access-model pairs, including non-nested ones, we derive an exact geometric characterization of the possible shifts of the full Shapley attribution vector. For fixed learning pipelines, we further obtain an operational Shapley-observable representation for finite-copy valuation. Numerical experiments demonstrate that identical quantum samples can receive different values and rankings when only the physical access model is changed. These results establish that quantum data value is not an intrinsic property of the underlying states alone, but emerges from the interaction between quantum states, physical access, and the downstream learning task.

Spin-exchange optical pumping (SEOP) is a method for producing spin-hyperpolarized noble gas nuclei, such as 129Xe and 131Xe, which are used in various magnetic resonance applications from fundamental physics to quantum sensing and medical imaging. In SEOP, optically polarized alkali-metal atoms transfer their spin polarization to the noble gas nuclei in gas-phase collision events via the hyperfine coupling (HFC) between the alkali valence electron and the noble gas nucleus. While the polarization transfer physics of spin $I = 1/2$ nuclei, such as 129Xe, is relatively well understood, that of spin $I > 1/2$ nuclei, such as 131Xe ($I = 3/2$), has been far less studied, and no rigorous theoretical model has been presented to date. To this end, we derive a simple analytical model for the upper limit, neglecting relaxation, of the SEOP polarization transfer, applicable to noble gases with arbitrary nuclear spin. Analytical evaluation of the Baker-Campbell-Hausdorff expansion for the time evolution of the spin density operator $\hatρ(t)$ reveals that only even-order terms in the HFC contribute to the polarization transfer, with the leading-order quadratic term being the most significant. We obtain a result similar to that derived for the spin-exchange cross section by Herman [Phys. Rev. 137, A 1062 (1965)], but in a more general framework for the time evolution of $\hatρ(t)$ that is also more familiar to magnetic resonance researchers. The model is applied to understand the difference in the polarization transfer efficiency between 129Xe and 131Xe, yielding results in agreement with previous experiments. We also validate the model by comparison to detailed numerical multiscale simulations of the SEOP process, where full quantum-chemically computed spin Hamiltonians sampled from molecular dynamics simulations of the gas-phase collision events are used to propagate the spin dynamics.

Quantum sensing using nitrogen-vacancy (NV) centers in diamond has emerged as a powerful platform for detecting ultra-low magnetic fields under ambient conditions. Owing to their long spin coherence times, optical addressability, and compatibility with aqueous environments, it has found widespread applications in biosensing and bio-imaging. This review presents the fundamental principles and recent advances in NV-based quantum magnetometry for biosensing applications, with a particular focus on measurements in aqueous medium and at cellular and molecular length scales. We discuss the underlying spin physics of NV centers and highlight two primary detection modalities: optically detected magnetic resonance (ODMR) and T1 relaxometry-based sensing and how these approaches aids in the detection of both static magnetic fields and dynamic magnetic noise arising from biological processes. The review explores key application areas, including nanoscale nuclear magnetic resonance (NMR), monitoring of neural activity, detection of abnormal or rogue cells using NV-based platforms etc. In addition, strategies for enhancing sensitivity, such as surface functionalization of nanodiamonds, femtosecond (fs) laser-written photonic structures, and integration with microfluidic and lab-on-chip systems have also been discussed in depth. We also address the critical challenges, including surface-induced decoherence, charge-state instability, and signal-to-noise limitations in biofluids associated with NV-based biosensing applications. Finally, we outline future prospects, highlighting how NV-based magnetic biosensing provides a promising pathway for translating quantum sensing technologies into practical biomedical applications.

Charging a quantum battery through a collective non-adiabatic stroke stores energy in a shared bosonic mode, but part remains locked in correlations with the collective spin and is inaccessible to cyclic unitaries acting on the mode alone. A demon holding one bit can unlock this energy, quantified by the daemonic ergotropy. We investigate the value of one bit and its dependence on where the information is obtained. Two protocols are compared at matched stored energy and matched information, using balanced two-outcome measurements carrying exactly one bit. We find that one bit about the collective coordinate unlocks N ln(2) times as much work as one bit about a single ion. For three stored-energy settings and N = 4-24, the measured scaling exponent is 0.990 +/- 0.043, while double extrapolation gives a prefactor of 0.69298 +/- 0.00044, within 0.02% of ln(2). To leading order, the daemonic gain equals nu mu^2 times the between-outcome variance of Jx, verified numerically to 1.3%. A balanced single-ion measurement resolves 1/4 of this variance, whereas a balanced collective split resolves (ln(2)/4)N. The microscopic origin of the prefactor remains open; a Gaussian median-split estimate of 1/(2pi) is excluded by 9%. One bit recovers a constant fraction of the locked energy independent of N and yields roughly twice as much work per bit as a complete readout, indicating strong diminishing returns. We also show that unnormalized gain comparisons can reverse the conclusion and that the break-even ion number does not collapse onto the Dicke superradiant threshold when the mode frequency is varied.

Identifying the origin of the superfluid stiffness of electron-electron and electron-hole pair condensates is an important issue in flat-band physics. Here, we study the stiffness of bilayer exciton condensates using exact diagonalization and realistic Coulomb interactions across a wide variety of flat Chern band systems, including Landau levels, mixed Landau levels, and moiré bands. We find that stiffness is non-monotonic in the trace of the quantum metric and that it develops peaks when the band wavefunctions are engineered to be similar to those of Landau levels. The stiffness predicted by mean-field theory agrees quantitatively with exact diagonalization in these optimal cases, but systematically overestimates it otherwise. Flat bands with identical quantum geometry tensors can exhibit substantial differences in stiffness. The stiffness of condensates formed between moiré flat bands, which typically have strong variations in Berry curvature and quantum metric across their Brillouin zones, tends to be larger when the bands have non-zero Chern numbers and can be larger than that of Landau levels. Our results reveal a behavior that is richer than that suggested by simple geometric bounds and provide new guiding principles for the design of robust flat-band condensates with large superfluid stiffness.

Strong microwave drives enable fast measurement and parametric control in superconducting circuits but can induce transitions out of the intended low-energy manifold. We develop a unified description of strong-drive limits in flux- and charge-driven Josephson circuits across drive frequency and dc flux bias. Using classical phase-space analysis and Floquet--Markov simulations, we identify distinct low- and high-frequency mechanisms. At low frequency, we characterize bound-state resonances and separatrix chaos and find that the flux-drive chaos threshold depends strongly on dc flux bias. At high frequency, these mechanisms are suppressed, and the dissipative steady state transfers from the central bound-state sector to outer resonances formed by above-barrier running trajectories. The resulting unbound-resonance threshold is nearly independent of drive frequency and circuit parameters over the regime studied and is controlled primarily by dc flux bias. Coherent simulations show that parametric operation persists beyond this threshold, but at a reduced rate, setting an effective upper bound on the achievable operation speed. We derive analytical criteria for both thresholds, validate them numerically, and experimentally confirm the predicted dc-bias dependence of the low-frequency threshold in a flux-driven SQUID. We also determine the timescales for transfer into the unbound-resonance regime and relaxation back to the bound-state manifold after the drive is removed. Finally, we relate the stability limits to a complementary picture based on the junction critical current and extend the framework to multitone drives and inductively shunted circuits. Together, these results identify the mechanisms limiting strong driving and suggest routes to extend the stable operating range of Josephson circuits.

As quantum computing continues to scale, quantum measurement and control (QMC) are increasingly constrained by calibration workflow complexity and by requirements for low-latency execution, robust exception handling, and traceable workflow governance. Existing frameworks for QMC are specialized and task-specific, while language-model-based agents for QMC suffer from excessive latency and cannot satisfy the strict timing and control-density demands of large-scale quantum systems. Here we propose QMClaw, a general, workflow-oriented framework for QMC built, featuring a local-first, tool-governed, robust architecture. At its core is a RuleEngine-centered control layer that processes structured context, performs rule-based state transitions, and generates execution plans for typical calibration workflows. Language models are used only for natural-language interaction, high-level task understanding, and exception support, keeping the critical fast path efficient. We implement a single qubit tune-up workflow as a demonstration and validation using real quantum device dataset. We also prove that the framework achieves quantitatively acceptable levels in terms of resource cost, LLM calling times and decision latency, enabling its practical deployment in large-scale quantum qubit measurement and control scenarios. This work presents a general workflow-oriented framework for QMC and provides evidence that rule-centered architectures are a promising design choice for scalable quantum-system calibration.

Dynamic polarization controllers are key devices with broad applications in many fields. However, most on-chip polarization controllers still rely on traditional blind-search methods, whereas analytical optical-computing approaches remain insufficiently explored, particularly with respect to calibration and endless polarization control. With the accurate relative phase of Mach-Zehnder interferometer (MZI) being fully controllable on an integrated photonics chip, we present an analytical polarization control (APC) method using four phase shifters and optical computing, eliminating the need for the traditional inefficient blind-search procedure. The basic structures and operations of APC are clarified. The proposed calibration method and endless control method enable continuous APC while compensating for phase differences within the MZI structures. We simulate the influence of the endless control unit on polarization control and quantify the effect of the fourth phase difference on the output extinction ratio. With the fourth phase shifter, the phase difference encountered during Stokes vector measurement can be effectively compensated, and rotations around all three axes on the Poincaré sphere can be realized. These results establish a practical APC architecture based on optical computing for photonics chips. The proposed APC methods, combined with a FPGA-based hardware acceleration, will enable high speed on-chip polarization controllers.

Selecting an effective encoding quantum circuit is a key challenge in quantum kernel methods because different feature maps can lead to different performance. Conventional methods require constructing and evaluating every circuit for each new dataset, making it computationally expensive. We present Qmes, an open-source Python package that automatically recommends circuits through meta-learning. Qmes characterizes a dataset using classical complexity measures and queries a pre-trained model to recommend circuits without quantum evaluation at inference time. The package provides modular components for meta-feature extraction, quantum-kernel evaluation, recommender training, model selection, and user-defined circuit extension. We validate Qmes on 105 classification and 86 regression benchmark datasets. Qmes reduces the mean recommendation regret by 2.2x and 4.2x for classification and regression, respectively, compared to a non-adaptive baseline, with statistical significance confirmed via a paired Wilcoxon signed-rank test ($p < 10^{-4}$). Qmes thus enables efficient and practical encoding-circuit selection for quantum kernel methods.

The laboratory-frame anti-Jaynes--Cummings (AJC) interaction retains a residual detuning $2fλ$ that is absent from the rotating-frame model. We map two proposed remedies---a Kerr shift $χ(\hat a^\dagger\hat a)^2$ and collective Dicke coupling of $N$ two-level emitters---for a squeezed vacuum on that ladder ($r=1$, $\langle n\rangle=\sinh^2 r\simeq 1.38$). All quoted contrasts are the amplitude of the first turning point of the atomic ground-state population, which coincides with the two-level formula $\mathcal{C}=1/[1+(2f+χ)^2]$ at $r=0$ to $10^{-9}$. Three results follow. (i)~A single Kerr strength never restores unit contrast at $r=1$; the $r=0$ $n$-dependent shift $χ(2n+1)$ cannot cancel $2fλ$ on every occupied Fock component. (ii)~The exact $r=1$ contrast at $χ=0$ is not reproduced by an incoherent sum $\sum_n P_n(r)\,\mathcal{C}_n$ built from the $r=0$ two-level formula; pointwise deviations are several tenths. (iii)~Collective coupling raises the contrast systematically. At $f=5$ one finds $\mathcal{C}=0.140$ ($N=1$) and $\mathcal{C}=0.575$ ($N=8$), above the unsqueezed value $8/[8+(2f)^2]=0.074$. The $N=16$ point at this $f$ remains truncation-limited and is not quoted to three digits. The same $N\sim(2f)^2$ estimate for $\mathcal{C}=1/2$ places trapped-ion values $f\sim 10^{2}$--$10^{3}$ outside the present construction. The relevant platform is ultrastrong circuit QED with $f\sim 1$--$10$. The calculation is a numerical control landscape, not a new solvable limit.

Insider Brief Quantinuum and Aramco have signed a non-binding MoU to explore industrial quantum computing applications and potential research collaboration in fault-tolerant quantum computing. The companies plan to identify energy and digital transformation challenges that could be suitable for quantum computing research and benchmark different quantum computing modalities. The agreement also covers technical onboarding and knowledge exchange as Aramco evaluates how future quantum systems could address scientific and industrial problems. PRESS RELEASE &#8212; Quantinuum , a leading quantum computing company, today announced the signing of a non-binding MOU with Aramco , one of the world&#8217;s leading integrated energy and chemicals companies, to explore a series of industrial use cases, enhance quantum computing capabilities, and prepare for a potential research collaboration focused on fault-tolerant quantum computing. Under the MOU, the companies intend to undertake preliminary technical onboarding and engage in knowledge exchange activities. They will also identify Aramco &#8216;s challenges that may be suitable for quantum computing research with an emphasis on solving complex problems in energy and digital transformation. The collaboration aims to assess how future generations of quantum systems may address relevant scientific and industrial challenges, and to benchmark different quantum computing modalities. The collaboration complements Aramco &#8216;s existing initiatives to position itself as a leader in the application of advanced quantum technologies within the energy industry, reinforcing its efforts towards supporting the digital transformation of the sector and contributing to the evolving quantum computing roadmap for the energy industry. &#8220;Organizations that expect to benefit from quantum computing need to begin developing their expertise, algorithms and workflows today,&#8221; said Dr. Rajeeb Hazra, President and CEO of Quantinuum . &#8220;Th

Insider Brief Quantum Motion has announced the second close of its Series C funding round, with new investments from Imec.ventures, Lansdowne Partners, Sony Innovation Fund, S3 Ventures and Inkef. The funding will support silicon quantum computing development, custom silicon co-development, semiconductor manufacturing partnerships and the company’s international expansion, including its new U.S. lab in Maryland. Quantum Motion is targeting fault-tolerant quantum hardware based on silicon CMOS manufacturing, with the company also participating in Stage B of DARPA’s Quantum Benchmarking Initiative. PRESS RELEASE &#8212; Quantum Motion , the leader in silicon spin-based quantum computing, today announced the second close of its series C funding round to accelerate the scale-up of its fault-tolerant quantum hardware. This second close of the series C round led by DCVC and Kembara contributes investments from Imec.ventures, Lansdowne Partners, Sony Innovation Fund, S3 Ventures, and Inkef. The funding will drive custom silicon co-development, leverage global semiconductor manufacturing pipelines and build upon key milestones including international expansion, notably opening US lab in Maryland, and participation in stage B of DARPA’s Quantum Benchmarking Initiative (QBI). Quantum Motion is deliberately focused on industrial scalability. While many alternative quantum computing architectures carry a price tag upwards of $100 million per machine, because of the need for bespoke specialised hardware, Quantum Motion ’s silicon transistor-based approach using the standard silicon CMOS fabrication technology used in everyday chip manufacturing enables a 100-fold reduction in cost to single digit millions. Its systems are designed to be deployed into standard data-centre environments and racks, with a 100-fold reduction in space and 1000-fold reduction in energy consumption compared to alternatives. “Silicon technology transformed classical computing and it remains the only plat

The hidden world of quantum mechanics exists at scales many orders of magnitude smaller than living organisms, yet scientists have long theorized that quantum effects play an important role in biology. Birds' ability to sense magnetic fields during migration is one of the best-known mysteries in this field, with leading theories suggesting that this sensing could be achieved by exploiting quantum entanglement.

Digital quantum computing platform developer SEEQC has signed a Memorandum of Understanding (MoU) with Taiwan’s Quantum Industry Technology Promotion Office (QITPO)—an agency established under the Ministry of Economic Affairs (MOEA)—to formalize a cross-border quantum technology and supply-chain partnership. Signed at SEMICON Taiwan 2026 in Taipei, the agreement creates a structured framework for technology transfer, joint [...] The post SEEQC Signs MoU with Taiwan Quantum Industry Technology Promotion Office to Build Cryo-Chip Supply Chain appeared first on Quantum Computing Report .

Insider Brief IBM has released Nighthawk r2, a 120-qubit processor designed to deliver more useful computation through substantially faster qubit resets. The processor can execute more than 100,000 circuits per second, 25 times the throughput of IBM ’s Heron systems, while maintaining comparable gate accuracy. Nighthawk r2 has demonstrated accurate estimates on circuits containing more than 7,500 gates and supports in-circuit resets for quantum error-correction research. IBM has released its fastest quantum processor to date, using a new qubit-reset system to run substantially more computations without sacrificing accuracy. The IBM Quantum Nighthawk r2 processor can execute more than 100,000 quantum circuits per second, according to a post published on the IBM Quantum site . That is 25 times the circuit throughput of the company’s Heron processors , which run about 4,000 circuits per second. Nighthawk r2 has 120 programmable quantum bits, or qubits, the same number as the first version of Nighthawk. Its main advance is speed rather than size. IBM said the processor reduces the time required to reset qubits between circuit runs, addressing a bottleneck that limits how much work a quantum computer can complete in a given period. The processor is now available through the IBM Quantum Platform under a system called IBM Phoenix. IBM said early tests suggest the faster system could reduce the runtime of some large, repetitive quantum workloads by as much as 10 times without reducing their accuracy. The information from IBM also reflects a wider change in how quantum-computing companies measure hardware progress. Qubit counts once served as the industry’s most visible benchmark, but a larger processor is not necessarily more useful if its qubits are prone to errors or operate too slowly. IBM now evaluates its quantum hardware according to much broader measures, such as scale, quality and speed. Nighthawk r2 retains the scale of its predecessor, introduces targeted improvem

Quantum software engineering platform Classiq Technologies has entered into dual market development agreements in Taiwan with technology distributors Scientek Corporation (a Zen Voce company) and Kensho. Timed alongside SEMICON Taiwan 2026, the partnerships establish local distribution, customer enablement, and joint application R&amp;D channels across Taiwan’s semiconductor manufacturing, defense, material science, and academic research ecosystems. [ [...] The post Classiq Expands in Taiwan via Go-to-Market Partnerships with Scientek and Kensho appeared first on Quantum Computing Report .

Insider Brief Andhra University plans to establish Centres of Excellence in quantum technology, AI systems and semiconductors over the next two to three years. Vice-Chancellor G.P. Raja Sekhar said the proposed laboratories would focus on applying quantum technology and AI research to practical solutions. Speakers at the QUEST-AI conference also highlighted hybrid quantum-classical computing, sustainable data centres, semiconductor development and workforce skills as areas for regional development.\ Photo Credit: KR DEEPAK . Andhra University intends to set up Centres of Excellence covering quantum technology, AI systems, and semiconductors, Vice-Chancellor G.P. Raja Sekhar said Tuesday, The Hindu reported . Raja Sekhar made the announcement while opening a three-day international conference on Quantum-Enhanced Sustainable Technologies for AI Systems (QUEST-AI), hosted by the cluster departments of Andhra University College of Engineering in Visakhapatnam. &#8220;Following the conclusion of the centenary celebrations of Andhra University, we are focusing on quality developmental activities,&#8221; Raja Sekhar said, as quoted by the publication. He said he expects the conference discussions to push the university toward setting up the three planned labs within the next two to three years, and argued that quantum and AI research needs to move past theory and produce solutions with real societal use. K.N. Satyanarayana, Director of IIT Tirupati, delivered the conference&#8217;s inaugural address, telling attendees the central government had committed ₹6,000 crore to its National Quantum Mission, according to the outlet. Satyanarayana said quantum computing is unlikely to displace classical computing outright, predicting instead a hybrid model where the two work in tandem. He described an opening for Andhra Pradesh to go beyond a standalone quantum hub and instead build a combined quantum-AI ecosystem, bringing together government, universities, industry, startups, and

Research means asking questions of the universe. For centuries, clever minds have advanced science by devising ingenious experiments designed so their results reveal something about the laws of nature as clearly and unambiguously as possible.

Munich-based security technology group Giesecke+Devrient (G+D) has joined uPQComing (Enhancing Cyber-Resilience for the Upcoming Post-Quantum Era), a European research consortium co-funded by the European Union's Chips Joint Undertaking (Chips JU). The project focuses on migrating critical public digital infrastructure and resource-constrained embedded secure elements—specifically smart card integrated circuits and electronic identity (eID) operating systems—to Post-Quantum [...] The post Giesecke+Devrient Joins European uPQComing Consortium to Develop Quantum-Safe eID Operating Systems appeared first on Quantum Computing Report .

A new study has demonstrated that it is possible to make a network of atoms and photons that could improve how artificial intelligence stores and recalls memories. This network, called a quantum-optical spin glass, works as an associative memory, a form of AI that enables the recall of full memories from partial information—much like how humans can recognize a person's face in a blurred photograph.

Neutral-atom quantum hardware vendor Pasqal (Nasdaq: PSQL) and Saudi deep-tech startup True Nexus have announced a technical milestone in applying quantum computing to structural biology. Supported by Saudi Arabia’s Ministry of Communications and Information Technology (MCIT), the teams successfully encoded protein structures associated with molecular gelation—the phase transition that converts protein liquids into gels to [...] The post Pasqal and True Nexus Encode Protein Gelation Structures on Neutral-Atom QPUs appeared first on Quantum Computing Report .

Quantum computing developer Rigetti Computing and researchers from Purdue University have published joint research extending Rigetti's quantum preconditioning framework to hard-constrained combinatorial optimization problems. By using two-point variable correlations extracted from shallow Quantum Approximate Optimization Algorithm (QAOA) circuits to modify the objective function of commercial Mixed-Integer Programming (MIP) solvers, the team demonstrated that quantum preconditioning [...] The post Rigetti and Purdue University Demonstrate Quantum Preconditioning Framework for Constrained Optimization appeared first on Quantum Computing Report .

Insider Brief SEALSQ and wolfSSL have announced wolfTPM support for the SEALSQ QVault TPM, adding software support for post-quantum algorithms implemented in the TPM hardware. The integration supports ML-DSA, Hash-ML-DSA and ML-KEM parameter sets, with testing performed on physical QVault hardware and wolfSSL’s firmware TPM environment. wolfTPM includes QVault-specific support, a new pqc_ctrl tool, post-quantum examples, build instructions and hardware benchmarks for embedded development. PRESS RELEASE &#8212; SEALSQ Corp (NASDAQ: LAES) (&#8220;SEALSQ&#8221; or &#8220;Company&#8221;), a company that focuses on developing and selling Semiconductors, PKI, and Post-Quantum technology hardware and software products, and wolfSSL Inc., a recognized leader in embedded cryptography, today announced wolfTPM support for the SEALSQ QVault TPM. Market First The SEALSQ QVault TPM is on track to be the first shipping TPM 2.0 device on the market to implement in silicon the post-quantum algorithms introduced in the Trusted Computing Group’s latest TPM 2.0 v1.85 specification. wolfTPM gives developers a direct path to use QVault’s ML-DSA and ML-KEM capabilities in embedded applications. Perfect Interoperability and Scalability This integration demonstrates the perfect interoperability of QVaultTPM with the TPM 2.0 standard and with widespread components like wolfTPM that follow this standard, thereby facilitating the market launch and scalability of QVaultTPM based quantum resistant solutions to protect connected devices. “QVault implements post-quantum algorithms directly in TPM hardware, while wolfTPM provides the embedded software support needed to use them,” said Jean Pierre Enguent, CTO at SEALSQ. “Together, SEALSQ and wolfSSL are bringing hardware-based post-quantum security closer to deployment and scale.” Bringing Post-Quantum TPM Support to Embedded Development The integration adds dedicated SEALSQ QVault support to wolfTPM, including manufacturer detection and device-spec

Insider Brief Researchers from JPMorganChase and Argonne National Laboratory developed a method to evaluate high-depth QAOA calculations for large Sherrington–Kirkpatrick model problems without running the algorithm end to end. The approach maps the QAOA state in the infinite-size limit to a spin-boson system, allowing researchers to use matrix product state simulations instead of more costly calculations. The researchers used supercomputers at DOE computing facilities to simulate the system and optimize QAOA parameters, providing a way to study the performance and limits of quantum optimization algorithms. PRESS RELEASE &#8212; Quantum computers have arisen as a possible solution for highly complex mathematical problems, offering ​“quantum advantage” over classical computers in certain cases. The Quantum Approximate Optimization Algorithm (QAOA) is a leading candidate for realizing this advantage, and some success has been achieved for small problems. But demonstrations on large problems have remained too computationally costly to run on classical computers and current quantum hardware. Researchers from JPMorganChase and the U.S. Department of Energy ’s (DOE) Argonne National Laboratory have now found a way to make such calculations possible. Their results were published in Physical Review Letters. Overcoming the Computational Barrier The team focused on the Sherrington–Kirkpatrick (SK) model, a disordered system with random interactions between every pair of variables. “As problem size grows, the SK model’s optimal value is known in the large-system limit. This value provides a baseline to measure how well QAOA is performing,” said Jeffrey Larson, a computational mathematician in Argonne ’s Mathematics and Computer Science division and a coauthor of the paper. The researchers discovered that in the infinite-size limit, a high-depth QAOA state for the SK model converges mathematically to a single quantum spin coupled to bosonic modes. By translating the problem int

Post-quantum semiconductor hardware vendor SEALSQ Corp (NASDAQ: LAES) and embedded cryptography developer wolfSSL Inc. have announced native wolfTPM software support for SEALSQ’s QVault TPM hardware security chip. Designed to implement post-quantum cryptography (PQC) primitives in silicon under the Trusted Computing Group’s (TCG) TPM 2.0 v1.85 specification, the integration provides an open-source software layer to execute [...] The post SEALSQ Integrates wolfTPM Support into Post-Quantum Silicon Semiconductor Platform (QVault TPM) appeared first on Quantum Computing Report .

The BESIII Collaboration, led by the Institute of High Energy Physics of the Chinese Academy of Sciences, has achieved the world's most precise measurement of the electric dipole moment (EDM) of the Lambda (Λ) hyperon using quantum-entangled Λ–anti-Λ pairs produced in J/ψ decays. The result improves the experimental sensitivity by about three orders of magnitude compared with the previous measurement, providing a new way to probe charge-parity (CP) violation in particles containing strange quarks.

George Mason University has entered into a strategic hardware partnership with Oxford-based quantum infrastructure firm TreQ to deploy an open-architecture quantum computer at its Northern Virginia campus. Supported by catalytic funding from the Virginia Innovation Partnership Corporation (VIPC) alongside university capital, the $7.7 million system will represent the first U.S. deployment of TreQ’s proprietary Open [...] The post George Mason University Partners with TreQ to Install $7.7M Open-Architecture Quantum QPU in Virginia appeared first on Quantum Computing Report .

Researchers from MIT have designed a new qubit architecture that enables qubits to interact with each other much more quickly while remaining very stable. This advance could someday help scientists build practical quantum computers that can run long, complex algorithms with high accuracy.

When simulating the dynamics of open quantum systems with quantum computers, it is essential to accurately approximate the system&amp;apos;s behaviour while preserving the physicality of its evolution. Traditionally, for Markovian open quantum systems, this has been achieved using first and second-order Trotter-Suzuki product formulas or probabilistic algorithms. In this work, we introduce novel non-probabilistic algorithms for simulating Markovian open quantum systems using randomisation. Our methods, including first and second-order randomised Trotter-Suzuki formulas and the QDRIFT channel, not only maintain the physicality of the system&amp;apos;s evolution but also enhance the scalability and precision of quantum simulations. We derive error bounds and step count limits for these techniques, bypassing the need for the mixing lemma typically employed in Hamiltonian simulation proofs. Furthermore, we implement these randomised algorithms using Classical Sampling (CS), demonstrating their gate complexity advantages over deterministic TS product formulas. This work systematically extends powerful randomisation techniques from Hamiltonian simulation to the general setting of Markovian open quantum systems, highlighting their potential to enable faster and more accurate simulations.

Quantum Max Cut (QMC) problem for systems of qubits is an example of a 2-local Hamiltonian problem, and a prominent paradigm in computational complexity theory. This paper investigates the algebraic structure of a higher-dimensional analog of the QMC problem for systems of qudits. The Quantum Max d -Cut ( d -QMC) problem asks for the largest eigenvalue of a Hamiltonian on a graph with n vertices whose edges correspond to swap operators acting on ( C d ) &amp;#x2297; n . The algebra generated by the swap operators is identified as a quotient of a free algebra modulo symmetric group relations and a single additional relation of degree d . This presentation leads to a tailored hierarchy of semidefinite programs, leveraging noncommutative polynomial optimization (NPO) methods, that converges to the solution of the d -QMC problem. For a large class of complete bipartite graphs, exact solutions for the d -QMC problem are derived using the representation theory of symmetric groups and Littlewood-Richardson coefficients. Lastly, the paper addresses a refined d -QMC problem focused on finding the largest eigenvalue within each isotypic component (irreducible block) of the graph Hamiltonian. It is shown that the spectrum of the star graph Hamiltonian distinguishes between isotypic components of the 3 -QMC problem. For general d , low-degree relations for separating isotypic components are presented, enabling adaptation of the global NPO hierarchy to efficiently compute the largest eigenvalue in each isotypic component.

