Quantum Computing Research Archive

Yuval Boger interviews Mehmet Sanliol, managing director at Evercore covering quantum technologies and semiconductors. They discuss how investors value public quantum companies, when private companies should consider IPOs or SPACs, and why consolidation may shape the next phase of the industry. Mehmet also shares his perspective on technical and market signals that could affect valuations, the outlook for quantum software, and the recent developments in quantum that caught his attention most. Transcript Yuval:  Hello, Mehmet, and thank you for joining me today. Mehmet:  How are you, Yuval? My pleasure. Yuval:  So, who are you and what do you do? Mehmet:  So, my name is Mehmet Sanliol. I am the managing director at an investment bank called Evercore, and I focus on quantum technologies and semiconductors. Yuval:  So, why don’t I start from the end? So if you’re speaking with the CEO of a private quantum computer company, one that has delivered the product, has investors, has some good technical progress, what would you advise them to do about the public markets? Mehmet:  So the way that, look, you’ve seen a number of companies, I think we’re now up to kind of seven and having entered the public markets. Thankfully, all seem to be trading well enough so far. And the older companies are kind of well in excess of the $10 stock price and the few others that have joined are hovering around that level. I really think about it as a de-risking strategy because access in the public markets does provide you with the ability to tap liquidity in a manner that’s not necessarily always going to be available on the private side. You do open yourself up to public scrutiny and at some point you see some of the companies that had been traded for a few years now from kind of ’21 onwards go through some tough times and you really need to kind of weigh those two things against each other. To my mind if you are already full

Abstract Fast electrical spin rotations in quantum dots require strong spin-charge hybridization, but the same hybridization can increase sensitivity to detuning noise. In a double-quantum-dot (DQD) flopping-mode qubit, the sweet-spot width and the Rabi enhancement are both tied to the same orbital splitting, limiting post-fabrication optimization of the speed-coherence trade-off. Here, we demonstrate a GaAs triple-quantum-dot (TQD) flopping-mode qubit in which the detuning of the third dot, ϵ 34 , provides an additional electrical tuning parameter for orbital-band flattening. Tuning ϵ 34 flattens the qubit-frequency dependence on the detuning of the target DQD while maintaining strong spin-charge hybridization, enabling electrically driven Rabi frequencies above 100 MHz. We then use feedforward-neural-network (FNN) feedback to track slow qubit-frequency drift and connect this engineered operating point to high-fidelity gates. This feedback suppresses slow qubit-frequency fluctuations, reducing their standard deviation to 388 kHz, and yields a π /2 gate fidelity of 99.56% with a 4.05 ns gate time. These results identify TQD orbital-band engineering as an electrical route for tuning the speed-coherence trade-off, complementary to material-intrinsic spin-orbit coupling and fixed micromagnet geometry.

Inteli, a Brazilian higher education institute, has become an accredited ICT and partnered with IBM Quantum. This collaboration grants Inteli researchers cloud access to IBM Quantum systems to explore quantum algorithms for decision-making under uncertainty, with a focus on practical industrial applications in Latin America. The partnership aims to advance quantum computing capabilities and workforce development in the region. The post Brazil’s Inteli Becomes Accredited ICT and Partners with IBM Quantum to Research Decision-Making Under Uncertainty appeared first on Quantum Computing Report .

What would it take to watch an electron move through a material? Researchers would need to see individual atoms and capture an electron's motion at incredibly short timescales. A Technion-led team has brought those two capabilities together in a scanning tunneling microscope, using carefully shaped laser pulses to control the direction of electron flow while preserving nanoscale spatial resolution.

Iceberg Quantum's Pinnacle 1.2 architecture, featuring the Crevasse QLDPC decoder, significantly reduces the resources needed to factor RSA-2048. They achieved logical error rates below 10^-12 per logical qubit-cycle, a critical threshold for this task, through direct circuit-level simulations. This breakthrough could factor RSA-2048 in as little as 0.98 days with 48,000 physical qubits. The post Iceberg Quantum Validates Pinnacle 1.2 Architecture with Crevasse QLDPC Decoder to Reduce RSA-2048 Factoring Resources appeared first on Quantum Computing Report .

Insider Brief Quanova has selected Quandela ’s MosaiQ photonic system for a program at Quang Trung University that the partners say will deploy Vietnam’s first quantum computer. Supported by Nam A Bank, the initiative includes faculty training, dedicated curricula, software access, a Quantum Experience Center and technology events. The partnership will establish a Quantum Innovator Residency Program to develop local expertise and support quantum education, research and entrepreneurship. PRESS RELEASE — Quandela , a European leader in photonic quantum computing, announces a major milestone in its expansion in Southeast Asia. Quanova, a Vietnamese quantum company, has selected Quandela ’s MosaiQ solution as the foundation of a new quantum research, innovation, service and entrepreneurship (quantum-RISE) program at Quang Trung University (QTU) in Quy Nhơn, Gia Lai. The project marks the first France–Vietnam collaboration in quantum computing and will lead to the deployment of Vietnam’s first quantum computer, with the support of Nam A Bank. Vietnam’s first quantum computer at the heart of a strategic education and research program This long-term partnership, developed with Quanova, Quandela ’s strategic local partner in Vietnam, will provide Quang Trung University with a comprehensive platform for education, research and innovation. Nam A Bank is supporting the initiative as part of its commitment to advanced technologies. As Võ Hoàng Hải, Deputy CEO of Nam A Bank, explained: “Nam A Bank invests in core technologies, including quantum technology, to help build high-tech capabilities in Vietnam through strong and effective cooperation with French organizations.” The program includes: Deployment of the MosaiQ photonic quantum computer; Faculty training and development of dedicated curricula; Provision of the software suite and support for the creation of a Quantum Experience Center and launch of the Quantum Innovator Residency Program; Organization of technology ev

Quantinuum and Oracle have launched the OCI Quantum AI Compute Beta Program, offering early cloud-based access to Quantinuum's Helios quantum processor for hybrid quantum-AI workflows. This program integrates Helios within Oracle Cloud Infrastructure (OCI) AI data centers, providing a browser-based Python development environment for various applications. The initiative will be further detailed at Oracle AI World 2026. The post Quantinuum and Oracle Launch OCI Quantum AI Compute Beta Program for Early Access to Helios appeared first on Quantum Computing Report .

Insider Brief Telefónica and IQM Quantum Computers plan to install the first quantum computer in Spain’s Community of Madrid at the Technical University of Madrid (UPM) before the end of 2026. The IQM Spark system is designed for research, education and early-stage development, giving universities, hospitals, research centers and start-ups access to quantum hardware. The project aims to build regional expertise, support the development of industry use cases and expand Madrid’s role in Europe’s quantum technology ecosystem. PRESS RELEASE — Telefónica and IQM Quantum Computers, a global leader in superconducting quantum computing, have joined forces to deploy the first quantum computer in the Community of Madrid. The initiative will strengthen the region’s scientific and technological capabilities, while driving the development of real-world cases for companies across the Community of Madrid. The IQM Spark quantum computer, an all-in-one solution specifically designed for research, education and early-stage development, will be installed at the Technical University of Madrid (UPM) before the end of 2026. It will enable universities, hospitals, research centers and start-ups, direct access to real quantum hardware to develop and test quantum algorithms and build the expertise needed to explore future use cases. This will be the first quantum computer of its kind in the Community of Madrid, significantly increasing the region’s capacity to develop quantum capabilities locally and through hands-on experience. The computer will join the other two quantum computers provided by Telefónica and IQM to CESGA (Galician Supercomputing Centre). Once the new quantum computer is operational, the Community of Madrid will have greater capabilities to foster the creation of its own quantum ecosystem, bringing together all stakeholders involved in developing real-world use cases that deliver direct benefits to local industry. This ecosystem will help attract talent and strengthen

Researchers at AIST have directly observed magnetic flux quanta generated in a superconductor by photon absorption and demonstrated a new principle of photon detection that identifies the number of photons based on the number of these flux quanta.

Chalmers University of Technology has developed TRIO pulses, a new quantum control framework for superconducting processors. These pulses enable single-qubit gates to maintain high fidelity even with significant control-amplitude miscalibrations and frequency detuning errors. This breakthrough offers a way to reduce recalibration overheads in large-scale quantum processors and has been demonstrated with an X-gate achieving 99.90% fidelity. The post Chalmers University Demonstrates TRIO Pulses for Control-Error-Robust Single-Qubit Gates in Superconducting Processors appeared first on Quantum Computing Report .

IQM Quantum Computers and NVIDIA have successfully automated the calibration of a 20-qubit quantum processor using NVIDIA Ising Vision-Language Models (VLMs). This agentic AI system analyzes experimental data, autonomously adjusts parameters, and generates diagnostic logs for human review. They also released QCalEval, an open benchmark for AI-driven quantum processor bring-up, where NVIDIA Ising Calibration models outperformed general-purpose VLMs. The post IQM and NVIDIA Automate 20-Qubit Chip Calibration via NVIDIA Ising Vision-Language Models and QCalEval Benchmark appeared first on Quantum Computing Report .

Insider Brief Google Quantum AI launched a $150,000 Kaggle competition to develop smaller, more efficient quantum circuits for calculations related to fusion energy, optimization and chemistry. Participants will reduce qubit and gate counts while meeting accuracy requirements, potentially lowering the hardware demands of useful quantum algorithms. The competition uses Google ’s open-source kickmix software to efficiently test circuit designs on conventional computers, providing confidence in approximate correctness without proving exact equivalence. Google Quantum AI is launching a competition to use artificial intelligence to shrink the circuits needed for useful quantum computing. The competition offers a total prize pool of $150,000, organizers said. The competition, hosted on Kaggle , challenges participants to reduce the number of computing steps and quantum bits required for tasks related to fusion energy, mathematical optimization and chemistry. Google is providing starting circuits and software to check whether proposed improvements produce sufficiently accurate results. The effort targets a central obstacle to practical quantum computing. Even as researchers build more capable processors, many potentially useful calculations remain too demanding for available hardware. Reducing the work required by an algorithm could lower the hardware requirements for running it. According to Google’s announcement , the competition draws on a method that allows conventional computers to efficiently test a particular class of quantum circuits. That creates a way for AI systems to repeatedly propose changes, check their accuracy and search for further savings. Reducing the Cost of a Calculation A quantum circuit is a sequence of operations used to carry out a calculation. Those operations, called gates, act on qubits, the basic units of quantum information. Current processors have limited numbers of qubits, and their gates can introduce errors. Quantum error correction is de

Guest Post by Liam Wang COO, Logical Qubit Technology. The World Economic Forum’s Quantum Economy Day 2026 was held in Geneva, Switzerland, on October 13–14. Logical Qubit Technology attended as the only quantum computing company representing China. The company’s Chief Operating Officer, Liam Wang, joined business executives, researchers, and representatives of international organizations from around the world to discuss the global development of quantum computing. This June, I took part in a World Economic Forum discussion on global quantum science and technology development at the Summer Davos meeting in Dalian. Representing the company again at Quantum Economy Day 2026 in Geneva gave me a close-up view of how quantum computing is developing in other countries and regions. What Is Everyone Talking About? My first and most immediate impression: China and other countries share many of the same concerns about this industry — how to persuade policymakers, capital, and industry to commit more resources to quantum computing; which application scenarios will see the first breakthroughs; how geopolitics continues to shape the global industry (supply chain security, the setting of global quantum standards, and so on); how to broaden quantum computing’s social reach, steadily moving beyond academia into industry and the wider public; and how the convergence of quantum computing and AI will unfold, and what major opportunities that super-cycle will create. Although the industry is still at an early stage, the overall mood among participants was optimistic . AI was the most common point of comparison: since ChatGPT launched in November 2022, the pace of progress in large AI models has exceeded almost everyone’s expectations. Quantum computing is likely to follow a similar logic. Of course, at this stage, quantum computing still has to be viewed pragmatically. Two terms came up most frequently in the discussions: “use case” and “geopol

Florida Atlantic University received a nearly $400,000 NSF grant to advance post-quantum cryptographic protocols. Led by Dr. Edoardo Persichetti and Dr. Veronika Kuchta, the project will develop advanced functionalities beyond basic primitives to secure decentralized systems against future quantum attacks. The initiative also supports student mentoring and cybersecurity outreach, building on FAU's leadership in quantum-safe security. The post Florida Atlantic University Awarded $400,000 NSF Grant to Expand Post-Quantum Cryptographic Protocols appeared first on Quantum Computing Report .

Leiden University and Riverlane research uncovered a flaw in correlated decoding, causing a loss of effective code distance and higher logical failure rates in quantum error correction. They introduced a new regularization parameter to fix this, restoring nominal distance scaling and improving accuracy without adding computational overhead. This discovery offers a crucial design principle for future quantum decoding architectures. The post Leiden University and Riverlane Research Reveals Distance-Losing Flaw in Correlated Decoding Below Threshold appeared first on Quantum Computing Report .

IBM Quantum has released Qiskit SDK v2.6, significantly enhancing its C API layer with a new pass-manager framework and native QPY serialization. This update allows for custom compiler passes and hardware-native quantum operations in C, C++, and Julia without a Python runtime, moving towards Python-optional execution in high-performance computing. The release also updates the Qiskit GitHub Roadmap, outlining future versions that will focus on C ABI/API stability, fault-tolerant compilation, and a Rust-native execution interface. The post IBM Releases Qiskit SDK v2.6 with C API Pass-Manager Framework, Native QPY Serialization, and Custom Operations appeared first on Quantum Computing Report .

NVIDIA has invested in Riverlane to advance real-time quantum error correction (QEC) and GPU decoder calibration. This collaboration utilizes NVIDIA H100 GPUs to accelerate Riverlane's Local Clustering Decoder (LCD), significantly reducing the time for surface code training cycles and enabling dynamic recalibration of QEC decoders. This advancement helps mitigate qubit drift and hardware defects, paving the way for more stable and reliable fault-tolerant quantum computing systems. The post NVIDIA Takes Strategic Stake in Riverlane to Accelerate Real-Time Quantum Error Correction and GPU Decoder Calibration appeared first on Quantum Computing Report .

Insider Brief A state-commissioned study ranks New York second nationally in quantum-related businesses, research groups and patents, identifying greater coordination as an opportunity to accelerate commercialization. New York has committed $360 million to quantum development, including $300 million for a Stony Brook research hub and $60 million for up to four regional commercialization hubs. The study estimates these investments could support $2.3 billion to $5 billion in economic activity and 7,200 to 10,100 job-years through 2036. PRESS RELEASE — Governor Kathy Hochul today announced the release of a comprehensive study of New York State’s quantum technology landscape, finding that the Empire State ranks second nationally in quantum-related businesses, research groups and patents. Commissioned by Empire State Development’s Division of Science, Technology and Innovation (NYSTAR), the study highlights New York’s position as a national leader in the emerging industry and identifies opportunities to strengthen collaboration, accelerate commercialization and support future economic growth. “New York is building the foundation for the next generation of technological breakthroughs, and quantum technology represents an enormous opportunity for our economy,” Governor Hochul said. “With world-class research institutions, advanced manufacturing capabilities and a growing network of innovative businesses, we have the tools to lead this emerging industry. Our $360 million investment will help turn that potential into progress, bringing new technologies to market, attracting private investment and creating good-paying jobs across New York State.” Empire State Development President, CEO and Commissioner Hope Knight said, “Under Governor Hochul’s leadership, New York is making strategic investments to lead the next generation of technological innovation. This study confirms that our state has the research institutions, manufacturing capabilities and industry expertise nee

Google Quantum AI has launched a $150,000 Kaggle competition running from October 22, 2026, to January 20, 2027. The competition challenges participants to use AI agents to compress fault-tolerant quantum circuits, focusing on "kickmix" circuits which are verifiable by classical computers. This initiative aims to optimize quantum algorithms for applications in fusion energy, optimization, and quantum chemistry. The post Google Quantum AI Launches $150K Kaggle Competition to Compress Fault-Tolerant Quantum Circuits Using AI Agents appeared first on Quantum Computing Report .

Quantum systems can occupy superpositions, quantum states that combine different possibilities. For instance, a microwave field can be prepared in a superposition of an empty state and a state that contains microwave light.

Periodically driven quantum systems exhibit many fascinating phenomena absent in equilibrium systems, but their simulation is more challenging than that of static systems. Consequently, quantum simulation of these systems offers greater opportunity for achieving quantum advantage. To build the foundation for simulating time-periodic Hamiltonians, we utilize the Floquet-Hilbert space formalism to transform the Hamiltonian into a time-independent form and provide its Pauli decomposition. Within this formalism, we develop a hybrid quantum-classical algorithm, Floquet-ADAPT-VQE, that produces three key quantities that govern periodically driven quantum dynamics: the quasienergy, the associated Floquet eigenstates, and expectation values of observables with respect to these eigenstates. The latter is achieved by applying a fixed-depth quantum circuit to an initial Floquet eigenstate—an efficient construction made possible by the Floquet-Hilbert space formalism. We also identify a suitable auxiliary initial state whose squared Floquet energy is independent of the number of auxiliary qubits as well as the driving frequency, which leads to better convergence with fewer ADAPT iterations. We demonstrate our algorithm by performing numerical simulations on a periodically driven XYZ model with a magnetic field. We also explore potential applications of our algorithm for studying various non-equilibrium phenomena in periodically driven systems.

Abstract We propose a Trace-distance binary Tree AdaBoost (TTA) multi-class quantum classifier, a practical pipeline for quantum multi-class classification that combines quantum-aware reductions with ensemble learning to improve trainability and resource efficiency. TTA builds a hierarchical binary tree by choosing, at each internal node, the bipartition that {heuristically} maximizes the trace distance between average quantum states; each node trains a binary AdaBoost ensemble of shallow variational quantum base learners. By confining intrinsically hard, small trace distance distinctions to small node-specific datasets and combining weak shallow learners via AdaBoost, TTA distributes capacity across many small submodels rather than one deep circuit, mitigating barren-plateau and optimization failures without sacrificing generalization. Empirically TTA achieves top test accuracy ($\approx $100\%) among quantum and classical baselines, is robust to common quantum errors, and realizes aggregate systems with almost 10,000 cumulative layers and 0.2M parameters, implemented as many shallow circuits. Our results are empirical and implementable on near-term platforms, providing a resource-efficient route to scalable multi-class quantum machine learning.

Abstract We present a framework combining Lie group theory and feed-forward neural networks to efficiently generate quantum optimal control pulses for arbitrary unitary operations in superconducting qubit systems, bypassing the need for explicit optimization at inference time. The exponential scaling of the Hilbert space dimension with qubit number makes standard optimization approaches computationally prohibitive when large ensembles of distinct propagators must be processed, a bottleneck that is particularly acute in Trotterized quantum simulation. Our method addresses this limitation by pre-computing a representative set of control pulses via Lie group theory and training neural networks to map target propagators to their corresponding pulses. We demonstrate the approach on superconducting qubit systems of 2, 3, and 4 qubits, finding high reconstruction fidelity for specific combinations of Lie algebra parameters. As a physically motivated benchmark, we apply the methodology to reconstruct control pulses for the Trotter propagators of a neutrino system undergoing collective flavor oscillations. The successful generalization across system types demonstrates that a single model -trained once on hardware-specific random propagators -can serve as a universal control-pulse generator for any target quantum system of compatible Hilbert space dimension, offering a promising route toward scalable quantum simulation.

Abstract Equivariant quantum neural networks are designed to preserve symmetries in quantum machine-learning data, but this property is usually verified only before hardware compilation. We show that a transpiler can preserve the expected unitary symmetry relation while compiling symmetry-related inputs into circuits with different two-qubit gate counts and physical-qubit layouts, so ideal-circuit equivariance does not guarantee symmetry at the level of compiled circuit structure. We formalise this gap with a three-level compliance hierarchy and a taxonomy separating topology-input ansätze, where the symmetry changes the gate topology the compiler sees, from parameter-input ansätze, where it changes only numerical gate parameters and provably leaves controlled-Z counts unchanged under topology-based transpilation. Auditing four published ansatz families, we observe the effect only in the topology-input case. For the Skolik permutation-equivariant weighted-graph ansatz compiled to the IBM Heron Fez simulator target at twelve qubits, sparse graph inputs produce a mean relative controlled-Z asymmetry of 7.3\% across fifty random vertex permutations, with a worst case of 22.5\%. The effect persists across all four Qiskit optimisation levels and is not removed by matched-layout compilation, implicating routing-stage sensitivity to the ordered sparse-edge gate sequence. A density sweep shows that the asymmetry is comparable across intermediate graph densities and vanishes for complete graphs, where the ansatz degenerates into the parameter-input class, and stochastic baselines attribute the realised differences to heuristic routing sensitivity rather than to differing optimal compiled costs. Finally, we propose compile-once-and-relabel, a deployment pattern that removes controlled-Z count asymmetry by construction and reduces compilation cost for orbit-based workflows.

Abstract Entanglement distillation is a fundamental operation in quantum information processing used to obtain higher-fidelity entangled pairs from a supply of less entangled quantum states using local operations aided by classical communication (LOCC). In a physically relevant setting, where states with an initial fidelity of f 0 , probabilistically generated over multiple, m, memory pairs distributed between two parties, Alice and Bob, are pairwise distilled, the optimal policy identifies the system configuration dependent sequence of entanglement generation and distillation operations that need to be performed in order to minimize the expected time to reach some target fidelity f T > f 0 . Here, we formulate and systematically analyze this task as a Markov decision process and using a value iteration algorithm, obtain optimal deterministic policies that minimize the expected waiting time required to achieve a target fidelity. Our results show that the expected waiting time under the optimal policy decreases with increasing generation probability p and number of quantum memories m -as expected. In contrast, it exhibits non-monotonic behavior with respect to f 0 for a fixed fidelity gap, (∆f = f T - f 0 ). While the optimal policy consistently outperforms baseline policies such as the greedy, nested and entanglement pumping policies, its relative advantage is regime-dependent, being determined by the system parameters (p, f 0 , f T , m), and exhibits a nontrivial dependence on the fidelity gap ∆f . Our results highlight the value of formulating entanglement distillation as a Markov decision problem, enabling the systematic design of policies that achieve target fidelity thresholds for quantum information tasks in realistic resource-constrained settings.

Abstract Machine learning (ML) and quantum machine learning (QML) have gained significant importance, as they offer powerful tools for tackling complex computational problems across various domains. An overview of QML's uses in quantitative finance is presented here. The connection between quantum computing and machine learning in financial applications, spanning a range of use cases including portfolio optimization, market prediction and trading, pricing and risk management is examined. The different applications from the literature review are categorized based on specific use cases, ML approaches, optimization methods, and the types of quantum hardware utilized. To facilitate this examination, we employ a morphological box, which allows us to analyze different combinations of these elements across financial use cases.

Abstract We study a family of sparse positive maps on qutrits for which positivity, decomposability, and PPT entanglement can all be analysed explicitly. The block structure of the associated Choi matrices reduces positivity to a Hermitian biquadratic form and leads to exact positivity boundaries for three representative parametric families. For the same families we determine the exact transition between decomposable and non-decomposable maps and construct associated PPT states of two classes. The first consists of witness-adapted deformations naturally tied to the non-decomposability analysis. The second consists of analytically tractable families whose full PPT-entangled branch is detected by fixed positive maps, yielding exact thresholds between separability and bound entanglement. For the trace-preserving subclass, we further compare positivity with a recent eigenvalue bound for 2-positive maps, thereby making the gap between positivity and higher-order positivity fully explicit within this family.

Abstract Calibration summaries are used both to select physical qubits and to parameterize noisy emulators, creating a risk that agreement within a calibration-derived model is mistaken for validation on hardware. We test whether calibration-aware compiler rankings transfer to hardware using weighted-MaxCut instances implemented with the quantum approximate optimization algorithm (QAOA). The evidence comprises four stages: 3,240 historical calibration-derived simulations; a complete 54-pair hardware grid on three IBM Heron r2 processors; exact-circuit repeats 9.3–12.1 days later; and a contemporaneous five-arm refresh experiment. Full-calibration selection improves the median hardware approximation ratio by 0.74 percentage points (pp), with 29 resolved gains and 11 resolved losses. This is a mean-objective effect: its translation to exact-solution probability is instance- and size-dependent, and we do not extrapolate it beyond the tested n ≤ 10 regime. A Qiskit Aer model constructed from the calibration state available before execution reproduced the direction of the measured full-calibration-versus-topology advantage in 35/54 comparisons, but systematically overestimated its size: the simulated advantage exceeded the subsequently measured hardware advantage by a median 1.35 pp. Regressing the measured hardware advantage on the simulated advantage gave a slope of 0.28 (workload-depth case-cluster 95% interval 0.06–0.52), rather than the unit slope of a calibrated predictor. The emulator identified the exact best of six backend-compiler configurations in only 5/18 cases (95% Wilson interval [0.125, 0.509]). By contrast, identical circuits preserved the compiler-effect sign in 16/18 later repeats (r = 0.92). Refreshing the full-calibration mapping yielded a median +0.72 pp gain, whereas the calibration-score difference agreed in sign with the measured refresh benefit in only 9/18 cases. Calibration data are therefore useful for candidate discovery and timely refresh, but their scalar scores are not calibrated predictors of hardware performance or configuration ranking.

Insider Brief A new study analyzes an unpublished Schrödinger manuscript that challenged claims that hidden information could not explain apparently random quantum outcomes. Schrödinger’s model reproduced the expected results of polarization measurements, serving as a mathematical counterexample rather than a complete theory of quantum physics. The manuscript illustrates the complexity of Schrödinger’s views, showing that he could construct a deterministic model while favoring fundamental randomness in nature. Image: Photo by Robert Stump on Unsplash PRESS RELEASE — An unpublished manuscript by Erwin Schrödinger shows how apparently random quantum results could follow definite rules, challenging an argument that such explanations were impossible. The handwritten draft , analyzed in a new historical study posted on arXiv , adds a missing contribution to a wartime dispute over whether quantum mechanics had ended the scientific case for a predictable universe. It also complicates a familiar picture of Schrödinger as a defender of determinism, the idea that events are fixed by preceding conditions. According to physicist Flavio Del Santo, Schrödinger constructed his model to expose a weakness in an argument, rather than to establish how nature actually works. His draft combined a mathematical counterexample with a defense of the possibility that randomness is fundamental. The study presents what Del Santo describes as the first transcription and analysis of the manuscript with a central finding concerning the limits of scientific claims. Schrödinger showed that ruling out one proposed explanation does not necessarily rule out every explanation of the same kind. A Missing Contribution The document survives in the Erwin Schrödinger Archive at the University of Vienna ’s Austrian Central Library for Physics. Titled “Collapse of Determinism,” it consists of three handwritten pages and is undated. Del Santo, affiliated with the University of Geneva and Constructor Univ

Insider Brief Qblox has integrated NVIDIA DGX Spark with its quantum system controller using NVIDIA NVQLink, reporting round-trip latency below 4.0 microseconds on NVIDIA RTX PRO 6000 Blackwell and below 7.2 microseconds on DGX Spark. The integration connects GPU computing with quantum control to support real-time hybrid quantum-classical workloads, including GPU-accelerated calibration and quantum error correction. The system uses NVIDIA CUDA-Q to support development on desktop hardware, with the same code designed to transfer to GPU servers as quantum systems scale. PRESS RELEASE — Qblox , a leader in scalable quantum control architecture, today announced the integration of NVIDIA DGX Spark with a quantum system controller using NVIDIA NVQLink , achieving measured roundtrip latency below 4.0 µs on NVIDIA RTX PRO 6000 Blackwell and below 7.2 µs on NVIDIA DGX Spark. This enables Qblox to support real-time hybrid quantum-classical applications, with a single desktop system that can host quantum, AI, and simulation workloads via NVIDIA CUDA-Q . The same code then carries over to data center graphics processing unit (GPU) servers as systems scale. The integration brings GPU acceleration into the real-time control loop, a key building block for scaling quantum systems to support logical qubits. Qblox ‘s Q1 sequence processors and LINQ deliver the low latency and high throughput the Qblox Cluster needs to work hand in hand with the GPU. GPU-accelerated calibration routines update qubit parameters while experiments run, instead of between them. For quantum error correction, syndrome data reaches GPU-based decoders with low latency, helping identify and correct errors in real time. The milestone builds on the previous work from Qblox with NVIDIA NVQLink announced in October 2025 and on Qblox’s support for the NVIDIA CUDA-Q realtime API in March 2026. It moves the integration from architecture to measured hardware performance, demonstrating Qblox’s a

Insider Brief QCentroid has announced QCentroid Missions, a new QuantumOps capability that helps enterprise teams evaluate computational approaches against business objectives and defined validation criteria. The system uses agents to test classical, quantum-inspired, GPU-simulated and quantum processing unit (QPU) approaches, with recommendations based on benchmarking evidence and the option to retain an existing classical solution. QCentroid Missions uses NVIDIA CUDA-Q for accelerated circuit simulation and is being demonstrated at NVIDIA GTC Berlin from 20–22 October 2026, with rollout to QCentroid Platform customers planned from Q4 2026. PRESS RELEASE — QCentroid today announced QCentroid Missions , a new goal-driven capability in its QuantumOps platform designed to take enterprise teams from a measurable business objective to validated evidence for deciding whether, and how, to evolve an existing computational solution. QCentroid Missions is being demonstrated this week at NVIDIA GTC Berlin. Rather than starting with a quantum algorithm or a predefined technology, a Mission starts with an outcome such as reducing execution time, improving solution quality or reaching a target business metric. Teams define the objective, the computational and operational limits, and the validation gates that must be cleared. Expert agents in QuantumOps then run the experimentation cycle, evaluating potential evolutions of the current solver across classical, quantum-inspired, GPU-simulated and QPU-ready approaches. The resulting recommendation may be classical, hybrid or quantum, including a recommendation to retain the current classical solution when the evidence supports it. “Quantum teams are small, while the number of questions coming from the business continues to grow,” said Carlos Kuchkovsky, CEO and co-founder of QCentroid . “With Missions, teams no longer have to manually drive every stage of an experiment. They define what they want to improve, how far the system

Insider Brief Black Kite has introduced Quantum Readiness controls within its Cyber Rating platform to assess observable signs of post-quantum cryptography readiness across an organization’s third-party vendors. The new controls examine indicators such as hybrid post-quantum key exchange, certificate signature readiness and assets without an identified migration path, integrating the results into the platform’s SSL/TLS Strength category. The feature is designed to help organizations track vendor readiness, identify potential gaps in supply-chain cryptographic security and prepare for post-quantum migration requirements. PRESS RELEASE — Black Kite , the leader in third-party cyber risk management, today announced the release of Quantum Readiness, a new set of controls within the SSL/TLS Strength category of the Black Kite Cyber Rating that evaluates quantum agility across an organization’s third-party vendor ecosystem. Quantum Readiness surfaces which vendors are quantum-ready or adopting quantum-safe encryption methods, providing an early indication of security maturity and preparedness for the post-quantum era. Quantum computers capable of breaking today’s encryption do not exist yet, but experts predict “Q-Day” could arrive as early as 2028. The risk is also retroactive: in “harvest now, decrypt later” attacks, bad actors are already collecting encrypted data to decrypt once quantum computers are powerful enough. Organizations need to prepare now – for many, the shift to quantum-safe encryption is underway, making quantum agility a key indicator of vendor security maturity and readiness. “Third-party cyber risk management needs to account for where risk is going, not only where it exists today,” said Ferhat Dikbiyik, Chief Research & Intelligence Officer (CRIO), Black Kite. “We built Quantum Readiness to give customers early visibility into quantum agility across their supply chains and help them understand

Insider Brief Florida’s first statewide quantum-safe network segment is operational, connecting Palm Beach State College and Florida Atlantic University in Boca Raton using IonQ quantum key distribution technology. Supported by a $1 million FloridaCommerce grant, the connection went live Oct. 15 over Palm Beach County’s dark fiber infrastructure to strengthen data security between the institutions. Connections to Miami Dade College and FAU’s Jupiter campus are planned within three months, with further statewide expansion dependent on funding. PRESS RELEASE — Palm Beach State College (PBSC) President Ava L. Parker , JD announced Wednesday night that the first segment of Florida’s statewide quantum-safe network is operational. The system links PBSC to Florida Atlantic University in Boca Raton over Palm Beach County’s dark fiber infrastructure. Supported by a $1 million defense infrastructure grant from FloridaCommerce, Palm Beach State College is leading the development of the network’s first segment in partnership with Florida LambdaRail, Florida Atlantic University, Palm Beach County and IonQ. The segment uses IonQ quantum key distribution technology to strengthen the security of data transmitted between the participating institutions and establishes a foundation for expanding quantum-secure communication across Florida. Parker made the announcement at the college’s Historic Building in West Palm Beach, the future home of PBSC’s Quantum Innovation Center, the evening before Quantum Beach 2026 . The link went live Oct. 15, 2026. “”This partnership is a model for how higher education, industry and government can work together to build the infrastructure and talent that will drive Florida’s future,” said Parker. “By connecting students to leading-edge technologies while strengthening secure communications across our region and state, we are creating opportunities that extend far beyond our campuses. At the same time, we are pre

Researchers at Fraunhofer IAF have developed a laser-enhanced quantum sensor that combines high magnetic-field sensitivity with a large dynamic range. Using laser threshold magnetometry, they improved the ratio of sensitivity and dynamic range by a factor of up to 590 compared with state-of-the-art approaches. The breakthrough is enabled by the first demonstration of 100% optical contrast, combined with strong laser readout signals. The results, published in Nature Communications, open up new prospects for medical diagnostics, navigation, and resource exploration.

Insider Brief ZuriQ and Rhonexum have signed a multi-year commercial agreement under which Rhonexum will supply cryogenic integrated-circuit technologies and customization services for ZuriQ ‘s trapped-ion quantum computing roadmap. The agreement includes an initial product delivery scheduled for the end of 2026, future product orders and deployments, and technical cooperation that gives ZuriQ access to selected Rhonexum technologies and product developments. The companies aim to address quantum processor scaling challenges, including control-signal overhead per qubit, by combining ZuriQ ‘s trapped-ion architecture with Rhonexum ‘s cryogenic electronics expertise. PRESS RELEASE — ZuriQ and Rhonexum have announced a multi-year commercial framework agreement. Under the agreement, Rhonexum will supply cryogenic integrated-circuit technologies and customisation services to ZuriQ, which will evaluate the potential of each of these solutions to advance its trapped-ion quantum computing roadmap. This partnership brings together ZuriQ ’s trapped-ion quantum computing expertise and Rhonexum ’s cryogenic electronics technologies to address future scaling and performance requirements. It establishes a framework for future orders, product deployments, and technical collaboration. Quantum computing is rapidly accelerating toward industrial deployment and scalable commercial systems. As quantum processors scale, demand is growing for specialised hardware and electronics that improve performance, reduce complexity, and enable more compact system architectures. A longstanding challenge in scaling trapped-ion quantum computing is to reduce the overhead in control signals per qubit that travel from room-temperature sources into a cryogenic environment. ZuriQ ’s architectural advances, together with Rhonexum ’s cryogenic electronics expertise, provide a unique approach that can enable denser qubit arrays while retaining flexible reconfiguration capabilities. Th

Insider Brief The UK and Singapore held their 11th Financial Dialogue in Singapore, discussing cooperation in digital finance, AI, quantum technologies, capital markets and sustainable finance. On quantum technologies, both countries reviewed quantum security approaches, guidance for financial institutions transitioning to post-quantum cryptography, and lessons from Singapore’s Quantum Key Distribution sandbox with industry partners. The two countries also discussed financial market innovation and regulatory cooperation ahead of the UK’s G20 Presidency and Singapore’s ASEAN Chairmanship in 2027. PRESS RELEASE — The United Kingdom (UK) and Singapore held the 11th UK-Singapore Financial Dialogue in Singapore today. Reaffirming their strong and longstanding partnership, the discussions focused on advancing cooperation in digital finance and innovation, capital markets, sustainable finance, and regional and multilateral initiatives. Digital Finance and Innovation The UK and Singapore exchanged views on digital finance and innovation, including taking stock of and advancing their cooperation in digital assets, artificial intelligence (AI), and quantum technologies.  Discussions on digital assets and financial market infrastructure covered initiatives from both jurisdictions aimed at supporting cross-border use cases for tokenisation and wholesale digital markets. These included the Monetary Authority of Singapore (MAS)’s Project Guardian [footnote 1] and BLOOM, [footnote 2] Global Layer One (GL1), [footnote 3] alongside the UK’s Wholesale Financial Markets Digital Strategy, [footnote 4] the work of the UK Wholesale Digital Markets Champion, [footnote 5] the Digital Securities Sandbox, [footnote 6] and ongoing work of the Bank of England (BoE) and the Financial Conduct Authority (FCA) on tokenisation and wholesale digital markets. Developments in crypto-assets and stablecoins and the implications of digital money for wholesale markets and inst

Ever since quantum mechanics first described particles, like electrons, as rippling waves, researchers have wondered if those waves could be trapped in place. Writing today in Science a century later, a team of Columbia University researchers reports waves of electrons becoming trapped for the first time in a metal called Pd₅AlI₂.

Insider Brief Sparrow Quantum has appointed founder Peter Lodahl as CEO, succeeding Kurt Stokbro, who will remain involved as an executive advisor and board member. The company plans to focus on integrating, controlling and connecting its photonic quantum chip technology into larger computing systems designed for fault-tolerant quantum computing. Sparrow has strengthened its leadership team with new commercial and financial appointments and established a Scientific Advisory Board to guide its technical roadmap. PRESS RELEASE — Sparrow Quantum today announced that its founder and former Chief Quantum Officer, Professor Peter Lodahl, has been appointed Chief Executive Officer as part of a planned leadership transition. He succeeds Kurt Stokbro, an early investor who led the company’s development into a growing commercial quantum technology scale-up. Kurt will remain closely involved as Executive Advisor and member of the board. The appointment completes a strengthening of Sparrow Quantum ’s leadership team that began in May, when former Danish Tech Ambassador Anne-Marie Engtoft Meldgaard joined as Chief Commercial Officer. The company has also established a new Scientific Advisory Board to provide external guidance on its technical roadmap. Having developed and delivered its quantum photonic chip technology, Sparrow Quantum will now focus on the integration, control, and connection of reliable quantum light within larger computing systems. Peter Lodahl is uniquely positioned to lead that work. As a world-leading expert in photonic quantum technology, his research has been instrumental in establishing Sparrow’s position in photonic quantum hardware. Since the company spun out of the Niels Bohr Institute at the University of Copenhagen, it has built world-leading capabilities, an ambitious team, and growing engagement from customers and partners. “Kurt has been instrumental in turning Sparrow ’s scientific foundations into a growing technology company. He he

Insider Brief SEEQC reported simulation results showing that combining its chip-based pre-decoder with NVIDIA Ising reduced quantum error-correction decoding time and logical error rates by approximately 50% compared with using Ising alone. The architecture places specialized processing closer to the quantum processor to reduce data transfers and support faster communication with GPU-based computing systems. SEEQC plans to integrate the demonstrated components into a quantum processor connected to high-performance computing infrastructure and evaluate further improvements in error correction and scalability. PRESS RELEASE — –   SEEQC , Inc. (“SEEQC” or the “Company”),a chip-based quantum computing company, today announced results demonstrating significant performance improvements in quantum error correction decoding through a digital interface optimized multi-stage decoding architecture combining SEEQC’s chip-based pre-decoder technology with the NVIDIA Ising open family of AI models . SEEQC’s chip-based pre-decoder was integrated in a simulated quantum processor and architecture stack incorporating realistic decoder latency at scale, as a backend to NVIDIA Ising Decoding with SEEQC Digital Link and NVIDIA NVQLink providing the framework for low-latency communication between quantum and GPU-accelerated compute environments. Compared with operating NVIDIA Ising as a standalone pre-decoder, the combined multi-stage pre-decoder architecture demonstrated an approximately 50% reduction in decoding latency and logical error rate performance, the two key metrics that dictate the scalability of a fault tolerant quantum system. The overheads associated with error correction are enormous and can increase exponentially as systems scale towards useful computation. Therefore, a 50% improvement in these key scaling bottleneck metrics have a significant impact on the overall scalability and efficiency of a quantum processor. The results demonstrate how specialized proce

Insider Brief Ericsson Canada and École de technologie supérieure (ÉTS) have launched a Mitacs-supported research project to develop quantum computing methods for improving telecom network operations. The research team will investigate variational quantum algorithms, focusing on error mitigation and optimization through experiments using quantum hardware and simulations. The project is the second Mitacs-funded academic collaboration under Ericsson Canada’s Montreal Quantum Research Hub, which supports quantum research and talent development in Quebec. PRESS RELEASE — Ericsson Canada and École de technologie supérieure (ÉTS) have teamed up to further quantum computing research in Quebec, one of the country’s primary quantum computing centres. With support from the Mitacs Accelerate program, the project aims to develop better quantum computing methods that will help run and manage telecom networks more efficiently, while also training students and researchers in cutting-edge quantum technology that supports Canada’s leadership in this field. “Quantum computing will unlock new ways to make telecommunications networks more efficient, and Canada is well positioned to lead that work,” says Nishant Grover, President, Ericsson Canada. “Through our Montreal Quantum Research Hub and our partnership with ÉTS, supported by Mitacs Accelerate, we’re bringing together world-class research and industry expertise to advance practical quantum methods for telecom network operations.” The Honourable Mélanie Joly, Minister of Industry and Minister responsible for Canada Economic Development for Quebec Regions, says: “Quantum technologies will shape the course of our future and Canada is a world leader in this emerging technology space. As a long-trusted partner in Canada’s technology ecosystem for more than 70 years, we were encouraged by the establishment of Ericsson Canada’s Quantum hub in Montreal, and we welcome this new partnership which will further strengthen Canada’s

Insider Brief Symmatrics has appointed Andrew Hallman, a former senior CIA and ODNI official who now works at Leidos, to its Strategic Advisory Board. Hallman brings more than 30 years of intelligence and security experience, including serving as Deputy Director of the CIA for Digital Innovation and performing the duties of Principal Deputy Director of National Intelligence. Symmatrics is developing cybersecurity products based on One-Time Pad Symmetric Key (OTPSK) encryption, which the company says are designed to protect data and communications against AI-driven and quantum-related threats. PRESS RELEASE — Symmatrics , the cybersecurity company pioneering one-time pad encryption at internet scale and building the new trust layer for the AI and post-quantum era, today announced the appointment of Andrew Hallman to its Strategic Advisory Board. Hallman joins the company as organizations across government, defense, and critical infrastructure sectors face escalating cybersecurity risks driven by artificial intelligence and the emergence of quantum computing. A respected national security leader, Hallman  brings more than three decades of intelligence and security experience, including senior leadership roles at both the Central Intelligence Agency (CIA) and the Office of the Director of National Intelligence (ODNI).  He is currently Vice President and Strategic Account Executive for the Intelligence Community at Leidos, Inc. “Andrew’s experience leading the nation’s most critical intelligence and security initiatives makes him a valuable addition to our advisory board,” said Walter Raquet, Chairman and CEO of Symmatrics . “As AI accelerates cyber threats and quantum computing challenges traditional encryption, Andrew’s perspective will help guide our efforts to develop technologies protecting governments, enterprises, and critical infrastructure from the next generation of cyber risks.” From 2019-2020, Hallman

Join us online on October 22 as Quantum Beach 2026 brings researchers, entrepreneurs, investors and industry leaders to the Palm Beach County Convention Center in West Palm Beach, Florida. Explore the ideas, investments and partnerships shaping the quantum economy, from advances in quantum computing to the practical work of building businesses, preparing a skilled workforce and developing the infrastructure needed to support growth. With a focus on Florida and connections across the wider quantum community, Quantum Beach examines what it takes to move quantum technology from research toward commercial use. Watch the livestream below to follow the conversation and hear perspectives on the opportunities and challenges ahead.