Stabiliser codes with large weight measurements can be challenging to implement fault-tolerantly. To overcome this, we propose a Floquetification procedure which, given a stabiliser code, synthesises a novel Floquet code that only uses single- and two-qubit operations. Moreover, this procedure preserves the distance and number of logicals of the original code. The new Floquet code requires additional physical qubits. This overhead is linear in the weight of the largest measurement of the original code. Our method is based on the ZX calculus, a graphical language for representing and rewriting quantum circuits. However, a problem arises with the use of ZX in the context of rewriting error-correcting codes: ZX rewrites generally do not preserve code distance. Tackling this issue, we define the notion of distance-preserving rewrite that enables the transformation of error-correcting codes without changing their distance. These distance-preserving rewrites are used to decompose arbitrary weight stabiliser measurements into quantum circuits with single- and two-qubit operations. As we only use distance-preserving rewrites, we are guaranteed that a single error in the resulting circuit creates at most a single error on the data qubits. These decompositions enable us to generalise the Floquetification procedure of Townsend-Teague et al \cite{townsend-teagueFloquetifyingColourCode2023} to arbitrary stabiliser codes, provably preserving the distance and number of logicals of the original code.

Abstract Non-Hermitian quantum systems exhibit qualitatively distinct physical behavior compared to Hermitian systems, a prime example being spectral singularities known as exceptional points. Their relevance in, e.g., quantum sensing, unidirectional transport, and robust lasing makes it important to be able to identify exceptional points through observable features of a many-body system. Here, using as an example a one-dimensional complex XY spin chain realizing both rotation-time RT- and parity-time PT-symmetric regimes, we develop a framework for detecting exceptional points based on the distinction between left and right eigenvectors of the Hamiltonian, which in a non-Hermitian system are no longer the adjoint of each other. We first show that a global measure constructed from the difference between the Hamiltonian and its adjoint locates exceptional points via distinct non-analytic behavior. At the level of observables, differences in local spin correlations evaluated on the right and left eigenstates provide a reliable static detection scheme. In contrast, static bipartite entanglement measures fail to capture this distinction, urging us to study the quantum dynamics of the model. Following a sudden quench, we demonstrate that the time-averaged right-left entanglement entropy difference directly encodes signatures of the exceptional point. In the RT-symmetric regime, it exhibits a pronounced peak at the exceptional point, whereas in the PT-symmetric regime it behaves as an order-parameter-like quantity, remaining finite in one phase and vanishing at the transition. Our results establish a direct link between the structure of non-Hermitian eigenstates and observable signatures of exceptional points, providing a practical route to identify them in existing quantum simulators.&amp;#xD;

Quantum error-correction decoders are typically benchmarked against synthetic circuit-level noise, under the assumption that a decoder's ranking under such noise transfers to hardware and improves as the noise model becomes more realistic. The Willow processor, the first to operate below the surface-code threshold, allows us to test this assumption. We rank a panel of six decoders using a four-rung ladder of noise models with increasing fidelity, evaluated against real data across three code distances, two bases, and fifteen round counts. Rank agreement with hardware appears once the noise model gives each operation type its own error rate. Calibrating the model to the device improves absolute error rates but not rank agreement. We additionally provide the first independent evaluation of NVIDIA's Ising pre-decoder on hardware, at code distances below its training receptive field and via a mapping onto the lattice on which it was trained. Under these conditions, it holds no accuracy-latency advantage: another panel decoder matches or improves on it in both per-cycle error rate and decode latency in 278 of the 280 evaluations. We release the full pipeline and the per-shot outcome of every evaluation, so future decoders and devices can be compared.

Distributed quantum computing (DQC) offers a promising approach to scale quantum computing by overcoming the resource limitations of a single quantum processor. However, inter-node communication remains a major bottleneck of DQC due to inefficient and error-prone entanglement distribution. Optimizing inter-node communication can not only reduce the amount of entanglement resource needed to execute a quantum circuit but also improve execution speed and accuracy of the results. This paper proposes DPRQ, a qubit routing algorithm for minimizing inter-node communication in distributed quantum circuits divided into collective communication blocks. Unlike current approaches that utilize greedy block-level qubit routing strategies, DPRQ employs a dynamic programming-based technique focused on global circuit-level optimization, while capturing inter-block dependencies. We evaluated DPRQ on four sets of quantum circuits and a variety of DQC configurations. The results demonstrate that DPRQ's innovative routing strategy achieves an average of 24.40% reduction with a maximum of 85.06% reduction in inter-node communication, when compared to the state-of-the-art collective communication-based DQC compiler QuComm.

This work describes the calculation of spin-orbit spillage from a crystal structure. Spin-orbit spillage provides a measure of the likelihood that a material has topological character. The spillage also provides the reference quantity for the machine-learning classifier of Choudhary et al., which predicts whether the spillage exceeds a specified threshold rather than the calculation of its numerical value directly. The complete computation workflow was applied to the insulating compound BaMg2Bi2, yielding a spillage of 2.094 compared with the published VASP spillage of 2.075, corresponding to a difference of 0.9%. The calculation is described in terms of two Quantum ESPRESSO (QE) calculations of spillage performed with and without spin-orbit coupling, the role of relativistic pseudopotentials, and the subsequent wavefunction-overlap analysis. The limitations of the same calculation procedure for semimetals are also examined.

We introduce chameleon gates as a natural generalization of conventional quantum controlled-gates. Chameleon gates are state-based quantum controlled-operations that retain standard elements such as control and target systems, while introducing a new feature: the quantum knob. This knob is a quantum signal (state) that determines the operation performed by the gate. Consequently, the action and form of a chameleon gate depend dynamically on the quantum knob, allowing the gate to adapt its operation and implement transformations that are not necessarily unitary. This shapeshifting property is in stark contrast to conventional quantum controlled-gates, whose actions are fixed and cannot be modified. We also propose how chameleon gates can be realized using conventional quantum gates available in current quantum technologies. We then employ chameleon gates as a useful building block within the recently proposed state-based quantum computation (SBQC) framework. Using this approach, we demonstrate the simulation of state-dependent (nonlinear) quantum evolutions.

We study the one-shot and concurrent hitting for the discrete-time Grover-coined quantum walk on cubelike graphs $G=\text{Cay}(\mathbb Z_2^d,Ω)$ of degree $Δ=|Ω|$. Starting from the vertex labeled $0$, we identify $σ=\bigoplus_{ω\inΩ}ω$ as a natural target vertex; for the hypercube, $σ$ is precisely the antipodal vertex. For families with $Δ\to\infty$, let $T$ be an integer having the same parity as $Δ$ and satisfying $ \left|T-\frac{πΔ}{2}\right|\leq 1. $ We show that the probability $p_T(σ)$ of finding the walker at $σ$ when it is measured at time $T$ satisfies $$ p_T(σ)=1-O(Δ^{-1/5}). $$ Thus the target is found with probability tending to one after $Θ(Δ)$ steps. For the concurrently measured walk, let $H_T^{\mathrm{Conc}}(σ)$ denote the probability that the target is detected at or before time $T$ when it is tested after every step. We prove $$ p_T(σ)\leq T H_T^{\mathrm{Conc}}(σ), $$ which implies $H_T^{\mathrm{Conc}}(σ)=Ω(Δ^{-1})$ over the same time scale. The proof uses the Walsh-Fourier decomposition, an exact two-dimensional reduction of each Fourier mode, and a universal second-moment identity for the associated character sums. Our results extend Kempe's hypercube hitting phenomenon (J. Kempe, Probab. Theory Relat. Fields 133, 215-235, 2005) to arbitrary cubelike generating sets and establish the conjectured asymptotic hitting behavior for cublelike and augmented cubes in Mulherkar, Rajdeepak and Sunitha (Int. J. Quantum Inf. 20,2250020, 2022)

In single-port non-Hermitian sensors the Petermann factor offsets susceptibility gains, imposing a strict resource bound on metrological precision. We test whether a multi-port geometry can evade this bound: a double-chain optomechanical ladder with opposing non-reciprocal hoppings spatially separates signal amplification from quantum-noise drainage, and gradient-based differentiable optimal control (DOC) maximizes the resource-normalized Fisher information $\Fnorm$ subject to a Hurwitz-stability constraint. Across system sizes $N\in\{\num{6},\dots,\num{16}\}$ the optimizer returns $\Fnorm>0$ in every case, with two coexisting solution classes whose selection is initialization-dependent: deep-stability configurations achieve $\Fnorm\in\numrange{0.937}{0.987}$ with attenuated transmission, while marginal-stability configurations deliver directional gain $\Gfwd\in\qtyrange{13.5}{15.5}{\dB}$ with isolation $\Iso\in\qtyrange{40}{64}{\dB}$. A multi-restart ensemble reveals these classes are the endpoints of a precision--gain frontier. All solutions remain Hurwitz-stable under \qty{5}{\percent} disorder (\qty{87.5}{\percent} recovery), and the deep-stability advantage survives realistic preamplifier noise at $\Fnormeff\approx\num{0.3}$--$\num{0.5}$. Mapped onto circuit-QED parameters, the architecture enables sub-attonewton force sensing and broadband axion searches across the \qtyrange{1}{10}{\giga\hertz} band.

The scalability of variational quantum algorithms is fundamentally limited by the barren plateau effect, where the cost-function variance vanishes with system size, rendering optimization impractical. Recent Lie-algebraic approaches for deep parameterized have enabled a unified analytical understanding of this challenge but require either the initial state or the measurement observable to belong to the dynamical Lie algebra generated by the circuit. Here, we introduce a representation-theoretic framework under $2$-design hypothesis showing that variational quantum landscapes admit a natural decomposition into irreducible representation channels. This yields exact expressions and analytical bounds for the cost-function variance applicable to arbitrary initial states and observables, with previous Lie-algebraic results emerging as a special case. We illustrate the framework by analyzing the energy landscape of the one-dimensional ANNNI model for several circuit architectures, revealing trainability regimes inaccessible to existing methods. Our results establish a general representation-theoretic framework for analyzing variational quantum landscapes, substantially extending the analytical theory of barren plateaus.

High-rate quantum low-density parity-check (qLDPC) codes can substantially reduce qubit overhead relative to surface codes, but their advantage depends on efficiently realizing nonlocal syndrome extraction. We study the \([[144,12,12]]\) bivariate bicycle code on a neutral-atom architecture with native three-dimensional (3D) geometry, comparing planar and 3D embeddings while holding the code fixed. We characterize spatial efficiency using the logical-qubit density, defined as the number of encoded logical qubits per unit spatial footprint. Because the optical controller's field of view limits the transverse extent of an array, this metric estimates the number of logical qubits that can be accommodated within a fixed optical field of view. The 3D embedding achieves approximately \(4\times\) greater areal logical-qubit density than the planar layout and \(42\times\) greater than a surface-code baseline. It also reduces the bivariate bicycle syndrome-extraction time by roughly \(2\times\) compared to a planar baseline, with fewer movement operations and substantially shorter atom-transport distance. Native 3D geometry can improve both the packing density and executable realization of nonlocal qLDPC codes, making practical performance depend jointly on code structure, optical geometry, transport scheduling, and hardware-level noise. This motivates further development of control techniques in 3D.

Interactions between a quantum system and its environment can inject ergotropy into the system, raising the question of the minimal dimensionality and physical resources required for such injection. We first show that ergotropy injection is impossible under thermal operations when both the system and environment are qubits, whereas it becomes possible when the environment is enlarged to a qutrit. We further show that already in the qubit-qubit setting, relaxing environmental thermality and allowing interactions between system and environment allows ergotropy increment under energy-conserving unitaries. To elucidate the role of interactions, we consider a two-qubit isotropic XY interaction Hamiltonian and identify its distinct degeneracy regimes. We show that, in the central-block regime, when both the initial system and environmental states are incoherent, no ergotropic gain is possible when the environment is initially thermal, irrespective of the interaction strength. In contrast, environmental athermality in the form of population inversion, while retaining incoherence, enables ergotropic injection. We derive the optimal ergotropic gain and show that environmental coherence can enhance it, while system coherence alone need not be beneficial and can even reduce the gain. We further consider the double-degenerate regime, characterized by a finite interaction strength, and demonstrate positive ergotropic gain even for a thermal environment.

Twin-field (TF) quantum key distribution (QKD) offers a promising approach to long-distance QKD networks due to its superior performance over large channel losses. Due to specialized hardware requirements, nearly all long-distance TFQKD demonstrations have only two users exchanging keys, rather than a network with three or more users. In this work, we experimentally demonstrate a proof-of-principle three-user-pair Sagnac TFQKD network spanning 127-km using single-photon avalanche detectors without any active phase stabilization or postcompensation. We implement efficient procedures for maintaining polarization stability and circumventing Rayleigh backscattering noise to achieve a stable Sagnac interference visibility of $93\pm1$% over one hour. A secure key rate of $1.398\times10^{-5}$ bits per pulse is achieved over an asymmetric communication channel with 102-km fiber and 45-dB overall loss. To our knowledge, this is the first TFQKD network without active phase stabilization or postcompensation achieved over long fibers. Our results represent a highly practical and cost-effective approach to long-distance QKD networks.

We prove a structure theorem for the dimension towers~$\{d_k(D)\}_{k\geq0}$ which arise in the number-theoretic formulation of Zauner's SIC-POVM conjecture over a real quadratic field~$K=\Q(\qD)$. If~$\eps$ denotes the first totally positive power of a fundamental unit of~$K$ and $t_k = \eps^k + \eps^{-k}$ the trace of its $k$-th power, then the SIC dimension tower~$\{d_k=1+t_k\}_{k\geq0}$ is the level~$m=3$ row of an infinite two-dimensional cyclotomic array~$\{Ψ_m(t_k)\}_{m\geq1,k\geq0}$ attached to~$K$, while the auxiliary factors~$(d_k+1)$ and $(d_k-3)$ are its ramified levels $m=2$ and $m=1$. Here~$Ψ_m$ denotes the minimal polynomial of~ $ζ_m+ζ_m^{-1} = 2\cos{2π/m}$. This construction arose initially from an attempt to formulate relations among SIC dimensions in $q$-algebraic terms. The central object is a single closed composite norm relation for the two-parameter family $c_{m,k}=1-ζ_m\eps^k$ over the cyclotomic field tower $\{K(μ_m)\}_{m\geq1}$. This framework sheds new light on the mod-$p$ analogue of Leopoldt's conjecture, by placing the central 3-symmetry of Zauner's conjecture within a broader arithmetic context. Away from the primes dividing~$2mD$, the valuations $v_p(Ψ_m(t_k))$ at every fixed level~$m$ are described exactly in terms of a single local unit valuation, which is then related, through the~$p$-adic class number formula, to the corresponding $p$-adic $L$-value.

The problem of the effective excitations of a gauge theory in the nonperturbative regime remains not completely understood. Using the Refined Gribov-Zwanziger (RGZ) theory as effective model for pure gauge Yang-Mills theories, we revisit the quasiparticle (quadratic) excitations of the theory. A novel interpretation of such quasiparticles is proposed, in the case of real mass poles, taking into account the manifest ${\cal PT}-$symmetry of the RGZ Lagrangian.

There is an extensive body of research probing the potential of adiabatic quantum computation and quantum annealing to solve hard computational problems. This research endeavor is complicated by noise afflicting hardware during the computational process. An error-correcting approach called quantum annealing correction (QAC) was suggested to mitigate this noise. The QAC approach employs a centralized version of the repetition code in which the qubits are configured in a star-graph pattern with one special qubit playing the role of the hub. In this paper, we explore the thermal physics of the centralized repetition code, using a Lindblad equation framework to analyze its lifetime when coupled to a thermal bath. We show that its centralized configuration leads to thermal stability, enabling the robust storage of a logical bit of information, despite the fact that there is only 1 ferromagnetic Ising interaction per qubit like a 1-dimensional Ising chain.

Modern atomistic simulations increasingly employ localized orbitals to represent quantum operators, yielding sparse block matrices whose block shapes vary with chemical species and basis choice. Conventional scalar sparse formats store the entries of each block individually, obscuring this local structure and limiting the use of efficient block algorithms. We present VBCSR, a distributed sparse matrix library that preserves variable-size atomic blocks and accelerates the core linear algebra of large-scale atomistic simulations. A unified interface automatically maps scalar, uniform-basis, and multispecies operators to compressed sparse row (CSR), block sparse row (BSR), or variable-block compressed sparse row (VBCSR). Our advanced acceleration method groups blocks of equal shape and dispatches them to optimized dense kernels. In the reported benchmarks, VBCSR outperforms the tested Python-accessible reference implementations for several block-sparse benchmarks. We further demonstrate VBCSR in an InP nanoparticle application containing more than \(10^6\) atoms.

Quantum simulations of correlated many-body systems will inevitably operate with imperfect information: the prepared states may arise from incomplete or approximate ansatze, while their measured Hamiltonian and overlap matrix elements are additionally affected by hardware and statistical noise. Robust quantum algorithms will be those that can improve upon reliable lower-level descriptions in spite of these imperfections. We introduce a dual-space nonorthogonal configuration-interaction (DS-NOCI) framework built around this principle. Rather than replacing a classically accessible NOCI reference manifold with correlated quantum states, DS-NOCI retains both spaces and couples them variationally. The reference sector provides a stable many-body backbone, while the quantum states contribute whatever additional correlation directions they contain. With exact matrix elements, the enlarged dual space gives a ground-state energy no higher than either the reference-only NOCI or correlated-only quantum-NOCI spaces, ensuring that an incomplete correlation model cannot degrade the underlying variational description. The additional reference--correlated matrix elements require only one correlated state preparation and are therefore less demanding than the correlated--correlated block already required by quantum variant of NOCI. Molecular benchmarks further show enhanced resilience to imperfect amplitudes and noisy matrix elements. DS-NOCI thus provides a general strategy for building quantum many-body formulations that remain useful when both correlation models and quantum computations are necessarily incomplete and noisy.

We present a unified theoretical analysis of three-photon quantum interference in a Six-Port Mach-Zehnder Interferometer (6p-MZI) constructed from two cascaded tritters, with two independent phase modulators placed between the tritter arms. We analytically derive the transfer matrix of the 6p-MZI and show how they organize into three symmetry classes, governed by the discrete Fourier transform (DFT) structure of the tritter and the conjugate relations. Furthermore, we analyze two input regimes: First, three indistinguishable single photons are injected into the tritter, and the output probability distributions $P_{[111]}$, $P_{[\{300\}]}$, and $P_{[\{210\}]}$ are derived as functions of the two relative phases $(φ_1, φ_2)$. At $φ_2 = 0$, the single-phase limit is recovered, which confirms 100\% visibility of the even-distribution fringe. Second, a hybrid coherent-Fock input $|α\rangle_1|α\rangle_2|1\rangle_3$ is analyzed via the density matrix formalism. The average photon number at each output port exhibits amplitude-dependent phase shifts. Our results establish the 6p-MZI as a programmable platform for tripartite quantum state manipulation and coherent amplitude sensing.

Jets are central to the physics programs of both current and future colliders, from precision Standard Model measurements and searches for new physics at the Large Hadron Collider to studies of nucleon structure at the future Electron-Ion Collider. Motivated by these applications, we explore quantum machine learning for jet classification and present a permutation-invariant Quantum Graph Neural Network (QGNN) applied to particle-cloud representations of jets. We apply the model to two such discrimination tasks: quark vs. gluon and up vs. down quark flavor tagging, with the latter being, to our knowledge, the first application of a quantum model to this problem. In the ideal simulation, the QGNN performs competitively against the Particle Flow Network and traditional QCD observables. We further deploy scaled-down models to IBM and IonQ quantum processing units (QPUs), where we train and evaluate them, obtaining promising results. Finally, we perform an interpretability analysis to characterize the observables learned by the quantum model, relating them to generalized angularities for the quark-gluon study and to jet charge for the flavor study.

We develop a quantum sensing framework for the phase independent detection of weak coherent optical displacements based on SU(1,1) interferometry. Unlike conventional quantum measurement protocols that require prior knowledge of the signal phase and coherent homodyne detection, the proposed approach estimates the displacement magnitude independently of its phase. We show that, under ideal lossless conditions, a conventional SU(1,1) interferometer employing only total intensity detection saturates the quantum Cramer Rao bound for displacement magnitude estimation. We further derive the analytical expression of the quantum Cramer Rao bound and the sensitivity of the conventional SU(1,1) interferometer with total intensity detection and systematically investigate its performance in the presence of optical loss. The proposed phase-independent intensity detection scheme achieves comparable performance over experimentally relevant operating regimes while eliminating the need for local oscillators, phase locking, and quadrature tracking. These results establish SU(1,1) based intensity detection as a practical platform for phase independent quantum sensing.

We study edge-state transport in a two-dimensional topological insulator with a periodically deformed edge subjected to a uniform magnetic field. Zeeman coupling breaks time-reversal symmetry and enables elastic backscattering, producing oscillations of the forbidden-band widths. In the strong-field regime, the gaps can close completely at discrete field values. In the weak-field regime, we identify an important class of periodic deformations for which the dominant semiclassical scattering is controlled by complex infinity rather than by the nearest turning points. We develop a semiclassical treatment of this process and establish its agreement with perturbation theory and direct numerical calculations. The gap modulation should produce observable oscillations of the edge conductance. Unlike conventional magnetic quantum oscillations, which are periodic in inverse field, the predicted oscillations are periodic in the magnetic field itself, with a period determined by the Fermi velocity and effective g-factor

We introduce a new class of p-adic Dirac equations, formulated in the standard axiomatic framework of quantum mechanics, in which the ordinary spatial derivatives are replaced by non-local operators built from arbitrary integrable kernels. We diagonalize the resulting free Dirac Hamiltonian in momentum space, construct its plane-wave solutions, determine its spectrum, and establish a p-adic charge-conjugation symmetry relating particle and antiparticle sectors. We then discretize the free equation in two ways, both giving genuine continuous-time quantum walks rather than the discrete-time, coined walks that dominate the existing literature: a first construction on a countable covering of the underlying p-adic space, and a second, more explicit construction on a finite, tree-structured graph, for which we prove that the transition probabilities, once the internal (particle/antiparticle) components of the wavefunction are combined, form a genuine, properly normalized set of transition probabilities at every instant of time; in other words, ignoring the internal structure of the walk, it behaves exactly like an ordinary random walk on that graph. Building on this stochastic-matrix property, we discuss how the resulting construction can serve as the foundation of a quantum network with genuinely relativistic-type internal degrees of freedom, complementing earlier, non-relativistic p-adic quantum neural networks. To the best of our knowledge, this is the first continuous-time quantum walk whose free dynamics coincides exactly with a Dirac equation on a hierarchical graph. We close with a discussion of the open mathematical and computational problems raised by this construction.

Let $$X_n=\sum_{i=1}^s t_i A_i^{\otimes n},$$ where $A_1,\ldots,A_s\in M_d(\mathbb C)$ and $t_1,\ldots,t_s\in\mathbb C$ are fixed, while $n$ grows. Direct computation of determinants or Schatten norms of $X_n$ is exponential in $n$. For a single tensor power these quantities are elementary, and even the determinant of a generic two-term combination admits a reduction to polynomially many scalar factors; however, no analogous elementary reduction is available for three or more terms. We give an exact representation-theoretic method which, for fixed $d$ and $s$, computes $\|X_n\|_p$, $0<p<\infty$, and determinants in polynomial time in $n$. Schur--Weyl duality yields a simultaneous block decomposition, while Jacobi--Trudi identities in the Grothendieck ring replace Schur modules by signed combinations of tensor products of symmetric powers. For $d=3$, each irreducible contribution reduces to the difference of two explicitly computable symmetric-power terms, leading to an open-source implementation. In a single-thread CPU benchmark, a genuine three-term $3\times3$ trace-norm problem with $n=18$ is evaluated in about $47$ seconds, whereas just storing the unreduced matrix would require approximately $2.4\times10^{18}$ bytes. Direct and reduced computations agree to relative error below $3.4\times10^{-15}$ throughout their common range $n\leq9$.

Recent experiments on multilayer graphene systems have reinvigorated the study of electron crystallization, now with the inclusion of quantum geometry. In this work, we apply time-dependent Hartree-Fock (TDHF) to the $λ$-jellium model to analyze the impact that quantum geometry has on the electronic liquid--crystal phase diagram and how it modifies the collective modes and responses of the liquid and crystal phases. In agreement with recent results utilizing neural quantum states, we find that quantum geometry favours electron crystallization, shifting the transition to higher densities. We also study the instabilities revealed by TDHF in the Fermi liquid ground state at low densities, providing insight into the fluctuations driving the crystallization transition. We further find that quantum geometry reduces the dispersion of the plasmon mode and suppresses Friedel oscillations deep in the liquid phase. Resolving the density response in terms of individual orbitals, we find that this suppression is caused by spectral weight transfer to an out-of-phase inter-orbital mode. Finally, we show that an analogous mode that emerges in the crystal phase corresponds to the breathing mode of an emergent real-space pseudospin skyrmion lattice.

We clarify the meaning of a probabilistic no-signalling strategy in Ref [Proc. R. Soc. A 481, 20240601]. For every fixed input, the deterministic strategy constructed using the Axiom of Choice can indeed be represented by a Dirac probability distribution over the outputs. The relevant distinction arises when one considers the complete process from input to output, with the input itself sampled according to a probability distribution. In this case, the input and output spaces must be measurable and the dependence of the conditional output distribution on the input must also be measurable. Equivalently, the conditional distributions must form a Markov kernel. The Axiom-of-Choice strategy fails precisely this measurability requirement.

Quantum technologies may revolutionize optical interferometry through new means to distribute and preserve electric-field amplitude and phase correlations between widely separated telescopes. After reviewing existing techniques, I survey proposed quantum-sensing and quantum-networking applications and highlight recent laboratory demonstrations of key building blocks. By easing field-transport demands for baselines beyond $\sim$1 km, quantum-enhanced interferometry could enable sub-milliarcsecond imaging and microarcsecond-class differential astrometry. That said, "going quantum" is not a magic shortcut to sensitivity because many of the most compelling science cases remain photon- and turbulence-limited. I therefore emphasize the practical constraints -- loss, bandwidth, coherence time, synchronization, and wavelength limits of quantum interfaces -- that must also be overcome to make these capabilities useful for astronomy, whether deployed on the ground or from space.

Floquet driving uses periodic controls to tailor the behavior of quantum systems, with applications in quantum analogue simulation, sensing, and the protection of quantum information. Most approaches are designed using idealized, instantaneous pulses, even though experiments necessarily use pulses with finite duration and shape. This mismatch becomes especially challenging for interacting $d$-level systems, or qudits, because the number of possible controls grows rapidly with the number of levels. We develop a strong-drive Floquet theory that incorporates experimentally realizable pulse waveforms directly into the design of the effective interactions. The pulse duration, amplitude, and shape therefore become useful control parameters rather than sources of error. We show that systems with more than two levels offer capabilities unavailable in qubit systems: finite-duration driving can create new interactions that are absent from the original system and can substantially change its symmetries. We demonstrate these capabilities for interacting three-level systems. A single pulse transforms a diagonal interaction into a quantum spin-1 model dominated by nematic interactions, while pulse protocols motivated by trapped ultracold polar molecules produce models with enlarged $SU(2)\times U(1)$ and $SU(3)$ symmetries. Numerical tests of both short-time evolution and many-body dynamics confirm the accuracy of the resulting description. Our results provide a scalable analytical framework for designing finite-duration controls in interacting qudit platforms.

Our main claim is that Bohr adopted a principle-theoretic approach to quantum mechanics in order to reconcile two principles: the distinction principle, which asserts the necessity of a clear epistemic distinction between a classical apparatus and a quantum system, and the non-separability principle, which asserts that the two systems are ontologically non-separable in any measurement process. The latter principle is a consequence of Bohr's argument that, during a measurement interaction, the quantum system and the measurement apparatus form a 'new kind of individuality'. To support our argument, we first demonstrate the overlooked fact that, according to Bohr, the measurement interaction is a physical, irreversible process and not merely an epistemic acquisition of new information. In this respect, quantum mechanics must be regarded not only as a universal theory, but also as revealing no non-arbitrary difference between a quantum realm and a classical realm; the distinction is purely pragmatic. The tension between the epistemic necessity to rely on a neatly distinguishable classical realm and the ontic non-separability of the quantum system and the classical apparatus inclined Bohr to refuse to provide a constructive account of the measurement process, such as that later proposed, for instance, by spontaneous dynamical reduction models.

Anyon superconductivity arises from the condensation of mobile anyons rather than from a conventional Cooper instability, yet a systematic wavefunction description remains lacking. We develop a hierarchy-wavefunction construction for superconducting states derived from parent topological orders and identify their off-diagonal long-range order, condensate charge, chiral central charge, and residual topological order through the plasma analogy and topological field theories. We construct Abelian and non-Abelian examples descending from the semion state, a $ν=2/3$ hierarchy state, the $ν=1/3$ Laughlin state, $ν=1$ integer quantum Hall state, and Pfaffian state. Remarkably, for the semion case, the superconducting many-semion wavefunction is equivalent to a state of fermionized anyons filling two effective Landau levels, recovering Laughlin's original construction of semion superconductor. Finally, we show that hierarchy wavefunctions emerge naturally in the dilute, long-distance limit of the anyon-Hilbert-space formulation, which applies to ideal Chern bands and moiré bands of twisted bilayer MoTe$_2$. Our results establish a unified wavefunction-level framework linking anyon condensation, superconducting order, and topological field theory.