Insider Brief RhymeQ raised $2.2 million in pre-seed funding to develop software designed to let Python developers program quantum computers. Its Rhyme compiler translates conventional code for multiple quantum processors and NVIDIA CUDA-Q, supporting both quantum simulators and hardware. The funding will support engineering hires, enterprise platform development, hardware partnerships and expansion of its developer community. RhymeQ, a startup making quantum computers accessible to software developers across the world, has raised a $2.2 million pre-seed round led by Ground State Ventures , with participation from Vanagon Ventures, Plug and Play , and Freiraum Ventures. Quantum computers promise to solve significant problems and expand the reach of supercomputing and AI, for instance in chemicals, pharmaceuticals, finance, or manufacturing. However, coding for a quantum computer currently requires a PhD in quantum physics. Relatively few people globally are currently capable of that.  RhymeQ has developed Rhyme, a new abstraction layer that allows every developer with basic Python skills to code for quantum. The actual coding is familiar and conventional, while the company’s compilers handle the translation for quantum computers. What’s more, it’s compatible across multiple quantum processors, with no hardware lock-in. “We are on a mission to make quantum computers programmable by every developer on the planet,” says RhymeQ founder and CEO Daniel Volz. “While vibe coding is taking over the classical programming world, the situation is not so simple in the quantum world. Quantum circuits can only be debugged by PhD-level physicists. With Rhyme, any programmer can both develop and debug production-ready code to run on quantum computers at enterprise level.” Volz previously led quantum computing initiatives for McKinsey and BASF and co-founded quantum startup Kipu Quantum. He co-founded RhymeQ in 2026 with CTO Tamás Varga and COO Christina Wu. Varga, the inventor

Unlike classical physics, quantum mechanics generally cannot tell us exactly what will happen in an individual event. Instead, it predicts the probabilities of different outcomes. As one of the theory's early pioneers, Erwin Schrödinger played a key role in debates about what this randomness really means. However, part of his contribution has stayed hidden for more than 80 years.

Determining the steady state of an open quantum system is crucial for characterizing quantum devices and studying various physical phenomena. Often, computing a single steady state is insufficient, and it is necessary to explore its dependence on multiple external parameters. In such cases, calculating the steady state independently for each combination of parameters quickly becomes intractable. Perturbation theory (PT) can mitigate this challenge by expanding steady states around reference parameters, minimizing redundant computations across neighboring parameter values. However, PT has two significant limitations: it relies on the pseudo-inverse – a numerically costly operation – and has a limited radius of convergence. In this work, we remove both of these roadblocks. First, we introduce a variational perturbation theory (VPT) and its multipoint generalization that significantly extends the radius of convergence even in the presence of non-analytic effects such as dissipative phase transitions. Then, we develop two numerical strategies that eliminate the need to compute pseudo-inverses. The first relies on a single LU decomposition to efficiently construct the steady state within the convergence region, while the second reformulates VPT as a Krylov space recycling problem and uses preconditioned iterative methods. We benchmark these approaches across various models, demonstrating their broad applicability and significant improvements over standard PT.

We present a symmetry-enabled direct quantum protocol for computing many-body Green's functions, a central tool for studying strongly correlated quantum systems. Our protocol relies only on native time evolution and straightforward measurements available on current hardware platforms. By exploiting parity symmetry—satisfied by a broad class of Hamiltonians in condensed matter physics and quantum chemistry, including the Fermi–Hubbard and Heisenberg models—we introduce a tailored quench spectroscopy scheme that recovers both the real and imaginary parts of two-point time correlators, from which Green's functions can be reconstructed via efficient classical signal processing. We further develop a tailored symmetric quantum Gibbs sampler that prepares parity-resolved (symmetric and antisymmetric) thermal states, enabling finite-temperature extensions within the same framework. Finally, we show that the same symmetry-based measurement primitive extends naturally to out-of-time-ordered correlators (OTOCs). Our results provide a practical route to estimating symmetry-resolved dynamical correlators on near-term and early fault-tolerant quantum hardware.

Mean-field Hartree theory is a central tool for reducing many-body dynamics to an effective one-particle evolution. This approximation has been employed when the Hamiltonian governing the many-body dynamics is not Hermitian. Indeed, non-Hermitian Hamiltonians model particle gain/loss or the evolution of open quantum systems between consecutive quantum jumps. Furthermore, the validity of the Hartree approximation for generic non-Hermitian Hamiltonians lies at the basis of a quantum algorithm for nonlinear differential equations. In this work, we show that this approximation can fail.First, we consider the most general bosonic mean-field Hamiltonian with two-body interactions and we prove that, for non-Hermitian Hamiltonian, the Hartree equation does not capture the correct second time derivative of the one-particle marginal state at t = 0 in the thermodynamic limit. Then, we analytically solve a model of N bosonic qubits with a purely anti-Hermitian Hamiltonian, compute the limit for N → ∞ of the one-particle marginal state and show that it does not agree with the solution of the non-Hermitian Hartree equation. We further show that there exists an initial condition such that the exact one-particle marginal state undergoes a finite-time transition to a mixed state, a phenomenon that is completely absent in the case of Hermitian Hamiltonians. Finally, we simulate a non-Hermitian Hamiltonian with real spectrum and show that, also in this case, there are initial conditions for which the Hartree equation does not reproduce the correct one-particle marginal state in the limit N → ∞ .Our findings challenge the validity of the mean-field Hartree approximation for non-Hermitian Hamiltonians, and call for additional conditions for the validity of the mean-field regime to model the dynamics of particle gain and loss and the open-system dynamics in bosonic many-body systems.

In this work, we examine the consequences of the existence of a finite group of matrix product unitary (MPU) symmetries for matrix product states (MPS). We generalize the well-understood picture of onsite unitary symmetries, which give rise to virtual symmetry defects given by insertions of operators in the bonds of the MPS. In the MPU case, we can define analogous defect tensors, this time sitting on lattice sites, that can be created, moved, and fused by local unitary operators. We leverage this formalism to study the gauging of MPU symmetries. We introduce a condition, block independence, under which we can gauge the symmetries by promoting the symmetry defects to gauge degrees of freedom, yielding an MPS of the same bond dimension that supports a local version of the symmetry given by commuting gauge constraints. Whenever block independence does not hold (which happens, in particular, whenever the symmetry representation is anomalous), a modification of our method which we call state-level gauging still gives rise to a locally symmetric MPS by promotion of the symmetry defects, at the expense of producing gauge constraints that do not commute on different sites.

We construct an important missing piece in the entanglement theory of pure three-qubit states, which is a polynomial measure of W-entanglement. This works in parallel to the three-tangle, which is a polynomial measure of GHZ-entanglement, and to the bipartite concurrence, which is a polynomial measure of bipartite entanglement. We also show that these entanglement measures are ordered, the bipartite measure is larger than the W measure, which is larger than the GHZ measure. It is meaningful then to consider these three types of three-qubit entanglement, which are also ordered, bipartite is weaker than W, which is weaker than GHZ, in parallel to the order of the three kinds of equivalence classes of entangled three-qubit states.

We show that, for sudden quenches, the work distribution reduces to the statistics of the traces of powers of Haar unitaries, which are random unitary matrices drawn uniformly from the unitary group. For translation-invariant quadratic fermionic chains with interactions extending to m neighbors and periodic boundary conditions, the Loschmidt amplitude admits a unitary matrix model / Toeplitz representation, which yields a work variable of the form W = ∑ r ≤ m a r ℜ Tr ⁡ U r (and in models with pairing terms -superconducting pairing- additional b r ℑ Tr ⁡ U r terms appear). By invoking multivariate central limit theorems for vectors of traces of unitaries, we obtain a Gaussian distribution for P ( W ) with variance V a r ( W ) = 1 2 ∑ r r ( a r 2 + b r 2 ) and asymptotic independence across different powers. We also characterise the conditions under which non-Gaussian tails arise, for example from many interaction terms or their slow decay, as well as the appearance of Fisher-Hartwig singularities. We illustrate these mechanisms in the XY chain. Various numerical diagnostics support the analytical results.

Abstract Quantum batteries are quantum systems that store energy and deliver it on demand, and their practical value hinges on how fast they can be charged. While collective charging protocols and global control are known to enhance charging power, it remains unclear how the battery’s internal interaction architecture itself constrains performance. Here we study interacting fermionic batteries whose internal couplings are encoded by a graph adjacency matrix and which are charged through a uniform interaction with an external fermionic device. We prove that the star topology uniquely maximizes the initial slope of the charging power at zero local field. At finite field, we derive an exact spectral criterion for outperforming the star and construct a star-like family that satisfies it. Based on numerically established correlation, we expect these findings to extend to the maximal average charging power as well. To confirm the dominance of the star architecture, we complement the analysis by an exhaustive sweep over all connected graphs with N ≤ 7 vertices, and by larger
random-graph benchmarks.

We examine the conditions under which quantum parameter estimation is compatible with the concept of a ``true'' quantity value: a unique value of the estimated quantity that exists prior to and independently of measurement. While quantum parameter estimation typically assumes that the quantity to be estimated is a parameter, we argue that this assumption can be lifted, opening the way to a more general formulation of estimation that may apply even in situations where the quantity to be estimated is no longer a parameter, but instead a quantum variable susceptible to quantum fluctuations. We identify three assumptions that characterize the way estimation is often presented in the quantum metrology literature, namely, as a procedure for inferring an unknown ``true value", which is assumed to be unique and to exist prior to and independently of measurement. Using our more general framework, we prove a no-go theorem showing that the preceding assumptions are jointly incompatible with two further assumptions: the completeness of the quantum state (no `hidden variables'), and the presence of entanglement between the probe systems and the system under measurement. We note that the presence of such entanglement is a generic prediction of standard quantum theory. Consequently, if one is not willing to accept hidden variables, nor willing to modify standard quantum theory by introducing a new physical mechanism that destroys entanglement at some scale or regime, then a realist account of estimation is ultimately impossible.

We develop an end-to-end framework for assessing a quantum-computing application in industrial materials science: the screening of strongly correlated oxygen-electrode materials for SOFCs and SOECs. We formulate the materials problem in terms of interface observables including oxygen-vacancy formation energies, vacancy migration barriers, and electronic conductivity. We describe how these observables can be obtained using a diagrammatic GW-based embedding, either GW+DMFT or self-energy embedding theory (SEET), applied to a DFT-screened shortlist. The atomistic electrode/electrolyte interface defines the electronic structure problem from which the correlated impurity models are constructed. Quantum impurity solvers would provide the finite-temperature impurity Green's functions required by the embedding. The computational challenges that classical solvers may encounter as the interacting active space grows, together with the polynomial scaling of quantum Hamiltonian simulation for efficiently represented discretized models, open an opportunity for quantum advantage. We identify the benchmarks needed to assess this opportunity through convergence of vacancy and migration energetics and comparison with the best applicable classical solvers. We provide illustrative logical qubit counts and identify the thermal state preparation, simulation, measurement, and repeated-solve costs needed for a complete resource assessment. We connect microscopic observables to macroscopic engineering metrics using a continuum model for mixed ionic--electronic conducting oxygen electrodes that couples oxygen surface exchange, solid-state oxygen transport, electrode microstructure, and finite electrode thickness. Finally, we estimate the potential worldwide business value of improved electrode materials under SOFC and SOEC deployment scenarios informed by public technical targets and electrolyser deployment data.

Pure-state deep thermalization predicts that, after sufficient scrambling, projected ensembles approach universal distributions that contain information beyond the reduced density matrix. In realistic quantum systems, however, noise is unavoidable and the projected states are generally mixed. Whether mixed-state deep thermalization admits an analogous universal limiting distribution has remained unclear. Here we answer this question for quantum dynamics containing local quantum channels, i.e., errors. We show that the late-time mixed-state projected ensemble is completely determined by the normalized Choi state of the error channel and is universal, independent of the microscopic details of the underlying unitary dynamics. We establish this result analytically for dual-unitary circuits, global Haar-random dynamics, and local Haar-random circuits at large local dimension, and verify it numerically in qubit circuits and kicked Ising dynamics. In a solvable setting, we further find exponentially fast convergence to the limiting ensemble. Our results extend deep thermalization to noisy quantum dynamics and establish a direct correspondence between quantum errors and universal random mixed-state ensembles.

We propose a new method for proving $L^2$ and modified logarithmic Sobolev inequalities with constants independent of system size for quantum Gibbs samplers whose Lindblad generators satisfy Kubo-Martin-Schwinger (KMS) detailed balance. We first establish the $L^2$ logarithmic Sobolev inequality by transporting it along a temperature-dependent path from the infinite-temperature product state to the target Gibbs state while maintaining a size-independent decay rate for the sandwiched Rényi-2 divergence. A tensor-power argument, combined with the quantum asymptotic equipartition property, then transfers this decay bound to relative entropy, yielding the modified logarithmic Sobolev inequality. This approach provides a general framework for proving size-independent logarithmic Sobolev inequalities for quantum Gibbs samplers. We apply it to two regimes: one-dimensional quantum spin chains at every finite temperature, and finite-range quantum spin systems at sufficiently high temperature in any fixed dimension.

Tensor-network simulation of quantum circuits depends on contraction orders with low computational cost and small intermediate tensors, found without excessive planning time. We present ArcTN, a contraction-order optimization framework with two search presets. Light keeps planning overhead low, and Heavy spends more effort on refinement. Both combine randomized-greedy construction, subtree reconfiguration, and parallel tempering with stage-specific stopping rules. ArcTN also provides Fixed and Dynamic slicing to meet tensor-size limits and executes the returned orders. On the 30 QC32 quantum-circuit networks completed by all eight compared configurations, Light reduces FLOPs by 61.32% and plans 1.62$\times$ faster than Cotengra Auto/CMA-ES, and Heavy reduces FLOPs by 43.83% and plans 7.21$\times$ faster than Cotengra AutoHQ/Optuna. Heavy also needs 11.85% fewer FLOPs than OMECO TreeSA-8 and plans 1.33$\times$ faster. Dynamic slicing meets the size limits in all 90 runs on 18 scalar-output networks and reduces total sliced FLOPs by 31.99% relative to Fixed slicing, at the cost of longer planning. With a common NumPy executor, Heavy has the lowest combined planning and execution time among five configurations on the runs that all of them completed. On 672 networks built from 320 MQT Bench circuits, Heavy obtains the lowest geometric-mean FLOPs on the 142 large networks while planning 3.1$\times$ and 31$\times$ faster than Cotengra AutoHQ and Hyper128.

Randomised quantum simulation algorithms such as qDRIFT reduce circuit depth by replacing deterministic product formulas with stochastic compilations, but achieving high accuracy can require many steps. In vanilla qDRIFT, Hamiltonian terms are sampled with probabilities proportional to their coefficient magnitudes. We propose StateDRIFT, a variant of qDRIFT which optimises its sampling distribution to estimate time-evolved quantities using knowledge of the initial state and target observable, with a provable truncation bound that keeps qDRIFT's guarantees. The distribution at each depth is chosen by solving an optimisation problem targeting bias and/or variance. StateDRIFT can significantly reduce the bias and variance of estimators, and hence circuit depth, which we test on short-time dynamics of lattice models and molecules under Jordan-Wigner up to 18 qubits. For example, with BeH2 StateDRIFT can reduce the number of two-qubit gates required to achieve a given accuracy from 11,201 to 983. StateDRIFT involves measuring observables and commutators on the initial state, so we propose two practical ways to estimate these: classical surrogates such as tensor networks, and classical shadows, which recover most or all of the saving from exact oracles in the systems tested.

Metallo-DNA nanowires serve as a versatile, programmable scaffold for molecular-scale electronics. In this work, we demonstrate that periodic heavy-metal coordination fundamentally reshapes the electronic landscape of DNA, generating dispersive, metal-centered conduction bands rather than isolated localized states. Driven by enhanced inter-layer coupling, where second nearest-neighbor hopping plays a crucial role: the conduction bandwidth can approach 1 eV, more than double that of canonical DNA. These broad bands suggest enhanced robustness of transport against structural fluctuations. As a result of relativistic effects, in these quasi-one-dimensional materials, spin-orbit (SO) coupling enhances band dispersion and governs spin-dependent transport. We predict that although ligand hybridization reduces atomic SO splitting, the effective SO splitting in these nanowires is comparable to the next-nearest-neighbor hopping strength, which results in considerable spin mixing. We find that Hg2+-coordinated nanowire exhibit pronounced spin-flip conductance comparable to spin-conserving conductance across the LUMO manifold. This efficient spin conversion remains robust over extended molecular lengths and is accompanied by a set of highly delocalized unoccupied states with oscillating nodal structures, readily accessible under low-bias transport measurements. In contrast, the Ag+-coordinated nanowires exhibit weak spin-flip scattering that is more than an order of magnitude smaller than spin-preserving transport. This duality establishes the choice of coordination metal as a decisive parameter to govern metal-metal interaction, electron delocalization, and spin-dependent transport. Overall, our findings demonstrate how relativistic effects and quantum confinement intersect in these bio-templated, quasi-one-dimensional molecular conductors.

How much entanglement can two distant laboratories share when their connection is noisy? We relate this question to deciding which of two quantum hypotheses is present. Our one-shot bounds apply to entanglement generation over a quantum channel and to one-way entanglement distillation from a shared state. We use Cheng's trace inequality to bound the infidelity of a Petz decoder in terms of a binary hypothesis testing cost. Applying the inequality before averaging over codes reduces the error analysis to computing a second moment of random subspaces. The proof covers every integer target dimension and treats rank-deficient states explicitly. A corollary expresses the achievable entanglement through hypothesis-testing coherent information, with a single logarithmic error slack and exact integer rounding. We also prove an error-preserving conversion from entanglement generation codes to entanglement transmission codes: the target dimension decreases by only a constant factor at fixed error, and the decoder is the original decoder followed by local processing. Consequently, for both entanglement generation and entanglement transmission, arbitrary pure reference-input states yield the same coherent-information rate, second-order Gaussian correction at the original error tolerance, and explicit achievable logarithmic remainder. For commuting testing hypotheses, the logarithmic remainder improves to a constant. These results give a direct route from binary distinguishability to explicit recovery guarantees and finite-resource quantum communication rates.

Randomized benchmarking (RB) returns a single decay parameter or gate error rate, but when the noise is gate-dependent that parameter is notoriously difficult to interpret. We study RB and related random-circuit benchmarks under small gate-local Markovian noise by factorizing each noisy gate into its ideal action followed by the exponential of a small error generator and then perturbing the RB $\mathscr{L}$ matrix, which models the RB decay. For any low-error gate set that satisfies the requirements of RB (it is a sequence-asymptotic unitary 2-design), we show that Pauli-stochastic error rates contribute linearly to the RB decay parameter, while Hamiltonian error rates contribute through a gauge-invariant quadratic form. Pauli-correlation and active generators are absent from the linear term and enter only at higher order. For the single-qubit native gate set $\{X_{π/2},Y_{π/2}\}$ we derive this quadratic form explicitly in terms of three first-order gauge-invariant (FOGI) coordinates: the two intrinsic over-rotations and one relational axis-tilt error. The resulting formula explains the dependence of DRB on the sampling distribution and the compilation dependence of CRB. These results turn RB decay rates into interpretable functions of experimentally meaningful elementary error rates.

Mechanically compliant mirrors are key components in cavity optomechanics. However, the requirements to achieve the best optical and mechanical performance are usually in direct competition. A high reflectivity for tightly focused beams entails thick reflectors, whereas ultracoherent flexural nanomechanics necessitates thin membranes. We eliminate this trade-off by introducing high-refractive-index nanopillar metasurfaces on top of a thin membrane. We pattern a 50 micrometer-diameter array of nanopillars to form a photonic crystal. The flat band behavior of guided resonances in the photonic crystal enables a reflectivity of 99.82(1)% for a tightly focused beam of 7 micrometer waist. The combination of two guided resonances creates a 100 nanometer-wide high-reflectivity band around 1550 nanometer. Simultaneously, the nanopillar patterning realizes a density-modulated phononic crystal that isolates an ultracoherent localized mechanical mode with a $Q\cdot f$-product of $2\cdot 10^{14}$Hz. The demonstrated nanopillar metasurfaces enable lightweight mirrors for room-temperature quantum optomechanics and for use as levitated mirrors or lightsails.

Quantum error-correcting code (QECC) implementations are hybrid software-control systems: measured syndromes drive decoder dispatch, recovery actions, and logical checks. Existing QECC verification techniques can prove formal obligations, and general quantum testing can expose final failures, but developers still lack a scalable testing workflow that generates concrete faults and explains where a QECC repair path first diverges. This paper presents ConQEC, to our knowledge the first concolic testing framework for QECC implementations. By combining concrete (Pauli) fault replay with symbolic repair-path constraints, ConQEC generates tests that expose not only final logical failures but also fault--syndrome--decoder--recovery (FSDR) diagnostics: the injected fault, observed syndrome, decoder decision, recovery action, oracle result, and earliest divergent stage. Its symbolic encoding of Pauli faults, syndrome predicates, decoder and recovery relations, and oracle checks enables this diagnostic workflow to scale beyond exponentially increasing amplitude-level quantum-state reasoning. We implemented ConQEC and evaluated it on generated source-level QECC families and public QECC artifacts with up to thousands of qubits. ConQEC detects the seeded bug in every experimental case and reports a replay-valid, fault-localizing FSDR witness for each.

We construct a quantum theory of light in nonlinearly responding materials with dispersion and absorption and, in particular, show the emergence of non-Gaussian noise associated with nonlinear absorption processes. Our theory is based on a path-integral formulation of the microscopic Huttner-Barnett model including cubic matter self-interaction required for $χ^{(2)}$ nonlinear processes. We show that the noise polarization emerges naturally from a decoupling of the stochastic weights of the bath response which, in case of cubic self-interactions, leads to a decoupling via Airy functions. As the theory is, by construction, consistent with the nonlinear fluctuation-dissipation theorem, it constitutes a viable quantum theory of light in nonlinear media.

Narrow-linewidth lasers are essential for various key atom-laser interaction processes and optical setups in quantum coherent control, quantum precision measurement, and quantum information science. The Pound-Drever-Hall (PDH) technique is the standard method for the frequency-stabilization of narrow-linewidth lasers, but the inherent time delay in its feedback loop inevitably induces excessive phase noise, commonly known as servo bumps. Previous solutions primarily rely on additional optical components outside the electronic feedback control loop. Here, we propose and implement a generic method based on the Smith predictor to address the time-delay issue entirely within the electronic part of the PDH feedback control loop. We systematically demonstrate its capability to suppress phase noise and reduce servo bumps by adding only a single Field-Programmable Gate Array (FPGA) controller to the loop. This class of methods is demonstrated to be conceptually concise with minimal hardware overhead, effective in practice, and holds potential for a wide variety of future applications.

We investigate the behaviour of Krylov complexity as the number of degrees of freedom of a quantum system increases. Specifically, we show that for tensor products of commuting subsystems, the leading excess complexity is controlled by a weighted variance of the subsystem Lanczos coefficients. This provides a quantitative measure of dynamical heterogeneity and a precise characterization of synchronous evolution. We also show that Krylov entropy is able to disambiguate the information associated with subsystems composition from that generated by dynamical mismatch, and that the same Lanczos variance controls the leading mismatch contribution to both complexity and the entropy. Our results establish excess complexity and Krylov entropy as complementary probes of the emergence of collective dynamics in large quantum systems.

Amplitude encoding stores an N-degree-of-freedom structural mode using ceiling(log2 N) qubits. This article develops an evaluation framework for variational quantum eigensolvers in finite-element structural dynamics. A Cholesky transformation maps the generalized eigenproblem to a symmetric mass-orthonormal Hamiltonian, ensuring Euclidean quantum-state orthogonality equals structural mass orthogonality. For higher modes, the deflation penalty condition is sharpened to a necessary-and-sufficient threshold, with a Davis-Kahan bound quantifying effects of approximate projectors. Numerical studies separate mapping correctness, ansatz expressibility, preprocessing, Pauli growth, finite-shot uncertainty, and damage localization. For 128-DOF chains, consistent-mass whitening increases transformed-operator density from 0.023 to 0.308 and Pauli terms from 576 to 2950. Exact state-vector experiments show qubit count and circuit expressibility are distinct. At 10^5 shots per Pauli term, first-mode frequency RMS error is 2.45%. In an oracle-state study, 10% stiffness loss is localized in 84.5% of trials. Results sharpen the deflation condition, quantify resource bottlenecks, and claim no speedup.

An internal electronic coherence changes electrical transport only when it feeds back on the physical current. We develop a reduced description of this feedback and distinguish its exact consequences from the assumptions required for a microscopic realization. An opposite-parity two-orbital Hamiltonian identifies a current-coupled orbital force. Under an explicitly stated moment closure and collision ansatz, it yields a passive three-state response with an exponentially damped oscillatory memory. The resulting conductivity redistributes a fixed optical weight and predicts a nonmonotonic dependence of dc conduction on coherence damping at fixed remaining parameters. The orbital reduction constrains the coupling and internal frequency through a shared bare splitting, providing a test beyond unconstrained spectral fitting. A charge-conserving spatial extension couples to Maxwell equations through a positive energy balance and separates the constitutive response from longitudinal collective and transverse electromagnetic modes. We formulate complex-conductivity and transmission tests, including the limits of parameter identification over a finite bandwidth. The model supplies a conditional connection between orbital dynamics, transport memory, and electromagnetic observables; conductivity alone does not establish a uniquely quantum mechanism, and a material-specific collision calculation and closure-error assessment remain necessary.

We investigate the dynamics of two-level systems using the quasidistribution $Q$ function projected onto the space of collective measurements. Particular attention is given to evolution under Hamiltonians that are invariant under particle permutations, for pure states that are either invariant or noninvariant under such permutations. This requires constructing an approximate analog of the star product between quasidistribution functions: the projected $Q$ function of a product of two operators is expressed approximately in terms of the individual operators' $Q$ and $P$ functions. We rewrite the Liouville equation to determine approximate state dynamics and compare the result with exact evolution using the Hellinger distance. Overall, the method performs well for permutation-invariant pure states and Hamiltonians, whereas deviations arise for arbitrary pure states and noninvariant Hamiltonians.

Compiling quantum algorithms for real devices involves hard optimization problems that can decide whether an algorithm runs at scale. We present a general method for solving such problems with AI agents, with every result certified. It builds on autoresearch loops, in which agents iteratively improve programs against a fixed evaluator and which have recently improved quantum cryptanalysis circuits, and adds two elements: a frozen, exact verifier certifies every result, and this verifier, together with the challenge around it, is built by an agent that formulates the problem with a researcher and validates the verifier against a solved case, deliberately broken solutions and published results before any solution exists. The method applies to any optimization problem whose solutions can be verified exactly and efficiently. We apply it to three compilation problems in quantum simulation, namely fermion-to-qubit encoding, Hamiltonian layout and unitary synthesis. In each, the agents improved substantially on published or standard constructions, reducing the cost being optimized by up to 73% at the largest sizes tested and outperforming a state-of-the-art optimizer for fermion-to-qubit encodings. Every submission is a program accompanied by its agent's notes, so the ideas behind each improvement are recorded in human-readable form; later agents built on them, and we describe them here. These results open the way to automated, certified discovery across quantum circuit design and beyond.

We develop and analyze generative models based on quantum solvers of stochastic differential equations. Unlike the common approach based on layered variational quantum circuits with parameterized rotations, we parameterize the potential of a Langevin process. The associated Fokker-Planck (FP) equations are Hermitianized and solved using a linear combination of cosine operators implemented through quantum singular value transformation. By encoding the square root of the stationary density, the model enables sampling through computational-basis measurements and is efficiently controlled by coefficients of the block-encoded diagonal potential. We train the proposed model to match empirical distributions within the family described by FP equations, demonstrating parameter recovery for multivariate probability distributions. Crucially, the model remains trainable at scale. Sample-efficient and convex optimization for in-distribution targets arises from a physics-informed inductive bias and holds regardless of the dimensionality of the problem. We provide circuit constructions and efficient block encodings of the main components of the algorithm and analyze resource requirements. Our approach frames quantum generative learning as quantum model discovery and provides a foundation for extending this framework to high-dimensional, strongly correlated scientific data.

Solid state quantum emitters with electronic spin properties can be entangled using optical interferometric which-path erasure techniques that rely on identical frequencies and linewidths of the emitters. This promises a powerful, fast and scalable platform for quantum technologies. Using current protocols, a pair of emitters embedded in a waveguide interferometer can be deterministically prepared in a maximally entangled state. However, the amount of entanglement diminishes rapidly with increasing separation of the emission lines and variations in the linewidths of the emitters. Solid state emitters such as quantum dots are subject to intrinsic variations in the fabrication process. Therefore, manufacturing the required number of identical emitters on a chip is not scalable. In this Letter, we present a method that uses readily available pairs of entangled photons to entangle solid state emitters with large transition frequency separations and linewidth variations, circumventing the need to fabricate optically identical emitters. We demonstrate a concurrence of C = 0.95 for typical quantum dots using narrowband photon inputs.

We consider finite-dimensional non-Hermitian systems in which all modes coalesce at a single exceptional point. For a rank-one anti-Hermitian contribution, the spectral response strength is computed exactly. For passive systems, we then derive a sharp upper bound at fixed exceptional-point decay rate and show that it is reached only when the decay operator has rank one, corresponding to a single independent dissipative direction. This establishes rank-one loss as the optimal configuration for enhancing the response of a full-order exceptional point. The bound holds for arbitrary order and improves on earlier passive estimates beyond second order. Two third-order trimers illustrate the result: a rank-one-loss system saturates the bound, whereas a passive rank-two-loss realization remains below it. The result turns dissipation into a design resource: concentrating the loss into a single effective dissipative direction maximizes the highest-order spectral response of a passive full-order exceptional-point device.

Projected quantum kernels (PQKs) have emerged as a notable approach to circumvent the hardness of machine learning tasks arising from the exponential dimensionality of the quantum Hilbert space. However, recent PQK studies often rely heavily on extensive classical hyperparameter tuning of the radial basis function (RBF) kernel parameter and the support vector machine regularization parameter. The extensive tuning can mask the true representational power of the underlying PQKs induced by quantum feature maps, which has not been explored in detail. Thus, this work aims to expose the structural capabilities of PQKs by isolating and evaluating their native inductive bias through comparisons between untuned and tuned PQKs against the RBF baseline. Furthermore, we propose novel quantum feature maps that leverage two-qubit entanglement to capture multivariate correlations in IoT data. The results show that extensive tuning can lead to competitive performance architectures, while our proposed entanglement topologies exhibit a significantly stronger native inductive bias. This reveals that superior quantum architectural design can yield structurally better PQKs with improvements arising from quantum-mechanical properties rather than from classical hyperparameter tuning.

Quantum metrology is ultimately shaped not only by measurements, but also by the dissipative dynamics that prepare and maintain the probe. Nevertheless, a general mechanism for enhancing both steady-state and transient precision in open quantum systems has been lacking. Here we show that adding a simple reset channel provides such a mechanism: reset acts as a minimal dissipative control that can enhance metrological precision without modifying the intrinsic Hamiltonian or applying continuous coherent driving. We derive a unified quantum-Fisher-information (QFI) reset-rate response identity, showing how reset enhances steady-state and transient estimation while revealing a sharp transient distinction. For static-parameter estimation in diagonal dynamics, reset leaves the leading short-time QFI unchanged; for the separate task of elapsed-time estimation, it generates an immediate drift contribution that can scale quadratically with the reset rate in the short-time limit. For frequency estimation, the enhancement is instead dominated by a genuinely quantum eigenvector contribution. These results establish reset as a simple dissipative resource for open-system quantum metrology.

The implication of entanglement in quantum battery charging remains poorly understood. In addition, intrinsic quantum randomness poses a fundamental challenge to charging uniformity across distinct trials. To address these issues, we study a three-qubit system within a cascaded collision frame, with two qubits acting as the charger and the third serving as the battery. After each collision, an adaptive measurement is performed on the charger, yielding four conditional post-measurement battery states with identical expected stored energy. For arbitrary fixed charger states, we derive analytical expressions for the recurrence relation of stored energy. We find that stored-energy fluctuations depend on whether the dynamics relies on the battery phase \(γ_n\). For two Bell-like families of entangled states, together with their computational basis states termed Bell-like separable states, the dynamics is \(γ_n\)-independent and fluctuations vanish, whereas for other entangled and separable states, fluctuations emerge. These insights establish a paradigm for engineering charger states to design uniform-charging quantum-battery architectures despite inherent quantum randomness.

Local pure dephasing suppresses single-spin coherence, yet we show that it sustains continuous time-crystalline order in a fully connected ferromagnetic spin-$1/2$ ensemble with local decay. An exact operator identity reveals the mechanism: dephasing raises the interaction energy, while energy relaxation on a finite timescale converts this charging into delayed feedback. Within homogeneous mean-field theory, we prove that dephasing is necessary for periodic motion in this model and that feedback exactly balances transverse damping over each cycle. Beyond mean field, the identity fixes the relative amplitude and phase of energy and longitudinal magnetization in oscillatory Liouvillian modes. Liouvillian spectra and stationary two-time correlations characterize temporal order through decay rates that decrease algebraically with system size, frequencies approaching nonzero mean-field values, and comparable per-spin oscillatory weights. Semiclassical trajectories further reveal recurrent switching between a limit-cycle region and two symmetry-related stationary regions: fluctuations interrupt and reactivate collective oscillations, and oscillatory episodes provide an intermediate channel between stationary regions. These results establish local dephasing as a resource for autonomous collective motion and show how the resulting temporal order can participate in metastable dynamics.

The emergence of entangled quantum optical states in high-harmonic generation raises a fundamental problem about its characterization, namely, \textit{how can entanglement of extreme-ultraviolet radiation be certified for attosecond light fields?} Here, we provide experimentally accessible separability tests, particularly showing that attosecond photoelectron interferometry provides a direct solution to this problem. This is achieved by a quantum optical treatment of mapping photoelectron interferometry to the measurement of optical correlation functions. This yields a negative-partial-transpose witness for infrared-XUV entanglement and a sufficient witness of genuine multipartite entanglement without auxiliary optical measurements. We evaluate both witnesses on explicit optical states and identify how the protocol can be extended to XUV-XUV entanglement certification. Hence, we establish attosecond photoelectron interferometry as a general framework for entanglement certification across a wide range of optical frequencies.

Ultracold quantum gases offer a controllable and microscopically accessible platform for understanding and engineering superfluidity. Yet, realizing a superleak that selectively transports the superfluid while suppressing normal flow has remained elusive. Here, we harness an optical superlattice to realize such a superleak through dynamical selectivity. The superfluid undergoes coherent Josephson transport, whereas the normal component exhibits slow, thermodynamically limited response, resulting in a flow-rate contrast of 500(49). Exploiting this contrast, we demonstrate repeated filtering of the normal component and dynamical purification of the superfluid, while sustaining coherent driven oscillations for up to 100 cycles. Our results establish a controllable atomic superleak and open possibilities for manipulating transport and thermodynamics in quantum fluids.

We propose Quantum Constrained Hamiltonian Descent (QCHD), a continuous-time quantum framework for optimization under smooth equality constraints. The unconstrained counterpart, Quantum Hamiltonian Descent (QHD), minimizes a cost function by simulating the Schrödinger dynamics of a particle in the potential given by the cost function. Applying Dirac's formalism to the classical dynamics with constraints, we construct an intrinsic quantum Hamiltonian with a Laplace--Beltrami operator on the constraint manifold in a kinetic term. Its evolution preserves the constraints exactly without penalty terms and is expected to solve quantum-dynamically the constrained optimization problem. We analyze its relation to Quantum Hamiltonian Descent supplemented by a strong penalty term. For a squared-distance penalty, the effective tangential dynamics acquires an extrinsic-curvature potential and, in nontrivial normal-rotation sectors, a coupling to the normal-bundle connection. These embedding-dependent terms remain in the strong-penalty limit, generally yielding quantum dynamics different from QCHD. Numerical comparisons for circular, elliptical, and two simultaneous constraints show faster optimization and improved concentration near global minima for the initial states and finite penalty strengths considered.

Formulated a hundred years ago, the Bridgman formula for thermal conductivity of liquids postulates a proportionality between sound velocity and thermal conductivity. This designates phonons as heat carriers in a liquid. Its empirical success has been under-appreciated and its conceptual implications overlooked. It is not mentioned in well-known condensed-matter textbook. Here, we review its origin, its links to hydrodynamic Euler equations and to the fundamental paradox surrounding the parabolic heat equation and its fate across the quantum-classical crossover.

Magic-state factories are a major cost of fault-tolerant quantum computing, yet how few noisy inputs they need is known only for restricted protocols. We show that, for tolerating input faults, any stabilizer protocol, however adaptive, postselected or multistage, is no better than a projection onto one stabilizer code, and that for rational targets a fault pattern is harmful exactly when its complement is. Searches over all codes show that quadratic distillation of one T state needs exactly nine inputs and that the eight-input CCZ factory is optimal. At order $d$, one T state needs $n\geq2d$.

With the target of efficiently solving the quantum-mechanical Schrödinger equation on future quantum computers, first- and second-order product formulas for the time-evolution operator are proposed, designed to exploit hierarchies in the operator norms of the individual Hamiltonian components. Inspired by the THRIFT product formula, these decomposition schemes achieve a suppression of the leading error term by a factor of alpha<1 with respect to the standard Lie--Trotter--Suzuki splitting of the same order, where alpha quantifies the norm ratio between the dominant and subdominant parts of the Hamiltonian. Unlike THRIFT, the proposed formulas retain the general product-formula structure, making them applicable to Hamiltonians whose terms act on an arbitrary number of qubits. The advantages of this approach are demonstrated through numerical experiments on engineered two-dimensional spin-1/2 XY model systems and isolated molecules within the double-factorization framework.

Scale-free localization is a distinctive phenomenon in non-Hermitian systems, where specific eigenstates, known as scale-free localized states (LSs), possess localization lengths that scale linearly with the system size. Here, we show that a single non-Hermitian defect in one-dimensional quantum walks (QWs) induces scale-free localization. Driven by non-Hermiticity, the QW system undergoes a pseudo-Hermitian (PH) phase transition and the PH symmetry breaking is accompanied by the emergence of scale-free localization. As non-Hermiticity is further increased, the system undergoes a second phase transition, marked by the emergence of two pairs of bound states. Crucially, we identify the critical points of both transitions using localization properties. Furthermore, we extend our investigation to two-dimensional QWs, where a single non-Hermitian defect also induces scale-free localization, thereby demonstrating the universality of this phenomenon. Our work provides a valuable perspective for further exploring defect physics and a type of novel LS in non-Hermitian quantum systems.

We present an organizing framework for concatenated quantum error correction based on the observation that the syndrome projection of a stabilizer code reshapes the noise channel in a code-determined manner. For any stabilizer code, one level of QEC maps the physical noise to a block-diagonal logical channel whose diagonal Pauli weights are fixed by the code geometry. Coherences between different syndrome classes vanish, and no physical Pauli twirl is required to reach this block-diagonal form. Concatenation can then be viewed as the iteration of the same redistribution step: the dominant logical error after one level selects the code used at the next. We instantiate the framework with the two smallest stabilizer codes, the bit-flip and phase-flip codes, and apply it to amplitude damping. The redistribution rules give the concatenation protocol $C_2(\hatσ_y) C_1(\hatσ_x)$, whose ideal-recovery fidelity scales as $f_l=1-\mathcal O(γ^2)$. Solving the crossover condition $F_l>F_{l-1}$ in the ideal-gate limit yields a critical damping parameter $γ_c\approx0.30$; in terms of the initial channel fidelity, $f=1-1.72755γ^2$. Under the same ideal-recovery assumption, we compare the overall gate accuracy rate with that of the five-qubit code. The scope of the framework, in particular for coherent and correlated noise, is stated explicitly.

This oral history interview provides Yakir Aharonov's personal and conceptual recollections from the 1950s to the 2000s, focusing on his academic trajectory, some of his major contributions to quantum foundations, and his perspective on the development of the field. The interview traces Aharonov's academic career through the Technion, University of Bristol, Brandeis University, Yeshiva University, University of South Carolina, Tel Aviv University, George Mason University, and Chapman University. The interview also traces the development of Aharonov's work and collaborations on the EPR paradox, time-energy uncertainty relations, quantum measurement theory, quantum frames of reference, the two-state vector formalism, weak values, protective measurements, and several other contributions. It includes recollections of meetings and discussions with David Bohm, Niels Bohr, John Clauser, Paul Dirac, Rudolf Peierls, Aage Petersen, and Abner Shimony. Also mentioned: David Albert, Jeeva Anandan, Peter Bergmann, Gideon Carmi, Avshalom Elitzur, Dave Finkelstein, Vladimir Fock, Itzhak Kalugai, Ed Lerner, Joel Lebowitz, Stanley Mandelstam, Yuval Ne'eman, Sandu Popescu, Maurice Pryce, Daniel Rohrlich, Nathan Rosen, Joseph Safko, Paul Singer, Daniele Struppa, Leonard Susskind, Lev Vaidman, Chien-Shiung Wu.

We demonstrate a monolithic telecom C-band single-photon platform based on low-density InAs/InP quantum dots grown on an InGaAsP/InP distributed Bragg reflector, with simulated upward light-extraction efficiency exceeding 10% within the 40 nm spectral band. Enhanced light extraction is crucial for wide-field photoluminescence imaging, enabling approximately 3 nm statistical centroid-localization precision of QD emitters due to improved signal-to-noise ratio. The identified charged exciton emitting at 1549.5 nm exhibits single-photon emission purity up to 94.7%, validated by a raw peak-area integration under pulsed quasi-resonant excitation. Under these conditions, photons emitted sequentially from the unprocessed planar structure reveal a raw two-photon interference visibility of 51% of the photon wave packet within the 2 ns time window and 41% over a 4 ns integration window, all without Purcell enhancement typical for cavity-embedded emitters. Combining broadband extraction, high photon coherence, and emitter preselection on a native III-V wafer, this architecture paves the way for marker-based deterministic fabrication of high-quality monolithic nanophotonic devices.