A quantum system of any fixed dimension can be prepared in a continuum of states, yet it cannot be used to transmit an unlimited amount of classical information. Similarly, the correlations observed between measurement outcomes on separate parts of a shared quantum system can be stronger than classical correlations, but they cannot transmit information. These fundamental limitations suggest that the statistics observed from quantum communication and quantum correlations may admit a simulation using a finite amount of classical communication. This expectation is confirmed in the smallest nontrivial quantum dimension, with two classical bits being necessary and sufficient to exactly simulate qubit communication and all correlations between qubits. Despite significant efforts during the previous decades, this remained the only solved case. Here we resolve both problems for every quantum dimension. The solution reveals an unexpected qualitative transition starting at dimension four: no finite amount of classical communication can exactly simulate ququart communication nor all quantum correlations of two entangled ququarts, even with unlimited shared randomness. One might have expected this transition, if it existed, to appear already for qutrits. Instead, we construct an explicit protocol that exactly simulates qutrit communication using $357$ classical bits, and consequently, all correlations of two entangled qutrits.

The entangled states of composite quantum systems are well studied. The particle-like nature of these systems also means that, while entangled, they can be physically separated and measurements performed on the separated subsystems. Measurements on the separated subsystems A and B should pertain to vectors in the local Hilbert space of each subsystem, but to date it has not been clear how to elucidate the relevant states of the separated subsystems because it is not obvious how to resolve them from states given in the tensor product basis, except for the separable states. Here it is shown that the projections of any general entangled state that are detected by measurements on the separated subsystems can be obtained considering the corresponding (cosets of) states in the free vector space from which the tensor product space is defined. The result eliminates the need to invoke random collapse, and from this perspective nonlocality arises because of the way measurements on each separated subsystem projects possible measurement outcomes.

Photonic chips with silicon nitride ($\mathrm{Si_3N_4}$) microring resonators are well established as heralded single-photon sources, but their operation as frequency-degenerate twin-photon sources has not previously been demonstrated. Here, we realise a twin-photon source at telecommunication wavelengths in a $\mathrm{Si_3N_4}$ ring microresonator via an inverse four-wave mixing (FWM) process, in which two photons from spectrally distinct pumps are converted into a pair of identical twin photons. The measurements show a maximum coincidence-to-accidental ratio (CAR) of $5.4\pm0.6$. In addition, the microresonator functions as a heralded single-photon source through pump-degenerate spontaneous four-wave mixing (SFWM), exhibiting a spectral purity of $P=0.67\pm0.05$ and a heralded anti-bunching of $g^{(2)}_h(0)=0.0042\pm0.0015$. Together, these results demonstrate both photon-generation schemes on a single integrated $\mathrm{Si_3N_4}$ platform, highlighting its potential for scalable, tailored quantum light generation.

Parameterised graph theory studies how the complexity of graph-theoretic problems depends on structural parameters of the input graph. This perspective has proved useful in analysing tensor-network simulation (Markov and Shi, 2008). Its implications for tensor-network representations and tomography are less well understood. In particular, which graph parameters determine whether a tensor-network state (TNS) admits a tractable matrix product state (MPS) or tree tensor network (TTN) representation, and which control the complexity of learning the state? We address these questions using parameterised graph theory. First, we show that cutwidth and tree-cutwidth bound the bond dimension overhead required to represent a TNS as an MPS or TTN. In the TTN case, tree-cutwidth also bounds the local dimension of the grouped subsystems. The proofs are based on entanglement rerouting, a tensor-network analogue of rerouting information in a classical network. Second, we derive graph-dependent upper bounds on the sample and computational complexity of realisable TNS tomography, with exponents that depend on cutwidth, tree-cutwidth, and a new graph parameter, learning complexity, which we bound in terms of degree and treewidth. We obtain these results by extending the disentangling MPS learner of (Cramer et al., 2010), as analysed further in (Bakshi et al., 2025; Lin et al., 2025), to TTNs and to tensor networks on arbitrary known graphs. Finally, we extend the framework beyond the realisable setting. For an arbitrary input state, our agnostic learner outputs a pure state whose fidelity is within additive error $ε$ of the optimum over tensor-network states on the given graph with a given bond dimension, with explicit graph-dependent bounds on sample and computational complexity.

Exact CNOT synthesis asks for a minimum-size CNOT circuit implementing an invertible linear transformation. Although several related synthesis models have been shown to be computationally hard, their hardness proofs rely on additional structure such as restricted qubit connectivity, encoded inputs, or unrestricted intermediate variables. The complexity of the most basic setting---identity input, a fixed number of labelled qubits, no ancillas, and all-to-all CNOT connectivity---had remained unresolved. In this work, we prove that the decision version of this vanilla exact CNOT synthesis problem is NP-complete, and consequently that its optimization version is NP-hard. Our proof gives a polynomial-time reduction from the Hamiltonian-path problem on grid graphs in two steps. First, we isometrically embed the grid graph into a hypercube via a unary encoding map. We then encode this hypercube Hamiltonian path problem into vanilla exact CNOT synthesis. The main challenge is that CNOT synthesis specifies only the final parity matrix and cannot directly enforce the intermediate vertex visits required by a Hamiltonian path. To overcome this difficulty, we introduce extra recorder qubits that encode the required intermediate vertex visits into the final transformation, forcing any CNOT circuit implementation to realize the intended path structure. Beyond CNOT synthesis, our result directly implies hardness for several related problems, including the shortest word problem over $\mathrm{GL}(n,2)$, distance computation on Cayley graphs over $\mathrm{GL}(n,2)$, minimization of sequential XOR programs, and exact synthesis of phase polynomial circuits.

In his seminal paper, Bell [Physics Physique Fizika 1, 195 (1964)] considers the correlations that result from space-like separated measurements on a pair of entangled particles. He uses relativity theory to motivate the Bell causal structure, then shows the existence of quantum correlations that cannot be explained classically within this causal structure. Classical explanations of such quantum correlations are possible in alternative causal structures, for instance, those that allow superluminal causal influences, but, as shown in [New Journal of Physics 17 033002 (2015)], all such alternative explanations require fine tuning (causation without correlation). Here we discuss the existence of spurious quantum correlations --- correlations that look quantum in one causal structure, but have a natural classical explanation in another. More precisely, there are causal structures that admit non-classical quantum correlations, but for which the same correlations have a classical explanation in another causal structure without fine tuning. The realisation in the other causal structure can also be achieved without breaking any natural constraints on the causal structure that follow from relativity theory. However, similarly to non-classical quantum correlations in the Bell causal structure, we find other causal structures with non-classical quantum correlations that do not have a classical causal explanation in any alternative causal structure without fine tuning.

Coherent interfaces between optical photons and mechanical excitations provide a promising route towards phonon-state engineering and hybrid quantum information processing. Cavity optomechanical systems enable such interfaces via optomechanically induced transparency (OMIT), allowing coherent mapping between traveling optical fields and localized mechanical modes. However, previous implementations of OMIT conversion protocols were limited to classical input signals with large coherent state photon numbers due to room temperature operation and corresponding thermal mechanical noise. Here, we demonstrate efficient low-noise photon-phonon state transfer close to the single-quantum regime in an optomechanical crystal operated at Millikelvin temperatures. Using weak coherent optical input pulses at the few-photon level, we achieve a record-level photon-phonon conversion efficiency of $η=0.76$, a mechanical storage lifetime of $T_\mathrm{1}=7.3~μs$, and a tunable conversion bandwidth exceeding 4.5 MHz. Hanbury Brown-Twiss measurements of the retrieved signal demonstrate the coherent nature of the converted phononic state, evidencing low added thermal noise in the conversion process ($n_\mathrm{th}=9.0$). These results establish optomechanical crystals as efficient optical interfaces to GHz mechanical modes and provide a pathway toward deterministic single-quantum-level mechanical state preparation.

Describing competing phases of strongly correlated systems often requires trial wave functions built from phase-specific assumptions. We propose the \emph{hyperdeterminant (HyperDet) wavefunction} as a phase-agnostic ansatz for both bosonic and fermionic quantum many-body systems exhibiting spontaneous symmetry-breaking order, fractionalization, and/or topological order with anyonic excitations. The HyperDet structure emerges naturally by fusing auxiliary fermionic parton Slater determinants into physical orbitals through a fully learnable \emph{fusion tensor} $\mathcal F$. Optimized using variational Monte Carlo, a single HyperDet architecture can achieve exceptionally high overlaps $\geq 99.9\%$ with exact-diagonalization ground states throughout the entire fractional Chern insulator phase in both bosonic and fermionic models, and across their nearby competing phases. We introduce the singular-value spectrum of the \emph{bipartite fusion matrix} as a structural diagnostic of fusion tensor, and find that its redistribution tracks many-body phase transitions without computing phase-specific observables. The optimized fusion tensor also encodes the parton-level topological data: it reproduces the parton Chern numbers expected for the bosonic and fermionic FCI states, completing their field-theory descriptions and the resulting topological order. Its intrinsic gauge structure further determines whether physical symmetries admit virtual lifts and, when faithful lifts exist, extracts their projective class; for the bosonic FCI, this recovers the expected parton translation fractionalization. We thus anticipate the HyperDet wavefunction to be a promising variational platform for both accurate ground-state searches and phase-diagram explorations across strongly correlated phases, and for providing interpretable theoretical insights from parton-level microscopics to field-theory descriptions.

Quantum benchmarks provide compact measures of performance that are important for evaluating and comparing quantum systems. Circuit-level benchmarks are particularly valuable because they capture the accumulated effects of noise across interacting operations, but existing approaches may require structured gate sets and costly compilation, classical simulation of reference outputs, or subsystem decompositions that do not capture full-register behavior. We introduce Error Per Circuit Layer (EPCL), an overlap-based circuit-level benchmark that estimates an effective layer polarization by applying identical random circuits to two disjoint quantum registers and measuring the overlap between their output states as a function of circuit depth. EPCL avoids classical simulation of ideal output distributions and recovery to a known reference state, and is compatible with arbitrary gate sets, including non-Clifford gates. We derive the expected overlap decay under an ensemble-averaged depolarizing model and identify the assumptions under which the fitted decay parameter represents an effective layer polarization. Numerical simulations show that EPCL recovers the predicted polarization under weak local stochastic noise and remains well described by a single-exponential decay at stronger stochastic noise levels. The simulations further show that coherent errors associated with fixed entangling layers may require Pauli twirling or randomized compiling to produce the expected decay, while inter-register correlations contribute an additional covariance term to the measured overlap. Finally, experiments on IBM quantum hardware demonstrate clear EPCL decay in 8- and 16-qubit implementations. These results support EPCL as a method for measuring aggregate register performance without requiring classical simulation of ideal circuit outputs or restriction to structured gate sets.

Quantum thermalization explains how an isolated many-body system naturally evolves towards a thermal state, rendering information about the initial conditions inaccessible to local measurements. This is precisely the mechanism utilized in quantum error correction, where information is protected by design through a nonlocal encoding. In this work, we leverage this connection to port the rigorous framework of (approximate) quantum error correction to the study of quantum thermalization. Treating typical late-time states as codewords, we characterize the error-correcting properties of generic thermalizing dynamics. We numerically uncover a universal relationship between the encoding rate, distance, and thermal entropy density of the emergent code. At infinite temperature, this universal curve saturates the quantum Singleton bound, achieving the same optimal limit as Haar-random codes. At finite temperature, we introduce a code family based on the Scrooge ensemble, the natural thermal analogue of the Haar ensemble, and prove it saturates the entropic quantum Singleton bound, establishing this family as optimal within entropic constraints. Our extracted universal curve independently saturates this same bound, revealing that finite-temperature thermalization is itself optimal. Finally, we show how conserved quantities limit the error-correcting behavior of thermalization: codewords with differing energies, or other conserved charges, leak only classical information, and correctability persists until the difference reaches the scale of thermal fluctuations. Our results reveal a universal optimal coding structure in thermalizing dynamics, while introducing new optimal codes that achieve fundamental limits of approximate quantum error correction.

Non-local magic quantifies the non-stabilizerness of a bipartite quantum state that cannot be removed by local unitary transformations. Despite its natural definition, its evaluation generally requires a difficult optimization over local unitaries. Here, we show that for the log-stabilizer fidelity this optimization admits an exact closed-form analytic solution depending only on the Schmidt spectrum. We then introduce the magic of purification, defined as the minimum pure-state magic over all purifications of a mixed state, and show that it naturally induces a resource theory whose free states are normalized stabilizer-code projectors. For the log-stabilizer fidelity, the magic of purification admits a distance-based formulation in terms of the Uhlmann fidelity. Remarkably, we prove that non-local magic coincides with the minimum magic of purification along the unitary orbit of the reduced density operator. Our results provide both an efficient analytical characterization and a mixed-state resource-theoretic interpretation of non-local magic.

Open-system lattice gauge theory (LGT) has so far been developed predominantly in Abelian settings, leaving open how genuinely non-Abelian gauge structure reshapes dissipative real-time dynamics. Here, we study a $1+1$D SU(2) Yang--Mills LGT with dynamical matter coupled to a thermal scalar environment through a gauge-preserving Lindblad evolution, which we solve using tensor networks. Starting from a quark--antiquark pair connected by a chromoelectric flux string, we find that the thermal medium melts the string by delocalizing the color charges and screening the flux; on resonance, this dissipative melting competes with and delays coherent string breaking. The thermalization time is non-monotonic in the environment coupling, decreasing through environment-assisted transport at weak dissipation before increasing in a quantum-Zeno regime. In the strong-dephasing limit, a Schrieffer--Wolff expansion maps the dynamics to a classical exclusion process and yields the Liouvillian thermalization time analytically. Beyond these generic open-system effects, the non-Abelian matter structure produces a systematic mesonic bias in the steady state, while the thermalization time decreases with temperature, in contrast to the Abelian Schwinger model trend and in qualitative agreement with pNRQCD studies of the quark--gluon plasma. These results establish a gauge-preserving framework for thermalization and string dynamics in open non-Abelian lattice gauge theories.

Understanding real-time string dynamics in three spatial dimensions is essential for connecting quantum simulations of lattice gauge theories (LGTs) to the physical dimensionality of QED and QCD, where transverse fluctuations and competing local processes proliferate. We present the first real-time simulations of string breaking in $3+1$D lattice quantum electrodynamics. Using tree tensor networks, we simulate the quench dynamics of electric flux strings in a $3\!+\!1$D U(1) LGT with dynamical matter. At strong coupling, the string breaks resonantly at a sharp resonance condition of mass and gauge couplings, converting electric energy into matter--antimatter pairs that screen the static charges. Off resonance, we classify all competing channels---pair production, string deformations and extensions, and flux loops---whose multiplicity, extensive for pair production and flux loops, depletes the string sector even far from resonance. A channel-resolved perturbation theory quantitatively reproduces these dynamics and their Fourier spectrum. Our results establish diagnostics and benchmarks for upcoming quantum simulators of higher-dimensional LGTs.

It has long been assumed that a particle---having crossed a black hole event horizon unentangled with another particle in the exterior universe---can no longer dynamically entangle with that particle. Here, we demonstrate within a gravitational retarded-potential model that entanglement can in fact be created from scratch between freely falling spatial superpositions across an event horizon. Yet, extracting this state radially requires non-inertial deceleration, triggering soft-graviton bremsstrahlung, and establishing a strict dephasing bound in terms of entangling phase, $Γ\ge\frac{729}{160π}Φ$. This decoheres the entangled state. By contrast, equivalent macroscopic optical masses allow local tangential harvesting of entanglement via quantum erasure, thus revealing a remarkable geometric duality: Spacetime irreversibly degrades entanglement the moment the localized mass is dragged away from the horizon, while allowing the transverse teleportation of its entangled state to infinity.

The hydrodynamic regime of electron transport, induced by fast inter-electron collisions, was discovered in high-quality nanostructures in recent ten years. However, signs of hydrodynamic transport, primarily, the giant negative magnetoresistance, were observed even at very low temperatures, when electron-electron scattering is too weak to affect the transport. To address this puzzle, here we develop a theory of mixed, hydrodynamic and non-Markovian, magnetotransport of two-dimensional electrons at zero temperature in samples with weak but still important disorder. Namely, we account for both the memory effects at electron scattering by localized defects in magnetic field and an unconventional viscosity effect due to electron scattering by defects in bulk and by rough sample edges. Solution of the model yields a strong negative magnetoresistance, which exhibits at zero magnetic field a sharp maximum in narrower samples or a blunt maximum in wider samples. This and other our results explain various properties of the giant negative magnetoresistance observed on ultra-high-quality GaAs quantum wells, thereby we apparently reveal the nature of low-temperature magnetotransport in these systems.

We investigate the structures of effective Hamiltonians governing monitored dynamics of a one-dimensional Majorana chain through the Lyapunov spectral analysis. We focus on a gapless phase characterized by finite-size scalings different from those in conventional critical and/or frustration-free systems; the spectral gap closing faster than $1/L$ but slower than $1/L^2$ and the entanglement entropy growing as $[\ln(L)]^2$ with $L$ being the system size. We find that the corresponding effective Hamiltonians have random long-range power-law hoppings with nontrivial magnitude correlations, rather than being independently and identically distributed. To elucidate the role of these non-Gaussian correlations, we construct random power-law hopping models that capture the essential features of the effective Hamiltonians. The spectral gaps of the constructed models decay faster than $1/L$ but slower than $1/L^2$. We find that, in the absence of hopping correlations, the ground-state entanglement exhibits $\ln(L)$ scaling. In the presence of correlations, by contrast, the entanglement entropy is enhanced and its system-size dependence is consistent with $[\ln(L)]^2$ scaling over the system sizes studied. These results suggest that correlations among long-range hopping magnitudes are responsible for the entanglement scaling that seldom appears in ground states of conventional isolated quantum systems.

Quantum low-density parity-check (qLDPC) codes admit high encoding rates but require nonlocal entangling gates for syndrome measurement. Instead of physically moving the qubits which slows down with the increasing qubit number, here we propose to achieve parallel nonlocal entangling gates on a two-dimensional (2D) ion crystal using frequency-multiplexing. Adiabatic conditions ensure the suppression of gate infidelity and crosstalk error, as well as their robustness against slow drift in the trap frequency which is a leading error source in ion trap. We consider a numerical example of a $[[248,10,18]]$ bivariate bicycle code on a 2D crystal of 512 ions. By optimizing the mapping of the qubits and the assignment of the frequency bands for multiplexing, we show that a moderate laser power is sufficient for parallelism, and that a logical error rate of $10^{-12}$ can be achieved under realistic noise parameters.

We present an operator-decomposition architecture that mathematically maps a global operator into independently executable local operators, reducing the maximum quantum circuit depth at the cost of classical reconstruction and sampling overhead. By framing complex Quantum Circuits around an operator in a vector space that can be algebraically pre-decomposed, AOD complements quantum error correction and error-mitigation approaches by performing algebraic decomposition before quantum execution. Our approach leans in the computer science definition of a Monoid: a design pattern and mathematical concept consisting of a data type, a combining function that is associative, and a safe identity (neutral) element that does not change other values when combined. Simulation wise we define a MapReduce programming model where the addition (+) is the reducer, thus leveraging a naturally stable commutative monoid which carries zero "negative-probability tax" or phase conflicts. Furthermore, we define a Vector Space of Linear Operators over Additive Abelian Groups that benefit from this paradigm, including: Inner Products, Series expansions, Traces and Convolutions. Finally, we present the mathematical foundations and simulation results for this paradigm.

We study the short-time Loschmidt dynamics after a small sudden quench near a quantum critical point. We show that the initial quadratic growth of the Loschmidt rate function is governed by the variance of the quench operator per system size. For a local quench operator, this variance density is exactly equal to the spatial sum of the equal-time connected two-point correlation function in the initial ground state. This relation connects the early-time Loschmidt response to static critical correlations. Assuming power-law correlations at criticality, we classify the finite-size scaling of the short-time coefficient by the scaling dimension of the quench operator. In one dimension, the coefficient is finite, logarithmically enhanced, or algebraically enhanced with system size. We illustrate this operator dependence in the transverse-field Ising chain, where transverse-field and longitudinal-field quenches couple to different critical operators. We also discuss the first correction beyond the quadratic regime using the fourth cumulant of the post-quench Hamiltonian.

We investigate phase estimation in an SU(1,1) interferometer employing $m$-photon-added even and odd coherent states as nonclassical input resources. The phase sensitivity is evaluated through intensity detection and the error propagation method, while the ultimate precision limit is determined from the quantum Cramér-Rao bound with the quantum Fisher information serving as the relevant metrological quantity. Our results demonstrate that photon addition significantly enhances the phase sensitivity, increases the quantum Fisher information, and reduces the quantum Cramér-Rao bound, leading to a clear improvement over the corresponding even and odd coherent states. Furthermore, the achievable sensitivity exceeds the standard quantum limit and gradually approaches the Heisenberg scaling with increasing photon-addition number. We also find that the $m$-photon-added even coherent states exhibit a modest advantage over their odd counterparts. As $m$ increases, however, this distinction becomes progressively weaker, suggesting that photon addition diminishes the role of the initial parity of the coherent state in determining the interferometric performance.

We investigate limits of semigroups of stochastic matrices defined by their invariant distribution. Given probability vectors $γ(β)$ depending on a parameter $β$, we introduce a notion of convergence as $β\to\infty$ for the corresponding semigroups of $γ(β)$-preserving stochastic matrices and investigate the structure of the resulting limit. In general, the limiting semigroup differs from the semigroup preserving the limiting distribution, showing that these two operations do not commute. We develop a general framework for such limiting semigroups and study in detail the case in which the invariant distributions are Gibbs vectors at the inverse temperature $β$. We show that the limiting semigroup consists of block-upper-triangular stochastic matrices subject to additional substochasticity constraints. We characterise and enumerate their extremal elements and determine the preorder on probability vectors induced by the action of the semigroup. The resulting notion of Block-Triangular majorisation interpolates between ordinary majorisation and upper triangular (aka unordered) majorisation. We show that it is completely characterised by a finite family of monotones and analyse the corresponding behaviour of Rényi $α$-entropies as $β\to\infty$.

A discrete time crystal is an out-of-equilibrium phase of matter characterized by the spontaneous breaking of discrete time-translation symmetry. Using extensive numerical simulations based on matrix-product-state methods, we provide evidence for discrete time-crystalline behavior in strongly disordered spin chains with Heisenberg interactions, including the isotropic point, subject to periodic driving. Starting from a many-body localized regime, we observe that rotations induced by delta kicks produce a pronounced subharmonic response at half the drive frequency in spin observables. We investigate the stability of this response against rotation-angle errors through entanglement entropy, quantum Fisher information, short-range spin correlations, and restricted-control ergotropy. Increasing the rotation error reveals an intermediate dynamical regime separating the time-crystalline and Floquet-localized responses. In this regime, most observables exhibit signatures of weakly correlated dynamics reminiscent of Anderson localization.

We study robust K-ary quantum-state discrimination when all candidate states are affected by the same unknown common unitary perturbation. The unknown perturbation does not represent the label to be identified, but acts as a nuisance factor that changes the performance of a fixed measurement. We formulate the problem as a minimax decision problem over the possible perturbations and propose using the Bayes-optimal collective measurement associated with a least favorable prior (LFP) on the nuisance-parameter space. For a finite discretization of this space, we show that the LFP can be computed by a semidefinite program and that the corresponding value coincides with the finite-grid minimax success probability. As numerical demonstrations, we consider a binary nonorthogonal qubit model and a nonorthogonal three-state qutrit model with an unknown common unitary perturbation. The LFP-based measurement substantially flattens the success-probability profile and improves the worst-case success probability compared with a reference-point optimal measurement and a uniform-prior Bayes measurement. The resulting LFP concentrates its weight on regions of the nuisance-parameter space that actively limit the robust discrimination performance, thereby providing both a constructive measurement design and a diagnostic description of the difficult nuisance-parameter regimes.

The fixed-ray escort integral representation expresses $α$--$z$ Rényi divergence as an average over ordinary relative entropy of a family of escort states. Working in the standard UV-regulated density-matrix description of QFT subregions, we use this representation to derive an escort-averaged entanglement first law, an escort-averaged representation of the $α$--$z$ information kernel, and an escort-averaged Bekenstein-type bound for ball-shaped regions in conformal field theories. For the conjectural $α$--$z$ quantum null energy condition (QNEC), we obtain a quasi-local form in which the null energy is evaluated in an escort-averaged state and is corrected by an escort-transport term encoding the failure of escort formation to commute with restriction to a null-deformed region. The $z=α$ specialization gives a similar quasi-local form of the Rényi QNEC for sandwiched Rényi divergence. We explicitly compute the Rényi QNEC, including the explicit escort transport term, for coherent-state excitations in a free scalar field theory. For the same coherent family, we obtain a positive $α$--$z$ null Hessian, verifying the conjectured diagonal $α$--$z$ QNEC for this family.

Strongly anisotropic non-Kramers rare-earth ions combine giant longitudinal g-factors with a vanishing transverse component imposed by time-reversal symmetry, a combination that makes their spin transitions exquisitely sensitive to the orientation of the applied magnetic field. We show that this sensitivity carries a dual identity: it is simultaneously an overlooked decoherence channel and the basis for a spin-coherence-based angular probe. Using pulsed electron paramagnetic resonance at X-band, we report the first measurements of the quantum coherence of Tb$^{3+}$ in a native-doped CaWO$_4$ crystal (15 ppb) and map the Hahn-echo coherence time $T_2$ as a function of temperature (2 to 10 K) and resonant field ($10^3$ to $10^4$ G). A parameter-free model combining spin-lattice relaxation, instantaneous diffusion and spectral diffusion from all independently quantified impurities overestimates $T_2$ by an order of magnitude at low temperature and wrongly predicts the field dependence of $T_2$, inconsistent with the observed monotonic decrease of $T_2$ with $B_r$. A two-parameter extension, including dynamical angular fluctuations of the crystal axis, reproduces the full dataset across multiple setups and laboratories. Two controlled experiments nominally identical except for different mechanical configuration of the setup establish the mechanical origin of the dominant contribution. The two-parameter extension corresponds to an angular amplitude noise spectral density of overall order 36 n°/$\sqrt{Hz}$ from global external vibrations (ranging from 10 to 66 n°/$\sqrt{Hz}$ depending on the exact setup mechanical configuration) estimated at $\sim$ 2.5 kHz plus a temperature-dependent contribution assumed to come from local phonon-driven angular jitter. It identifies and highlights a decoherence pathway of practical relevance to any anisotropic solid-state spin system.

We prove that, for an $n$-qubit system of dimension $d=2^n$, every state satisfying $\operatorname{Tr}(ρ^2)\le 1/(d-a_\ast)$, with $a_\ast=0.458327\cdots$, lies inside the stabilizer polytope and is therefore magic-free. Combining this result with general geometric properties of high-dimensional polytopes, we establish quantitative estimates for the Hilbert--Schmidt inradius and volume radius of the stabilizer polytope, and use them to characterize the typicality of magic in random induced states obtained by tracing out a $k$-dimensional subsystem from a $d\times k$-dimensional Haar-random pure state. We prove a sharp phase transition in the probability of such states having magic, whose transition dimension $k_\star$ is bounded between $Ω(d^2/\log^2d)$ and $\mathcal{O}(d^2)$. We further prove that the number of facets of the stabilizer polytope lies between $\exp[Ω(d^2/\log^2 d)]$ and $\exp[\mathcal{O}(d^2\log^2 d)]$, substantially improving upon the previous quasipolynomial lower bound and implying that any exact description of the magic-free region requires a doubly exponential number of linear inequalities in the number of qubits. Overall, our results show that the stabilizer polytope exhibits near-maximal geometric complexity allowed for a high-dimensional polytope with a certain number of vertices.

Maximum-likelihood decoding (MLD) achieves the minimum logical error rate of stabilizer codes under known i.i.d. Pauli noise, but its exact evaluation is \#P-hard. Practical pipelines therefore approximate MLD by minimum-weight decoding (MWD), retaining only the lowest-weight recovery per syndrome and discarding the coset degeneracy. The minimum-weight search is in turn implemented by stochastic solvers. We introduce approximate maximum-likelihood decoding (AMLD), a black-box framework that recycles the candidate samples discarded by stochastic inner decoders into a per-class truncated free-energy estimator. For every logical class represented in the candidate pool, the estimator is provably bounded below by the exact free energy and above by the empirical minimum weight. AMLD returns the logical class minimizing the estimated free energy with linear classical overhead. In SA-based Ising-decoder benchmarks, AMLD closes up to $83\%$ of the MWD--MLD threshold gap across the toric and color codes under bit-flip and depolarizing noise. The largest threshold improvement, from $17.28\%$ to $18.62\%$, occurs on the $6.6.6$ color code under depolarizing noise. We further demonstrate AMLD on the $[[144,12,12]]$ bivariate-bicycle code, whose bit-flip decoding problem has a hypergraph structure. This application requires neither matching-based enumeration nor code-specific tensor-network contraction. At $p=0.05$, AMLD reduces the logical error rate by $13\%$ relative to MWD evaluated on the same BP-OSD candidate pool.

Random quantum objects are powerful resources for quantum information processing, yet exact Haar randomness is costly and typically unnecessary. We introduce an explicit sparse commuting circuit ensemble on $n$ qubits that reproduces low-order Haar moments in the stringent relative-error sense. The circuit consists of a sparse Clifford phase layer followed by independent single-qubit Clifford gates. Acting on a simple product state, the resulting ensemble forms $ε$-approximate projective $2$- and $3$-designs in relative error, with the required logarithmic interaction degree being asymptotically optimal within this circuit family. It admits an ancilla-free implementation of quantum depth $O(\log(n/ε))$ on an all-to-all architecture, as well as an adaptive constant-depth implementation---in fact, depth seven---using $O(n\log(n/ε))$ ancilla qubits. Departing from existing shallow-design paradigms, our analysis exploits the intrinsic moment structure of commuting phase circuits; at third order, this requires a new block decomposition and combinatorial analysis that also suggests a route toward higher-order shallow designs. Our results show that precise Haar-like statistics can emerge from sparse commuting dynamics with remarkably low quantum resources, with applications to randomized characterization, quantum metrology, quantum algorithms, and many-body physics.

Coherent light-matter interfaces controllably modifying the state of a photon upon interaction with a stationary qubit are a key resource for implementing deterministic entangling gates for optical quantum technologies. This requires a one-to-one mapping between the state of the scattered photon and that of the embedded qubit. Here, we present an experimental signature of such a bijection by leveraging the spin-induced Kerr rotation present in a low-noise charged quantum dot-micropillar cavity device. Through time-resolved polarization measurements, we project the electron spin to one of its eigenstates with $95\pm2\%$ fidelity with a single reflected photon detection, and follow the subsequent spin relaxation through the detection of a second reflected photon. We demonstrate that, after a transient regime governed by the trion radiative lifetime, two orthogonal polarization states can be produced, each associated to a given spin eigenstate. While the current results are limited by a timescale competition between electron spin relaxation and trion radiative lifetime, they could be improved using hole spins displaying increased relaxation times. Our work paves the way towards deterministic logic gates exploiting this one-to-one mapping between a spin and the polarization of a scattered photon.

A theoretical framework is proposed to engineer both first and second-order topological superconducting phases in a two-dimensional (2D) heterostructure, consisting of a quantum spin Hall insulator (QSHI) and an unconventional $p$-wave magnet in presence of proximity-induced $s$-wave superconducting pairing. Our analysis establishes that the transitions between the trivial and topological superconducting (TSC) phases can be regulated though the parameters of $p$-wave magnet. Presence of chiral symmetry leads to the characterization of both types of TSC phases by the respective invariants, one-dimensional winding number and quadrupolar winding number. These results are supplemented by an analytical effective low-energy edge theory that yields a deeper insight into the emergence of the different topological phases of the system. Bulk pairing analysis reveals the competition between the effective $(p_x+p_y)$ and $(p_x+ip_y)$ type pairings that are governed by the intrinsic spin-orbit coupling inherited to the QSHI and spin-split bands of the $p$-wave magnet, respectively.

We present a permutation-symmetric supporting relation between the pairwise concurrences and the three-tangle in three-qubit system, whose extrema are attained only by the symmetric $W$ and GHZ local-unitary classes. Furthermore, by introducing the concept of a four-dimensional compatibility body, we show that our proposed global relation and the previous CKW relation can be uniformly viewed as different supporting directions of the same achievable set. Subsequently, we provide a necessary-and-sufficient semi-algebraic characterization of the complete four-dimensional compatibility of a three-qubit pure state. Based on this, we can conversely describe the compatibility between entangled components: given the remaining entangled components, the missing two-body entangled component can only take values within a precise parameter-free interval. We demonstrate that the above construction also applies to arbitrary concurrence-generated entanglement measures.

The Kibble-Zurek mechanism (KZM) and finite-time scaling (FTS) provide a foundational framework for driven critical dynamics, yet their predictive power has been largely confined to local observables. Here, we establish a universal finite-time scaling theory for the nonequilibrium dynamics of quantum entanglement. Using unbiased quantum Monte Carlo simulations, we investigate the corner entanglement entropy of (2+1)-dimensional interacting Dirac fermions driven from ordered phases toward a quantum critical point. We find that the corner entanglement accurately obeys a universal driven scaling governed by the driving rate and system size, persisting whether the initial ordered state is fully gapped or hosts gapless Goldstone modes. Crucially, this dynamical entanglement exhibits a logarithmic dependence on the driving rate, from which the universal corner coefficient of the underlying conformal field theory can be robustly extracted far from equilibrium. These results generalize the KZM from local observables to the intrinsic nonlocal quantum information measures, offering a practical blueprint for characterizing quantum criticality and entanglement on programmable quantum simulators.

Using the Lifshitz theory of the van der Waals and Casimir forces, we calculate the Casimir free energy of thin peptide films deposited on silicon substrates. The Casimir free energy is found as a function of film thickness for different fractions of water in the film, in the presence of either nonmagnetic or magnetic nanoparticles, and under the impact of irradiation of a silicon substrate with laser pulses or dopants resulting in the dielectric-to-metal phase transition. It is shown that for a dielectric silicon there is the borderline value of the film thickness, such that the Casimir free energy is negative and contributes to the film stability for thicker films, but is positive and makes the film less stable for thinner ones. According to our results, the borderline value of peptide film thickness decreases with increasing volume fractions of water and in the film. This decrease is more pronounced for the magnetic nanoparticles and becomes stronger with increasing their radius. The borderline value of peptide film thickness is found as a function of the fraction of water in the film. If the silicon substrate is in metallic state, the Casimir free energy of peptide coating is always positive, which makes it less stable. Possible applications of the obtained results in organic electronics and biomedicine are discussed.

The entanglement spectra of fractional quantum Hall states contain universal fingerprints of their underlying topological order, as posited by the Li-Haldane conjecture. In this work, we uncover a finer universal structure within the entanglement spectra unravelled by projective measurements. Concretely, we study the projected ensemble of fractional quantum Hall states, defined as the collection of quantum states on a subsystem conditioned on measurement outcomes of its complement. We find that this ensemble exhibits a hidden hierarchy inside the Li-Haldane edge manifold: by conditioning on measurement outcomes, the entanglement spectrum's support is split into measurement-dependent sectors whose ranks we demonstrate are fixed by conformal field theory counting, an observation we dub the measurement-resolved Li-Haldane conjecture. For the non-Abelian Moore-Read state, this hierarchy is particularly rich: each parity-resolved edge manifold contains internal subspaces whose dimensions reproduce the conformal field theory counting of the opposite-parity sector. This structure persists even in realistic Coulomb-interacting ground states, establishing the projected ensemble as a sharp new probe of topological order beyond what the entanglement spectrum alone can detect.

For a general class of two-dimensional non-interacting semi-metallic electron systems on a lattice, we derive an explicit formula for the whole conductivity matrix, by using Euclidean many-body formalism. The semi-metallic phase takes place whenever two Bloch bands touch at the Fermi energy with conical intersections and generally occurs at the transition between distinct integer quantum Hall phases. Unlike the longitudinal conductivity (which depends solely on the shape of the cones at the Fermi level), the transverse conductivity is remarkably determined both by the conical structures of the bands and by the nature of the two nearby topological phases. Generically, in the semi-metallic state, neither the longitudinal nor the transverse conductivities are quantized in integer multiples of a universal conductivity quantum; however, universality of the conductivity matrix is restored under the assumption of emergent rotational symmetry of the linearized Hamiltonian at the Fermi points. Using our formula, we compute the conductivity matrix for several physically relevant models of quantum Hall fluids at the topological phase transition, exhibiting cases where the transverse conductivity is quantized in half-integer multiples of $e^2/h$ and cases where it depends continuously on an external strain parameter, thus shedding light on its universality or non-universality features.

Quantum error correction acts as an entropy pump, transferring noise-induced uncertainty from a protected quantum system into syndrome information stored in an auxiliary memory. Repeated operation requires this memory to be cleared which unavoidably contributes to the energetic cost of error correction. Here, we characterise this contribution for subspace quantum error-correcting codes and identify how it depends on the joint structure of the code, the noise, and the representation of the retained syndrome information. Starting from the Knill-Laflamme conditions, we construct an effective syndrome state whose von Neumann entropy sets a lower bound on the ideal work required to maintain a reusable syndrome register. Projective syndrome readout generally generates additional entropy, and we quantify the resulting gap through measurement inefficiency. We then specialise to stabiliser codes under independent local Pauli noise and analyse two classical levels of syndrome representation. At the level of abstract error labels, degeneracies among single-qubit errors reduce the leading-order entropy of processed recovery labels. At the parity-check level, lower-weight checks reduce the marginal entropy generated by individual measurement outcomes in the low-noise regime. We identify the additional burden associated with retaining and separately erasing these outcomes as a bit-level inefficiency, and illustrate both costs for the five-qubit, Steane, generalised Shor, and rotated surface codes. Our results establish a hierarchy of syndrome-memory energetic costs and identify the code, noise, and measurement structures that control the ideal thermodynamic burden of subspace quantum error correction.

The Knaster-Tarski fixed-point theorem states that every monotone function over a complete lattice has a fixed point. Beyond its fundamental role in order theory, the theorem and its algorithmic variants have found broad applications in areas such as economics, game theory, and programming languages. While the query complexity of finding a Tarski fixed point has been extensively studied in classical models, comparatively little is known in the quantum setting. We prove an $Ω(k\log n)$ quantum query lower bound for finding a fixed point of a monotone function on $[n]^k$, using the nonnegative spectral adversary method. In the two extremal regimes $n = 2$ and $k = 1$, our quantum lower bound matches the previous classical lower bounds $Ω(k)$ and $Ω(\log n)$, respectively. For $n, k\geq 2$, our bound improves the best previous classical lower bound when $n < k$ and is within a factor of $\log n / \log k$ compared to the known classical lower bound when $n \geq k$. To construct the adversary matrix, we develop the Tree--Filtration Adversary Method. Besides yielding our lower bound, the method offers a more transparent combinatorial interpretation of the nonnegative spectral adversary method. When the hard instances of a problem admit a tree-like organization and suggest an intuition analogous to classical decision-tree lower bounds, our method provide a promising approach to establishing quantum complexity lower bounds.

In this paper, we introduce a notion of abstract quantum data type within the framework of universal algebra. This notion provides an algebraic foundation for describing data abstraction in quantum programming. We formally define a quantisation of classical data types and show that their equational specifications can be soundly lifted to the quantum setting. Two standard quantisation methods for classical functions, namely the bit oracle and the phase oracle, arise as special cases of this general construction. We illustrate the framework with applications to quantum arrays and quantum error-correcting codes, showing how they can be understood through the lens of data-type quantisation. We further establish conditions under which quantisation preserves structural relationships and constructions of classical data types, including embeddings, isomorphisms, and products.

We prove that the square root of the separable quantum optimal transport cost associated with the orthogonal projection onto the antisymmetric subspace defines a genuine distance between density matrices. Equivalently, this establishes the triangle inequality for the order-two Beatty-França quantum optimal transport construction induced by the Hilbert-Schmidt distance between pure states. The result also proves metricity of the corresponding distance derived from separable SWAP fidelity. The proof replaces the unavailable gluing argument by convex-roof duality and a dimension-independent interpolation result for Hermitian operators.

The computation of the Bures-Wasserstein (BW) barycenter of an ensemble of positive definite matrices arises throughout machine learning, optimal transport, and quantum information. Riemannian gradient descent (RGD) at unit step size -- the fixed-point iteration used in practice -- converges rapidly, yet existing analyses present a dichotomy: unit-step guarantees carry worst-case exponential dependence on the dimension, while dimension-independent guarantees require small step sizes that forfeit the empirical speed. We resolve this dichotomy, not by improving the guarantees for unit-step RGD, but by proposing a Projected RGD algorithm that achieves dimension-independent linear convergence at unit step size. The achieved rate, $(1 - κ^{-3/2})$, where $κ$ is the condition number of the ensemble, also polynomially improves on the best small-step guarantee ($κ^{3/2}$ versus $κ^{5/2}$ iteration complexity). The crux is a novel Projection Lemma: clipping the eigenvalues of a positive matrix to an interval $[α, β]$ is the closed-form, non-expansive (1-Lipschitz) BW-metric projection onto the set $\{S : αI \leq S \leq βI\}$ -- a statement which, unlike its known one-sided counterpart, does not follow from convexity. The projection is moreover free: it reuses an eigendecomposition the next iteration must perform in any case, so the projected and unprojected iterations cost the same per step. The same analysis covers the invariant matrix projection problem of Brahmachari et al. (2025), whose fixed-point algorithm we identify as unit-step RGD on a totally geodesic submanifold, thereby extending the dimension-independent guarantee to that setting verbatim.

Floquet engineering usually treats light as a uniform control field that changes the topology of an entire driven material. Here we show that structured light carrying orbital angular momentum (OAM) enables a different regime, in which topology is written directly in real space. For ultrathin topological insulator films, circularly polarized Laguerre--Gaussian beams generate a radial Floquet mass whose sign changes define a topological annulus bounded by two concentric chiral ring modes. The transition is helicity selective: below a thickness-dependent critical frequency, left-circularly polarized light drives mass inversion, whereas right-circularly polarized light increases the gap and leaves the film trivial. Independently, the OAM quantum number shifts and reshapes the annulus without changing the frequency, intensity, or helicity. In the decoupled-surfaces limit, the same mechanism produces a purely Floquet-induced topological mass and a vortex-core zero mode. These results identify photon OAM as a control parameter for nonequilibrium topology and provide a route to programmable topological landscapes in quantum materials.

Microscopic unitary dynamics preserves all fine information, yet an isolated finite system can show a robust thermodynamic window in which the entropy associated with a restricted record rises. We ask why information hidden from the current record usually fails to rebuild a low-entropy macrostate. For a fixed projective record, every finite step separates exactly into the evolution predicted from the record alone and an exact correction carried by unresolved microscopic structure. The record-only contribution starts only at second order in time, so all instantaneous change of the record comes from hidden currents between macrostates. We derive the exact entropy rate, separate entropy-spreading from return-oriented currents, and resolve those currents into energy-gap amplitudes. Transitions with the same gap add coherently, revealing how the Hamiltonian and the microscopic state organize hidden information for return. In interacting mixing dynamics the current power is spread over many frequencies; free and deliberately commensurate controls progressively concentrate it, and the engineered dynamics reconstructs a low-entropy macrostate. An independent distribution-level test separates hidden dynamical activity from finite-step return, and an exact classical measure-preserving counterpart shows which parts of the construction are not uniquely quantum. Within the specified record and observation window, irreversibility is therefore not loss of microscopic information, but the failure of that information to organize currents that restore macroscopic order.

The recent discovery of excitons coupled to the magnetic order, and the consequent strong magneto-optic responses, in some van der Waals magnetic semiconductors has triggered intense activity at the interface of magnetism and semiconductor optics. Here, we present an analytically tractable minimal model that describes magnetic order, electrons, holes, and excitons within a unified framework, thereby capturing a wide range of phenomena. It treats the magnetic order and itinerant carriers to be comprised by distinct electronic orbitals that are mutually coupled via orbital-dependent onsite exchange, similar to the treatment of metallic magnets using an s-d model. Investigating CrSBr bilayer as a case study, we benchmark our model and its predictions against recent experimental and ab-initio results finding good agreement as well as new insights enabled by the model's simplicity. Examining the optical selection rules, we find the conservation of a quantum number formed from a combination of spin and layer pseudospin to be a useful guiding principle, even in noncollinear magnetic configurations. Our analysis finds a series of bright and dark excitonic states in such layered A-type antiferromagnets. The presented framework should be valuable in achieving intuitive understanding of recently discovered excitonic phenomena and guiding the discovery of other excitonic states in layered magnetic semiconductors.

When quantum particles interact, many-body phenomena that are hard to simulate classically emerge. Quantum analog simulation offers an alternative in which the target system's dynamics is directly realized in controllable quantum hardware. Here, we give a general protocol for simulating the Bose-Hubbard and anyon-Hubbard models using lattices of capacitively coupled flux-tunable transmons. By modulating the transmon frequencies in an alternating pattern, we resonantly drive multiple many-body transitions and can tune the on-site interaction and density-dependent hopping amplitudes for up to three bosons per site, with no additional restriction on the total particle number. By adding phases to the modulation, which renders the transition amplitudes complex-valued, we propose the first simulation protocol for the anyon-Hubbard model with transmons. Numerical simulations of the driven transmon arrays with experimentally realistic parameters reproduce the characteristic dynamics of the target models across a range of interaction strengths and statistical phases, including the interaction-dependent localization and the statistics-dependent asymmetry of the anyonic quantum walk.

High-dimensional simulation of multivariate extremes is fundamentally limited by the combinatorial complexity of dependence, often more than by the scarcity of extreme observations. We show that symmetry admits a lossless orbit-space representation that preserves structured extreme dependence while replacing an exponentially large dependence space with a compact set of symmetry classes. Based on this principle, we develop Q-Edge (Quantum Extreme Dependence Engine), a symmetry-reduced quantum framework that operates directly in orbit space, enabling scalable simulation and digital twins of structured extreme systems. By transferring symmetry into the data representation rather than the quantum circuit, Q-Edge allows unconstrained quantum generative models to exploit dramatically reduced state spaces. For a 30-dimensional problem, approximately 1.6 million angular states collapse to 256 orbit states, reducing the required quantum representation from about 21 qubits to 8. Our results establish a general computational principle for scalable quantum simulation of structured extreme dependence.

We generalize fractalization, a procedure for the construction of fracton models, from space to spacetime. We apply spacetime fractalization to construct fracton floquet codes with syndrome excitations that have limited mobility in space and time. This extends the notion of fracton order to intrinsically dynamical quantum phases of matter that are inequivalent to static fracton phases. We find spacetime type-II fracton floquet codes which have no topological excitations that are mobile in space or time. These codes exhibit an extreme form of quantum discrete time crystal order with response periods that scale exponentially in their linear system sizes. In this context, the no-strings rule that characterizes type-II fractons leads to a superlinear scaling of the floquet code fault-distance with time, potentially lowering the time overhead required for quantum error correction.

Bilayer graphene (BLG) quantum dots (QDs) are a promising platform for semiconductor qubits. However, the low-frequency charge noise that may ultimately limit coherence has remained largely unexplored. Here, we systematically characterize charge noise in gate-defined BLG QDs using transport-based noise spectroscopy. We extract a median amplitude of $ S_μ^{1/2} (1~\text{Hz}) = 1.16~μ\text{eV}/\sqrt{\text{Hz}}$, placing BLG well within the range reported for established semiconductor quantum-dot platforms. Across variations in charge occupation, confinement, source-drain bias, and charge-sensor operating conditions, neither the noise amplitude nor the spectral dependence shows a reproducible trend in electrostatic tuning, indicating that we extracted the intrinsic semiconductor noise. Consistent noise levels are further observed in double QDs and confirmed using an independent superconducting resonator-based dispersive readout. Extending the study to BLG devices incorporating transition metal dichalcogenide layers reveals no measurable charge noise increase in weakly proximitized QDs. These results validate BLG as a viable platform for coherent quantum information processing.

We introduce Coherent Quantum Learning (CQL), a training framework for quantum learning models in which the model parameters are quantum degrees of freedom evolved under a Hamiltonian that encodes the loss function. Current quantum machine learning retains classical optimization: parameters are updated by a classical outer loop using gradient estimates from measurements, and quantum coherence has no role in the training dynamics, just as in any classical treatment of the same problem. In the quantum case, a parameter register initialized in superposition evolves unitarily, and probability amplitude concentrates near low-loss configurations through interference, without gradient computation or classical feedback. We give an explicit construction using block encodings and Hamiltonian simulation, applicable to arbitrary parameterized circuits. Numerical experiments on binary classification and interferometric phase estimation confirm that the evolved distribution peaks at the optimal parameters, matching gradient-based performance. The construction is compatible in principle with fault-tolerant implementations and extends to batched training via sequential Hamiltonian evolution.

We investigate the influence of environment-induced interactions on the entanglement dynamics of two uniformly accelerated atoms coupled to a fluctuating massless scalar field with a reflecting boundary. The two atoms are aligned vertically to the boundary. The entanglement behaviors are influenced by the competition between the environment-induced interatomic and the environment-induced atom-plate interactions, which can be characterized by certain critical values. The maximum of concurrence generated during evolution decreases non-monotonically with the acceleration, which implies the anti-Unruh phenomenon can exist for some situations even when both environment-induced interatomic and the environment-induced atom-plate interactions are considered.

We give exponential quantum query separations between the standard XOR interface and two forward-only interfaces that supply neither an adjoint nor an inverse oracle. Let $X=\F_2^n$, $N=|X|$, and $f_{h,r}(x)=(h(x),x,r_x)$, where $h:X\to X$ is promised to be either a permutation or a Simon two-to-one function, and $r$ is a fixed table of $n$-bit tags, unrestricted by the promise and reused on every query. The resulting problem is solvable with at most $n+2$ standard XOR queries, but has forward-erasing query complexity $Θ(\sqrt N)$. This answers affirmatively open question 11 in [Scott Aaronson. Open problems related to quantum query complexity. ACM Transactions on Quantum Computing, 2(4):14:1-14:9, 2021] . We also embed these instances into permutations. The detailed construction retains the copy of $x$ in each prescribed output, but for these promises that copy can be replaced by one bit that distinguishes the two inputs in every Simon pair. This gives a permutation domain of size $L=4N^2$ and a permutation problem with the same standard-query upper bound and forward-only in-place query complexity $Θ(\sqrt N)=Θ(L^{1/4})$. Both lower bounds remain valid with a clean coherent bypass. The common lower bound uses an analysis-only recording replacement. In the replacement computation, tracing out the fixed random tag table after $T$ calls gives a sum of positive-semidefinite operator contributions, each depending on $h$ at no more than $T$ addresses. On such a set, the restrictions induced by random permutations and random Simon functions differ only if the set contains a hidden Simon pair, an event of probability $O(T^2/N)$.

Numerical integration with Monte Carlo methods is a central computational task in many scientific and industrial applications, including financial derivative pricing and risk management. Classical Monte Carlo algorithms are computationally demanding: achieving an accuracy $ε$ typically requires a number of function evaluations scaling as $O(1/ε^2)$. Quantum-accelerated Monte Carlo methods based on quantum amplitude estimation can in principle quadratically improve this dependence. However, \textit{quasi}-Monte Carlo methods have not been explored in the quantum context. In this work, we introduce a quantum quasi-Monte Carlo algorithm that combines low-discrepancy nets with quantum amplitude estimation. The proposed method prepares the quasi-random point set coherently in superposition. The method does not yield an asymptotic improvement over classical quasi-Monte Carlo, since the total error separates into a discretization error, determined by the finite net, and a quantum estimation error. Instead, we explore a pre-asymptotic advantage window: for a target accuracy that would classically require $2^q$ low discrepancy points, one can prepare a higher-resolution net of size $2^Q$, with $Q>q$, in superposition and reach the same accuracy using significantly fewer function queries. This window can be controlled by tuning the circuit resolution and amplitude-estimation parameters, making the approach relevant for practical regimes where the number of queries is finite rather than asymptotically large.

We present an efficient implementation of the Parity Architecture for neutral-atom quantum processors. We adapt Parity Twine Networks (PTNs) to different atom layouts, native entangling gates, and atom-shuttling capabilities. This provides a general framework for hardware-aware optimization of gate count, circuit depth, and atom transport for quantum circuits encoding arbitrary interaction graphs in a common basis. Specifically, we develop PTN constructions based on different native entangling-gate realizations, namely CZ, CZSWAP, and iSWAP, providing flexibility to accommodate different hardware capabilities on both static and mobile neutral-atom platforms. Using the quantum Fourier transform (QFT) as a representative example, we demonstrate substantial reductions in two-qubit gate count, atom transport, and circuit depth. These resource savings translate into an estimated circuit fidelity three orders of magnitude higher than competing compilation strategies for a 30-qubit QFT. We further extend the construction to the recently introduced optimistic QFT and discuss the broader applicability of PTNs to other quantum algorithms on neutral-atom platforms.

The absence of translational symmetry in quasiperiodic systems invalidates conventional band theory, posing the central challenge in the field. Building upon the incommensurate energy band (IEB) concept, we establish a unified spectral theory for quasiperiodic systems by introducing two key advances. First, we develop an efficient spectral function method that calculates $A(k,ω)$ using a small truncated Hamiltonian matrix, bypassing full diagonalization. It converges via a distinctive successive locking of energy moments, yielding exact thermodynamic-limit results without finite-size scaling. Second, we introduce that quasiperiodic eigenstates possess Janus quantum numbers: a single eigenstate, continuously tracked across localization transitions, carries dual labels in momentum and real space, which naturally reduce to the familiar Bloch momentum and band index in the commensurate limit. Together with IEB, these advances constitute a ``band theory'' for quasiperiodic systems, enabling us to define, compute, and label states with the same facility as in periodic ones.

Conference key agreement allows multiple remote parties to establish a shared secret key with information-theoretical security. In device-independent conference key agreement, security can be guaranteed with minimal assumptions on the devices used, provided that a violation of a Bell inequality is observed. However, implementations are extremely challenging because high detection efficiency is required to observe loophole-free Bell violations. Here, we enhance the robustness of device-independent conference key agreement by introducing a new family of multipartite Bell inequalities called the asymmetric parity-Clauser-Horne-Shimony-Holt (CHSH) inequalities. We derive a tight analytical lower bound on the conditional von Neumann entropy of the outcomes of one of the parties in a protocol based on this inequality, including noisy preprocessing. Using this bound, we analyze robustness to detection inefficiencies as well as local and global depolarizing noise. We show that the combination of the asymmetric parity-CHSH inequality and noisy preprocessing can significantly improve the robustness to imperfections.

Quantum batteries have emerged as a promising new generation of energy-storage devices for powering quantum technologies. Long-distance charging is particularly attractive because it minimizes interference between the charger and the battery, thereby attracting considerable interest. Here, we propose a topologically protected long-distance charging protocol for quantum batteries based on a pulse-controlled superconducting qubit chain. By dynamically modulating the pulse-mediated couplings, we realize topologically protected energy transfer from the charger to the battery. We show that the charging process is free of energy backflow and remains robust against imperfections in pulse control. Moreover, the energy stored in the battery at the target time is fully extractable, and the protocol remains effective for relatively large system sizes. To further accelerate charging, we optimize the pulse shape and elucidate the underlying physical mechanism. Our pulse-controlled topological quantum battery protocol provides a versatile framework for implementing long-distance topological charging and establishes a theoretical foundation for designing optimal-control strategies to enhance quantum battery performance.

The manifold coincidences and singles counting provides a resource-saving quantum-optics analysis tool, since it is appropriate even in the presence of heavy experimental imperfections. Here, we prepare cross-polarized twin beams in the telecommunication wavelength range via parametric down-conversion in a periodically-poled KTiOPO$_4$ waveguide and herald photon-number states up to three photons. First, we show that the single-click probability is a versatile tool not only for extracting the state's mean photon number but also for sampling values of the moment generating function being the core behind any quantum optical state. Second, we measure values of the normalized factorial moments of photon number, $g^{(m)}_{\text{h}}$, up to the order $m = n+1$ for the heralded $n$-photon state. These normalized photon correlations provide an expedient method for examining the higher-order non-classicality of light by violating the condition $g^{(m+1)}_{\text{h}} \ge g^{(m)}_{\text{h}} \ge 1$.

Quantum repeaters are essential for establishing long-distance quantum communication to overcome the exponential decay of entanglement due to photon loss. Traditional repeater architectures rely on physical quantum memory, which introduces decoherence and poses significant practical implementation challenges. The repeater graph state (RGS) architecture offers a promising memory-less alternative that is inherently resilient to photon losses. A key challenge in implementing RGS lies in the requirement for highly efficient graph state generators and complex qubit measurement. In this work, we aim to investigate the strategies for extracting the maximum number of Bell pairs from the RGS structure via its qubit connection to resolve the well-known bottleneck problem of RGS in which only a single Bell pair can be extracted from a complete bipartite graph state. From simulations, we observe that the maximum number of extracted Bell pairs depends on its connection topology, where the Bell-pair yield tends to be maximal at low to moderate edge densities. As the number of network hops increases, the RGS must be equipped with higher inner-qubit connectivity to maintain a sufficient yield of extractable Bell pairs. Thus, the expected resource requirement shifts toward the use of RGSs with higher inner-qubit connectivity.