We first prove a sharp Lieb-Thirring inequality with semi-classical constant and gradient correction in one dimension. In the periodic setting, the corresponding inequality also includes a parity dependent shell-correction term, which appears to be new. Moreover, we also characterize the optimizers of these inequalities. In particular, the optimizing density profiles form a two-dimensional manifold, which we call here the Poincaré density manifold. We then apply these results to study the Thomas--Fermi--von Weizsäcker (TFW) approximation of the kinetic energy in Density Functional Theory. More precisely, we first obtain an explicit and non-asymptotic bound on the global and local error made by the TFW approximation. These bounds are controlled by the distance of the normalized density profile from the Poincaré density manifold times the number of particles. In particular, these bounds show that the TFW approximation is exact on the Poincaré manifold. We then show that, in the periodic setting, the distance between the Kohn-Sham potential and the inverse TFW potential in the natural dual Sobolev space can also be controlled by explicit density dependent constants times the distance to the Poincaré manifold. As a corollary, we prove that for a fixed density profile, the Kohn-Sham potential converges towards the inverse Thomas--Fermi potential in the high-density limit $N \rightarrow \infty$ with asymptotic rate of order $N^{-2}$. This rate is shown to be optimal.

Millimeter-wave and terahertz technologies offer new opportunities for high-capacity communications, sensing, and quantum systems, but electronic signal chains above 100 GHz are limited by weak sources, noisy receivers, and lossy interconnects. Photonic approaches mitigate these constraints by enabling chip-scale high-frequency components, yet existing implementations generally retain lossy off-chip electrical or free-space links, hindering dense and compact integration for cryogenic or space-constrained settings. Here, we show a monolithic lithium tantalate photonic chip, termed a signal core, which generates, modulates, routes, and detects continuous-wave signals at discrete frequencies between 100 GHz and 2.5 THz. The architecture integrates high-frequency functional modules on chip and uses exclusively fiber-based optical interfaces. Bidirectional coherent electro-optic conversion enables signal generation, detection, and nanosecond-scale amplitude and phase modulation, while micro-coplanar striplines interconnect the modules into an end-to-end signal chain on a single chip. Our modules achieve single-photon electro-optic coupling rates of g_0/2π=10 kHz and peak drive-power-normalized photon-flux conversion efficiencies of 1.0%/mW for generation and 0.5%/mW for detection. It also operates at 4 K in a dilution refrigerator through the same fiber-only optical links. Together, these capabilities establish an all-photonic platform for millimeter-wave-to-terahertz systems and offer a broadly applicable architecture for applications constrained by electrical-interconnect loss, heat load, and footprint.

The rate operator quantum jumps (ROQJ) is a general method to unravel a master equation describing the dynamics of an open quantum system into stochastic pure state trajectories. By post-selecting on no jumps occurring, one obtains a trajectory generated by a non-Hermitian Hamiltonian. The ROQJ allows for versatile modification of this non-Hermitian evolution, with each non-Hermitian Hamiltonian corresponding to a different continuous measurement scheme. We apply the ROQJ to modify the non-Hermitian dynamics of the open three-particle Bose-Hubbard dimer model under environmental non-local dephasing to construct a $PT$-symmetric non-Hermitian Hamiltonians with a general two parameter $PT$-symmetric imaginary diagonal part, which generalizes the well-known gain-loss Bose-Hubbard dimer. We characterize the symmetry structure of the spectrum for different on-site interaction strengths. For vanishing on-site interaction, we find the unbroken $PT$-symmetry region enclosed by order two exceptional lines of different character and four order four exceptional points, two of which are not found in the usual gain-loss Bose-Hubbard dimer. Additionally, we find regions with degenerate imaginary parts of the eigenvalues, also not found in the gain-loss Bose-Hubbard dimer. In this parameter space, we use time-dependent rate operator transformations to investigate state transfer under slowly varying parameter loops. Loops encircling an order four exceptional point exhibit chiral state transfer. Because the loops cross exceptional lines, the final states are superpositions of eigenstates. Chiral state transfer is also found with non-zero homogeneous on-site interaction when the loop crosses over broken $PT$-symmetry regions of different character. Using inhomogeneous on-site interactions, we find direction dependent state transfer between eigenstates without crossing or encircling exceptional points.

Port-based teleportation (PBT) is a variant of quantum teleportation that does not require corrections on the teleported state: starting with $N$ shared EPR states, Alice can teleport a qudit to Bob by performing a measurement on her system and informing Bob which of his $N$ `ports' to retrieve the state, up to infidelity decaying with $N$. Existing quantum circuits of PBT rely on representation theory tools and the mixed Schur transform. In this note, we report an elementary efficient circuit for PBT, which has depth $\operatorname{polylog}(N,d)$. As a corollary, this gives a simple proof that all $n$-qubit unitaries can be parallelized to $\operatorname{poly}(n)$ depth, recovering a recent result due to Nehoran--Slote--Yuen and OpenAI.

Lattice-surgery compilation places logical qubits on a grid of surface-code tiles and routes their interactions. Sparse static layouts limit routing contention but reserve space that often remains idle. Reducing this reservation requires balancing area savings against additional gate serialization and qubit movement. In this paper, we present a co-designed dynamic architecture and compiler that allocates routing space according to circuit demand. The architecture preserves a fixed virtual qubit floorplan while allowing its physical spacing to change between execution stages. The compiler coordinates placement, scheduling, and routing to implement lattice surgeries using fewer physical qubits. Across our application benchmarks, our method reduces space-time volume by 55.6% in geometric mean and compiles 75.5 times faster than the evaluated DasCot configuration. A circuit-synthesis case study shows how our compiler exposes optimization tradeoffs.

The elementary charged excitations of fractional quantum Hall states are anyons. Without continuous translation symmetry, they acquire a dispersion and richer dynamics. We study the Laughlin quasihole at filling $1/3$ in a periodically modulated magnetic field, a common model of fractional Chern insulators in two-dimensional materials. From the microscopic wave functions, we derive the commutator of its guiding-center coordinates, set by a many-body Berry curvature that governs its wave packets. A modulation with two flux quanta per unit cell splits the quasihole band into bands with Chern numbers $6$ and $-3$; such opposite signs are generic as long as a weak modulation opens a gap between the anyon bands. In the $C=-3$ band, the quasihole drifts against $\mathbf{E}\times\mathbf{B}$, although the magnetic field has the same sign everywhere. Perturbation theory in the modulation explains these results, and large-scale Monte Carlo calculations confirm them. Anyon bands thus acquire their own topology, which controls anyon motion and may shape the phases of itinerant anyons.

We investigate quantum-enhanced time-reversal-based metrology using the central spin model, in which a single ancilla spin of magnitude $S_{\rm cen}$ mediates interactions between $N$ bath spins through a star-graph topology. We demonstrate that the SATIN (Signal Amplification Through Time-reversal Interaction) echo protocol can be implemented in this setup to achieve a Fisher information of $N^2/e$ with the collective $\langle J_y\rangle$ readout, corresponding to a $4.34\,\mathrm{dB}$ offset from the Heisenberg limit. Furthermore, we establish that this platform provides a pathway to perform the butterfly echo protocol by conjugating each evolution step with a random collective bath rotation, thereby achieving axis-agnostic Heisenberg-scaled sensing. Crucially, with a small $N-$independent number of random steps, the butterfly echo reaches a Fisher information of $N^2/4$ ($6\,\mathrm{dB}$ below the Heisenberg limit) for any unknown encoding axis, with the plateau gain tracking the Haar limit. Finally, we demonstrate that the central-spin magnitude $S_{\rm cen}$ provides a powerful knob to reduce the optimal protocol timescale without altering the metrological ceiling or the circuit depth required to reach isotropy. The proposed scheme is relevant to cavity QED and NMR quantum processors, where the central spin architecture arises naturally.

In the companion paper (Part I), we developed an optimal-control framework to suppress intrinsic and decoherence-induced errors in controlled-Z (CZ) gates between directly coupled, frequency-tunable transmons. Here, we extend this framework to incorporate uncertainties in coupling strength, anharmonicities, and zero-flux qubit frequencies, enabling the design of high-fidelity gates robust against noise and parameter uncertainties. We classify these uncertainties by whether they perturb the off-diagonal coupling strengths or the diagonal detunings of the Hamiltonian, and we identify distinct suppression mechanisms for each class. Coupling errors are mitigated through dynamical decoupling induced by strong detuning modulation. For a 30-ns gate, this strategy reduces the coupling error to $6.21\times10^{-7}$ and tolerates coupling-strength uncertainties up to $2π\times4$ MHz while keeping total gate infidelity below $10^{-3}$. Detuning errors are minimized near a symmetric-detuning operating point that balances the two dominant leakage-mediated interactions. A 24-ns gate operated near this point tolerates individual uncertainties of up to $2π\times5$ MHz in each relevant diagonal parameter under the same infidelity threshold. We further optimize gate performance under realistic conditions where intrinsic errors, decoherence, and parameter uncertainties coexist across six representative stages of progressively improving hardware performance. The resulting stage-specific controls achieve lower infidelity and greater robustness. Together with the companion study (Part I), this framework offers a practical approach to balance speed, fidelity, and robustness while reducing the need for exhaustive characterization and frequent recalibration in large-scale superconducting quantum processors.

Quantum key distribution (QKD), whose security is derived from quantum mechanics rather than computational assumptions, is moving into standardization and commercial deployment. Yet its security guarantees rest on technically delicate proofs checked by hand. Formal verification closes this gap, establishing a two-factor assurance: unconditional security from physical principles, and machine-checked proofs against reasoning errors. We present FVQKD, a Rocq library for machine-checking QKD security proofs. Its first result is a complete, end-to-end machine-checked proof of composable, finite-key security for BB84. The mechanization reconstructs the complete proof infrastructure from first principles, including the smooth entropy framework, the entropic uncertainty relation, and the Quantum Leftover Hash Lemma. It uncovers necessary side conditions that the published argument leaves unstated, one of which reveals a missing proof branch, and it grounds the information-theoretic bound in a formal semantics of protocol execution, which the pen-and-paper analysis lacks. The proof is entirely admit-free, relying only on the Rocq kernel and standard foundational axioms. To our knowledge, this is the first end-to-end formal verification of a QKD security proof. Built on MathComp, MathComp-Analysis, and CoqQ, the development provides quantum-information infrastructure designed for reuse across broader QKD variants and quantum cryptography applications.

Set coherence and set imaginarity are two important quantum resources defined by sets of states. We investigate tuples of qubit states under vanishing higher-order Bargmann invariants and show that their set coherence and set imaginarity are each related to whether they contain a pair of orthogonal states. Specifically, when the relevant higher-order Bargmann invariants vanish, the tuple contains a pair of orthogonal states if and only if removing some state makes the remaining tuple incoherent. Moreover, when maximally mixed states are excluded, the same vanishing conditions imply that the tuple is imaginarity-free if and only if it contains a pair of orthogonal states. As a consequence, under these conditions, a tuple of single-qubit states has imaginarity precisely when every tuple obtained by deleting one of its states is coherent.

The purpose of this paper is to conduct a comprehensive structural analysis of quantum finite-level systems in the Heisenberg picture, where the evolution of system observables is modeled by bilinear quantum stochastic differential equations (QSDEs). Firstly, real coordinate transformations that preserve commutation and anticommutation relations are characterized, and relative admissibility between different orthonormal Hermitian bases is formulated. Secondly, strongly aligned subspaces are introduced, based on which decoherence-free subsystems (DFSs) are constructed in general orthonormal Hermitian basis as well as the generalized Gell-Mann basis. Thirdly, conditions for the existence of quantum nondemolition (QND) variables are given in terms of both linear systems theory and spectral separation by output-signal observables. Finally, a sufficient condition for quantum back-action-evading (BAE) measurements is established. A four-qubit nearest-neighbor Heisenberg chain with collective dephasing illustrates these structural properties of quantum finite-level systems.

Excess micromotion induced by stray DC electric fields limits the control fidelity of trapped-ion experiments. Various techniques have been developed to detect and compensate ion displacements from the RF null by monitoring modulated fluorescence, ion positions, or micromotion sidebands. Although these approaches are effective, they do not probe the displacement through a ground-state-cooled motional mode and therefore offer limited compatibility with quantum-enhanced sensing protocols. Here, we demonstrate a micromotion compensation method based on the driven coherent amplitude of a ground-state-cooled motional mode. In this approach, the ion displacement is converted into a coherent motional excitation by an auxiliary RF drive and detected through the qubit. We determine the optimal compensation field with a $1σ$ statistical uncertainty of 8 mV/m. The method is naturally compatible with quantum-enhanced sensing protocols employing nonclassical motional states, including Fock, squeezed, and Schrödinger-cat states, providing a pathway toward quantum-enhanced micromotion compensation.

We investigate a hierarchy of invariant Hilbert-space structures connecting Hilbert-space fragmentation, partial solvability, and quantum many-body scars. For spin chains with fragmented spin-$1/2$ subspaces and their local deformations, we show, using the spin-$1$ $XXC$ chain as a representative example, how successive local deformations reduce extensive irreducible-string fragmentation through an implicitly embedded spin-$1/2$ invariant space and ultimately to a single scar tower, connecting the $XXC$, perturbed $XXC$, and spin-$1$ $XY$ scar models. Through the intermediate embedded space, local dynamics couples states from distinct frozen irreducible-string sectors and selects a new decomposition into representations, from which smaller invariant spaces can be retained. We also establish a rigidity constraint on isolating nonsymmetric towers and a constructive correspondence that transfers a reduction between locally realizable representations of the embedded dynamics. The latter demonstrates that the reduction hierarchy can be transferred through a unitary transformation within the embedded subspace, yielding an exact scar tower built on a Néel reference state without requiring unitary equivalence of the full Hamiltonians.

We present the conditions for satisfying the cluster property in the superconducting state. Using these conditions, we show that the cluster property employed when deriving the order parameter of the superconducting state (OPSS) holds true, and that the OPSS is given by ${}_S\langle Ψ| \hatψ(x)\hatψ(x') | Ψ\rangle_S$, where $|Ψ\rangle_S$ is the superconducting state, and where $\hatψ(x)$ is the field operator of superconducting electrons. This provides a resolution to the long-standing concern raised by Leggett et al.\ regarding particle-number fluctuation in the superconducting state. In addition, by considering the entanglement between two particles composed of the maximum geminal of the BCS ground state [J.\ Phys. Commun. 5, 095003 (2021)], it is confirmed that the larger the deviation from the conditions for satisfying the cluster property becomes, the greater the magnitude of the entanglement becomes. This shows not only the effectiveness of the conditions for satisfying the cluster property but also the justification of the OPSS that has been commonly used.

Quasiperiodic systems combine sharply different spectral and localisation regimes with a dense hierarchy of dynamical time scales. We show that a finite-rate quantum Otto cycle can use this structure as a thermodynamic probe, revealing which parts of the spectrum become dynamically accessible and thermodynamically relevant during a driven transformation. For a generalised Aubry-André-Harper chain, the resulting response is not determined by the static quasiperiodic regime alone: extended, near-critical, and crossing protocols do not exhibit universal ordering of work fluctuations. Instead, the statistics reflect transition pathways that are simultaneously dynamically coupled, thermally occupied, and energetically significant. The same spectral accessibility separates thermodynamic recovery from microscopic adiabatic recovery. Positive mean work can reappear while the population transfer dynamics remain strongly nonadiabatic because finite-rate population transfer is redistributed toward energetically less costly channels rather than suppressed. The full work distribution reveals a further separation, with a finite rate window in which positive-work cycles form a majority although the mean work remains negative. This behaviour persists in finite-size analysis. A thermally weighted spectral susceptibility connects these effects to a distributed hierarchy of dynamically active spectral regions rather than to a single minimum-gap bottleneck. Finite thermal contacts preserve this picture while introducing a second time scale and intercycle memory. Quantum Otto cycles can therefore provide a fluctuation-resolved thermodynamic probe of quasiperiodic spectral accessibility, complementary to direct spectroscopic and eigenstate-resolved diagnostics.

Insider Brief Plurilock shareholders will vote Nov. 18 on a proposed acquisition by Quantum eMotion that would combine quantum-based security technologies with Plurilock’s cybersecurity operations and customer network. Shareholders would receive C$0.084 in cash and 0.0763 Quantum eMotion shares for each Plurilock share, implying an offer value of C$0.28 per share. Plurilock’s board recommends approval, with completion expected in late November subject to shareholder, court and other required approvals. Plurilock Security shareholders will vote Nov. 18 on a proposed acquisition by Quantum eMotion , a deal intended to pair quantum-based security technology with an established cybersecurity business and its customer network. Plurilock said in a news release that it has filed and mailed documents explaining the transaction ahead of a special shareholder meeting in Vancouver. The companies expect to complete the acquisition in late November if shareholders, the court and other authorities approve it. The announcement marks another step toward completing the proposed purchase, rather than a completed acquisition. Under the agreement, Quantum eMotion would acquire all outstanding Plurilock common shares. Shareholders would receive C$0.084 in cash and 0.0763 of a Quantum eMotion share for each Plurilock share they own. For example, an investor holding 1,000 Plurilock shares would be entitled to C$84 in cash and 76.3 Quantum eMotion shares before any provisions governing fractional shares. The companies put the implied value of the offer at C$0.28 per Plurilock share. Because the payment includes stock, its value will depend partly on Quantum eMotion ’s share price. The agreement specifies how many Quantum eMotion shares investors would receive, rather than guaranteeing a fixed cash value for that portion. A Route to Customers The business rationale centers on bringing Quantum eMotion ’s technology to more customers through Plurilock’s existing sales and service operations,

Insider Brief Toshiba launched its Quantum-Safe Networking Platform to help organizations protect critical data connections and expand coverage across existing network infrastructure. The platform combines post-quantum cryptography, quantum key distribution and quantum random number generation with centralized network control and key management. Toshiba says optical switching, integrated transceivers and shared-fiber capabilities reduce equipment requirements and deployment costs, with a single hub able to serve hundreds of remote sites. PRESS RELEASE &#8212; Toshiba Corporation today announced the launch of its Quantum-Safe Networking (QSN) Platform, marking a major step towards delivering true scalability, flexibility and greater efficiency in the deployment of quantum-safe networks. The Toshiba QSN Platform brings together interoperable equipment and deployment capabilities within a unified architecture. It is designed to help network operators, data center service providers, enterprises and public-sector organizations protect their most critical data paths first and expand as their security, operational and commercial requirements evolve. Importantly, those organizations do not need to rebuild their networks to get started. The platform integrates with existing network infrastructures and can support deployments from a single dedicated connection to large metro, hub-and-spoke, ring, mesh and long-distance networks.&nbsp; By simplifying the deployment of quantum-safe networks and improving the economics of expanding across multiple sites, the platform helps turn the quantum-safe transition into a strategic advantage. Organizations can strengthen network resilience while scaling protection in line with their needs. Service providers can also begin to offer differentiated quantum-safe services to create new revenue opportunities. The quantum-safe transition is under way The prospect that sufficiently powerful quantum computers could render many of today’s encryptio

Insider Brief Researchers from Rutgers , IBM and collaborating institutions demonstrated real-time quantum feedback on up to 100 qubits, using repeated measurements and resets to control chaotic behavior. The experiment used a 156-qubit IBM Heron processor to perform nearly 5,000 two-qubit operations and nearly 5,000 measurements and resets while the system continued running. The researchers observed a sharp transition from chaos to control when resets outpaced scrambling, confirming theoretical predictions and demonstrating a capability needed for future fault-tolerant quantum computers. PRESS RELEASE &#8212; Researchers from Rutgers , IBM and collaborating institutions have shown that a quantum computer can check what is happening inside it and respond while it is running, repeatedly resetting parts of the system to bring chaotic behavior under control. The advance is a critical step toward building larger, more reliable quantum computers.&nbsp; Today’s quantum computers operate according to the unusual rules governing atoms and other extremely small particles. They could one day solve problems beyond the reach of conventional computers — designing better batteries and cleaner industrial catalysts, simulating molecules and materials too complex for today’s computers, and running certain artificial intelligence programs. In a study published in Nature Physics , researchers from Rutgers , International Business Machines Corp., and collaborating institutions showed that a quantum computer can repeatedly check and reset parts of itself while running. The experiment is among the largest demonstrations to date of real-time quantum feedback control, a capability considered essential for future quantum computers that will be fault tolerant. Scaling quantum computers will require them to identify and correct errors while they are working, a capability known as error correction, which will allow for the construction of a fault-tolerant quantum computer.&nbsp;A fault-toleran

For the first time, Northwestern University physicists have coaxed a single positron—the antimatter counterpart of an electron—into an exquisitely controlled quantum state.

Scientists from the Quantum Technologies Group at the Institute of Physics Zagreb, in collaboration with a colleague from the Physics Department at the Faculty of Science (PMF), have experimentally demonstrated for the first time the existence of discrete one-dimensional (1D) solitons in an optically induced photonic lattice in warm rubidium vapor.

Quantum networks, systems that connect devices and allow them to exchange information encoded in the quantum states of particles, could enable more secure communications. To build these networks, physicists need to devise strategies that allow distant particles to share quantum states, preserving them long enough to perform calculations or enable communication between devices.

Insider Brief Vulcan Elements is partnering with the North Carolina Collaboratory and UNC-Chapel Hill to develop higher-performance rare earth magnets for defense and commercial applications. Supported by a $600,000 research award, the team will use quantum-mechanical simulations to predict how atomic-level changes affect magnetic properties. Vulcan’s factory under construction in Benson, North Carolina, is planned to produce 10,000 metric tons of magnets annually and create 1,000 manufacturing jobs. Vulcan Elements, an American rare earth magnet manufacturer, today announced a partnership with the North Carolina Collaboratory to advance the development of high-performance rare earth magnets for critical defense and commercial technology applications.&nbsp; The collaboration brings together Vulcan Elements and leading scientific expertise at the University of North Carolina at Chapel Hill (UNC-Chapel Hill), where research led by chemistry professor Yosuke Kanai, PhD, will develop a novel analytic capability using quantum-mechanical simulations to predict with significant accuracy how changes at the atomic level affect magnetic properties, ultimately setting a new standard for Vulcan&#8217;s magnetic performance. The partnership represents a convergence of two research fields that are foundational to national security and the future economy: rare earth magnets and quantum mechanics. The research will pair Kanai&#8217;s more than 25 years of experience in computational materials research with Vulcan Elements&#8217; expertise in manufacturing rare earth magnets. The Collaboratory is supporting the partnership through a $600,000 research award, helping support the application of UNC-Chapel Hill&#8217;s scientific expertise to advance rare earth magnet innovation. Established by the North Carolina General Assembly in 2016, the Collaboratory works with academic experts across the state to transform research into practical applications for the benefit of North Carolina. Si

Insider Brief The National Physical Laboratory (NPL) has secured Government Office for Technology Transfer (GOTT) funding to advance trapped-ion quantum computing technology , with a focus on manufacturing scalability. The project will develop a batch packaging process for ion-trap devices to address production yield and manufacturing bottlenecks that limit large-scale production. The work aims to support reliable manufacturing of ion traps for networked quantum computing architectures, building on NPL technology already used at NPL, the University of Oxford and the National Quantum Computing Centre. PRESS RELEASE &#8212; The National Physical Laboratory (NPL) has secured funding through the Government Office for Technology Transfer (GOTT) to accelerate the development of next-generation trapped-ion quantum computing technologies, helping address one of the sector&#8217;s most significant barriers to commercial adoption: scalability. Quantum computing has the potential to transform industries by solving complex problems that are beyond the reach of today&#8217;s most powerful classical computers. Rather than relying on conventional binary transistors, quantum computers use quantum bits, or qubits, which exploit the principles of quantum mechanics to perform calculations at unprecedented speeds.&nbsp; Trapped-ion systems have emerged as a leading platform, among competing quantum computing technologies being developed worldwide, due to their exceptional fidelity, stability and scalability. NPL plays an important role this field, having developed a microfabricated, chip-scale ion microtrap capable of confining and manipulating arrays of ions. The technology provides a highly scalable architecture that is ideally suited for quantum computing and quantum networking applications. NPL&#8217;s ion microtrap devices are already supporting cutting-edge research activities at both NPL and the University of Oxford. Building on this success, a previous GOTT Knowledge Asset Gran

How hybrid infrastructure is making quantum commercially actionable today – and why the organizations building that infrastructure now will be the ones ready when the hardware arrives. Insider Brief Quantum readiness is an infrastructure problem as much as a hardware one: organizations are in a &#8220;prepare for quantum&#8221; era, and integrating isolated quantum processors with enterprise IT through secure, low-latency interconnection is the step most organizations are overlooking. Paris-based Qubit Pharmaceuticals shows this approach in practice. Its four-layer ATLAS platform combines polarizable molecular dynamics, a synthetic quantum chemistry data engine built with Sorbonne University, the FeNNix-Bio1 foundation model, and the Hyperion-1 emulator, which simulates up to 40 qubits on classical hardware. Quantum advantage has not yet been demonstrated in drug discovery, but the milestones that matter now (algorithm validation, workflow integration and ecosystem maturity) don&#8217;t require fault-tolerant hardware. Organizations that delay preparation risk falling further behind as a result. The Era Between Eras The prevailing assumption about quantum computing is that fault-tolerant hardware will arrive at some point, organizations will integrate it when it does, and until then there is nothing practical to do. That framing is both inaccurate and increasingly costly to believe. We are not in a &#8220;wait for quantum&#8221; era. We are in a &#8220;prepare for quantum&#8221; era, and preparation is an active, infrastructure-intensive undertaking. Organizations that treat it as passive will find themselves starting from scratch when quantum utility arrives. Those who build now will be able to absorb it. The distinction matters most in the life sciences, where the cost of falling behind can be measured in years of delayed discovery for diseases that are not adequately served by today&#8217;s therapeutics. This is not a problem exclusive to drug discovery; it also

Quantum computers today are fragile: they lose their quantum state to noise and decoherence faster than a useful algorithm completes. Quantum error correction (QEC) makes longer computations possible by encoding each logical qubit across many physical qubits, so that errors can be detected and removed without disturbing the encoded information. In practice, QEC runs as a repeating cycle (see Fig. 1): in each round, the hardware measures a set of parity checks, called stabilizers, whose outcomes (the syndrome) reveal where errors have occurred without collapsing the logical state. A classical decoder then reads the syndrome, infers the most likely errors, and either records a correction to apply later or triggers a physical recovery. Figure 1 – The quantum error correction cycle. On the quantum hardware, (1) a logical qubit is stored across many physical qubits, and (2) each round of stabilizer (parity-check) measurements produces a syndrome. The syndrome passes to classical processing, where (3) a decoder infers the likely error and (4) issues a recovery command that is fed back to the hardware. The cycle repeats every round. The challenge is latency [1] (see our earlier post, A framework for quantum-classical integration decisions ). On today’s superconducting hardware, for instance, one round takes on the order of one microsecond. If the decoder cannot keep up with that rate, a processing backlog builds and stalls the computation. Popular decoders such as minimum-weight perfect matching (MWPM) [2], which infers the most likely errors by pairing up syndrome signals in a graph, grow more expensive as the quantum error-correcting code size gets larger. A pre-decoder eases this bottleneck with a fast first pass that clears the easy, high-confidence errors, leaving the full decoder a much smaller problem. This is where AI-based pre-decoders [3,4] come in, such as NVIDIA Ising Decoding . In this post we show how we trained NVIDIA Ising Decoding on AWS, how a range of ac

Abstract Claims of quantum advantage in machine learning often rest on classical comparators that lack the same features, on simulation alone, and on unreported hardware cost. QBioBench is a benchmark of quantum machine learning on peripheral biosignals that holds quantum and classical models to the same features and reports calibration and hardware cost. It comprises three clinical tasks, 12-lead ECG diagnosis (PTB-XL), single-lead apnea detection (Apnea-ECG), and wearable stress detection (WESAD), each reduced to six to eight shared dimensions. A factorial grid of projected and fidelity quantum kernels and variational classifiers is screened in noisy simulation, and the promoted configurations are evaluated in an exploratory study on an IBM Nighthawk r2 processor on the full test pools of 510 apnea minutes and 512 PTB-XL records. Every prediction is recovered from the device records, intervals resample recordings or patients, and classical baselines are trained on the same units and tested on the same executed inputs. No quantum model reaches its matched support vector machine in ROC-AUC on either primary task, and none is separably better in balanced accuracy. The angle-encoded fidelity and projected kernels reach ROC-AUC 0.697 and 0.693 on apnea, paired differences of $-0.127$ and $-0.119$ to the support vector machine, and both are classical by construction, since the entangling layer of the encoding cancels from the fidelity kernel and leaves closed-form local expectations in the projected kernel. A variational classifier comes closest, reaching 0.797 on apnea (difference $-0.012$, 95\% interval $[-0.052, +0.027]$), and falls to chance without its two-qubit gates. Test sets of the size that circuit budgets favour are unreliable, as random 80-minute subsets of the apnea pool give the fidelity kernel a central 95\% range of ROC-AUC from 0.589 to 0.797. Readout mitigation changed ROC-AUC by at most 0.015.

Abstract Non-Hermitian quantum dynamics lie in an intermediate regime between unitary Hamiltonian dynamics and trace-preserving non-unitary open quantum system dynamics. Given differences in the noise tolerance of unitary and non-unitary dynamics, it is interesting to consider implementing non-Hermitian dynamics on a noisy quantum computer. In this paper, we do so for a non-Hermitian Ising Floquet model whose many-body dynamics gives rise to persistent temporal oscillations, a form of time crystallinity. In the simplest two qubit case that we consider, there is an infinitely longlived periodic steady state at certain fine-tuned points. Using a generalized Floquet analysis, we show that infinitely long-lived oscillations are generically lost for arbitrarily weak values of common types of noise and compute the corresponding damping rate; this result is confirmed numerically using IBM's Qiskit platform. We further show that the complex gaps responsible for oscillation damping are opened generically at first order in perturbation theory for any convex combination of depolarization, relaxation, and dephasing, establishing that no engineered mixture of these noise channels can stabilize the time-crystalline phase. Experiments on a real device (ibmq-lima) are consistent with rapid oscillation damping, though a significant mismatch between the manufacturer noise model and observed device behavior complicates quantitative comparison, illustrating the importance of rigorous analytical noise analysis.

Abstract Tracking the dynamics of a quantum system is conventionally achieved by monitoring the system continuously in time and filtering the information contained in measurement records via the causal quantum trajectory approach. However, in practical scenarios, there is often loss of information to the environment, leading to filtered states that are impure because of decoherence. If real-time tracking is not required, the lost information can be maximally extracted via acausal quantum state smoothing , which has been theoretically proven to better restore the system’s coherence (purity) than causal filtering. Interestingly, quantum state smoothing requires assumptions about how any lost quantum information (unobserved by the experimenter) was turned into classical information by the environment. In this work, we experimentally demonstrate smoothing scenarios, using an optical parametric oscillator and introducing ‘observed’ and ‘unobserved’ channels by splitting the output beam into two independent homodyne detectors. We achieve improvement in state purification of 10.3% ± 1.6%, squeezing restoration of 7.6% ± 2.6%, and show that smoothed states are better estimates of hidden true states than those from conventional filtering. The estimation techniques used in this paper are promising for many applications in quantum information that incorporate post-processing.

We study a finite-width two-dimensional quantum ring with a quadratic $d$-wave altermagnetic term, Tan--Inkson confinement, a perpendicular magnetic field, and independently tunable Aharonov--Bohm (AB) flux. The altermagnetic interaction mixes $m$ and $m\pm2$ angular channels while preserving their parity. Circular symmetry renders the crystal orientation spectrally irrelevant and makes the two spin blocks exactly isospectral. The resulting same-parity anticrossings are resolved at low filling, and multichannel mixing is found near the Fermi level of highly occupied rings. Independent converged calculations for $N_e=1400$ and $1800$ establish the reconstructed Fermi edge and magnetic response in a finite field window and the persistent current over a full AB flux period. The analytic conventional reference separates radial-subband depopulation (dHvA-type cycles) from finer finite-ring shell oscillations; we do not assign a global Fourier spectrum to unverified altermagnetic field scans. The few-electron thermal response is obtained from an exact fixed-particle-number canonical partition function, avoiding finite-system errors of a fixed-mean-number approximation. The circular model supports an equilibrium charge current but no persistent spin current.

Problem structure is regarded as a key factor influencing the performance of the Quantum Approximate Optimization Algorithm (QAOA), yet it remains an informal notion without a precise mathematical characterization. In this work, we address this issue by identifying a mathematical object that captures problem structure as seen from the perspective of the target state amplitude in single-layer QAOA. Specifically, we show that this structure is encoded in a joint probability distribution induced by the unique coarsest partition of the computational basis, determined by problem cost values and mixer-dependent walk counts. The statistical dependence between these classes provides a means of quantifying the available problem structure and identifying necessary conditions for exponential amplification. To assess the extent to which this structure can translate into algorithmic performance, we establish a mean-max non-separation bound relating the parameter-averaged probability of measuring the target configuration to its variational maximum. For NPO-PB problems with polynomially many distinct mixer eigenvalues, these probabilities exhibit the same scaling up to polynomial factors. This allows us to characterize the exponential scaling of optimal amplitude amplification by analyzing the parameter-averaged probability without explicitly optimizing the variational parameters. We then derive an exact expression for the parameter-averaged probability as a matrix inner product involving two objects that separately encode the joint structural distribution and the mixer dynamics. This representation provides a framework for identifying the structural mechanisms governing the amplification of the target-state probability or its exponential suppression relative to the mixer capacity. We demonstrate these mechanisms through analytically tractable examples involving transverse field and Grover mixers.

We review what it means for a relativistic particle to be localized and argue that the most useful approach is through local measurement. This perspective ties localization directly to relativistic causality and measurable outcomes in spacetime. Strict localization in quantum field theory is formalized by states that give the same expectation value as vacuum for all local observables outside some spacetime region. With this formalism, single photons cannot be strictly localized, but coherent states can. The structure and interpretation of local observables and local operator algebras are discussed in connection with the Reeh-Schlieder theorem. Since probabilities of local measurement outcomes cannot vanish in vacuum, particle detection events must be phrased carefully. Key characteristics of strictly localized states are surveyed alongside concrete strategies for constructing them. The relationship between localization, causality, and on-demand sources is analyzed, finding that strictly localized states can represent localized, propagating information in quantum field theory. Explicit examples of localized photonic states are presented with an emphasis on quantum optics, including states that approximate single photons and (entangled) Bell states.

We propose distributed dual-comb spectroscopy, a quantum-enhanced sensing architecture that simultaneously exploits spatial- and spectral-domain entanglement to improve the extraction of global spectroscopic information across broadband frequency ranges. Our scheme consists of a network of Mach-Zehnder interferometers interrogating spatially separated samples, each driven by a classical frequency comb at the bright port. A single two-mode squeezed frequency comb is distributed through a passive beam-splitter array into $K$ entangled combs, establishing multipartite correlations across sensors while preserving intrinsic spectral entanglement. The protocol is compatible with both heterodyne detection and division detection, and enables parallel estimation of weighted-average absorption features over multiple frequency components. Compared with spatially separable quantum strategies requiring $K$ independently engineered nonclassical comb sources, our approach achieves enhanced signal-to-noise performance using only a single quantum resource distributed across the network. These results establish a scalable route toward broadband distributed quantum spectroscopy with simultaneous spatial and spectral advantage.

Coherence preservation and environmental renewal offer competing ways of controlling quantum memory and transport. We show that a seemingly natural protocol which exactly replaces the bath occupations while preserving arbitrary system--bath coherences need not correspond to a physical fermionic state. We instead construct a two-reservoir protocol with independent, number-conserving thermal attenuators, for which complete positivity and fermionic admissibility hold by construction. Physical attenuation necessarily modifies bath populations as well as cross correlations; the coherence control is not an independent hard-reset knob. Quadratic dynamics reduces the stroboscopic problem to an exact matrix fixed-point equation without a weak-coupling or Markov approximation. Analytically, coherence retention enhances the leading short-cycle transfer rate, including the complete-erasure limit; no general endpoint-vanishing theorem exists. An exact stationary continuity theorem forces the through-current to vanish whenever either reservoir is left entirely unrefreshed, although no analogous theorem suppresses it at complete erasure. For biased structured reservoirs, exact finite-chain calculations display distinct coherence-, current-, and signed energy-transfer operating points; a resolved high-retention boundary layer exposes strong finite-size sensitivity of the coherence peak. The model provides a microscopic, fermion-admissible benchmark for the interplay of reservoir coherence, particle transport, and energetic exchange.

Group IV color centers in diamond -- silicon, germanium, tin, and lead-vacancy centers -- are a promising platform for quantum networking. Typical Group-IV creation utilizes ion implantation during diamond growth that leaves the color centers with a broad depth distribution and damage-induced strain inhomogeneity. Deterministic placement and damage reduction in Group IV generation are essential for improving this platform. In this letter, we report on the localization of germanium-vacancy (GeV$^-$) to a $<$ 10 nm layer via the timed injection of GeH$_4$ during microwave plasma chemical vapor deposition. In this layer we have realized 17 ppm of Ge and a strain-free environment for the GeV$^-$. Subsequent electron irradiation and annealing have generated a sheet density of 0.12 GeV$^-$/$μ$m$^2$. The minimal damage from color center generation mitigates spectral inhomogeneity and allows spectral resolution of isotopic clusters, with the best cluster having an inhomogeneous distribution of 2.14 GHz and an average linewidth of $47 \pm 11$ MHz. Our study gives insight into formation dynamics of GeV$^-$ in delta-doped systems and estimates our vacancy to GeV$^-$ yield to be $\geq$ 90%, establishing an athermal nearest-neighbor formation model. We further characterized the spin $T_2^*$ and set a lower bound of 730 ns, limited by a paramagnetic defect.

The two-dimensional Hubbard model was originally proposed as the minimal model of uniform $d$-wave superconductivity in the cuprate high-temperature superconductors, but recent calculations with relevant parameters in a realistic doping regime have often found other ground states. Further, uncertainty remains over such results due to the intrinsic bias of different computational methods. Here we address this uncertainty through state-of-the-art neural tensor network and neural backflow state simulations, enabled by large-scale GPU computation, that together reach an unprecedented variational accuracy on lattices with up to 1024 sites. At $1/8$ doping in the pure Hubbard model, as well as with next-nearest-neighbor hopping relevant to the hole-doped cuprates, we reveal a near degeneracy among a low-energy uniform $d$-wave state, superconducting stripes, and non-superconducting stripe states on the milli-$t$ energy scale. Our work rebalances the narrative that the Hubbard model supports a single dominant order in relevant parameter regimes towards a picture of extreme competition between stripes and superconductivity.

Pauli-based computation (PBC) is a measurement-based model of quantum computation that samples from output distributions of universal Clifford+$T$ circuits. Here, we provide a normal form (NF) that completely characterizes its adaptive and entanglement structures. These insights unify PBC with one-way quantum computing as dual or `time-reversed' counterparts. We use the NF to advance strategies for distributed computation and investigate magic-state injection rates. We also demonstrate an exponential improvement in the detection of unnecessary magic-state qubits, allowing their efficient removal. Our NF further enables ahead-of-time circuit compilation using PBC, reducing CNOT gate count and quantum memory of random quantum circuits on average by 50% and 40%, respectively, beating other state-of-the-art compilers.

Belief Propagation combined with Ordered Statistics Decoding (BP OSD) is an open-source decoding tool used widely within the community due to its versatility and ease of application to Quantum Low Density Parity Check (QLDPC) codes. However, the degeneracy of quantum codes has been observed to degrade the performance of BP OSD, particularly leading to error floors for low physical error rates. Here, we investigate the low-weight error configurations responsible for such failures in Bivariate Bicycle codes. We show that, at code capacity, BP OSD fails on errors whose weight is significantly smaller than d/2, arising from global symmetries of the decoding graph that prevent the convergence of parallel BP. Furthermore, our analysis reveals new pitfalls that can arise when analysing the performance of BP OSD in the rare events regime, such as loss of ergodicity in splitting methods and numerical instabilities in the decoder. We show how to mitigate these failure mechanisms by modifying the BP update rules and the decoder implementation, leading to substantial improvement in logical error rate.

The promise of efficiently solving classical optimisation problems on quantum computers is tantalizing. As many such problems can be mapped to approximating the ground state of spin-glasses, paradigmatic models for studying many-body localisation, it is natural to ask if some of the intuition coming from quantum statistical mechanics can help guide the construction of novel quantum optimisation algorithms. In this work, we discuss how continuous reverse quantum annealing crossing a many-body localisation transition can be accelerated by considering the density of Landau-Zener crossings as the system is quenched. We provide an interpretation of this behaviour in terms of an effective Fokker-Planck equation for the success probability of the algorithm. This interpretation suggests an improvement in the required annealing time as a function of the system size $N$, which goes from $\mathcal{O}({\rm poly}(N))$ to $\mathcal{O}(1)$ for reference states with non-vanishing energy density. We show that the continuous dynamics can be Trotterised with a number of steps that remains modest as system size increases, making it appealing for near-term devices. For the resulting circuit implementation, we provide a quantitative strategy for determining the parameters of the time-dependent Hamiltonian. We compare the performance of our digitised algorithm, which we call FRIO, against that of the QAOA for finding the ground state of spin-glass problems, in particular the SK model. The numerical results suggest that with suitably selected circuit parameters which can be efficiently found using thermalizing dynamics, FRIO almost always outperforms the conventional QAOA ansatz with pre-optimized angles.

We consider the discrimination of two quantum channels acting on bosonic modes, with a probe state of fixed mean photon number and no ancilla. We prove that pure probes are optimal: for every mixed probe there is a pure probe with exactly the same mean photon number that performs at least as well. The result holds for arbitrary channels and for every figure of merit built from the Chernoff quantities $\Tr[ρ_1^sρ_2^{1-s}]$, including the quantum Chernoff exponent, as well as for the single-shot error probability. The proof relies on a decomposition of any state of mean photon number $\nb$ into pure states of mean photon number exactly $\nb$, which extends a matrix rank-one decomposition of Huang and Zhang to density operators of infinite rank.