Spontaneous breaking of continuous time-translation symmetry in driven-dissipative systems gives rise to boundary time crystals (BTCs), characterized by persistent oscillations sustained by coherent driving and collective dissipation. Conventional BTCs, however, typically require strong driving and exact atom-drive resonance, imposing stringent constraints on their realization. Here we consider two atomic ensembles coupled to a common Markovian reservoir and show that shared dissipation organizes dissipation-free and low-dissipation modes into dynamically accessible low-dissipation channels, enabling BTCs under weak driving and finite detuning. Finite detuning further selects a unique stable limit cycle from an initial-state-dependent family of oscillatory trajectories. Our results establish low-dissipation dynamical channels as a route to robust BTCs under relaxed driving and resonance conditions.

Quantum many-body systems exhibit rich and complex behaviour. Magic has recently emerged as a powerful new diagnostic for probing such systems, complementing other key features such as many-body entanglement. Here, starting from an investigation of the onset of magic within subsystems of a larger many-body quantum system, we show that intricate structures emerge which shed important light on the underlying many-body physics. Focusing on the Kitaev honeycomb model, we first identify the temperature below which local subsystems acquire magic. Remarkably, we find that the optimal magic witnesses active at the onset of magic reveal compact operator spaces that continue to capture the local thermal states throughout their subsequent evolution. For the six-site hexagonal marginal, this connection can be made stronger: the same operator space emerges independently from the symmetries of the local marginal and forms the symmetry-resolved plaquette algebra. When these symmetries are realized exactly, the local state lies entirely within this algebra and the reduced robustness of magic is equal to the full robustness of magic. The same reduced description can also be applied to other local quantum resources, which we illustrate using genuine multipartite entanglement. Furthermore, the operator spaces possess a rich algebraic structure in the form of finite-dimensional Euclidean Jordan algebras, with a natural interpretation in terms of bond and bond-cycle operators. Our general methodology therefore show how the onset of local magic can reveal a compact, physically meaningful operator structure underlying the finite-temperature Kitaev spin liquid, and opens up a new avenue towards reduced descriptions of quantum resources in many-body systems.

Explicit quantum circuits for the wave equation, built by Hamiltonian simulation, are restricted to closed domains, in which outgoing waves reflect off the edge of the computational region and return. We lift that restriction with absorbing boundaries of the convolution type - a complex-frequency-shifted perfectly matched layer realised through exponential-kernel memory variables - and make the resulting non-unitary dynamics quantum-implementable by Schrodingerisation. We obtain three results. First, explicit gate-level circuits for the absorbing evolution, obtained by extending a Bell- basis term-evolution circuit to projector-valued operator strings and Trotterising to second order; these run end to end on seventeen to twenty-one qubits and agree with exact references to within a tenth of a percent to a percent. Second, a structural obstruction: the memory form of the absorbing generator carries an irreducibly indefinite Hermitian part, whose largest eigenvalue grows as the square root of the absorption strength divided by the grid spacing and survives any diagonal rescaling of the memory fields. The known recovery threshold for Schrodingerisation then makes the post-selection cost grow exponentially in the simulated time. Third, a remedy: a Lyapunov symmetrizer, precomputed classically, renders the transformed generator dissipative and replaces that time-dependent penalty with a time-independent conditioning factor of several hundred, measured on grids of up to four thousand unknowns and saturating under mesh refinement. The crossover is early: past it the symmetrized recovery is cheaper by four to twenty-six orders of magnitude in post-selection cost, and at the longest horizons tested it is the only recovery that works.

The covariant quantum Fisher information (CQFI) has recently been established as the ultimate precision benchmark for pseudo-Hermitian sensors [Phys. Rev. Lett. 136, 080802 (2026)], yet existing analyses are limited to single-mode systems. Here we extend the CQFI formalism to multi-mode non-Hermitian Su-Schrieffer-Heeger lattices and reveal tunable topological enhancement enabled by the non-Hermitian skin effect (NHSE). Under open boundary conditions, the NHSE deforms the conventional Brillouin zone into a generalized Brillouin zone of radius r = exp(\k{appa}), where \k{appa} denotes the non-Bloch decay rate. While the total CQFI scales linearly with system size N, its prefactor depends critically on \k{appa}, yielding an enhancement factor E(N) = F_OBC / F_PBC that exceeds 30 for N ~ 30, substantially outperforming periodic-boundary sensors. The enhancement is robust against moderate local disorder and supports multi-parameter estimation, with the joint Cramér-Rao bound reduced by up to 15 orders of magnitude. These findings establish a spatial-domain mechanism for quantum metrology that complements time-domain strategies and is experimentally accessible using topoelectrical circuits, photonic lattices, and superconducting circuits with current technology.

Re-visiting the problem of the coupled electronic--nuclear motion, we prove that the so called `mean-field' Ehrenfest picture is an exact theory, rather than an approximation, in the classical limit for nuclei. By establishing its full equivalence to the much more involved Exact Factorization approach to the problem (Abedi {\it et al.}, Europhys. Lett. {\bf 106}, 33001 (2014)), our conclusion rehabilitates the mean-field Ehrenfest molecular dynamics as a simple, effective, while formally exact scheme, amenable to the use within the framework of the time-dependent density functional theory.

In this paper, we do not try to solve the measurement problem, but rather to properly formulate it. One of the reasons why it still lacks a precise, agreed definition is that the problem may take very different aspects depending on the interpretation of quantum mechanics embraced. Inspired by the methodology of theory-independent results like Bell's theorem, we propose to identify the common root of the puzzle in an interpretation-independent way i.e. as a property of the empirical statistics only, before deriving its philosophical consequences. The key observation is that quantum matter can not be described by a Kolmogorovian probabilistic theory. Arguing that the Kolmogorov axioms of probability theory are the postulates of epistemic uncertainty leads us to reformulate the measurement problem as the impossibility to build an ontology independent of epistemology for quantum matter. Said differently, there exists no God's-eye view on quantum systems. Although it is meaningless to solve the measurement problem as defined in this way, insofar as it is a feature of the universe's statistics, such a formulation may on the other hand bring side benefits. In particular, we argue that it allows to: (i) shed a new light on the variety of interpretations; (ii) propose a fundamental reason why quantum mechanics and general relativity are so incompatible, not relying on purely mathematical or technical arguments; (iii) guide the quest for quantum gravity.

Self-sustained oscillations in open many-body systems can be organized by two distinct dynamical ingredients: the selection of a finite-amplitude background attractor and the subsequent control of its neutral phase. We develop this bifurcation-based picture for driven-dissipative collective spins and show how the microscopic dissipative structure determines the available background and its response to explicit U(1) breaking. In the thermodynamic-limit mean-field dynamics, a single linear U(1)-covariant jump produces only polar fixed-point backgrounds, whereas nonlinear covariant dissipation provides amplitude-dependent saturation and stabilizes a finite-latitude self-sustained-oscillator manifold through a supercritical Hopf bifurcation. Under coherent U(1) breaking, exact resonance leads to a reversible double-zero degeneracy with vanishing critical frequency rather than a standard Hopf onset. Finite detuning unfolds this singularity into a genuine finite-frequency Hopf boundary, which exists only on the self- sustained-oscillator side and can be either supercritical or subcritical. By contrast, a single linear dissipative U(1)-breaking jump cannot generate a standard Hopf instability: when its phase-pinning invariant vanishes the azimuthal direction remains neutral, whereas otherwise the phase-locked fixed points have a purely real Jacobian spectrum. These results establish a general design principle: nonlinear covariant dissipation selects the self-sustained background, while the structure of the symmetry-breaking channel determines whether the resulting local response is double-zero, genuinely Hopf, or non-Hopf.

QBism understands quantum mechanics to be probability theory supplemented by additional nonclassical coherence conditions. In this dissertation, we develop these nonclassical coherence conditions from first principles, emphasizing the role of a well chosen reference measurement. After treating standard probability on subjective Bayesian lines, we demonstrate an equivalence between the QBist approach and the existing framework of generalized probabilistic theories. We show that the fundamental nonclassical coherence relation may almost always be taken to be a gentle modification of the law of total probability, and give a coherentist account of when an experimental scenario has a classical explanation. Finally, we show that when the reference measurement is chosen to correspond to a complex projective 3-design, the shape of quantum state space is implicit in the probabilities which characterize the reference measurement itself. Thus coherence with this single reference measurement, properly understood, implies coherence with all of finite dimensional quantum mechanics. We then attempt a modest reconstruction of quantum theory along these lines, one practical consequence of which is a method for self-testing complex projective $t$-designs for $t\ge 3$ in a theory-agnostic way.

Let $D=2^n$ and $M=3n+9\binom n2$. We study the right-invariant one-step-cliff metric $d_Q$ on $\operatorname{PU}(D)$, with unit penalty on Pauli weights one and two and penalty $Q$ on all higher weights. If $M/Q_D\to0$ and $MQ_D^{3/4}/D^2\to0$, then, for every fixed $0<x<π/\sqrt3$, \[ μ_D\bigl(B_{Q_D}([I],x\sqrt{Q_D})\bigr)\le e^{-c_xD^2}. \] Here $μ_D$ is normalized Haar measure. Thus the Haar-typical distance from the identity and the diameter are both asymptotic to $(π/\sqrt3)\sqrt{Q_D}$ throughout the window $M\ll Q_D\ll D^{8/3}M^{-4/3}$. Choosing $Q_D=κD^{8/3}M^{-4/3}$ with sufficiently small fixed $κ>0$ yields a Haar-typical lower bound of order $D^{4/3}M^{-2/3}$ for the corresponding infinite-cliff Carnot--Carathéodory distance, outside an $e^{-Ω(D^2)}$ exceptional set. The infinite-cliff diameter therefore has exponential lower rate at least $4/3$, disproving Brown's exponent-one conjecture. The same estimate gives a fixed-error no-ancilla two-qubit circuit lower bound of the same order.

Classically equivalent formulations of an optimization problem need not lead to equivalent quantum algorithms. For MaxCut, fixing the value of a single vertex removes a simple global symmetry without changing the underlying optimization problem, yet it can substantially alter the quantum dynamics generated by the Quantum Approximate Optimization Algorithm (QAOA). These dynamics are captured by the circuit's dynamical Lie algebra (DLA), whose direct construction can become exponentially expensive. Here we show that, for symmetry-reduced QAOA on trees, substantial information about the reduced DLA can instead be obtained efficiently from the graph alone. We introduce a polynomial classical algorithm that recursively distinguishes vertices using shortest path structure and degree parity. When all vertices are resolved individually, the method determines the complete reduced DLA and, under the corresponding graph conditions, certifies maximal expressibility of the reduced QAOA ansatz. Even when full resolution is not achieved, the algorithm identifies embedded subalgebras, provides rigorous lower bounds on DLA dimension, and certifies controllable subsystems. Our theoretical and experimental results show how classical graph structure can be used to diagnose and potentially guide the quantum dynamics of variational algorithms before running them on quantum hardware.

We propose all-optical tests of photon-photon interactions in the matter vacuum using standing-wave laser interferometers, which do not require external magnetic fields and use conventional laser sources. We show that the interferometric detection of photon-photon scattering predicted by quantum electrodynamics is within reach of laboratory-scale experiments with a sensitivity that improves nonlinearly with the circulating power within the cavity. We outline how such an experiment could be adapted to probe properties of quantum fields beyond the Standard Model of particle physics.

In this work, we extend the scattering quantum walk (SQW) framework to a lattice of energy-dependent point interactions. This yields, within the coined quantum walk (CQW) formalism, a coin operator that is directly related to the scattering matrix of zero-range potentials. The model thus provides a discrete-time quantum-walk (DTQW) analog of a periodic array of point interactions of the Kronig-Penney type, where the walker's wavenumber serves as a continuous, physically transparent control parameter for the coin operation. We analyze the spectra and the dynamics of position probability and entanglement, yielding distinct results for specific energies and point interactions. We relate the spectral structure to the spatial probability distribution and explicitly characterize the long-time entanglement behavior for each point interaction. The transmission modulus determines the quasienergy gap, bandwidth, and maximum group velocity, while also controlling the long-time coin-position entanglement for the initial state considered. The four families of one-dimensional point interactions ($δ$, $δ'$, crossed and asymmetric) realize qualitatively distinct transmission profiles and span the full range of behavior, including enhanced or strongly suppressed spreading and oscillatory entanglement.

Quantum Schrödinger bridge constructions establish the existence of a conditioned process under a positivity hypothesis on the endpoint data, and three independent ones adopt it. We show that hypothesis fails on a definite locus once the conditioned object is the two-state amplitude $φ^*ψ$ of a pre- and post-selected pair on configuration space, and that the failure is testable on recorded data. Whenever $φ^*ψ$ has a moving zero of order $k$ across which probability flows, no diffusion of constant diffusion coefficient can both carry the conditioned density and avoid the nodal curve: the current velocity it would need grows as the inverse $2k$-th power of the distance to that curve and points toward it on one side, placing the curve at finite scale distance, so it is reached and not merely approached. Identifying the weak momentum with a bridge drift fails independently: for a free particle post-selected in position the current velocity is exactly minus the drift of the bridge to the target. The positive Doob $h$-transform and the Bernstein conditioning built on it exist wherever $φ^*ψ$ is nodeless and fail on the nodal curve. There the osmotic part of the weak momentum diverges as the inverse distance to the zero and changes sign across it with a coefficient set by $k$, while the current part stays bounded; that boundedness rests on the signed factorization of the real-envelope class and hides the obstruction from any picture built on the current velocity alone. A measured fringe visibility fixes a single length, which puts a Lorentzian of order $10^{-3}$ into the current channel reconstructed in the two-slit trajectory experiment if the contrast is limited by an off-axis zero, and nothing there if by incoherence. The results are one-dimensional, covering the separable transverse field of a two-slit geometry, not general two-dimensional vortices.

Quantum computers promise advantages for simulating strongly correlated quantum many-body systems, like atomic nuclei, that are beyond the reach of classical computers. Realizing this potential requires understanding the quantum complexity structure of the target problem. We investigate the time-evolution of two key indicators of quantum complexity, bipartite entanglement entropy and non-local magic (non-stabilizerness), in nuclear reaction dynamics. We analyze two representative dynamical processes: scattering in a one-dimensional model of strongly interacting fermions governed by the Negele potential, and a realistic simulation of $^{240}$Pu fission within time-dependent Hartree-Fock-Bogoliubov (TDHFB) theory. In the former case, we find that interactions dynamically generate both entanglement and non-local magic, leaving persistent signatures of quantum complexity in the outgoing states. In the latter, we observe that substantial quantum complexity survives in the spatial bipartition of daughter fragments well beyond scission. The presence of significant non-local magic and entanglement in both cases strongly indicate that quantum computers would provide substantial advantages for accurately simulating nuclear reaction dynamics.

We introduce a diagnostic framework based on the full probability distribution of quantum coherence to probe single-particle and many-body phases at finite temperature. We first apply this approach to the localization transition in the non-interacting Aubry-André model and then extend the analysis to its interacting counterpart, whose phase diagram is substantially richer. We show that the moments of the coherence distribution provide clear signatures of quantum phase transitions and capture the emergence of many-body phases. More importantly, we find that the entropy of the coherence distribution emerges as an even more powerful indicator, retaining clear signatures of the underlying quantum phases while remaining remarkably robust against increasing thermal fluctuations.

Insider Brief PsiQuantum and Brookhaven National Laboratory have partnered to use PsiQuantum ’s Construct software platform for research into fault-tolerant quantum algorithms and scientific applications. Brookhaven researchers will use Construct to develop and study algorithms intended for the first generation of fault-tolerant quantum computers. The collaboration supports the DOE’s Quantum Genesis initiative, which aims to develop and deploy a scientifically relevant fault-tolerant quantum computing system by 2028. PRESS RELEASE &#8212; PsiQuantum and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory today announced a collaboration that will leverage PsiQuantum’s software platform, Construct, to support Brookhaven Lab scientists researching new algorithms and scientific applications for the first generation of fault-tolerant quantum computers. “We are excited to partner with PsiQuantum to give our researchers access to these new tools,” said Brookhaven Lab’s Associate Laboratory Director for Discovery Technologies Gabriella Carini . “DOE’s new Quantum Genesis initiative requires innovative partnerships across our national labs, industry, academia, and government. This is a great example of one such collaboration.” The Quantum Genesis initiative is focused on developing and deploying the world&#8217;s first fault-tolerant, scientifically relevant quantum computing capability for research and development by 2028. Quantum Genesis will serve as a foundational element of DOE’s broader artificial intelligence-focused Genesis Mission , which is designed to usher in a new era of computational power for the nation to accelerate scientific discovery and innovation.&nbsp; “We are excited to partner with Brookhaven National Laboratory to use these tools in support of its research into fault-tolerant quantum algorithms and applications,” said PsiQuantum ’s Vice President of Government Relations Heath Bumgardner . “Through this partnership, we&#8217;re demons

Insider Brief Researchers directly measured gravity’s predicted effect on the quantum phase of freely falling atoms, finding Einstein’s equivalence principle consistent with quantum mechanics under the tested conditions. The Quantum Galileo Interferometer split ultracold rubidium atoms into two quantum paths, holding one stationary while the other fell freely before recombining them to measure their phase difference. The experiment neither unifies gravity with quantum mechanics nor proves gravity is quantum, but the technique could support future tests using heavier objects such as nanodiamonds. Image: A general picture of the experimental setup. At the heart is a vacuum chamber in which conditions such as those in space mean that atoms can be kept undisturbed. On the left is a 2D MOT, a device that feeds atoms into the science chamber where the atom chip is positioned. Around the chamber are antennas, coils and optical fibres, enabling atoms to be trapped and cooled, then manipulated into two distinct paths. Finally, the relative phase between the two paths is detected. (Or Dobkowski.) PRESS RELEASE &#8212; An international team including Nobel Prize-winning physicist Professor Sir Roger Penrose has observed a long-predicted effect of gravity on a falling quantum object for the first time. The result shows that a fundamental principle at the heart of Einstein’s theory of gravity remains consistent with the behaviour of matter in the quantum world. The study, led by Ben-Gurion University of the Negev, The University of Ulm and the University of Oxford, has been published today (2 Sept) in&nbsp; Science Advances . For more than a century, physicists have relied on two extraordinarily successful descriptions of nature. Quantum mechanics explains the strange behaviour of atoms and other tiny objects. Einstein’s theory of gravity explains how objects fall and how gravity shapes the Universe. Yet physicists still do not fully understand how the two fit together. Now, an

Insider Brief The sixth annual City Quantum &amp; AI Summit will bring leaders from technology, defense, finance, government and research to London’s Mansion House on Oct. 7. The program will examine quantum and AI applications and risks across cybersecurity, finance, life sciences, space and national security. The summit will emphasize plain-language discussions, cross-sector networking and governance for technologies developing faster than existing institutions and regulations. Images: Paulina Roots Photography The technologies changing defense, medicine and finance are advancing faster than the institutions expected to manage them. Getting the right people in the same room is a critical step toward optimizing the good that these technologies can do, while minimizing potential adverse effects. The sixth annual City Quantum &amp; AI Summit is aimed at bringing those people – military leaders, technology executives, researchers, investors and policymakers – to the Mansion House in London on Oct. 7. The one-day event is organized around the theme “Connections in Chaos.” Karina Robinson , CEO of Redcliffe Advisory and founder of the summit, said the theme reflects a loss of predictability in international affairs, compounded by the rapid development of artificial intelligence and the emerging possibilities of quantum technology. “The modicum of predictability that existed in world affairs a decade ago has vanished,” said Robinson. “How to cope? Develop personal connections. The Summit’s focus has always been to create networks across countries and across sectors. It is the best source of innovation and, in our age of AI, the last refuge of humanity.” The summit’s program treats those human connections as practical infrastructure. It brings together industries that face related technological and security challenges but often operate separately. Defense officials will meet quantum and AI executives. Medical researchers will discuss computing with technology specialists.

The weak equivalence principle (WEP) is central to Einstein's general relativity. It posits that gravity must accelerate everything equally, regardless of what it is made from. For the first time, a team led by Ming-Sheng Zhan at the Wuhan Institute of Physics and Mathematics has tested the principle using clouds of continuously free-falling atoms aboard an orbiting space station.

Insider Brief Ramboll has completed the specialized Copenhagen facilities that will house MAGNE, enabling QuNorth to begin installing the Nordic quantum computer. EIFO and the Novo Nordisk Foundation have invested EUR 80 million in the initiative, which is being delivered with Microsoft and Atom Computing. MAGNE is expected to become fully operational in 2027 and provide Nordic researchers, companies and start-ups with advanced quantum computing capacity. Image: QuNorth PRESS RELEASE &#8212; Ramboll has completed the specialized facilities that will house MAGNE, one of the world&#8217;s most powerful commercial quantum computers. The milestone enables QuNorth to begin installation of the system in Copenhagen. Ramboll delivered the building and technical infrastructure required for MAGNE, including a computer room, server room and airlock, as well as systems for ventilation, power supply, cooling and fire suppression. &#8220;Quantum computers place extraordinary demands on their surroundings. The facility itself must function as a precision environment where vibration, dust, magnetic fields, static electricity, temperature and humidity are carefully controlled,&#8221; says Hans Kragh, Senior Chief Project Manager at Ramboll. A step forward for quantum technology QuNorth was established by EIFO and the Novo Nordisk Foundation, which have invested EUR 80 million in the initiative. MAGNE is being delivered in collaboration with Microsoft and Atom Computing and will provide researchers, companies and start-ups across the Nordic region with access to advanced quantum computing capacity. “With MAGNE, we will gain access to quantum computing capacity that can accelerate the development of new solutions in areas including life science, chemistry, materials science and the green transition. But the physical infrastructure surrounding the computer must be stable and precise. That is why the specially designed facilities are an important part of making the technology usable,” s

Spin-orbit coupling (SOC), an interaction between an electron's spin and its motion, plays a key role in creating topological insulators—unusual materials that are insulating in their interior but can conduct electricity along their surfaces.

Photonic quantum hardware developer PsiQuantum and the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have established a strategic software collaboration to accelerate the development of fault-tolerant quantum algorithms and scientific applications. Under the agreement, Brookhaven scientists will utilize PsiQuantum's open-access Construct software platform to design and optimize resource requirements for utility-scale quantum workloads. [ [...] The post PsiQuantum and Brookhaven National Lab Partner to Develop Fault-Tolerant Algorithms on Construct Platform appeared first on Quantum Computing Report .

Insider Brief QuSecure demonstrated its QuProtect R3 post-quantum cryptography platform on U.S. Army tactical mission systems during Project Convergence Capstone 6 (PCC6). The company said QuProtect R3 achieved Technical Readiness Level 7 after operating in live-force tactical conditions at the Army exercise. The demonstration included quantum-resistant communications, cryptographic agility, and cryptographic discovery and inventory capabilities for Army tactical networks. PRESS RELEASE &#8212; QuSecure , Inc., a leader in post-quantum cryptography (PQC) and cryptographic agility, today announced it demonstrated operational readiness at Project Convergence Capstone 6 (PCC6), the capstone event for Army Transformation and Training Command (T2COM). At the event, QuSecure ’s flagship PQC product, QuProtect R3, successfully provided quantum-resistant communications, cryptographic agility, and cryptographic discovery and inventory for Army tactical mission systems. The achievement comes as federal agencies operate under binding deadlines in Executive Order 14412, signed June 22, requiring PQC migration by 2030-2031. Hosted annually by the U.S. Army at the National Training Center (NTC) at Fort Irwin, PCC6 is a live experiment featuring thousands of soldiers conducting maneuvers and mission threads to test future concepts, capabilities and formations for the Army, Joint Force, and Multinational allies and partners. PCC6 brings together a diverse range of warfighting systems and personnel to enhance lethality, agility, and survivability through the integration of emerging technologies, enabling effective deterrence and, when necessary, decisive action against potential adversaries. As a result of QuProtect’s successful operation by soldiers in real-world conditions, QuProtect R3 attained Technical Readiness Level (TRL) 7, a critical step forward in delivering a product to field with the Department of War. The Post-Quantum Cryptography Coalition recently published the&nbsp;

Insider Brief Meissner raised $2.6 million in pre-seed financing to develop superconducting materials for quantum computing, fusion energy and other applications. The startup combines machine learning, quantum simulations and laboratory testing to identify materials that could operate at higher temperatures and with fewer performance problems. Meissner plans to begin testing its leading material candidates at the University of Waterloo’s Quantum-Nano Fabrication and Characterization Facility. Toronto-based materials startup Meissner has raised $2.6 million in pre-seed financing to search for superconductors that could support advances in quantum computing, fusion energy and other emerging industries. The $2.6 million U.S. round, equivalent to about $3.6 million Canadian, included backing from BDC Capital ’s Thrive Venture Fund and a group of Canadian technology entrepreneurs and investors. Participants included Andrew Talpash, Anthony Lacavera, Christian Weedbrook, Daniel Debow, Dennis Bennie, Eliot Pence, Greg Twinney, and Michael and Richard Hyatt, according to BetaKit . Meissner plans to use machine learning, computer simulations and laboratory testing to identify and develop materials with improved superconducting properties. The four-person company describes the system it is building as a “discovery engine” for superconductors. Superconductors can carry electricity without resistance or the resulting loss of energy. They are already used in technologies such as magnetic resonance imaging machines and magnetic-levitation trains. Companies are also exploring them as components for quantum computers and fusion-energy systems, both of which require precise control of electrical currents and magnetic fields. “They’re definitely the picks and shovels to unlocking high-growth, high-tech industries,” Meissner founder and CEO Olivia Leng told BetaKit. The company’s goal is to produce and sell superconducting materials tailored to particular commercial applications. Meis

Insider Brief Quobly and TNO have signed an MoU to strengthen technical cooperation on the development and industrialization of silicon spin qubit technology. The partnership combines Quobly ’s 300 mm FD-SOI platform with TNO ’s expertise in device characterization, materials analysis and systems engineering. The two organizations will work on measurement, simulation and high-throughput characterization capabilities needed to support larger-scale integration and manufacturing of silicon spin qubits. PRESS RELEASE &#8211; Quobly , a French quantum computing company developing industrially scalable quantum computers based on silicon spin qubits, and TNO , the Netherlands Organisation for Applied Scientific Research, have signed a Memorandum of Understanding (MoU) to strengthen their technical cooperation on the development and industrialization of silicon spin qubit technology. The agreement builds on the collaboration initiated between the two organizations in 2025, focused on materials research and device characterization for silicon spin qubits. This work has laid the foundations for further cooperation, bringing together complementary expertise and infrastructure to address the engineering challenges involved in scaling silicon spin qubits toward industrial manufacturing. The new MoU establishes a framework to further develop this cooperation, combining Quobly ’s manufacturable 300 mm FD-SOI platform with TNO ’s expertise and infrastructure in device characterization, materials analysis and systems engineering and supporting the development of the measurement and integration capabilities required for industrial-scale quantum hardware. Combining European Semiconductor and Quantum Capabilities Silicon spin qubits offer a distinctive route to scalable quantum computing because they can leverage the tools, substrates and process-control capabilities of advanced semiconductor manufacturing. Europe already has world-class capabilities across this value chain, from engin

Insider Brief Pasqal and True Nexus have used Pasqal ’s neutral-atom quantum technology to encode selected protein structures linked to the molecular mechanisms behind protein gelation. The collaboration combines AI-driven protein analysis with quantum computing to study the relationship between protein structure and functionality. The companies said the work could support future applications in food and biotechnology, with the project also tied to Saudi Arabia’s broader plans for applied quantum technology. PRESS RELEASE &#8211; Pasqal (Nasdaq: PSQL), a global provider of neutral-atom quantum computers, and True Nexus , a computational intelligence company focused on making protein functionality programmable for real-world food applications, today announced a major milestone in their collaboration: the successful use of Pasqal’s neutral-atom quantum technology to encode selected protein structures relevant to the molecular mechanisms that drive protein gelation — the process that turns liquids into gels and gives foods their structure and texture. The milestone marks a first, decisive step toward making protein functionality, one of the most valuable and least understood properties in the global food and biotech economy, computationally accessible and, ultimately, programmable. Proteins are the foundation of the modern food economy, and one of its greatest unsolved problems. Their commercial value rests not on their sequence but on their functionality: how they gel, bind, foam and give texture. For decades, that functionality has resisted design. Industry could read a protein’s sequence, yet the deeper chemistry that determines how a protein behaves under real-world conditions remained extremely difficult to model computationally — discoverable only through slow, costly trial and error at the bench. It is why, despite twenty years of effort and billions in investment, plant proteins have not consistently matched animal proteins across key functionalities associated

IBM Quantum has announced the official release of IBM Quantum Nighthawk r2 (deployed as ibm_phoenix), its fastest quantum processing unit (QPU) to date. Built on a square-lattice architecture, the 120-qubit processor introduces a high-speed dissipative qubit reset framework that eliminates long inter-circuit idle periods, achieving a maximum circuit throughput of over 100,000 circuits per second—a [...] The post IBM Releases Nighthawk r2 QPU Featuring Active Dissipative Qubit Reset and 25x Circuit Throughput appeared first on Quantum Computing Report .