Fault-tolerant syndrome extraction is fundamental to stabilizer-code-based quantum error correction, yet existing general protocols incur substantial costs in either circuit depth or width. In this work, we design ancilla stabilizer states for a general transversal circuit to construct a family of fault-tolerant syndrome-extraction gadgets that interpolate between Shor and Steane syndrome extraction for any stabilizer code. The result is a configurable trade-off between circuit depth and width.

We study variational preparation of ground states and sector-resolved excited states in the $(1+1)$-dimensional lattice Gross-Neveu model. We construct fixed circuits preserving either total fermion number or every flavor number, and a problem-specific scalable-circuit adaptive variational quantum eigensolver (SC-ADAPT-VQE). Classical circuit benchmarks cover massless and massive systems through 30 qubits, using exact-diagonalization and tensor-network reference results. Imposing flavor-number conservation improves the achieved energies in the completed two-flavor comparisons. Selected massive fixed-ansatz benchmarks with one to four flavors have relative energy errors of approximately $1 \times 10^{-5}$ - $2 \times 10^{-4}$, smaller than the quoted literature errors where available, although discretizations and computational resources differ. The adaptive pool combines translated bulk and boundary-sensitive generators with an interaction-sensitive cross-flavor family. Selected massive SC-ADAPT benchmarks with one to three flavors have relative energy errors below $2.1 \times 10^{-3}$. For one flavor, matrix-product-state evaluations extend the transferred circuits to 60-400 qubits without target-side operator selection or parameter optimization, giving energy deviations of approximately $0.35\%$ - $1.76\%$ from density-matrix renormalization-group reference values at maximum bond dimension 256. At fixed flavor number, range caps, and append count, the adaptive construction has a precompilation local-factor count linear in volume and a volume-independent shared-parameter count; fixed-accuracy performance at arbitrary volumes remains unestablished. Sequential deflation also prepares low-lying states within a fixed flavor-number sector, with projector fidelities providing a basis-independent assessment of degenerate target eigenspaces.

Discrete time crystals exhibit robust subharmonic oscillations, spontaneously breaking the discrete time-translation symmetry of a periodic drive. Since their emergence, the question of whether other types of temporal many-body order can exist has attracted considerable attention. Here we identify discrete time liquids -- a new form of spatiotemporal order characterized by short-range temporal coherence as a result of time-solitons. We study a two-dimensional spin system coupled to a finite-temperature cavity, whose fluctuations provide a noisy, approximately periodic drive with only finite temporal coherence. Remarkably, the spins nevertheless form a metastable state with robust period-doubled dynamics over an extended parameter regime. Unlike a time crystal, this state has only finite temporal coherence: individual trajectories stochastically switch between the two symmetry-related temporal configurations of the period-doubled response. We identify these switches as time-solitons: topological defects in temporal order that preserve local period doubling while destroying long-range temporal coherence, thereby producing the time liquid state. We propose a minimal model which reproduces the distribution of temporal correlations of the many-body system, suggesting a general description of the time liquid as a time crystal with a finite density of time-solitons. Because these solitons can occur at arbitrary times, ensemble averaging restores continuous time-translation symmetry, raising the intriguing possibility that discrete time liquids can exist in thermal equilibrium.

Numerically simulating quantum many-body systems is one of the central challenges in modern physics, as the exponential growth of the Hilbert space with system size renders large-scale exact solutions intractable. Over the past decade, generative artificial neural networks have emerged as powerful wave function ansätze that have powered advances in finding ground state representations, reconstructing quantum states from data, and modeling dynamics in quantum many-body systems. While recurrent neural networks (RNNs) are computationally efficient, the recurrent nature can limit their capacity to capture long-range correlations. Transformer models with their underlying self-attention mechanism excel at capturing these long-range correlations, but incur increased computational requirements, restricting applications to small physical systems. In this work, we address these limitations by exploring the multi-layer perceptron (MLP) mixer model as a wave function ansatz. By mixing information globally and locally through the system via a computationally lightweight mixing strategy, this architecture promises to combine the ability to capture long-range correlations with low computational costs. We benchmark the model on finding ground state representations of two-dimensional quantum many-body systems in various phases of matter and investigate the behavior of representational accuracy and computational efficiency for different physical system sizes. By comparing its performance to RNNs and transformer models with single-site and patched input definitions, we demonstrate that the MLP mixer architecture performs competitively with state-of-the-art network models. We further show that a hierarchical combination of this model with the transformer model outperforms other state-of-the-art architectures for large-scale quantum systems, opening new avenues for investigating quantum phases of matter.

Field-theoretic analysis has predicted that the edge of a double quantum spin Hall insulator (DQSHI) can undergo an interaction-driven transition from a phase with fermionic edge modes into one with only bosonic modes. All single-fermion edge excitations are gapped in this bosonic edge phase, but fermion pairs remain gapless, leading to distinct experimental signatures. We numerically simulate the interacting DQSHI edge and verify the existence of the bosonic edge phase. This calculation requires an explicit bulk embedding of the DQSHI edge, due to its mixed anomaly between charge and $S^z$ conservation. We hence employ segment DMRG on an infinite two-dimensional cylinder, where the DQSHI bulk is modeled in terms of two copies of the spin-up lowest Landau level, combined with their time-reversed counterparts. We find that interactions can open a single-fermion gap at the DQSHI edge while fermion pairs remain gapless, matching the predictions for the bosonic edge phase. We find the scaling of the single-fermion gap with interaction strength to be consistent with field-theoretic calculations, and discuss the relevance of the bosonic edge phase to twisted homobilayers of WSe$_2$ and MoTe$_2$. We elaborate on the methodological extension of the segment geometry used here to other topological phases with edge anomalies.

We provide a fully quantum-mechanical description of the continuous measurement of wavelike dark matter. Our focus is cavity haloscopes, although our results inform a broad range of axion searches. We extend the input-output formalism by treating the axion as a quantum field, finding how its quantum state is imprinted onto higher-order moments of observables of the outgoing transmission-line modes. We further develop a novel measurement-record formalism, which computes the joint probability distribution of all measurement outcomes and is well suited to studying the axion in the time domain. With it, we compute the exact axion-induced number distribution for the first time, demonstrating that it is not Poisson. We argue that virialized axion dark matter is expected to be in a Gaussian quantum state, and show that number or quadrature measurements can distinguish this from the predictions of a coherent state or even a Bose-Einstein condensate. Finally, we show that intrinsically quantum effects, such as those from Fock or squeezed axion states, are far too weak to detect.

AI agents are increasingly capable of constructing quantum algorithms and proofs, yet machine-checked proofs alone cannot guarantee that the intended problem is solved or that resource claims match the verified computation.Here we introduce Lean-QuantumAlg, a Lean 4 framework for trustworthy AI-assisted development of quantum algorithms.Its Algorithm-Solves-Problem contract binds correctness, success probability, borrowed-state restoration and quantum and classical resource bounds to a single execution, while separating the guarantees that Lean checks from the problem specifications and execution models that humans review. We demonstrate the framework on nine AI-formalized quantum algorithms, from Grover search to quantum attacks on RSA-2048 and P-256, with less than 1% of each algorithm's imported source code requiring statement-level human review once the shared framework has been audited. By integrating reusable mathematical foundations, certified algorithmic primitives and execution-grounded verification, Lean-QuantumAlg provides a basis for AI agents to construct and certify quantum algorithms, opening a path toward scalable AI-driven discovery of quantum algorithms.

Mechanical vibrations are fundamental to a wide range of physical phenomena and technologies, yet their ability to actively shape free-electron dynamics remains largely unexplored. Here we theoretically show how an optomechanical membrane provides a phonon-assisted optical interface for controlling free-electron recoil and sensing localized forces. Transverse membrane motion scatters cavity light into high-momentum evanescent sidebands that enable phase-matched interaction with electrons traveling in vacuum. Beyond supplying momentum for phase matching, the vibration amplitude controls the electron-light interaction strength and redistributes electron populations among recoil orders. External forces that perturb the vibration are thereby encoded in the electron recoil spectrum. Under the modeled conditions, electron readout of localized stochastic forces can yield a higher signal-to-noise ratio than a Gaussian optical homodyne benchmark at equal detected probe rates. These results provide a theoretical basis for mechanically reconfigurable free-electron optics and mode-selective mechanical sensing.

A two-level emitter chirally coupled to a waveguide imprints a $π$ conditional phase on a two-photon pulse, a key component assumed in quantum photonic neural network architectures, but whether it survives the pure dephasing of a solid-state emitter is unknown, since no two-photon scattering treatment includes it. We derive the dephased two-photon amplitude in closed form and validate it against an independent Fock-state master equation. The conditional phase is pinned at exactly $π$ at every dephasing rate examined: dephasing destroys the amplitude carrying the nonlinear phase rather than rotating it. The one- and two-photon channels are not attenuated equally, so dephasing does not simply scale the node down but reweights it between photon-number sectors---an error no phase setting can train away. The standard factorization of two-photon correlators, exact for arbitrary loss, fails at first order in $γ_φ$, discarding $16$--$81\%$ of pairs over $γ_φ/γ=0.1$--$1$.

We prove a conjecture of Yu, Lai, and Oh: their rounded family of strengthened quantum Hamming bounds, which interpolates between Hamming-type bounds and the Singleton bound, holds for arbitrary exact quantum subspaces of dimension $K>1$. The result covers every integer local dimension $p\ge2$, every integer $t\ge1$, both distances $2t+1$ and $2t+2$, and every interpolation parameter $e\in\{0,\ldots,t\}$. Yu, Lai, and Oh proved these bounds for pure codes and for general codes of distance three or four; the case $e=0$ contains the ordinary quantum Hamming bound for general codes, recently proved by Zhang and Chen. More generally, for $p\ge3$, we prove the inequality $Kf(0)\le p^n\mathbb{E}f(X)$, where $X\sim\operatorname{Bin}(n,1-p^{-2})$, for every real polynomial $f$ of degree at most $D$, with $2\le D<d$, that is nonnegative on $\{0,\ldots,n\}$ and positive at zero; here $n$ and $d$ are the code length and distance.

We propose a quantum architecture that achieves addressable and parallel universal fault-tolerant logical in high-rate codes. The codes are obtained from the flexible concatenation of small-distance high-rate self-dual CSS codes. Addressable and parallel universal logic on the resulting $K$ logical qubits is injected by fault-tolerantly preparing and then consuming diverse logical $K$-qubit CSS stabilizer states and logical $\lvert H \rangle^{\otimes K}$ global magic states. Flag-at-origin is used to prepare the stabilizer resource states while a concatenated cultivation protocol prepares the global magic states. These resource states are consumed by Steane-QEC or Knill-QEC teleportation gadgets, which simultaneously perform quantum error correction. Any quantum algorithm with $T$-depth $D_T$ can be executed by consuming $12D_T$ or fewer resource states. We benchmark the fault-tolerant preparation of the resource states for several two-level concatenations of the $[[k+4,k,2]]$ H codes and the Hamming $[[15,7,3]]$ code. In particular, we find that the concatenated cultivation offers at least one order of magnitude spacetime reduction compared to cultivation in the surface code.

We propose an operational resolution of the FLRW big bang singularity using quantum probes satisfying a curvature coupled Klein-Gordon equation. Applying the Madelung-Bohm decomposition of a Klein-Gordon field on a classical near-singularity FLRW background, we show that the induced conformal geometry renders curvature invariants finite and makes past directed causal geodesics complete. The classical big bang surface is therefore inaccessible to this class of quantum probes in finite effective proper time, while the underlying FLRW spacetime remains singular.

We introduce a random sampling method for testing the weak Eigenstate Thermalization Hypothesis (wETH) that is particularly useful for large, sparse Hamiltonians. We test the method on a well-studied Rydberg atom system that exhibits both two- and three-body dipole-dipole interactions. Our results show that our method allows for the study of system sizes significantly beyond the limits of exact diagonalization. We find that the fluctuations in eigenstate expectation values decay as the Hilbert space dimension $D^{-1/2}$, consistent with wETH and in agreement with previous numerical results.

A recent work considered the Page curve for entanglement entropy of a freely expanding one-dimensional Fermi gas starting from a finite box (the system) in a zero-temperature initial state that then expands in to a semi-infinite vacuum (the environment). For the case with a single defect at the system-environment junction, it was shown that the Yang-Yang entropy of the system computed from semiclassical hydrodynamics agrees with the microscopically computed entanglement entropy, yielding the Page curve. On the other hand, the environment Yang-Yang entropy showed a monotonic increase. Here, we propose a hydrodynamic description to obtain the eigenvalues of the microscopic correlation matrix for a nonzero temperature freely-expanding Fermi gas. For the system, the phase space density directly gives the correlation matrix eigenvalues and thus, via the Yang-Yang formula, yields the von-Neumann entropy. For the reservoir, a modification of the phase space density is required in the Yang-Yang formula, to incorporate coherences, in order to reproduce accurately the entropy. The hydrodynamic description of correlation matrix eigenvalues also leads to a Levitov-Lesovik type formula for the full-counting-statistics for a finite system in the transient regime. We provide a heuristic derivation of the correlation matrix eigenvalues based on a semiclassical wave-packet picture.

Fault-tolerant quantum computing requires quantum gates that combine short duration, high fidelity, and robustness to noise. As quantum processors scale, robustness becomes increasingly important because exhaustive characterization and frequent recalibration of individual gates become impractical. We present a comprehensive optimal-control framework for controlled-Z (CZ) gates between directly coupled, frequency-tunable transmons that systematically accounts for intrinsic Hamiltonian errors and realistic decoherence mechanisms, including energy relaxation and dephasing. Using smooth, single-shot flux pulses, we obtain 12-ns CZ gates---close to the theoretical speed limit of 11.6 ns---with intrinsic errors suppressed to the $2\times10^{-5}$ level. We construct dephasing noise models, calibrated against published experimental measurements, that capture fast dephasing from room-temperature control electronics and slow dephasing from $1/f$ flux noise. Using these models, we identify dephasing sweet spots that suppress sensitivity to dephasing noise. We further exploit transmon asymmetry as a design parameter to access distinct noise-resilient operating regimes. These results establish an experimentally applicable framework for balancing gate speed, fidelity, and noise robustness while reducing characterization and recalibration overhead.

We prove that the randomized communication complexity of Vector-in-Subspace in $\mathbb R^n$ with error at most $1/3$ is $Θ(\sqrt n)$. Alice holds a unit vector $u$ and Bob holds an $n/2$-dimensional subspace $H$; they must distinguish $u\in H$ from $u\in H^\perp$. An exact one-way quantum protocol uses $O(\log n)$ qubits, making the problem a geometric example of an exponential quantum advantage over interactive classical communication. Our lower bound matches Raz's $O(\sqrt n)$ upper bound, improves the $Ω(n^{1/3})$ lower bound of Klartag and Regev, and removes the total-rank restriction in Grupel's $Ω(\sqrt n)$ result. The proof establishes a Gaussian moment bound over complete rectangle partitions. A complex Gaussian representation yields a vanishing even moment whose cancellation is preserved when averaging over the partition. We control the signed conditional moments around a real center by decomposing conditional Gaussian measures into fixed coordinates and sub-Gaussian components. Combining this estimate with spherical harmonic analysis gives the communication lower bound.

Majorana drew a symmetric multiqubit state as points on the Bloch sphere, antipodal to the zeros of its overlap with spin coherent states. Projecting only one qubit of a general state leaves the others in a state that varies with direction. Its entanglement invariants are eigenvalues of a non-Hermitian matrix and form bands over the sphere. Exceptional points appear, without gain or loss, where the entanglement family of the rest changes. Circling one exchanges two bands, so the bands form one Riemann surface. At five qubits it fixes the entanglement class up to finitely many choices.

I discuss two important quantum optics experiments which depend on two particle interference. In the years since their first demonstration many interesting and instructive variants have appeared, including the use of atoms instead of photons as the interfering particles. This chapter gives a pedagogical overview of some of these results and argues that the two effects are closely related.

Modular quantum architecture requires long-distance quantum interconnects to stitch together individual processor modules. Such interconnects, long-distance couplers or L-couplers, must support coherent quantum operation over meter-scale distances and scale to multiple connections between any two modules. Here we demonstrate four L-couplers operating between two 120-qubit IBM Nighthawk R1 superconducting qubit processors. Each L-coupler joins two Nighthawk lattice qubits through two frequency-tunable L-qubits, two RF-SQUID based "i2m" couplers, and 80 cm of superconducting aluminum coax. Each cable installs perpendicular to the processor surface, to enable denser connections, and is joined to the chip by an indium-to-indium room temperature pressure bond made after both modules were mounted. L-coupler modes near 5 GHz, with internal quality factors of 0.86 to 1.09e6, carry relay-based state transfer at a mean network benchmarking fidelity of 99.00%, with a best link of 99.29 +/- 0.07%. We then realize distant CZ gates between lattice qubits in separate modules at a mean fidelity of 94.75%, with a best link of 96.42 +/- 0.28%, and use them to generate entangled states across the two processors, including a demonstration of simultaneous Bell pair generation using two adjacent L-couplers. These four high-fidelity L-couplers establish a practical path to scalable quantum interconnects for modular quantum computing.

Two single-ion optical clocks, located in the United Kingdom and in Germany, are compared remotely via a 2220\,km long optical fiber link. Both clocks are based on the ${}^2S_{1/2} (F=0)\leftrightarrow {}^2F_{7/2} (F=3)$ electric octupole (E3) transition in $^{171}\text{Yb}^+$. Using more than $10^6$ seconds of measurement data, we determine a fractional frequency difference of $1.0(4.8)\times 10^{-18}$, demonstrating agreement of the independently developed systems. To our knowledge, this constitutes the first international clock comparison reaching a fractional uncertainty below $5\times 10^{-18}$, an important milestone towards an anticipated optical redefinition of the SI second. The measurement uncertainty is dominated by that of the relativistic redshift correction between the two sites, which includes time-varying gravity potential differences. We exploit the large baseline between the two clocks to search for violations of Lorentz invariance. In the absence of statistically significant modulations, we improve constraints on the Robertson-Mansouri-Sexl parameter $α$ by approximately a factor of five in the uncertainty, and provide limits on corresponding parameters within the Standard-Model Extension framework.

We establish that transversal diagonal gates on exact qubit codes of distance at least two can be exhaustively classified within a finite search space. Although code-preserving physical gates can have continuous phases, any projective logical action induced by a transversal diagonal gate can always be realized by a physical gate of finite order. Crucially, we prove that this physical order has an upper bound determined solely by the code parameters. This order bound enables the subset-sum-linear-programming (SSLP) framework introduced in arXiv:2504.20847 to exhaustively enumerate all candidate discrete symmetries, after which the Knill-Laflamme equations determine the remaining continuous code parameters. Applying this method to the nontrivial diagonal sector of exact $((6,2,3))$ codes, SSLP yields $66$ candidate symmetry classes, of which exactly $15$ are realizable, supporting full projective diagonal logical cyclic groups of orders $2$, $3$, and $5$. In particular, for order $5$, the code is unique up to local unitaries and qubit permutations, equivalent to the code constructed in arXiv:2504.20847. This code also attains the minimum length $n=6$ among exact $((n, 2, \ge 3))$ codes whose full projective transversal group cannot be conjugated into the projective Clifford group.

Variational Quantum Algorithms (VQAs) are promising approaches for solving combinatorial optimization problems on near-term quantum devices. However, the role played by quantum resources such as entanglement and coherence during the optimization process remains poorly understood. In this work, we investigate the evolution of these resources in two VQAs--the Quantum Approximate Optimization Algorithm (QAOA) and the Feedback-based Algorithm for Quantum Optimization (FALQON)--applied to the Minimum Vertex Cover problem. We employ a variational resource-quantification framework based on the Bures metric and Uhlmann's theorem, in which an auxiliary quantum circuit is optimized to identify the closest resource-free states. This approach allows us to quantify Bures entanglement and Bures coherence of the algorithmic states without requiring full quantum state tomography. For the considered problem instance, QAOA exhibits a pronounced accumulation of entanglement in its initial layers, followed by a progressive reduction as the algorithm converges toward the optimal solution. Its coherence likewise decreases overall with increasing circuit depth, although a finite residual value persists due to the degeneracy of the optimal-solution subspace. In contrast, FALQON exhibits a substantially lower entanglement peak, reached at larger circuit depth, followed by a decay as convergence proceeds. Its coherence decreases smoothly and monotonically together with the optimization error. These results reveal distinct quantum-resource trajectories associated with the two optimization strategies and illustrate how entanglement and coherence evolve as variational quantum states approach solutions of a classical combinatorial optimization problem.

Impedance matching is a crucial feature of an amplifier used to increase its instantaneous bandwidth and is typically achieved using static LC resonators. Here we show an approach to impedance matching in parametric amplifiers using arrays of unequal Josephson-junction-based elements (rf/dc SQUIDs, SNAILs, etc). The elements act either as small-footprint flux-tunable inductors forming an impedance-matching circuit, or 'active' amplifier elements which result in amplifier gain. We develop an analytical theory describing these systems, predicting a quasi-non-periodic amplifier frequency and gain modulation with applied flux and the broadening of gain bandwidths. We demonstrate this in devices using arrays of flux-focused SNAILs where flux biasing varies across the array. We find instantaneous bandwidths of 200 MHz with $>$17 dB of gain centred at $\sim$5.4 GHz in a device without a static impedance matcher. This broadening of amplifier bandwidth is stable with $>$100 MHz bandwidth at 17 dB gain across $>$1.2 GHz tunable bandwidth. Our analytical model captures flux dependence and qualitatively reproduces gain-bandwidths giving confidence in our understanding of these systems and allowing operational figures of merit to be optimised in future devices.