Insider Brief Cyprus and Greece have established their first quantum-secure satellite data connection using Sparkle’s Quantum Safe Interconnect (QSI) system and Hellas Sat’s satellite infrastructure. The connection links Sparkle’s data centre in Athens with Hellas Sat infrastructure in Cyprus, with data travelling about 72,000 kilometres through the satellite system. The companies said the trial demonstrates how software-based quantum-safe protection can be applied to existing terrestrial and satellite networks to address harvest-now-decrypt-later risks. Cyprus and Greece have established their first quantum-secure satellite data connection, Sparkle and Hellas Sat, a satellite operator serving Greece and Cyprus, announced on Wednesday, in a development aimed at protecting communications against future cyber threats, the Cyprus Mail reported . The connection links Sparkle &#8216;s data centre in Metamorfosi, Athens, with Hellas Sat infrastructure in Cyprus, following earlier successful testing of a secure IPsec connection between two data centres in Greece. The latest trial extends that protection to a live satellite connection between the two countries, with data travelling approximately 72,000 kilometres through the satellite system, including the uplink from Cyprus to the satellite and the subsequent downlink to Greece. According to the companies, this marks the first application of this specific form of quantum protection to a Greece-Cyprus satellite link. The link runs on Sparkle&#8217;s Quantum Safe Interconnect (QSI) system, built to counter what&#8217;s known as the &#8220;store now, decrypt later&#8221; risk: data intercepted and stored today, with the expectation that future computing power will eventually crack its encryption, the outlet reported. QSI works by transmitting data securely while automatically rotating encryption keys. Because the system is software-based, it can be layered onto networks and security infrastructure that already exist, meaning

Neutrinos are pervasive yet intangible particles that permeate the universe, streaming through whole planets, stars and our bodies by the trillions each second. The elementary particles are often described as "ghostly" for their near-zero mass and elusive nature, as they have very little interaction with normal matter.

What happens when a superconductor becomes so thin that electrons can no longer behave as if they were moving through an ordinary three-dimensional piece of metal? This question has been at the center of my recent work on quantum confinement in metallic films. Over the past few years, I have been developing this line of theory with my colleague Giovanni Ummarino at Politecnico di Torino. Our initial goal was to understand something rather concrete: Why does shrinking the thickness of a superconducting film change the temperature at which superconductivity appears?

Post-quantum cryptography (PQC) provider QuSecure, Inc. has demonstrated operational readiness for its flagship cybersecurity platform, QuProtect R3, at the U.S. Army’s Project Convergence Capstone 6 (PCC6) experimentation event. Held at the National Training Center (NTC) at Fort Irwin, California, the live-force exercise tested tactical capabilities under real-world combat conditions. The successful deployment elevated QuProtect R3 [...] The post QuSecure Achieves TRL-7 at U.S. Army Project Convergence Capstone 6 for QuProtect R3 appeared first on Quantum Computing Report .

Insider Brief BQP secured a strategic investment from IBM Ventures, bringing its total funding to $8 million to expand its physics-simulation platform beyond aerospace and defense. BQP said contracted and committed revenue has increased eightfold since its 2025 seed round, while its customer base has tripled and platform users have grown twentyfold. Its BQPhy platform runs physics and AI solvers on existing CPU and GPU systems while preparing customers for future hybrid quantum-classical computing. PRESS RELEASE &#8212; BQP , the physics acceleration company, today announced a strategic investment from IBM Ventures, the venture capital arm of IBM . The investment brings BQP &#8216;s total funding to $8M and funds BQPhy®&#8217;s expansion from engineering design into operational deployment, scaling delivery and go-to-market as BQP expands beyond aerospace and defense. Venn10 Capital and existing investor Monta Vista Capital also participated. Since its 2025 seed round, backed by New York State&#8217;s venture arm and other institutional investors, BQP has grown contracted and committed revenue 8x, tripling its customer base and growing platform users 20x. “An engineer with a deadline doesn&#8217;t care where the answer came from. They care that it arrived in time and that the physics is right. The industry spent years treating this as a hardware problem that warranted faster chips, more of them, and eventually a quantum one. But it was always a software problem,” said Abhishek Chopra, Founder and CEO of BQP . Chopra added: “We spent those years earning our way into engineering workflows, so when the quantum machines are ready, nothing about how those teams work has to change. That&#8217;s the path IBM has watched us build since 2023, and this investment says it&#8217;s the right one.” Mission-critical decisions have deadlines, and high-fidelity physics simulations rarely meet them. More hardware has not closed the gap. Classical physics solvers leave roughly 85% of a

French silicon quantum computing developer Quobly has signed two strategic cooperation agreements in the Netherlands with the Netherlands Organisation for Applied Scientific Research (TNO) and automated test equipment provider Orange Quantum Systems (OrangeQS). Executed during an official state visit by French President Emmanuel Macron and Dutch Prime Minister Rob Jetten, the partnerships establish a cross-border [...] The post Quobly Signs Dual Agreements with TNO and OrangeQS to Industrialize Silicon Spin Qubit Manufacturing appeared first on Quantum Computing Report .

By Doug Finke You may be a manager in a large enterprise and have been reading popular press reports on quantum technology and wondering if it is something that you might use to improve your operations to make them more effective and efficient. It is a good question. Because while quantum has great potential, it [...] The post A Four Step Process for End Users to Leverage Quantum Technology appeared first on Quantum Computing Report .

Insider Brief Quandela has signed an MoU with CMC Microsystems to join Canada’s Quantum Computing Sandbox as a cloud-based photonic quantum computing provider. The partnership will give participating SMEs, organizations and academic researchers access to Quandela ’s Canada-based photonic quantum computing platform and other quantum computing options. Quandela and CMC Microsystems will also provide technical and practical support to selected projects participating in the Quantum Computing Sandbox. PRESS RELEASE &#8211; Quandela , a leading player in photonic quantum computing technologies, has signed a memorandum of understanding with CMC Microsystems to join the Quantum Computing Sandbox as a provider of cloud-based computing services. Quandela’s expertise, based within the country, now joins forces with other providers to offer a comprehensive suite of quantum options made available to small and medium-sized enterprises, organizations, and academic researchers, with the aim of developing and accelerating the solutions that will be applied to a wide range of fields and needs. “As data sovereignty in the digital realm becomes an increasingly important issue given the current global context, we are proud to be the first to include a Canada-based photonic quantum computer among the cloud computing options available to the participants of the QCS program”, stated physicist Valérian Giesz, Co-Founder and Director of Strategic Partnerships at Quandela . “This will allow their work and data to be entirely hosted on Canadian soil, without having to go through a structure located in another country.” The Quantum Computing Sandbox (QCS) is supported by FABRiC, an organization funded by Innovation, Science and Economic Development Canada (ISED), whose mission is to build an ecosystem which strengthens Canada’s semiconductor sector. QCS’ role, through technical support and research grants, is to foster the development of quantum applications for Canada’s various industrial sect

Focusing on the real-time dynamics of the reduced density matrix of the multidimensional Caldeira-Leggett model, several techniques are adopted in this paper to reduce the spatial and temporal dimensionality, combined into an efficient algorithm. From a spatial perspective, an equivalent formulation of the Dyson series is presented. With the aid of a low-rank approximation, the spatial dimensionality of open quantum system simulations is halved. From a temporal perspective, the frozen Gaussian approximation is used to approximate both the evolution operator and the interaction operator in the multidimensional Caldeira-Leggett model. This reduces the high-dimensional integrals to one- and two-dimensional integrals independent of the truncation level of the Dyson series. Through these techniques, we design an efficient algorithm whose validity is verified through several numerical experiments, including a two-dimensional double slit simulation.

The study of real time dynamics of nuclear systems is of great importance to provide theoretical predictions of cross sections relevant for both terrestrial experiments as well as applications in astrophysics. First principles simulations of these dynamical processes is however hindered by an exponential cost in classical resources and the possibility of performing scalable simulations using quantum computers is currently an active field of research. In this work we provide the first complete characterization of the resource requirements for studying nuclear dynamics with the full Leading Order (LO) pionless EFT Hamiltonian in first quantization employing simulation strategies using both product formulas as well as Quantum Signal Processing. In particular, we show that time evolution of such an Hamiltonian can be performed with polynomial resources in the number of particles, and logarithmic resources in the number of single-particle basis states. This result provides an exponential improvement compared with previous work on the same Hamiltonian model in second quantization. We find that interesting simulations for low energy nuclear scattering could be achievable with tens of millions of T gates and few hundred logical qubits suggesting that the study of simple nuclear reactions could be amenable for early fault tolerant quantum platforms.

Abstract Accurate state preparation is a critical bottleneck in many quantum algorithms, particularly those for ground-state energy estimation.&amp;#xD;Even in fault-tolerant quantum computing, preparing a quantum state with sufficient overlap with the desired eigenstate remains a major challenge.&amp;#xD;To address this, we develop a unified cost-aware framework for filtered-state preparation that enhances the overlap of a given input state through spectral filtering.&amp;#xD;The framework covers polynomial and trigonometric realizations of filters and makes explicit the trade-off among overlap amplification, preparation success probability, and filter-implementation cost.&amp;#xD;As representative examples, we analyze Gaussian filters and introduce a modified Krylov-subspace-based filter that improves the success-probability/overlap trade-off relevant to filtered state preparation.&amp;#xD;Within this framework, we study a filtered variant of quantum phase estimation (FQPE) that mitigates the unfavorable dependence on the initial overlap present in standard QPE.&amp;#xD;Numerical experiments on Fermi–Hubbard models show that FQPE reduces the total runtime by more than two orders of magnitude in the high-precision regime, with overlap amplification exceeding a factor of one hundred.

A key challenge in practical quantum machine learning (QML), particularly for discriminative tasks such as classification, is the limited capacity of near-term quantum devices to encode high-dimensional classical data into small quantum registers. In optimized basis-encoded (bit-bit) settings, this constraint leads to cross-class collisions, where samples with different labels are mapped to the same discrete bit-string and thus become indistinguishable to any downstream model. In this work, we investigate how data representation affects QML performance under such severe information bottlenecks. We introduce discretization-aware fine-tuning (DAFT), a method that adapts a pre-trained chemical foundation model to produce representations that remain informative after quantization. DAFT reduces collision probability through a differentiable soft collision loss. We evaluate both quantum and classical models under a controlled setting in which they receive identical discretized bit-string inputs, isolating the effect of representation from model architecture. On the blood-brain barrier penetration (BBBP) molecular property prediction benchmark using ChemBERTa-77M, DAFT reduces collision counts by several orders of magnitude and improves quantum classification accuracy by more than 12 percentage points compared to a frozen backbone. Importantly, without DAFT, classical models outperform QML under the same input constraints. With DAFT, however, this comparison reverses at higher qubit counts. At 10 qubits, the quantum model surpasses a matched classical baseline trained on identical bit-strings (0.883 vs. 0.855, $p = 0.026$). These results show that, in information-constrained regimes, achieving a quantum advantage critically depends on aligning continuous representations with discrete quantum encodings.

Quantum error correction (QEC) is beginning to enable logical operations that outperform their unencoded physical counterparts, but useful fault-tolerant computation will require more than low-error quantum memory. An effective architecture must orchestrate efficient logical encoding, low-overhead logical operations, and access to the non-Clifford resources required for universal computation. Here, we introduce and experimentally validate such an architecture based on the $[[20,2,6]]$ $C_4$-Helix code, designed for the early fault-tolerant regime. Using Quantinuum Helios, a 98-qubit trapped-ion quantum processor, we experimentally demonstrate the principal components of this architecture: we perform repeated quantum error correction with an error of $4.6^{+6.2}_{-2.6}\times10^{-5}$ per logical qubit per QEC cycle. We benchmark the complete Clifford group on the two logical qubits of a single codeblock under active error correction, obtaining an error of $2.8^{+1.0}_{-1.6}\times 10^{-4}$ per two-qubit logical Clifford. We further demonstrate a fault-tolerant chain-map interface between $C_4$-Helix and a distance-5 surface code, preparing a heterogeneous three-logical-qubit GHZ state with a fidelity lower bound of $99.925^{+0.068}_{-0.245}\%$. In each case, the encoded implementation outperforms its corresponding unencoded physical baseline without relying on postselection. Circuit-level simulations indicate that improvements in physical fidelity bring the same architecture into the $10^{-6}$-$10^{-8}$ logical-error regime targeted for early fault-tolerant computation. Together, these results establish $C_4$-Helix as a hardware-validated fault-tolerant architecture rather than a bare quantum memory.

This letter introduces QSVT-3PF, a quantum singular value transformation (QSVT) based solver for three-phase unbalanced power flow with embedded single-phase grid-forming inverter (GFM) operation. The contributions are threefold: 1) reformulating the Newton correction as a QSVT-compatible inverse problem using a normalized block-encoded phase-domain Jacobian; 2) introducing a regularized singular-value filter to improve robustness under ill-conditioned and stressed operating conditions; and 3) validating the proposed solver on an IEEE 5-bus system and the IEEE 123-node test feeder with single-phase GFM integration. Test results show that QSVT-3PF matches the classical Newton benchmark in residual convergence, voltage profile, and final operating point, demonstrating the feasibility of QSVT-3 for large, unbalanced distribution systems.

Schrödinger bridges and entropic optimal transport are usually formulated as stochastic interpolation problems between initial and final probability distributions. In their computational form, the bridge potentials are obtained by Sinkhorn or iterative proportional fitting, and are often regarded as auxiliary scaling functions. We show that for continuously monitored quantum systems, these potentials acquire a direct measurement-theoretic meaning. The mathematical structure of conditional quantum trajectory theory induces a Fokker--Planck equation on quantum state space. Conditioning this diffusion on a terminal distribution or a terminal measurement effect produces a Doob/Sinkhorn potential whose directional derivative along a unitary control vector field is the imaginary part of a generalized weak value. The same construction connects the Schrödinger-bridge viewpoint to the optimal-path framework for continuously monitored trajectories: the backward bridge potential plays the role of an effect-like costate, and its weak-value directional derivative gives the local control signal. By specifying the desired endpoint distribution, the induced drift produced by the Schrödinger bridge solution is the control solution that minimizes the quadratic cost feedback law, guiding the distribution to its desired endpoint. We quantify the control score of the available control Hamiltonian as a logarithmic directional derivative of the bridge potential, or an imaginary weak value. Three explicit examples identify weak measurement as a natural entropic regularization mechanism for quantum state transport and gives a route from Sinkhorn scaling to quantum feedback and Hamiltonian control synthesis for practical optimal control.

Non-KAM (Kolmogorov-Arnold-Moser) systems, when subjected to weak time-dependent perturbations, exhibit an abrupt transition to classical chaos through the breakdown of invariant phase-space tori. We showcase the utilization of non-KAM systems in the quantum regime as quantum sensors, leveraging their sensitivity at \textit{resonances}. Quantum Fisher information (QFI) is a central quantity in quantum parameter estimation theory that measures how much information a quantum state contains about an unknown parameter that is encoded into it. In other words, it quantifies the sensitivity of a quantum state to small changes in that parameter. In this work, through numerical analysis in conjunction with analytical results, we study the performance of the non-KAM systems for quantum sensing applications by computing the QFI. We find that the growth of the QFI is remarkably enhanced when the resonance condition is satisfied. For frequency estimation under Floquet unitary encodings, we derive a transport bound: if the mean excitation number grows as $\langle\hat n(t)\rangle\sim t^α$, the QFI obeys $I(t)\lesssim t^{2α+2}$. The quantum kicked harmonic oscillator, a paradigmatic non-KAM system, realizes the full hierarchy: localized dynamics ($α=0$) yield quadratic growth, delocalized diffusion along stochastic webs ($α=1$) yields quartic growth, and translationally invariant resonances ($α=2$) saturate the bound with anomalous hexic growth, $I(t)\sim t^{6}$, established analytically at resonance $R=2$ and numerically at $R=4$. The enhancement stems from resonance-induced translational symmetry rather than exponential instability, identifying non-KAM resonances as a metrological resource distinct from chaos-assisted and criticality-based sensing.

Semiconductor quantum dots (QDs) are a leading platform for realising bright, wavelength-tunable sources of single and entangled photon pairs for photonic quantum technologies. Site-selected nanowire quantum dots (NWQDs) are a promising platform for fabricating such photonic devices in a scalable manner. However, implementing additional structures around the photonic nanowire while maintaining its vertical growth geometry has remained a challenge. In this work, we develop a deterministic pick-and-place technique to conduct a vertical-to-vertical transfer of NWQDs from the growth substrate to arbitrary templates. Using this transfer technique, we enhance the photon extraction efficiency to 75% by implementing a bottom gold mirror and tune the emission wavelength by 3.6 GHz via implementing electrostatic gates around the QD. Importantly, we measure low-multiphoton probability (g^(2)(0) = 0.002) and high indistinguishability (>80% for +/-100 ps) of the QD emission after the transfer process, yielding high-quality devices. These results demonstrate the repeatability and versatility of the developed transfer technique, which is an enabling step towards scalable single and entangled photon sources.

Simulating quantum error correction (QEC) circuits including non-Clifford gates at scale is important to accelerate progress toward fault-tolerant quantum computing. Here we demonstrate that matrix product state (MPS) techniques can handle many QEC circuits exactly and without restriction on gate types. Crucially, we find that MPS efficiency depends sensitively on implementation choices, and we introduce a series of targeted optimizations that reduce bond dimensions and simulation time by several orders of magnitude compared to naive approaches. We illustrate this with examples including: (a) a rotated surface code quantum memory up to distance 11, (b) logical Bell-state preparation up to distance 9, (c) a 15-to-1 magic-state distillation circuit including hundreds of QEC rounds that we optimize to be simulated with only 11 logical qubits (187 physical qubits) and a maximal bond dimension of 64 in under 40 seconds, and (d) a narrow, deep random circuit that scales linearly with the number of T gates. These results demonstrate the importance of circuit-level optimizations and position MPS as a valuable complement to near-Clifford simulators for QEC circuits.

Pseudorandomness is increasingly recognized as a key property of ensembles in quantum information theory, statistical mechanics, and quantum many-body physics. Yet it appears in two conceptually different forms: statistical pseudorandomness, embodied by unitary designs, and computational pseudorandomness captured by pseudorandom unitaries (PRUs). The relationship between these two forms of pseudorandomness remains surprisingly poorly understood. Existing PRU constructions reveal this interplay where a statistically randomizing ingredient, a unitary design, is combined with classical cryptographic primitives to produce computational pseudorandomness. We show that statistical pseudorandomness is not necessary for computationally pseudorandom unitaries. We do this by replacing the unitary $2$-design layer in the existing constructions with ensembles that are not even state $1$-designs, yet are sufficiently {\em distinct}, a property we identify to be necessary for any PRU. This yields new non-adaptively secure PRU ensembles whose computational pseudorandomness is obtained without an underlying statistically pseudorandom quantum ensemble, such as a $2$-design. We characterize distinctness via an entangled analogue of anticoncentration and use it to show that distinctness already captures constraints on coherence and imaginarity of PRUs, while identifying broad classes of inputs for which the latter obstruction disappears, enabling real-valued PRUs even for certain (maximally) entangled states. As an application, we use lack of distinctness to constrain the conjectured pseudorandomness of the random phase-Hadamard ensemble to form a PRU.

Flux noise is unanimously recognised as a leading dephasing mechanism for flux-tunable superconducting qubits. However, our microscopic understanding remains incomplete, and basic effects like Faraday's law of induction have only very recently come into focus. Based on a quantum geometric description of the Faraday effect, we provide an in-depth derivation of the coupling of generic magnetic sources to thin film superconducting structures, under appropriate consideration of the device geometry. We apply the resulting framework to time-varying magnetic dipoles, describing surface or substrate spins, as well as current-carrying flux lines. We show that flux noise not only affects dephasing, but also provides a fundamental limit for the qubit quality factor - notably, even when the qubit contains no loops and is thus nominally not flux-tunable. Assuming surface spins as the origin for universal flux noise, we expect that this quality factor limit might be reached in the near term. For flux lines, we formulate a minimal safety distance to conserve the qubit performance, potentially constraining the scale-up of quantum hardware. This distance is boosted in the presence of large capacitor wings typical for transmons, due to a lensing of the electromotive field which is largely independent of Meissner screening.

Unlike standard quantum teleportation, many-body teleportation uses scrambling to transmit quantum information. In this protocol, initially localized information spreads over many degrees of freedom and is later refocused at the receiver by a simple coupling between the systems, followed by further many-body evolution. The protocol was developed from models of traversable wormholes in holography and has become a useful probe of scrambling. In particular, it can distinguish genuine scrambling from decoherence or noise when out-of-time-order correlators fail, and can reveal signatures of different scrambling mechanisms, including the distinctive behavior expected in holographic systems. Holography predicts that related protocols can transmit information between selected boundaries of multi-boundary wormhole geometries. Motivated by this setting, we study single-qubit many-body teleportation among three systems of qubits. The initial state consists of EPR pairs distributed among them, providing a simple analogue of an infinite-temperature three-boundary holographic state. We analyze the protocol with one-dimensional and all-to-all dynamics, both analytically and numerically using random circuits. We find that the third system suppresses teleportation once the spreading message reaches the region of qubits that are entangled with it. In one dimension, both the minimum coupling required for successful teleportation and the fidelity depend on the distance from the injection site to this region, a feature reminiscent of holographic causal shadows. For all-to-all dynamics, successful teleportation is instead restricted to early times and to sufficiently few qubits entangled with the third system. A third system therefore provides spatial, or subsystem, resolution of information spreading that is absent from the two-sided protocol. Our results offer a step toward many-body teleportation networks.

Distributed architectures have been proposed as a pathway to large-scale quantum computers. Combined with the need for fault-tolerance, such architectures require distributed quantum error correction (DQEC) and distributed logical gates. An important challenge is how to realize DQEC primitives in the setting where interaction between modules is restricted to shared Bell pairs that are significantly noisier than on-chip operations. We extend the framework known as fault tolerance by construction to this setting, deriving different strategies for handling the additional noise. Through fault-improvement we recover conventional entanglement distillation, and also find more dynamical protocols that enable space-time trade-offs. We show that integrated decoding halves the required distillation code distance compared to entanglement distillation implemented using separate decoding, thus requiring significantly fewer Bell pairs. As a main focus of the work, we synthesize efficient circuits for an important primitive in distributed fault tolerance: distributed stabilizer measurements. These circuits can be adapted to resource constraints, e.g. on the Bell pair generation rate or the space available for on-chip auxiliary qubits. Noting that full local fault-tolerance is not always needed to preserve the correct scaling of logical error rates, we further optimize the circuits depending on the surrounding context. We consider in particular the surface code and the color code, both as distributed memories and in the case of lattice surgery across separate modules. Here, robustness to certain hook and readout errors reduces the number of required Bell pairs even further, compared to the context-free setting. We numerically benchmark the resulting implementations under circuit level noise with additional interconnect noise.

We present a robust protocol to reshape interactions in a spin ensemble based on global control pulse sequences applied to multiple subensembles in parallel. This setting arises naturally from ensembles of solid-state defects or multi-species atomic arrays. We show that it is provably computationally hard to find pulse sequences that simultaneously engineer interactions both within and between subensembles. Despite its formal hardness, we identify a set of necessary or sufficient conditions under which one can synthesize a target Hamiltonian from the native one. Moreover, we introduce efficient numerical strategies for designing pulse sequences that engineer target Hamiltonians robust against common control imperfections. As a specific application, we discuss the robust generation of two-mode spin squeezing in dual-species atomic ensembles, which is a challenging task without subensemble control. Our results provide a practical toolbox to design novel quantum simulation and sensing experiments with minimal control overhead.

The radiative properties of quantum emitters are profoundly influenced by their electromagnetic environment. When coupled to a waveguide terminated at one end by a mirror, distant emitters interact strongly via virtual photon exchange, leading to collective superradiant and subradiant states with enhanced or suppressed decay rates. We demonstrate that applying optimal frequency shifts to each emitter enables the formation of perfect single-excitation dark states (i.e. states with zero decay rate) and near-perfect multi-excitation dark states in small ensembles. These collective states can be deterministically prepared with high fidelity using classical driving fields or few-photon pulses propagating along the waveguide. These results, readily implementable in superconducting qubit platforms, open new avenues for quantum information storage, networking and control of light.

Many-body dynamics constitutes a promising approach for creating correlations between quantum particles which can be used for applications in sensing and metrology. However, utilizing this potential for substantial gains in practical settings is a challenging task with only a very few applications realized to date. Here, we demonstrate an approach to nanoscale magnetic sensing enabled by strongly interacting electronic spins in a room temperature solid. By coherently controlling collective many-body dynamics of a dipolar ensemble of $\sim 10^4$ nitrogen-vacancy (NV) centres in diamond with pulsed magnetic field gradients, we demonstrate practical metrological gain up to $7.9(2)\,\mathrm{dB}$ for magnetic signal detection and $8.8(3)\,\mathrm{dB}$ for magnetic noise sensing, fully accounting for experimental overheads. Finally, we combine these methods to demonstrate a momentum-space-resolved sensing modality that enables detection of spatially correlated magnetic noise at continuously tunable length scales down to 50 nanometers. These observations open the door toward practical applications of interaction-enhanced quantum sensors for nanoscale biological imaging and material characterization.

Universal quantum computation with continuous variables cannot be attained solely with a set of Gaussian operations, it requires the addition of a non-Gaussian element, at least of third order in the quadrature operators, such as the cubic phase state. In this work, we present a method to generate a quantum state in the vibrational mode of a trapped ion that exhibits characteristics compatible with the cubic phase state, such as the distinctive oscillating pattern in its Wigner function. This state emerges from the nonlinear Jaynes-Cummings interaction native to the trapped-ion model, and under the assumption of an initial coherent vibrational state with a large occupation number. Consequently, the evolved vibrational state approximates the cubic phase state with high fidelity, and we use the variance of a nonlinear combination of the quadratures to characterize it. Finally, we provide an analytical expression for its cubicity that shows the high performance of the approximate vibrational cubic phase state.

Gottesman-Kitaev-Preskill (GKP) codes provide a family of promising schemes for encoding discrete quantum information (qudits) into infinite-dimensional bosonic modes based on mathematical lattices. While such codes, when concatenated with discrete-variable codes, are relatively well studied, the construction and decoding of native GKP codes has largely remained open due to the computationally hard problems encountered. To address this challenge, we advocate a strategy of co-designing the decoder and the quantum error-correcting code itself by constructing lattices for which decoding is feasible: The requirement of efficient decoding effectively determines the quantum error-correcting code. This construction is built on classical low-density lattice codes (LDLCs), a lattice analogue of low-density parity-check codes, here lifted to families of GKP codes. Concretely, we introduce quantum versions of classical, randomly constructed LDLCs. We show that after suitable dimensionality reduction these codes have code properties comparable to or better than concatenated GKP-surface codes of equal number of modes. However, the GKP-LDLCs constructed here do not have a strictly sparse parity check matrix, which motivates our study of the performance of natively analog message-passing decoders originally developed for LDLCs when applied to concatenated GKP-LDPC codes. We show that the fully analog, linear-time decoder achieves performances close to state-of-the-art hybrid qubit-analog decoders. To facilitate future research on the structure and performance of general GKP codes, the relevant source code will be released in open-source Julia packages LatticeDecoder.jl and SymplecticGKP.jl.

We derive an exact transport equation for the quantum Calogero model, i.e. inverse-square interacting bosons on a line, from microscopic first principles.

Dynamical decoupling (DD) helps maintain high-fidelity quantum computations by suppressing dephasing noise through carefully timed refocusing pulses. In quantum charge-coupled device (QCCD) architectures, however, where ions are shuttled throughout the device, transport constrains when pulses can be applied and affects the phase accumulated by an ion. Conventional DD methods do not account for shuttling and may therefore schedule pulses that must be omitted or shifted after transport scheduling, weakening the protection from dephasing. We therefore introduce shuttling-aware dynamical decoupling (SADD), an offline compiler pass that jointly selects refocusing pulses and local ion rerouting while preserving logical-gate timings and the total schedule length. In benchmark simulations, SADD improves average final-state fidelity over both the original schedules and a simple nearest-feasible Hahn-echo baseline when dephasing dominates control and transport errors and varies slowly enough for DD. Rerouting enables otherwise infeasible pulse timings, while spatial information about the noise can provide further gains. These benefits disappear, however, when the added transport introduces too much error. Overall, our results show that coordinating DD with ion transport is an effective compiler strategy for reducing dephasing in QCCD processors.

We develop a framework for logical computation with qLDPC codes that places logical Pauli, Clifford, and non-Clifford operations on the same footing. This brings the simple homological description of Pauli logicals to the patchwork landscape of logical Clifford and non-Clifford operations, providing a tool for the discovery of new logical gates. In particular, we define the chain map hierarchy: a family of chain complexes whose homology classes encode logical unitary and code surgery operations at any level of the Clifford hierarchy, precisely analogous to the chain complex description of Pauli logicals. Consequently, intuition for Pauli logicals can be leveraged to discover new logical operations on qLDPC codes. For instance, the familiar ability to deform Pauli logicals with stabilizers---i.e. boundaries of the chain complex---becomes a way to search for constant-depth unitary implementations of (non-)Clifford logical gates. Using this strategy, we discover constant-depth unitary implementations of the full logical Clifford group on any number of blocks of the 2D toric code, including within a single block, and addressable logical CCZ gates on any triple of logical qubits on any number of blocks of the 3D toric code. Beyond manifold codes, we find addressable non-Clifford gates on codes with many encoded qubits. The chain map hierarchy naturally encompasses and extends other constructions of logical gadgets, for instance providing a universal parameterization of cup products. As such, our work provides a unified, useful, and intuitive language for computing with qLDPC codes.

We investigate even-denominator fractional quantum Hall (EDFQH) states in monolayer graphene, focusing on the experimentally observed filling fractions $ν= 1/2$ and $ν= 1/4$. Owing to the approximate SU(4) symmetry arising from spin and valley degrees of freedom, graphene hosts a rich variety of multi-component fractional quantum Hall states with different polarization configurations. Using the Chern-Simons composite fermion framework for SU(4) systems, we construct candidate variational wave functions corresponding to distinct spin, valley, and mixed polarization states. The ground-state energies of these states are evaluated numerically using the Coulomb interaction in spherical geometry. By comparing energies across different polarization sectors, we identify the energetically favored configurations at $ν= 1/2$ and $ν= 1/4$. Our variational energy comparison suggests that the energetically favored candidate states correspond to multi-component correlated quantum Hall liquids. Within the restricted family of trial states considered here, these states differ from a simple composite-fermion Fermi-sea description. These findings provide insight into the role of valley polarization and SU(4) symmetry in stabilizing even-denominator fractional quantum Hall states in graphene.

Physical decoherence can preserve the microscopic strategic neutrality condition of a quantum game while changing the thermodynamic regime of the corresponding interacting population. We demonstrate this for an Eisert--Wilkens--Lewenstein (\textit{EWL}) Stag Hunt embedded as independent nearest neighbor encounters on a square lattice. For the restricted strategies $\mathsf{Q}=i\mathbb{Z}$ and $\mathsf{D}=i\mathbb{Y}$, noisy two-player payoff matrices are determined for phase damping, depolarization, and amplitude damping and mapped exactly to channel dependent Ising parameters $\mathfrak{J}(Γ,p)$ and $\mathfrak{H}(Γ,p)$. Phase damping and depolarization show the clearest contrast: they share the same microscopic neutrality branch $\mathfrak{H}=0$, while only depolarization suppresses the interaction as $(1-p)^2$. At $β=1$, this produces an exact depolarization-driven square-lattice critical point at $p_{*}\approx 0.233460\ldots$, whereas phase damping remains in the ordered coexistence regime along the same neutrality branch. Monte Carlo finite size scaling is consistent with two-dimensional Ising criticality and distinguishes field driven coexistence below $p_{*}$ from a smooth crossover above it. Amplitude damping additionally reveals a strong dependence on channel placement: the post-strategy neutrality branch reaches $Γ=0$ at $p=1/3$ and then disappears. Resource negativity further shows that microscopic two-qubit entanglement and collective interaction strength are distinct quantities. The resulting extended lattice remains an ordinary classical Ising system.

We find a quantum oracle relative to which $\mathsf{QMA} \neq \mathsf{QMA}(2)$. As a consequence, we resolve the no-disentanglers conjecture of Watrous: for every $ε+δ<1$, any $(ε,δ)$-disentangler requires input size exponential in the number of output qubits. Our proof combines the unitarily invariant polynomial method of She and Yuen (ITCS '23) with a new construction based on the symmetric and antisymmetric subspace projectors, reducing the $\mathsf{QMA}$ lower bound to the approximate degree of $\mathrm{OR}$.

Fibre-based quantum networks distributing polarization entanglement require a stable and uninterrupted transmission basis for reliable operation. Bright classical reference light enables rapid polarization feedback but can introduce noise into quantum channels. Entangled-photon-based feedback avoids this noise, but typically interrupts the target entanglement channel during calibration and becomes prohibitively slow over long distances due to the product loss of fibre links. Here, we overcome both limitations by combining wavelength-bracketed probing with switch-enabled path decomposition. Spectrally adjacent entangled-photon sidebands track the polarization response of the central distribution channel without interrupting its transmission, while optical switches and local reference fibres independently determine the signal and idler network transformations. Transferring the resulting compensation settings to the central channel eliminates calibration-induced downtime and changes the acquisition-time scaling from the product of the link losses to the sum of losses. We demonstrate the method on a 133 km fibre testbed and achieve continuous closed-loop stabilization for more than 24 hours without classical reference light. The decomposition of multi-link quantum feedback into single-link measurements provides a scalable stabilization strategy for wavelength-multiplexed quantum networks.

The search for wave-like dark matter using microwave cavity haloscopes is constrained by the Standard Quantum Limit, which dictates that phase-preserving linear amplification results in a minimum of one quantum of total system noise for a narrow-band signal. We demonstrate that this limit is effectively halved for a non-monochromatic axion signal coupled to a high-$Q$ cavity. By operating a Josephson Parametric Amplifier such that the cavity resonance is centered exactly at the half-pump frequency, the axion signal symmetrically populates both the signal and idler bands. Through quadrature analysis of the homodyne readout, we show that the incoherent sum of these mirrored spectral components doubles the measured signal power while the vacuum noise remains constant. This operation yields an effective noise limit of 0.5 quanta per frequency bin, translating to an overall effective limit of $1/\sqrt{2}$ quanta after optimal matched filtering.

Within a normalised six-dimensional model of dissipative optomechanics (one cavity + two mechanical resonators), a synthetic-flux phase $Φ_{\rm syn}$ selects the \emph{order} of a drive- and coupling-gated hyperchaos transition---up to four simultaneously unstable Lyapunov directions, beyond any reported single-mode benchmark---while the same matched-resource force-sensing protocol yields no flux-induced enhancement on the chaotic attractor. Building on the topology of Muthukumar \emph{et al.}~[PR Applied \textbf{24}, 014053 (2025)], a phase-consistent Floquet--Lyapunov protocol (cross-checked by monodromy multipliers, dissipative volume balance and a 180-run three-seed audit) localises a Neimark--Sacker bifurcation at $E^{*}=\num{1.060}$ ($θ=0$). At a weakly coupled reference the matched Fisher gain reaches at most $\num{1.32}\times$ (flux-off) and $\num{1.16}\times$ (single-mode), with Monte-Carlo median $\num{1.039}\times$ (90\,\% CI $[\num{1.025},\num{1.053}]$); on the chaotic attractor the identical protocol returns a null result ($\mathcal{G}_{A/B}=\num{1.039}\pm\num{0.014}$). Truncated-Fock and truncated-Wigner checks support the mean-field description at selected points. Both the hyperchaos classification and the sensing result remain strictly model-level: the strong-coupling sector explored here lies $\num{2542}\times$ beyond anchored silicon optomechanical couplings. Closing that gap requires a measured inter-resonator hopping $J_m$ and fixed bath temperatures.

Variational preparation of thermofield double (TFD) states can require deep quantum circuits, particularly for interacting many-body systems. Reducing these circuits while retaining high fidelity is therefore crucial for TFD-state preparation on noisy quantum processors. We study this problem by applying the multi-angle quantum approximate optimization algorithm (ma-QAOA) to TFD-state preparation and introducing two top-down sequential angle-pruning algorithms. Starting from the optimized initial ma-QAOA circuit, both algorithms sequentially remove Pauli-string evolutions with small optimized angles and reoptimize the remaining parameters after each removal. We apply these algorithms to Gaussian and binary Sachdev--Ye--Kitaev (SYK) models in both dense and sparse cases. We find that ma-QAOA prepares the target TFD states with high fidelity and that sequential small-angle pruning retains high fidelity while reducing the circuit depth, particularly at low temperature. Moreover, using the post-reoptimization cost in sequential small-angle pruning further improves the fidelity. For the binary sparse $N=10$ SYK model at $β=10$, $88.8\%$--$92.1\%$ of the nonlocal Pauli-string evolutions are removed while retaining an average fidelity of approximately $95\%$. Finally, we propose extensions of the sequential pruning algorithms toward quantum--classical hybrid implementation.

The demonstration that enhanced yellow fluorescent protein hosts an optically addressable spin-1 qubit in its metastable triplet state raises the prospect of genetically encoded quantum sensing at molecular length scales. We develop a detection-limit theory for using this fluorescent-protein spin qubit (FPSQ) to sense paramagnetic neural signaling radicals by spin relaxometry. We derive the transition-resolved Redfield relaxation matrix of the zero-field-split triplet coupled to a diffusing radical bath, establish the regime in which it collapses to a single exponential, and validate it against Lindblad simulations and nitrogen-vacancy benchmarks. Propagating the effects of photon shot noise, photobleaching-grounded photon budget, and finite measurement bandwidth, we find that the native room-temperature sensor falls short of physiological sensitivity by six to eight orders of magnitude with the bottleneck being the phonon-limited intrinsic $\Tone$. Analyzing the underlying direct and two-phonon Raman processes, we show that room-temperature relaxation is Raman-dominated by $\sim\!720\!:\!1$ and that, because the Raman coefficient scales as $v^{-10}$ with sound velocity, a $\sim\!2\times$ stiffening of the chromophore environment recovers $\Tone\sim\SI{100}{\micro\second}$, sufficient for micromolar sensing. Nanomolar sensing is obstructed by a direct-process ceiling of \SI{79}{\micro\second} that vibronic decoupling alone cannot breach. We obtain quantitative design rules, identify photon yield as a co-equal bottleneck, and propose a frequency-resolved protocol for chemical specificity.

Claims about a deployed quantum machine-learning classifier can fail when target data shift or when finite-shot quantum evaluation randomizes the model itself. We develop an information-conditional, fail-closed auditing framework that returns supported, refuted or unresolved verdicts with anytime-valid per-claim error control under a declared sampling protocol. On a Higgs-to-tau-tau collider benchmark, stable classifier metrics do not guarantee valid signal-strength inference: at the studied finite-template statistics, the fixed-template profile can lose coverage, even in shift-free controls, when its templates are estimated independently and template-statistical uncertainty is not modeled explicitly. Across 30 frozen finite-shot quantum-kernel deployments, every realized Gram matrix is propagated through refitting, calibration and threshold selection; in the primary raw pipeline these perturbations leave ranking nearly unchanged yet move thresholded target metrics by about 0.02, flipping ideal-anchored claims, and the diagonal-loading sensitivity decomposes differently. Matched classical controls remove apparent quantum-specific nominal-performance and sensing effects. We claim no quantum advantage.

We show that vacuum Rabi oscillations can directly generate spin squeezing through geometric focusing on the Bloch sphere. Starting from a coherent spin state resonantly coupled to a cavity initially in the vacuum state, quantum fluctuations are focused by the curvature of the Bloch sphere as the collective spin approaches the atomic ground state, producing squeezing transverse to the direction of motion. The squeezing timescale is set by the collective Rabi frequency $t_s\sim 1/(g\sqrt{N})$. The optimal Wineland squeezing parameter scales as $ξ_{\rm opt}^2\propto N^{-1/3}$, which is an outcome of the competition between the geometric focusing effects and the cavity-field vacuum fluctuations. The squeezing remains robust against realistic dissipation. In the end, an application example of $^{171}$Yb is briefly discussed to show the feasibility of our protocol.

Semiconductor quantum-dot arrays are a compelling platform for scalable quantum technologies, yet their practical operation is hindered by the complexity of tuning large-scale devices. Existing automation tools rely on simplified physical models---such as constant-capacitance approximations and equilibrium Hubbard models---which assume instantaneous relaxation to a steady state. These frameworks fail in experimentally critical regimes where measurement rates exceed tunneling dynamics, necessitating more sophisticated non-equilibrium control strategies. To bridge this gap, we introduce QArray+, an extension of the QArray framework that incorporates gate-dependent tunnel coupling and a quantum open-system description of dissipative processes. This approach enables the unified simulation of coherent interdot charge-state hybridization and the non-equilibrium latching dynamics essential for training robust machine-learning models for automated device operation. Implemented in JAX with GPU acceleration, QArray+ scales across GPUs and multi-node systems. For example, a charge stability diagram for a 100X100 grid of gate voltages over 64 dots can be computed in $\sim0.17\,\mathrm{s}$ on multiple GPUs. Since interdot interactions are short-ranged and the corresponding tuning corrections are local, simulations at these scales capture the physics relevant to even larger devices. These capabilities support high-throughput dataset generation for automated device tuning.

Open quantum many-body systems are commonly described by Lindblad master equations, yet the treatment of Lindbladian operators in the thermodynamic limit remains a major challenge. We develop a framework for constructing effective quasiparticle-conserving Lindbladian operators directly in the thermodynamic limit. Our approach extends continuous similarity transformations to non-Hermitian open quantum systems and enables the systematic block diagonalization of Lindbladians with respect to the quasiparticle (qp) number. We formulate two complementary methods. The first, projective continuous similarity transformations (pcst++), generalizes perturbative continuous unitary transformations to Lindblad operators so that a linked-cluster expansion allows us to obtain high-order series expansions of the infinite system. The second, deepCST, extends directly evaluated enhanced perturbative continuous unitary transformations by combining the same qp-conserving generator with a perturbative truncation scheme that yields non-perturbative effective Lindbladian operators directly in thermodynamic limit. We apply pcst++ and deepCST to the dissipative transverse-field Ising chain with local dissipation. We focus on the low-Ising regime. We purify the Lindbladian by splitting each spin into two sites. A spin flip then corresponds to two qps. We derive and analyze the effective, qp-conserving Lindbladian in the sectors with zero to two qps. We show how the Ising interaction renormalizes the decay rates of elementary spin-flip excitations and provides the microscopic mechanism for a competition between coherent interactions and dissipation. Our work establishes perturbative and non-perturbative continuous similarity transformations as a versatile tool for deriving effective qp pictures of open quantum many-body systems in the thermodynamic limit.

Twistronics of layered materials has emerged as a highly active field due to its profound implications for quantum electronics and materials engineering. However, the controllable manipulation of interlayer stacking remains a significant experimental challenge. Here, the homogeneous contact between hexagonal boron nitride layers is shown to be reproducibly switched between two distinct stable stacking configurations via an externally applied torque. Combining experiments and computational modelling, we identify the stacking order of these stable states as the commensurate AA and AB modes. These two states are associated with different rotational torque maxima, exhibiting an asymmetry ratio of 0.7, and distinct dynamics as a function of the twist angle. Moreover, the peak torque values scale linearly with contact area, highlighting the dominant role of edge elasticity in the twisting process. Given that the AA and AB stacking modes correspond to different out-of-plane electric polarization states, our findings offer a pathway for reconfigurable nano- and micro-electromechanical devices.

Non-adaptive quantum amplitude estimation (QAE) fixes its Grover depths in advance, so every circuit can run in parallel, but it has so far needed more queries than the best adaptive methods. We show that most of this gap comes from two conventional choices: subspace-based post-processing and power-of-two depth ladders. We replace the first by the exact maximum-likelihood estimate, one matrix multiplication per batch of estimates, and the second by a geometric ladder with ratio $r \approx 1.45$. The result is a fully parallel, deterministic-schedule estimator with total query complexity $2.8$-$3.1/\varepsilon$ at 95% confidence for target errors from $3.5\times 10^{-3}$ to $10^{-6}$. This matches the average-case complexity of chebAE, the best benchmarked adaptive method, within statistical uncertainty (with the lower point estimate at every scale tested), beats its maximum-observed complexity by $1.6\times$, and needs a maximum sequential depth of only $0.21/\varepsilon$ against chebAE's $2.9/\varepsilon$. Relative to csAE, the best non-adaptive benchmark, the constants improve by 30-35% at 95% and $1.5$-$1.7\times$ at 99% confidence. The optimal ratio has a simple origin. Doubling is the fastest depth growth at which the data can still tell neighboring candidate values apart, so power-of-two ladders sit at the edge of confusion and must buy reliability with extra shots; a slightly denser ladder checks every scale redundantly. An error-probability analysis reproduces the measured failure rates and locates the optimum. The likelihood formulation extends directly to noise-aware estimation, and uniformly scaling the capped ladder covers the depth-limited regime, realizing the optimal trade-off $M N_{\mathrm{tot}} \approx (0.4$-$0.6)/\varepsilon^2$ within $\sim 1.1\times$ of the schedule's Cramér-Rao limit.

We initiate the time-bounded meta-complexity program for quantum cryptography. Recent work characterizes one-way puzzles, the minimal search primitive of quantum cryptography without one-way functions, by the average-case hardness of approximating the plain, uncomputable Kolmogorov complexity over quantumly samplable distributions; the classical program of Liu and Pass, by contrast, lives at polynomial time bounds. We define a probabilistic time-bounded quantum program complexity pKq^t for classical strings and prove two unconditional theorems. First, a quantum coding theorem: any string output by a quantum polynomial-time sampler with probability delta admits a description of the information-theoretically optimal length log(1/delta) plus logarithmic terms, decodable by a quantum machine in time O(sqrt(1/delta)) times a polynomial, via amplitude amplification over the coherently executed sampler. Second, an exact characterization at subexponential time: one-way puzzles exist if and only if the gap problem for pKq at time bound 2^(n/2) poly(n) is weakly quantum-average-hard, refining the plain-complexity characterizations. We then isolate the polynomial-time coding theorem as the single load-bearing open conjecture of the program, prove that it implies the full polynomial-time characterization, analyze why the classical derandomization proof resists quantization, and formulate a relativized barrier conjecture delimiting string-valued meta-complexity at one-way puzzles. Conjectures are labeled as such throughout.

Fault-tolerant quantum computing requires not only reliable logical qubit storage, but also the ability to perform high-fidelity logical operations between error-corrected qubits at scale. While much of the existing literature focuses on optimizing syndrome extraction for a single logical qubit, the co-design of physical architectures that support both robust error correction and efficient logical computation remains an open challenge. In this work, we propose a multi-qubit spin-qubit shuttling bus architecture that addresses both requirements simultaneously. The architecture optimizes the physical qubit layout for syndrome extraction and supports transversal two-qubit logical gates between an arbitrary number of logical qubits, achieving all-to-all logical connectivity through coherent spin shuttling. We further propose an ancilla-sharing scheme that encodes multiple logical qubits within a single logical element, compressing the physical footprint of the processor and improving long-range gate fidelity. Extending the architecture from a one-dimensional bus to a two-dimensional grid of shuttling tracks reduces the inter-qubit distance, yielding consistent improvements in logical error. Finally, we apply the Quantum Reverse Mapping methodology at the logical level to optimize the layout of a \textit{15-to-1} magic state distillation circuit, demonstrating how the transversal capabilities of the proposed architecture can be leveraged for universal fault-tolerant computation. Taken together, these results establish a principled co-design framework that bridges the physical, error-correction, and logical computation layers of the quantum stack, and demonstrate that spin-qubit shuttling architectures are a viable and flexible substrate for scalable fault-tolerant quantum computation.

A key task in many quantum-computing applications, e.g., quantum simulation and quantum state tomography (QST), is to partition an arbitrary set of operators into mutually commuting subsets for efficient measurements. However, brute-force approaches to this task quickly become intractable as the number and dimensionality of operators grow. Here, we reformulate operator partitioning as a graph-coloring (GC) problem and develop an efficient computational framework to solve it, balancing accuracy and efficiency. Our framework enables leveraging a range of GC algorithms, which we benchmark for operator partitioning. Then, we demonstrate their utility in optimizing QST experiments, where determining non-overlapping data acquisition settings for QST is a major challenge, and prioritizing among these settings, i.e., selecting the experiments that provide the most information. We further show how to perform these experiments by synthesizing Clifford circuits for joint measurement of commuting Pauli operators in multi-qubit systems. We validate our framework across multi-qubit (up to five qubits), multi-qutrit (up to three qutrits), and hybrid qubit-qutrit systems. Our results show that heuristic GC methods substantially reduce the number of required measurement settings for QST and enable priority-based scheduling that maximizes the information gain per experiment. The optimization converges within minutes on a student-grade laptop, providing speedups of several orders of magnitude over brute-force methods already for these relatively small quantum systems. This demonstrates the potential of GC heuristics as a scalable and practical tool for characterization of noisy intermediate-scale quantum devices. We have made the Python implementation of our GC framework to optimize and schedule QST experiments publicly available at https://github.com/ssm8015/QST_GT.git.

This study investigates the performance of extended nonreciprocal quantum batteries (QBs), as well as its advantages in energy storage and energy transfer compared to reciprocal charging and the original nonreciprocal batteries. After analyzing the detuning between the charging system and the external pump, we discover that resonance is a key factor in maintaining high-energy batteries and high charging power; furthermore, the detuning of the charger or battery determines the stability of the charging process for different structures. Research on steady-state energy storage in batteries revealed that single-threaded or multi-threaded charging can achieve nearly infinite energy storage in weakly localized environments, thereby demonstrating the significant energy advantages of extended nonreciprocal quantum batteries. Finally, by considering the energy distribution within the charging system, we observe that nonreciprocal charging offers energy transfer advantages unmatched by reciprocal charging; the former achieves a comprehensive balance between charging cost and energy storage capacity that the latter cannot match. As a novel and superior charging protocol, our findings are expected to provide a potent reference for the promotion and practical implementation of nonreciprocal charging.

Non-Hermitian physics endows the non-Abelian systems with exceptional topology characterized by non-commutative braid patterns. Interplay of distinct competing sources of non-Hermiticity may induce novel topological effects. Here, we provide a generalized Hatano-Nelson model with higher-order nonreciprocal hoppings, non-Abelian gauge fields, and staggered gain-loss processes showing the exceptional topological structure of the Hopf-link braids that undergoes a EP-mediated topological phase transition. We demonstrate that mixing multiple nonreciprocal channels drives the system into highly intricate, nested complex energy Hopf-link braids and expands the topological landscape up to higher-order braiding sectors. Furthermore, utilizing biorthogonal eigenvector tracking, we map the structural evolution of the exceptional phase boundaries via the maximum Petermann factor in the phase angle parameter planes. We show that the gain-loss non-Hermiticity drives a topological crossover where the extended exceptional contours constrict into isolated regimes. The demonstration of EP-mediated topological phase transition of Hopf-link braids and the associated rich exceptional phase portraits may offer new physical insights with promising applications in robust, fault-tolerant communication channels and quantum computing platforms.

Long-lived storage of single photons under the form of atomic excitations is at the foundation of long-distance entanglement distribution in quantum networks. To mitigate decoherence effects induced by the environment, rephasing of the hyperfine coherences using microwave pulses have been implemented in a variety of single-emitter and ensemble-based solid-state systems. However, the demonstration of storage of single photons in an absorptive quantum memory including such spin rephasing mechanism remains elusive. In this work, we show non-classical storage of telecom-heralded single photons in a Pr$^{3+}$:Y$_2$SiO$_5$ rare-earth ion doped crystal quantum memory using the atomic frequency comb (AFC) spin-wave protocol combined with a XY4 spin rephasing sequence. Long-lived AFC photon echoes are first observed in the classical regime for storage times of up to approximately 3 ms. We then demonstrate non-classical correlations between heralding photons and stored signal photons generated by a cavity-enhanced parametric photon-pair source for storage times of up to 180 $μ$s and with measured cross-correlation values as high as 4.6(4). Together with the capacity of Pr$^{3+}$:Y$_2$SiO$_5$ QMs to support highly efficient and multiplexed storage, this result represents a significant step towards scalable long-distance quantum repeater links.

In this paper, Thouless pumping in a one-dimensional semi-infinite Fock-state lattice is investigated. A distinctive feature of such lattices is the intrinsic $\sqrt{n}$-dependent coupling arising from the bosonic mode, which leads to spatially nonuniform hopping amplitudes. In the dimer limit, the topological invariants and the quantized transport dynamics in the Fock-state basis are numerically evaluated and analyzed. By introducing an additional inter-cell coupling and applying a squeezing transformation, the framework is then extended to Thouless pumping in the squeezed Fock-state basis, where a topologically protected scheme for preparing superpositions of squeezed Fock states is proposed. This study establishes Thouless pumping in Fock-state lattices as a useful tool for quantum state engineering, shifting the focus from observing topological transport to harnessing it for the preparation of non-classical states of the bosonic mode.

Lattice geometry plays a fundamental role in the behavior of Bloch electrons in a crystal. The diatomic Kagome lattice, an extension of the honeycomb and Kagome lattices, is predicted to give rise to emergent and topological phenomena, but its experimental investigation has been limited thus far. Here, we fabricate a diatomic Kagome lattice through self-assembly of a triptycene derivative with phenazine moieties (Trip-Phz)---a $\mathrm{C_3}$-symmetric, non-planar $π$-conjugated molecule. Our scanning tunneling microscopy (STM) observations show that Trip-Phz forms a highly ordered diatomic Kagome lattice terminated by zigzag-type edges on the Pb(111) surface. Combined STM measurements and tight-binding calculations provide direct evidence for the existence of the edge states that correspond to those of graphene. These states are topological edge states dictated by the quantization of the Zak phase and the bulk-edge correspondence.This work reveals an ideal platform for exploring quantum materials with unique lattice geometries using supramolecular technology.

We present a combinatorial optimization problem for the strategic deployment of UAVs equipped with 5G antennas to assist rescue operations in regions hit by natural disasters. Our goal is to optimize the placement of UAVs to provide coverage in flying ad-hoc networks among given candidate sites. Our formulation aims to maximize signal coverage and minimize interference while ensuring network connectivity. To mitigate interference effects, we incorporate the use of multiple frequencies. We formulate this problem as an integer quadratic program (IQP). We present numerical solutions obtained via the CPLEX solver and conduct a preliminary analysis of the problem's scalability in realistic network configurations. Our findings reveal a significant exponential increase in Time-to-Solution (TTS) as the number of sites grows, which poses a critical challenge in urgent, time-sensitive scenarios. To address this issue, approximate suboptimal solutions can be produced by enforcing a time limit on the solver. Although these solutions are not optimal, they preserve connectivity in most cases, providing a practical trade-off between solution quality and computational times that remain within feasible limits for real-time UAV redeployment. Recognizing the limitations of classical solvers in these contexts, we explore quantum computing as a promising alternative. Specifically, we reformulate the problem as a quadratic unconstrained binary optimization (QUBO) problem, suitable for most quantum algorithms. Through high-performance computing emulation, we show that the quantum adiabatic algorithm (QAA) can accurately solve small-scale instances, paving the way for future application of quantum computing to large-scale, time-critical optimization problems in disaster response.

Logical fusions are important for a number of tasks in quantum information, such as quantum error correction and quantum repeaters. In the photonic setting one must contend with the fact that physical fusions are probabilistic (i.e.~the associated qubits are measured in product bases), which---depending on the failures and the associated bases---can lead to a failure on the logical level. The choice of failure basis of each qubit is known as a fusion strategy, and finding good fusion strategies is important for optimizing performance of fusion-based quantum computation. Here we provide a complete characterization when $k=1$ qubits are encoded, and in particular characterize those codes and fusion strategies such that all but one physical fusion can fail, i.e.~\emph{perfect fusion strategies}. In doing so, we recover previously known perfect fusion strategies, and find perfect fusion strategies for quantum parity-check codes, answering an open question. We furthermore show that perfect fusion strategies are generic: random $[[n, 1, d]]$ graph codes admit a perfect fusion strategy with probability exponentially close to $1$. Additionally we motivate the study of a new graph parameter, namely the maximum degree of a graph at a given vertex taken over all LC-equivalent graphs, by giving a new operationally meaningful interpretation of it.

Entanglement distribution through optical fibers is essential for quantum communication networks; however, fiber transmission can alter photon polarization and modify the observed correlations of polarization-entangled states, necessitating polarization compensation to recover the desired entangled state in the measurement basis. Here, we experimentally evaluate two passive polarization compensation techniques: a free-space Quarter-Half-Quarter (QHQ) waveplate configuration and an in-fiber three-paddle Fiber Polarization Controller (FPC). The polarization transformation along each downconverted-photon path is independently compensated through a systematic path-by-path optimization procedure. Using both techniques, we recover high-quality polarization correlations and entanglement, with visibilities exceeding $93\%$ in three mutually unbiased bases and fidelities above $94.5\%$. The results demonstrate comparable restoration using free-space waveplate-based and fiber-based control, establishing a systematic framework for laboratory and short-reach quantum communication links.

Paper I introduced branching stochastic mechanics (BSM) by lifting the Schrödinger-Nagasawa pair to reciprocal forward and backward branching fields. Their centered connected kernel $C_{\rm FB}=\mathbb E_ω[ψ_Fψ_B]$ carries the organized reciprocal sector, where $\mathbb E_ω$ denotes expectation over branching-noise realizations, with $ρ_{\rm BSM}=-C_{\rm FB}(x,x)$ on the anticorrelated branch. Here we develop the stochastic field theory of the Bohm/Fisher feedback that acts on this connected sector. Starting from the multiplicative branching covariance of BSM, a Martin-Siggia-Rose-Janssen-de~Dominicis (MSRJD) formulation and a causal two-loop two-particle-irreducible (2PI) closure are used to determine response and correlation functions self-consistently. The free connected theory exhibits secular growth and ultraviolet accumulation, whereas the dressed theory develops a finite relative screening length. A reduced numerical evolution shows bounded formation of this localized sector, and a self-similar Fisher construction defines the saturated information velocity $c_\star$. A Born-Oppenheimer separation then distinguishes internal relative organization from collective propagation. Restoring the complete frequency structure gives two fixed-$q$ pole families: a gapless difference branch and a gapped sum branch. The infrared velocity of the difference branch approaches $c_\star$ at saturation. The common cone and the projected sum-sector gap are then formulated as additional fixed-point matching conditions for the collective theory.

We present a scheme to efficiently simulate nonreciprocal many-body spin models using a non-Markovian open system. Our scheme utilizes a single quantum emitter coupled to a waveguide mode that is fed back to the same emitter after a time delay. With this coherent delayed feedback, an effective nonreciprocal interaction can be engineered, wherein the emitter at earlier times affects itself at later times, creating a scalable spin chain. We show that all the steady-state quantities of such spin models can be accessed through measurement of the emitter and the output field. Furthermore, using classical feedback that resets the emitter, quench dynamics from arbitrary product states can be simulated. We demonstrate striking features of nonreciprocal models, such as the Liouvillian skin effect, anomalous relaxation dynamics, and quasi-long-range order of output photons. Finally, we show that the proposal is amenable to experimental realization and robust to imperfections. Our work establishes a feasible way to scale up a nonreciprocal many-body system, and provides a new route towards generation of exotic states of light.

Photon-number-resolving (PNR) detectors are essential for photonic quantum computing, where a single measurement outcome must reliably herald a specific quantum state. However, detector fidelity is conventionally evaluated using ensemble-averaged statistics obtained from many measurements, which can remain high even when individual photon-number assignments are frequently misidentified. Here we introduce a universal single-shot fidelity that directly quantifies the probability of correctly identifying a photon number in a single measurement. The framework combines an efficiency-based POVM with a resolution-driven confusion matrix derived from the detector response, allowing photon loss and photon-number misidentification to be treated separately and then recombined into a single operational metric. This distinction reveals two fundamentally different limitations. Detection-efficiency loss represents an unrecoverable hardware constraint, whereas resolution-driven misidentification can be reduced by introducing a rejection region, trading generation rate for confidence. Because the metric is defined independently of detector architecture, it enables direct comparison between energy-resolving detectors such as transition-edge sensors and multiplexed click-based detectors on the same footing. Applying the framework to calibration data from three distinct detector architectures, we demonstrate quantitative comparison across photon-number regimes relevant to both discrete-variable and continuous-variable photonic quantum computing. The resulting benchmark provides a common operational metric for evaluating photon-number-resolving detectors and connecting detector performance to photonic quantum-computing requirements.

Non-Hermitian evolution can be realized through post-selection on stochastic pure-state trajectories arising in continuously monitored open quantum systems. The rate operator formalism provides a versatile and systematic framework for unraveling a master equation into stochastic pure-state evolutions, offering enhanced control over the resulting non-Hermitian dynamics. In the present work, we explore the applicability of the rate operator formalism as a tool for engineering non-Hermitian dynamics. Specifically, we apply this approach to the Bose-Hubbard model subject to environmental dephasing, examining its consequences for controlled state manipulation. Our analysis is framed within the broader contexts of quantum state engineering and measurement-induced phase transitions. We demonstrate that the rate operator formalism enables the construction of effective non-Hermitian Hamiltonians exhibiting a unique steady state-even in regimes where the standard Monte Carlo wavefunction method fails to produce one. Furthermore, we show that this framework facilitates transitions between distinct steady-state phases, governed by tunable parameters such as the interaction strength and a non-Hermiticity control parameter introduced via the rate operator formalism.

We study the three-boson Schrodinger operator on the two-dimensional integer lattice with pairwise contact interactions. First, we obtain precise asymptotics of the two bound states below the essential spectrum at zero total quasimomentum in the strong-coupling limit mu to infinity: the ground state energy is -3 mu + 6 + O(1/mu), and the first excited state energy is - mu + C + O(1/mu), where C = 4 - delta approximately 3.96458, with delta determined by the transcendental equation b0(delta) = 1/(1+delta) involving the lattice Green's function. The associated spectral gap is 2 mu + O(1). Second, using the discrete Agmon comparison method and the Paley-Wiener theorem, we establish exponential localization of the ground-state wavefunction with a logarithmic upper bound on the decay rate alpha(mu) at most ln(3 mu) + O(1/mu), reflecting the bounded nature of the lattice dispersion; the sharp asymptotic rate is conjectured. Third, at quasimomentum pi, the parity symmetry is preserved, but the odd quadratic form becomes positive definite with a unique eigenvalue of order 1/mu that never reaches the Birman-Schwinger threshold, so the odd subspace yields only a virtual level. The even subspace supports exactly one bound state with energy -2 mu + 6 + 8/mu + O(1/mu^2), and the spectral gap to the essential spectrum is mu - 2 - 8/mu + O(1/mu^2). The reduction from two bound states at zero to one at pi preserves the total spectral flow and is a lattice-specific phenomenon. Our approach uses an invariant subspace decomposition of the Birman-Schwinger operator and the Krein-Rutman theorem to guarantee uniqueness and strict positivity of the ground state. These results have direct implications for quantum simulation of few-boson systems in optical lattices.

Single-photon ionization cross sections of molecular hydrogen in the electric dipole limit have been computed. Both time-dependent and -independent approaches within the clamped-nuclei approximation at equilibrium internuclear distance are employed, featuring the explicit time-propagation of the time-dependent Schrödinger equation and newly implemented multi-channel configuration-interaction free-boundary as well as complex-scaling methods using an explicitly correlated geminal basis set. The found results are compared to both experimental and previously published theoretical results, showing convincing mutual agreement despite their entirely different fundamental formulations. The novel CI-based approach demonstrates fast and controllable convergence while being able to provide full channel-resolved information.

We compare the Raussendorf-Harrington-Goyal (RHG) code, the Foliated Floquet Color Code (FFCC), and the reduced FFCC in a compound photon-atom architecture that directly generates measurement-based quantum computation (MBQC) resources with near-deterministic photon-atom CZ gates. RHG serves as a natural benchmark, while the FFCC variants allow us to study whether reduced graph degree improves performance under an architecture-aware circuit-level loss model with delayed heralding and correlated bond-loss propagation. We construct two generation schemes compatible with the compound hardware and evaluate circuit-level thresholds under periodic boundary conditions. RHG achieves the highest circuit-level threshold, 2.75%, and its threshold falls below that of reduced FFCC only for large excess loss on intermodule CZ connections. RHG also achieves the lowest logical error rate in most resource-matched comparisons, but some low-loss windows favor reduced FFCC. Overall, we show that when the hardware supports the native gates and connectivity required for MBQC, the benefits of lower graph degree must be weighed against each code's intrinsic IID loss tolerance, generation-scheme details, and hardware-aware resource overhead.

Continuous-variable quantum systems offer a resource-efficient route to universal quantum information processing and analogue quantum simulation of real-world processes, such as molecular physics and chemical reactions. Realising these applications, however, requires non-Gaussian operations that implement anharmonic potentials, which are challenging to engineer on demand. Here, we demonstrate a systematic framework to implement programmable non-Gaussian phase gates $e^{-iV(\hat{X})}$, corresponding to the impulsive action of a potential $V(\hat{X})$, in a superconducting harmonic oscillator coupled to a transmon qubit. Using modular circuits derived from bosonic quantum signal processing, we realise a range of target anharmonic potentials on a single piece of hardware by varying a set of qubit rotations interleaved with a fixed calibrated control unitary. We first demonstrate a cubic phase gate, a key ingredient for universal quantum information processing. The resulting high-fidelity non-Gaussian states and the potential reconstructed using our pointwise force reconstruction method jointly confirm the cubic nature of the target gate. We then engineer a family of double-well potentials, relevant models of tunnelling and biased transfer processes, and experimentally validate the double-well topology and the tunable asymmetry. Finally, we engineer an approximate Morse gate, a step towards realistic potentials of molecular vibrational systems, and provide a concrete path towards high-quality engineering and reconstruction of the exponential form. Together, these results establish a practical and reconfigurable route towards continuous-variable quantum information processing and anharmonic quantum simulation.

Finding the eigenstates of a many-body Hamiltonian is a fundamental challenge in physics and computational science. Since the search space grows exponentially with system size, numerous classical and quantum algorithms have been developed to address this problem. A practical strategy is to identify a physics-informed low-dimensional subspace that effectively accommodates the low-lying eigenstates, thereby reducing the computational complexity. In this paper, we propose a recursive module-coupling algorithm, which iteratively treats a system as a composition of locally-coupled smaller modules, with low-energy subspace estimated successively according to the same recursive structure. Unlike the density matrix renormalization group (DMRG) approach that optimizes a global matrix product state through repeated local sweeps and obtains excited states sequentially, our algorithm constructs a physically tailored variational basis from module eigenstates and obtains several low-energy states on an equal footing, leading to substantial speedups if targeting moderate accuracy. Our proposed method further leads naturally to a recursive quantum variational algorithm, providing a systematic and modular circuit-construction framework compatible with contemporary gate-based quantum architectures. At each recursive level, block encoders are trained to map logical basis states onto the retained physical subspace, within which a variational circuit is subsequently optimized.Such a quantum-circuit implementation provides not only a quantum multistate eigensolver, but also a systematic prescription for hierarchically constructing quantum state-preparation circuits. Classical simulations demonstrate the accuracy and efficiency of the proposed method, whereas experiments on IBM quantum processors show that eigenstate preparation with reasonable fidelities is achievable even in the current NISQ era.

Precise control of multi-qubit architectures remains a critical bottleneck in superconducting quantum processors. In this work, we investigate the synthesis of high-fidelity quantum operations and state transfer protocols within an extended superconducting linear chain, scaling from three to seven sites. Using Floquet theory, we model the periodic drive as a train of delta-like pulses, mapping the quantum control problem onto quasi-energy resonance conditions. Combining the Baker-Campbell-Hausdorff expansion with Floquet spectral decomposition, we analytically identify optimal driving parameters, refined via the Covariance Matrix Adaptation Evolution Strategy (CMA-ES). In the three-qubit architecture, this enables high-fidelity synthesis of the iSWAP gate. Extending to a seven-site chain, we implement periodic trains of finite-width Gaussian pulses to activate distinct double-excitation transport channels with ultra-short gate durations t_gate (~170 ns). This achieves a clear scale separation from energy-relaxation times (T1) typical of fixed-frequency transmon devices with tunable couplers, such as IBM Quantum hardware. Finally, we benchmark stability under realistic imperfections, revealing a heightened sensitivity to static parameter disorder at the sub-percent level (eta ~ 10^-3) driven by spectral crowding, and discuss how closed-loop topologies could mitigate this constraint. This framework bridges time-periodic control theory and practical quantum gate engineering.

Tensor networks have attracted much attention as a powerful tool for modeling quantum many-body systems. Their contraction is a significant challenge, however, especially in highly connected networks, as memory requirements become prohibitive and the optimal contraction order is increasingly hard to find. The belief propagation (BP) algorithm has emerged as an alternative to exact contraction. Being formulated in a graph-agnostic way, it offers great flexibility, but its accuracy suffers in the presence of loops. In this work, we combine BP with the DMRG algorithm to solve ground-state problems, thereby extending DMRG to higher dimensions and arbitrary lattices. We demonstrate the viability of BP-DMRG on the transverse-field Ising model on a $2\times 2$ hexagonal lattice, finding that it produces states with a fidelity between $0.9$ and $0.99$ to the true ground state, and energy estimates with a relative error between $10^{-2}$ and $10^{-3}$. Additionally, BP-DMRG can find ground states on randomly generated lattices, with fidelity improving as the transverse field increases. We conclude with a discussion of the limitations we encounter when using belief propagation, highlighting that the TFI tensor network operators lead to larger errors during BP iterations in BP-DMRG.

Moiré superlattices in heterobilayers of atomically thin transition metal dichalcogenides provide a versatile platform for exploring quantum many-body physics as they can trap excitons, leading to the formation of quantized moiré exciton states. However, such moiré excitons have been predominantly studied at cryogenic temperatures, which severely limits their practical applications. Here, we demonstrate room-temperature activation and control of moiré excitons in MoS$_2$/WSe$_2$ heterobilayers using local strain engineering. Applying mechanical strain with a modified atomic force microscopy tip, we observe a series of resonances attributed to interlayer exciton states confined in the moiré potential. Power-dependent photoluminescence measurements elucidate the population dynamics of the moiré exciton states, while controlled local strain enables continuous tuning of their emission wavelength to the center of the second telecom window. We provide a theoretical model that captures all experimentally observed features, including the unconventional spectral shape of the moiré exciton emission. Our findings establish local tip-induced strain as a powerful tool for the on-demand manipulation of moiré excitons, paving the way for room-temperature quantum excitonic devices.

Remote quantum computing exposes a confidentiality gap. Standard privacy mechanisms protect quantum states and outputs, but not the scientific structure of a workload. This work reveals that hardware-aware compilation leaves observable signatures, such as routing overhead, circuit depth, and gate composition, that correlate with hidden modelling choices like partial differential equation boundary conditions, discretisation scale, and molecular geometry. The leakage arises from the mismatch between logical topology and fixed hardware connectivity, forcing problem-dependent SWAP insertion. We formalise this threat as Scientific-Intent Indistinguishability and prove that passive security is asymptotically unachievable under routing-optimal compilation. Experiments on a 156-qubit IBM Heron processor achieve near-perfect classification of boundary regimes and molecular geometries, with leakage generalising across solver families via routing-scaling exponents. Conventional gate-padding fails as a defence, causing fidelity drops without reducing adversarial advantage. Our results show that protecting quantum data alone is insufficient; execution-level confidentiality must become a first-class design requirement.

We study how vortex--edge coupling reorganizes the low-energy sector of a finite two-dimensional \(p_x+ip_y\) superconducting disk as a function of the vortex--boundary separation \(d\) and examine what this reorganization implies for the parity memory associated with a prescribed vortex-core Majorana wave packet, a resource relevant to Majorana-based quantum operations. Bogoliubov--de Gennes calculations reveal nonmonotonic core--edge reorganization of the lowest positive-energy finite-disk eigenstate, with particularly rapid variation near \(d\simeq7ξ\), where \(ξ\) is the coherence length. To separate this eigenstate reorganization from the spectral representation of a prescribed state, we rigidly translate a centered-vortex core-reference packet to each fixed vortex position, restrict it to the target disk, and project it, without intermediate normalization, onto the particle-hole-complete low-energy subspace. For \(Δ_0/E_F=0.36\) and disk radius \(R=30ξ\), the resulting retained norm exceeds \(0.98\) at all six sampled separations, \(4.25\leq d/ξ\leq8.25\), while, depending on \(d\), the spectral measure is concentrated near zero energy, fragmented over several low-energy levels, or dominated by finite-energy weight. Correspondingly, the signed parity correlator displays slow temporal variation, rapid coherent dephasing, or sign-changing oscillations, with possible finite-size recurrences at later times. Thus a large retained norm does not by itself imply spectral concentration or persistent parity memory.

Hexagonal boron nitride (hBN) is known as a promising solid-state platform to host room temperature quantum emitters that produce high purity single photons. The bright and spectrally adaptable hBN emitters are space-compatible, making hBN well-suited for satellite-based free-space optical (FSO) quantum key distribution (QKD) at wavelengths where the atmospheric background is naturally suppressed. This paper presents a pathway to develop hBN emitters operating near the Ca-II Fraunhofer line (at 854 nm), enabling daylight FSO operation. Moreover, due to its compatibility with the first telecommunication window at 850 nm, it is possible to interface with optical fibers to bridge the `last mile' in a scenario where multiple end-users connect through a single optical ground station to a QKD satellite. We therefore introduce a concept that combines continuous operation of a quantum network, hybrid links to minimize deployment costs, and high data rates due to the use of realistic single photon sources. The realization would be an important milestone for the development of the quantum internet.

A central challenge in diagnosing quantum chaos is to distinguish genuine many-body scrambling from kinematic effects of the spectrum. Krylov state complexity, or spread complexity, has emerged as a powerful diagnostic, with its characteristic growth, peak, and relaxation often taken as signatures of chaos. However, previous work has shown that this criterion can give false positives: saddle-dominated integrable systems may display prominent peaks even without random-matrix level correlations. We argue, based on complementary numerical and analytical evidence, that this ambiguity can be resolved by unfolding the spectrum prior to constructing the ensuing Krylov dynamics. By removing the non-universal smooth density of states while retaining microscopic spectral correlations, unfolding suppresses spurious peaks in integrable systems while preserving the universal spectral signatures of chaotic systems. Analytically, the formulation of the Lanczos iteration in terms of orthogonal polynomials yields an exact complexity kernel with a robust near-diagonal structure whose fine-grained features reflect the underlying spectral correlations. Moreover, for the logarithmic model, unfolding can be performed exactly, mapping the spectrum to a uniform lattice and yielding an analytic spread complexity that removes the false-positive peak. These findings establish unfolded Krylov complexity as a more reliable probe of genuine many-body scrambling.

Microwave-to-optical quantum transducers are essential for entangling remote superconducting qubits. Among the available transduction platforms, ensembles of Er$^{3+}$ and Yb$^{3+}$ ions doped into solids have emerged as leading candidates. While external magnetic fields are needed to split the Zeeman levels of erbium ions and enable a microwave--qubit interface, superconducting qubits suffer decoherence in such fields. In contrast, ytterbium ions exhibit zero-first-order Zeeman transitions and large hyperfine splittings at zero magnetic field (when doped into inorganic crystals). Owing to its long optical and spin coherence times, Yb:YSO has been widely used as a quantum memory, yet its potential for quantum transduction remains largely unexplored. Investigating this material could enable the integration of quantum memory and transduction in a single platform. Here, we demonstrate microwave-to-optical transduction in the continuous-wave regime using a 5\,ppm doped Yb:YSO crystal. The internal transduction efficiency is $2\times10^{-8}$ with a bandwidth of 200\,kHz, achieved using a 3D loop-gap microwave resonator (LGR) and a single-pass optical configuration. We explore all the ground states that form a V-type three-level system with the first and second optical excited states and assert the use of the ground state, which provides the highest efficiency and isolated optical transition. We further establish strong spin-microwave coupling from avoided crossing measurements. With a strong microwave drive to saturate the spin transition, we estimate the spin population pumped into the excited state, close to the simulated value. Finally, we calculate target parameter values for maximum efficiency with our system and suggest using 50\,ppm doped Yb:YSO crystal. With the calculated target parameters, the internal transduction efficiency is predicted to reach up to $10^{-4}$ in the current LGR.

Light-matter interactions underlie many quantum technologies, yet whether quasiparticles formed from such interactions preserve the full quantum state of light remains unresolved. Surface plasmon polaritons (SPPs), a class of polaritons formed by interacting photons with free-electron oscillations at metal-dielectric interfaces, are prime candidates to explore this question. Here we demonstrate quantum interference between single photons and SPPs using an Au-SiN$_{\mathrm{x}}$ integrated photonic-plasmonic device. Our results reveal that SPPs retain the indistinguishability of their excitation photons, establishing SPP as a viable quantum information carrier and opening a potential route toward photonic-plasmonic quantum circuitry.

Quantum generative models offer a promising framework for exploring whether quantum computation can enhance generative machine learning. Flow matching is a generative method in which samples are generated by transporting a simple, known distribution to the target data distribution with a learned velocity field. Its quantum counterpart, known as quantum flow matching (QFM), was introduced recently, and, like its classical counterpart, requires integrating an ordinary differential equation over many time steps during inference. As each step requires the output from the previous step, the circuit submission is sequential and a drawback on quantum computers as they have high input/output costs. To alleviate this problem, we introduce Quantum MeanFlow (QMF), the quantum analogue of the MeanFlow formulation, which allows single-step sample generation. While the QFM learns an instantaneous velocity field at each time step, QMF learns the average velocity over a time interval. We use a parameterized quantum circuit to learn these velocity fields and benchmark the two methods on the MNIST dataset. We show that while single-step QMF has lower image quality compared to multi-step QFM, it performs better than the single-step QFM sampling at every shot count. Both of our models are executed on IBM quantum computers and best-of-N rejection sampling recovers most of the accuracy lost to device noise without modifying the circuit. This is especially advantageous for QMF which has only one circuit evaluation per image. Here, We establish QMF as a viable method for single-step quantum generative sampling, saving on quantum circuit evaluations per generated sample.

A departure of a mixed quantum state from a local Gibbs description is generally invisible to local observables but can be detected by the conditional mutual information (CMI). Here we study the relationship between the renormalization group (RG) and CMI, and in particular, how RG constrains CMI. We first show that the CMI between nonadjacent regions $A$ and $C$, conditioned on the buffer region $B$, is UV-finite whenever the state admits a locally reversible RG with a fixed on-site Hilbert space dimension. We then study two hierarchical models that have long-range CMI and yet admit a simple RG description. The first model has a divergent Markov length at every temperature $0<T<\infty$ but nevertheless flows to an infinite-temperature product state under RG. The second model satisfies the local Markov condition while violating the global one and is stable against weak noise. At the critical noise strength, the two-point CMI decays only polynomially as a function of the system size, while the two-point mutual information vanishes.

Semidefinite programming plays a key role in optimization, with broad impact across control theory, machine learning, and combinatorial optimization. Although semidefinite programs are polynomially solvable, several commonly used algorithms rest on a linear-algebraic step whose running time grows cubically with the matrix dimension and which requires the matrix itself to be held in memory, at quadratic cost. In this study, we propose replacing it with a variational quantum eigensolver, whose qubit requirement is logarithmic in the matrix dimension, and present the first end-to-end implementation of such an approach within a cutting-plane framework, together with an operator-derived ansatz whose entanglement structure is read directly from the Pauli support of the candidate matrix. Evaluated on the control family of SDPLIB against an identical scheme driven by an exact eigendecomposition, the variational oracle produces valid cuts throughout, closing 32 to 82% of the initial optimality gap against a near-constant 75 to 82% for the exact oracle. Implementing and measuring the method end to end surfaces several effects not visible from theoretical analyses alone: where memory is actually consumed, how the padding required to fit a matrix onto a quantum register can mislead the variational optimizer, and why the candidate matrices prove dense in the Pauli basis, reducing the operator-derived ansatz to full entanglement. We report these findings and discuss their implications for near-term hybrid quantum-classical approaches.

Classical and current quantum approaches to protein structure prediction (QPSP) face limitations, notably massive qubit requirements restricting near-term models to simplistic on-lattice simulations. We propose a logarithmic-scale variational quantum eigensolver (VQE) that reduces qubit requirements for N torsional degrees of freedom to O(log2N), enabling off-lattice, all-atom simulations. Our architecture extracts molecular torsions from relative phases in statevector simulations. On quantum hardware, a decoder maps the empirical cumulative distribution function (CDF) from basis-state probabilities to bounded torsional variables. These feed a classical algorithm to build heavy-atom coordinates. We use an EfficientSU2 ansatz and multi-stage relaxation to mitigate barren plateaus. Structures are evaluated via a custom hybrid quantum-classical Hamiltonian, alongside Rosetta and OpenMM benchmarks. Evaluation on chignolin and Trp-cage yielded native-like conformations. Chignolin reached a 0.623 Å Cα RMSD in retained snapshots and 1.199 Å in final models; Trp-cage achieved a 2.501 Å RMSD among snapshots (3.512 Å in final models). Execution on IBM processors (ibm_cleveland, ibm_miami) successfully recovered native-like structures with a best RMSD of 1.758 Å. The custom energy function performed best overall, though energy-ranking imbalances persisted across sampled landscapes for all functions. This introduces the first all-atom, continuous-space quantum algorithm for QPSP. By converting physical qubit constraints into circuit depth constraints, it proves high-resolution prediction is feasible with exponentially fewer qubits. Despite current limits like computational overhead and energy function sensitivity, it establishes a scalable foundation for hybrid quantum biophysics.

Extreme pressures can transform materials and their properties, but probing these in-situ is made challenging by the small sample volumes and access requirements demanded by diamond anvil cells. Quantum defects offer a route to local measurements under such conditions, yet their sensing performance can be dictated by pressure-induced changes in their own host material. On the other hand, pressure may also be harnessed as a tool to engineer and stabilize new quantum defects with emergent functionalities. Here, we demonstrate both aspects within a unified platform based on optically active spin-pair defects in hexagonal boron nitride (hBN). As robust quantum sensors under pressure, these spin-1/2 systems retain pressure-independent spin resonances up to 20 GPa while maintaining or even enhancing their optical emission, in stark contrast to the spin-1 boron-vacancy centre in the same material. Simultaneously, we show that compression acts as a means of quantum defect engineering: the starting hBN undergoes an irreversible transformation into wurtzite boron nitride (wBN), during which the defect landscape is reconfigured. Spin-pair sensors are seen to persist across this structural transition, however, depending on the starting material we also observe new, highly fluorescent defects in the wBN phase. These results establish spin-pair defects in boron nitride as pressure-resilient quantum sensors while highlighting high pressure itself as a versatile pathway for creating and tuning quantum emitters.

We revisit the calculation of the phase shift experienced by swift electrons on passing through the electromagnetic field of a laser. Such phase shifts are now utilized in the form of `laser phase plates' in transmission electron microscopes (TEMs), for example. We calculate the phase shift using three different methods, namely, perturbation theory applied to the Dirac equation, the Volkov solution to the Klein-Gordon equation, and the relativistic Hamilton-Jacobi equation. We find that all three methods are in agreement, and that the calculated phase shift is independent of the relative orientation of the electron and laser beams. The agreement between the quantum and classical theories is explained. Our Lorentz invariant result for the phase shift differs from certain results published in the literature.

Distributed quantum sensing requires spatially separated probes to acquire local parameters while maintaining compatibility with network-level quantum information processing. We develop an entanglement-assisted stabilizer framework based on the extended structure of entanglement-assisted quantum error-correcting (EAQEC) codes, in which the remote halves of pre-shared ebits are used directly as local phase probes while the joint state simultaneously carries an encoded logical subsystem. Each remote probe acquires a local Z-axis phase and subsequently returns through an X-type noise channel. Within the extended EAQEC stabilizer structure, the stabilizer containing $X_{B_j}$ provides phase-dependent measurement statistics, whereas its partner containing $Z_{B_j}$ records the corresponding return-error syndrome. A graph-code formulation is introduced to make this structure explicit, together with an illustrative [[5,1,3;2]] construction. We further show that, conditioned on the joint sensing-and-syndrome measurement record, the post-sensing state differs from the original encoded state only by a known Pauli transformation, so that the logical information remains available for subsequent encoded operations. For the local-phase model considered here, the stabilizer readout attains the available quantum Fisher information, while the finite-shot estimator approaches the corresponding $1/\sqrt{M}$ scaling as the number of repetitions increases. The framework therefore provides a common entanglement-assisted stabilizer structure for distributed local-phase sensing, restricted return-error identification, and post-sensing logical-state retention, without relying on an intrinsic metrological enhancement from EAQEC itself.

Every finite-dimensional real or complex Lie algebra has a largest solvable ideal, its radical. In the compact dynamical Lie algebra (DLA) of a closed quantum system, this radical is the center; projecting onto it isolates directions that commute with the supplied algebra. With sparse Lie-bracket data and a known spectral gap, we construct a quantum circuit that approximately encodes this coefficient-space projector. The general construction combines the derived-algebra map with the Killing form, whereas compactness makes the Killing form alone sufficient. This distinction matters for numerical sensitivity, and our main theorem gives its exact law under an invariant-orthonormal basis adapted to the center and semisimple part. In a compact real algebra with a nonzero semisimple part, the condition number of the general operator is the three-halves power of the Killing-form condition number on that part. The compact projector in turn yields a bounded-error test for whether the center is trivial, provided that any nonzero center has at least a stated minimum dimension. This gives a controlled test for internal conserved directions in compact quantum dynamics.

We analytically characterize the maximal quantum violation of the extended Mermin-Ardehali-Belinskii-Klyshko (EMABK) family of inequalities by $n$-qubit generalized Greenberger-Horne-Zeilinger (GHZ) states. We develop a correlation-tensor approach in which the Bell value is expressed as the Frobenius inner product of the quantum correlation tensor and an effective coefficient tensor. A rank constraint on the latter, together with the von Neumann trace inequality, yields an upper bound governed by the two largest singular values of the reshaped correlation-tensor. For generalized GHZ states, we determine the complete singular spectrum and obtain a piecewise analytic upper bound. We then construct two complementary measurement strategies that saturate the bound for EMABK throughout the entire parameter range. The first is a purely MABK strategy in which all measurement directions lie in the equatorial plane of the Bloch sphere. The second is a hybrid strategy that recursively combines lower-order MABK anti-diagonal operators with the fully-$σ_z$ tensor product. The resulting piecewise analytic expression recovers the standard MABK Tsirelson bound $2^{(n-1)/2}$ in the maximally entangled limit and approaches the classical local-hidden-variable bound in the product-state limits. It further shows that every entangled generalized GHZ state exhibits a strict quantum-classical separation under the EMABK inequality, thereby eliminating the nonviolation region of the standard MABK inequality in the partially entangled regime.