The superconducting diode effect requires the forward and reverse bias currents to differ, a scenario achieved via inversion and time-reversal symmetries broken together. The latter, and the more crucial one, is inevitably achieved by a magnetic field. Here, we show that a spatio-temporally driven chemical potential of the form, $μ_j(t)=μ+V\cos(ωt+\kd j)$, achieves both at once. Applied to a helical Shiba chain, the drive transmutes a traveling Peierls phase via generating an odd-in-momentum term, equivalent to an imaginary next-nearest-neighbour Haldane-like hopping in real space. Remarkably, the protocol is spin-blind, which renders the time-reversal breaking via a synthetic gauge flux rather than an effective Zeeman field. The rectification is odd in the drive wavevector, with exact zeros at $\kd=nπ$ and an analytical optimum at $\kd=2π/3$. It is however, even in the exchange coupling, $J$ and persists even at $J=0$. Furthermore, the rectification scales inversely with the pair-breaking gap, yielding approximately $50\%$ rectification in the topological phase and $10\%$ in the trivial phase. Symmetry breaking is thus drive-controlled, allowing it to be switched on, tuned, and reversed without an external magnetic field.

Teaching quantum mechanics at the secondary school level remains a major educational challenge. Traditional historical approaches often present the theory as a sequence of disconnected phenomena, requiring extensive prior knowledge of classical physics before students can appreciate the conceptual structure of quantum physics. In this work, we present the design, implementation, and evaluation of a curriculum based on the two state (qubit first) approach, in which the fundamental postulates of quantum mechanics are introduced through mathematically accessible two level systems and realized with light polarization. The curriculum integrates theoretical instruction, laboratory activities, a coherent progression grounded in the interactive simulations, and inquiry based learning into a coherent pathway that progresses from quantum states and superposition to entanglement and the experimental violation of Bell's inequalities. A distinctive feature of the project is the experimental realization of the violation of Bell's inequalities obtained in a newly established quantum optics laboratory in an Italian high school, where students performed, for the first time in Italy, an authentic Bell test using polarization-entangled photons. The same educational framework was adopted for in service teacher professional development courses. Learning outcomes were evaluated through mixed methods. Preliminary analysis indicates significant improvements in conceptual understanding, confidence in using mathematical formalism, and appreciation of the relationship between theory, experimentation, and the foundations of quantum mechanics. The proposed curriculum shows that two-state formalism and supported by real laboratory experiences enables secondary-school students to engage more meaningfully with both the conceptual foundations of quantum mechanics and their experimental verification.

In quantum mechanics, conservation laws are usually understood only statistically and only in the context of unitary evolution: during such evolution, if an observable commutes with the Hamiltonian, its expectation value and Born-rule probability distribution remain unchanged. Individual measurement outcomes, however, disrupt even this weak form of statistical conservation. Recently, though, it has been argued that a stronger, non-statistical form of conservation, valid at the level of individual measurement outcomes, can be recovered. The proposal relies on the claim that any superposition of eigenstates of a conserved quantity must ultimately be prepared relative to another physical system, which serves as the relevant reference frame and remains correlated with the system being prepared. On this enlarged description, the change observed in the measured system is claimed to be exactly compensated by an opposite change in the preparer, thereby restoring conservation at the level of individual measurement outcomes. We analyze this proposal and argue that it faces significant conceptual difficulties. We show that the proposed mechanism is not adequately justified and, moreover, does not establish conservation in individual measurement outcomes as claimed.

We show that the concept of particles and antiparticles is related to the Weyl-Heisenberg group $W\!H_3$. Its generators are the position operators $\hat x^a$, the momentum operators $\hat p_a$, and the central element $Q_{\sf{v}}$, which defines a subgroup U(1)$_{\sf v}$ of $W\!H_3$. We show that the wave functions have a charge relative to the group U(1)$_{\sf{v}}$ equal to either $q_+=1/\hbar$ (particle $ψ_+$) or $q_-=-1/\hbar$ (antiparticle $ψ_-$). We call these eigenvalues of the operator $Q_{\sf{v}}$ quantum charges: $Q_{\sf{v}}ψ_\pm^{}=q_\pm^{}ψ_\pm^{}$. The wave functions $ψ_+$ and $ψ_-$ belong to the Hilbert spaces $\mathcal{H}_+$ and $\mathcal{H}_-$, on which unitarily inequivalent representations $π_\hbar$ and $π_{-\hbar}$ of the Weyl-Heisenberg group $W\!H_3$ are defined. These representations are related to each other by the antilinear charge conjugation operator $\hat C$, which maps $\mathcal{H}_+, q_+$ to $\mathcal{H}_-, q_-$. Charges $q_\pm^{}$ are intrinsic characteristics of the wave functions $ψ_\pm^{}$, similar to spin and electric charge. The wave function possesses one of these charges, $q_+$ or $q_-$, prior to the specification of any equations. We show that negative probabilities/energies and the Klein paradox in Klein-Gordon and Dirac theories are consequences of the violation of U(1)$_{\sf v}$-invariance in these theories. Restoring this invariance separates particle and antiparticles and eliminates all paradoxes at the level of first-quantized relativistic theories.

Predicting molecular electronic structure using Quantum Computing approaches is a challenge in Computational Chemistry. Traditional Variational Quantum Eigensolvers (VQEs) are typically hindered by optimization challenges. The alternative Generative Quantum Eigensolver (GQE) mitigates this by reformulating ground-state search as discrete sequence generation, but its Transformer backbone suffers from quadratic computational complexity, bottlenecking scalability for larger molecules. To address this, we introduce the Mamba Quantum Eigensolver (Mamba-QE), which replaces the Transformer with a Selective State Space Model (SSM) to process operator sequences with linear $\mathcal{O}(L)$ complexity. Additionally, we integrate a distance-conditioned mechanism enabling the direct prediction of complete potential energy surfaces (PES). Evaluated on the $H_2$ molecule, Mamba-QE reproduces Full Configuration Interaction (FCI) reference energies well within chemical accuracy, achieving an energy error below $3\times10^{-6}$ Ha across 16 geometries with zero variational violations. Mamba-QE maintains high expressive power while establishing a robust, scalable foundation for quantum simulations of complex molecular systems.

We explore the space-time cost of encoding of a bosonic mode into a set of qubits via various encodings, and their resilience to noise. In particular, we compare the performance of the unary Fock state encoding, an unexplored encoding of Fock states into Dicke states (``Dicke'' encoding), and the binary quadrature encoding. We do so by considering a displacement as well as a simulation of a Dicke model, coupling a bosonic mode to a set of atoms represented as qubits. Using classical simulations, we assess the accuracy and optimized space-time costs in terms of number of qubits, circuit depth and CNOT count of a quantum simulation of the time dynamics using these encodings. Although our study is far from comprehensive, we find that the binary quadrature encoding is overall most favorable in terms of being very space-efficient and relatively time-efficient due to the use of the quantum Fourier transform. Our novel Dicke encoding leads to very shallow circuits, but pays in terms of using many more qubits. We probe the use of an H2-2 Quantinuum trapped-ion qubit device (56 qubits) for displacement and Dicke model simulation in the low boson-number regime, where we find that noise leads to visible deviations from ideal circuit dynamics.

Motional modes of trapped-ion crystals in Penning traps can now be cooled to near their ground states via electromagnetically induced transparency (EIT) cooling. Numerical simulations are valuable tools for interpreting EIT cooling results and optimizing experimental protocols, but existing molecular dynamics codes are limited to the simulation of Doppler cooling. In this work, we fill this gap by implementing a semiclassical model of EIT cooling in a novel MD code. By simultaneously evolving the ions' internal quantum states and classical motion, we are able to calculate the instantaneous EIT laser forces acting on the ions. We first validate our code by comparing the single-ion cooling rate to fully quantum simulation results. Next, we analyze cooling of the drumhead modes in planar ion crystals, quantifying the effects of planar ion motion and a finite laser beam width. Finally, we demonstrate efficient EIT cooling of the axial modes in 3D ellipsoidal crystals containing up to 500 ions. Such crystals are a promising platform for future quantum sensing experiments with enhanced sensitivity. We find that the mode spectra of 3D crystals can be engineered to enable sympathetic cooling of the low-frequency $\boldsymbol{E}\times\boldsymbol{B}$ modes. This numerical framework provides a powerful tool for modeling sub-Doppler cooling techniques and for optimizing future quantum sensing and quantum information experiments.

The same classical f-divergence admits inequivalent extensions to quantum states. The question is whether these extensions can be obtained from a common operational variational principle. Here we generalize Matsumoto's reverse-test optimization by introducing a reference prior state. More explicitly, we minimize the statistical distinguishability between a forward and a reverse prepare-and-measure process, related by retrodiction through the chosen reference and subject to prescribed quantum averages. Distinguishability is quantified by the classical f-divergence between their complete records. For faithful states in finite dimension, we prove that the same spectral implementation attains the minimum simultaneously for every operator-convex f. Varying the reference allows us to interpolate between standard and maximal quantum f-divergences of the prescribed states, passing through the geodesic family. More precisely, a flat reference yields the standard quantum f-divergences, thereby giving the Nussbaum-Szkoła distributions a variational characterization as optimal records. Choosing either prescribed state as reference recovers maximal quantum f-divergences and Matsumoto's reverse tests, while power references realize the geodesic interpolation. In the relative-entropy case, this gives the passage from Umegaki to Belavkin-Staszewski relative entropy by changing the prior for retrodiction.

Combining topological insulators with chiral magnetic multilayers offers the opportunity to greatly enhance the spin-orbit torque (SOT) driven manipulation of hosted spin textures, however this also exposes devices to the often poor temperature stability of the commonly used, Bi$_2$X$_3$-based (X is a chalcogenic element), topological insulator films. In this work we demonstrate through in-situ-annealing and polarised neutron reflectometry that the multilayer at a Bi$_2$Se$_3$ interface remains magnetically robust up to a temperature of 350 $^{\circ}$C: even as the Bi$_2$Se$_3$ epilayer structurally deteriorates. Through x-ray photoemission electron microscopy, an intermediate annealing temperature of $\sim$ 200 $^{\circ}$C was found to improve the domain ordering of the multilayer, allowing for field-induced skyrmion nucleation, all whilst sustaining minimal damage to the topological insulator

Quantum computing represents a fundamental shift in computation, promising to solve problems currently intractable for classical computers. However, misconceptions persist; quantum computers are not universally faster, nor do they replace classical systems. Current Noisy Intermediate-Scale Quantum (NISQ) devices face significant challenges, including decoherence, high error rates, and limited scalability. Additionally, leveraging quantum systems requires rethinking traditional computing principles, adopting different programming models, and addressing the complexities of integrating quantum and classical workflows, making their practical use in computer science both demanding and non-trivial. This article provides a system-level perspective on quantum computing for computer scientists, software engineers, and IT professionals, examining its current capabilities, key architectural and software challenges, and potential paths toward quantum advantage in real-world applications within hybrid quantum-classical environments.

The local distinguishability of five bipartite and tripartite orthogonal product states (OPSs) has been effectively resolved, while that of five quadripartite OPSs has not yet been effectively addressed. In this paper, we give the local distinguishability of five quadripartite OPSs, where any two of these five states are orthogonal on exactly one subsystem. Based on the vectors of the numbers of pairwise orthogonality relations, we classify different sets of five quadripartite OPSs into nine categories, which correspond to 371 distinct orthogonality graphs. We show that the sets of five quadripartite OPSs corresponding to 355 of the 371 cases can be perfectly distinguished by local operations and classical communication (LOCC), whereas the sets of five quadripartite OPSs for the remaining 16 cases cannot exactly distinguished by LOCC. Our results enrich the theory of nonlocality for sets of OPSs.

We apply a large Gaussian basis set of size up to $N = 500$ to calculate the all-order Wichmann-Kroll vacuum polarization correction in highly-charged ion. For a hydrogen-like system, this allows us to obtain an accurate correction value with a level of precision comparable to that of traditional methods. We demonstrate that values of effects that can be calculated as the difference between two quantities, such as the nuclear model correction, converge faster than the absolute value of the correction. We discuss the basis extrapolation methods and show their use in estimating the error due to incomplete convergence. Finally, we show an application of the Gaussian basis set to calculation of the vacuum polarization screening correction in lithium-like ions.

We propose a quantum-enhanced matter-wave interferometry protocol based on fractional-revival dynamics of a Bose-Einstein condensate in a ring, combined with a controlled interaction quench. Using the Truncated Wigner Approximation, we show that nonlinear evolution to the quarter revival generates modest spin squeezing of $-2.03\pm0.28\;$dB, which subsequently degrades under further nonlinear evolution. In contrast, starting from a non-interacting condensate, a controlled interaction quench applied after the initial quarter-revival beam-splitter operation generates substantially stronger spin squeezing of $-14.57\pm0.27\;$dB. We further show that phase control at $t=3T_r/8$ rotates the squeezed quadrature onto the phase-sensitive direction $\hat{J}_y$, producing a phase-squeezed state at $t=T_r/2$. The subsequent quarter-revival evolution converts this phase-squeezed state into a number-squeezed state, enabling population-difference readout. The resulting sequence provides a route to quantum-enhanced interferometry using the intrinsic fractional-revival dynamics of a ring together with controlled interaction and phase operations.

We consider a continuous-time quantum walk stroboscopically subjected to projective measurements on two distinct targets with sampling time period $τ$. We construct a general renewal framework for the first-detection amplitude at each target, from which we obtain the associated splitting probabilities. For Hamiltonians with reflection symmetry, we further show that each dual-target first-detection amplitude can be viewed as an interference effect between a pair of single-target first-detection amplitudes. This formulation yields exact expressions for the splitting probabilities and gives special sampling times at which they undergo pointwise discontinuous jumps due to a form of ergodicity breaking associated with dark states. As an illustrative example, we apply the framework to a one-dimensional tight-binding lattice chain with nearest-neighbor hopping, and study the splitting probabilities as functions of the initial position and sampling time. Below a critical sampling time, $0<τ< τ_c$ where $τ_c = 2 π/ ΔE$ with $ΔE$ being the energy bandwidth, the splitting probabilities for large system sizes become equal to $1/2$, independent of the initial position, as long as this position does not coincide with target sites. Above the critical sampling time, $τ\geq τ_c$, the splitting probabilities deviate from $1/2$ and develop oscillations as a function of initial position. The wavenumber associated with these oscillations is $Q=2\sin^{-1}(rτ_c/τ)$, where $r$ is a positive integer. We also explore the effects of relative phase and spatial separation between different components of a coherent initial state on the splitting probabilities. Finally, we study how a finite number of measurements modifies the splitting probabilities and broadens the resonances at special sampling times.

We describe a compact and simplified experimental setup for the production of ultracold strontium atoms. Thanks to its low-power oven and coil-free Zeeman slower design, the vacuum system has an overall length of only 40cm including oven, Zeeman slower and all-glass science cell. The oven has a power consumption of 14W at 460°C and produces a collimated flux of 3 10^10at/(s cm^2) at this temperature. The laser system employs master-slave laser architecture throughout and requires neither second-harmonic generation nor tapered amplifiers, reducing cost and complexity. The system has been in continuous use for more than a year.

Electron--electron interactions can reconstruct Bloch wave functions, changing their geometry and the associated thermoelectric response. We derive the linear thermoelectric response within the Hartree--Fock (HF) approximation using the thermal length-gauge density-matrix approach, resolving Drude, symmetric quantum-metric, and antisymmetric Berry-curvature contributions. In a noninteracting Bloch eigenbasis, we separate the reconstructed Berry connection into the noninteracting connection and an interaction connection. This gives bare, coherence, and interaction-connection contributions to the anomalous thermoelectric response. We determine the constraints imposed by spatial inversion, rotational, time-reversal, and combined symmetries on the three transport channels. In the relaxation-time approximation, the leading weak-broadening behavior is $Γ^{-1}$ for the Drude contribution, $Γ$ for the quantum-metric contribution, and $Γ^0$ for the Berry-curvature contribution. The interband scalings apply away from band degeneracies. Self-consistent calculations for the triangular-lattice extended Hubbard model illustrate how interactions generate Berry curvature and a quantum metric, change the symmetry of the system, and thereby contribute to transverse thermoelectric transport.

Nanoscale nonreciprocal elements are needed to control signal flow in scalable quantum technologies, but existing nonreciprocal components are often bulky. Here, we show that a strongly nonreciprocal current-voltage relation can arise entirely from coherent elastic scattering in a mesoscopic Rashba nanowire with gate-defined scatterers. We first identify the symmetry constraints that enforce reciprocal transmission in a phase coherent conductor even when inversion and time-reversal symmetry are broken. We then show how gates that are capacitively coupled to the leads, together with a magnetic scatterer or transverse subband mixing, can remove these constraints. In the weak-scattering regime, nonreciprocal conductance originates from interference between distinct backscattering paths. In the strong-scattering regime, nonreciprocity can be resonantly enhanced by the hybridization of the transmitting channel with bound states that arise from a higher transverse subband or spin-split band. In this regime, we find that a bias-induced change in the gate potentials of about one percent can produce an order-unity diode response, i.e., electrons are transmitted almost as in a clean wire for one bias polarity, whereas for the other polarity the current is strongly suppressed.

We construct short triorthogonal codes for qudits of odd prime dimension by generalizing doubling, which combines a triorthogonal code with a code admitting a transversal phase gate, and raises the distance by up to two. This gives codes with parameters $[[28,1,4]]_3$, $[[37,1,5]]_3$, $[[72,1,6]]_3$, $[[118,1,8]]_3$, $[[33,1,5]]_5$ and $[[20,1,4]]_7$, each shorter than the cyclic, concatenated and Reed-Muller codes of the same distance, and a doubling construction of the $[[15,1,3]]_3$ code. When the columns of a generator matrix are regarded as charged points, triorthogonality becomes the vanishing of multipole moments up to octupole order, and doubling becomes a double layer of opposite charges; this picture explains why inputs with nontrivial coefficients can give shorter codes. We also show by exhaustive search that the shortest codes of distance three have length $11$ for $p=5$ and length $7$ for $p=7$. Combined with high-rate distance-two codes, the new codes reduce the cost of qutrit magic state distillation by up to an order of magnitude in regimes with high input noise.

A recent formulation of quantum belief showed that quantum retrodiction depends not only on the reduced density operator of the system of interest, but also on correlations with a hidden reference system, which leads to the notion of quantum belief equivalence. In this paper we formulate a multi-shot problem, where the extended posterior obtained after one update is used again as the prior for the next update. We first define a formal notion of $n$-shot equivalence and derive several propositions for arbitrary extended beliefs. We then argue that the agent must also specify why the data obtained in different rounds concern the same underlying object. Through the quantum de Finetti representation, this narrows the one-copy belief to a special class: candidate-state ensemble belief. In that sector, we show that two beliefs are $n$-shot equivalent if and only if their $(n+1)$-th moments are equal. We also give a physical interpretation of this moment condition and illustrate it through the equivalence between Haar priors and projective-design priors at bounded update depth.

Optically addressable electron spin qubits that function at room temperature and under ambient conditions are essential for advancing quantum sensing. Solid state defect platforms offer robust spin-photon interfaces but lack precise defect positioning and electronic tunability. Molecular spin qubits enable bottom up chemical design yet suffer from limited photostability. Here, we introduce para-halophenyl (-Cl, -Br and -I) quantum defects in (6,5) single wall carbon nanotubes that trap triplet excitons with a spin-photon interface that is operable under ambient, room temperature conditions. These defects were shown to emit in the near infrared within the biological transparency window, and their placement on the nanotube surface provides nanoscale proximity to target environments. The deep optical traps formed by the defects yield exceptional photostability. Here, we demonstrate optical initialization and readout of these triplet states at room temperature, provide proof of principle sensing of paramagnetic molecules, and highlight potential for on chip detection. Together, these results establish SWCNT defects as a promising new platform for future quantum sensing.

Coherent multidimensional spectroscopy probes interactions and dynamics of molecular systems through nonlinear optical signals. Quantum light excitation has been explored as a means of controlling these signals, raising the question of how excitation-light correlations affect the precision of molecular parameter estimation from the emitted signal. In this work, we show that photon-number correlations and two-photon coherence play distinct roles in encoding molecular information in the emitted rephasing signal. In the weak-emission regime and within the single Schmidt pair approximation, we derive a normally ordered information law in which the joint photon-number moment and the squared magnitude of the two-photon coherence weight the amplitude and phase sensitivities of the molecular response, respectively. For matched temporal modes and mean photon numbers in each input mode, two-mode squeezed vacuum enhances both weights relative to coherent excitation, whereas independent displaced squeezing preserves the amplitude weight but reduces the phase weight. The background population and its parameter dependence also affect the total quantum Fisher information, which therefore cannot be inferred from the coherent mean-field signal alone. We derive a leading-order bound on its enhancement over coherent excitation when the background population is nonnegative and common to the compared sources. These findings provide criteria for selecting excitation sources according to how the target molecular parameter affects the amplitude and phase of the response.

Controlling transition rates is a central objective across quantum optics, condensed-matter physics, and chemical physics, encompassing processes such as spontaneous emission, energy and charge transfer, spin relaxation, and chemical reactions. Although Fermi's golden rule provides a powerful framework for calculating such rates of weakly coupled transitions, conventional calculations require the interaction to be specified in advance; the range of rate responses attainable over a broader interaction space remains unknown. We formulate spectral-overlap golden-rule rates as quadratic forms of the interaction and derive rigorous bounds on rate modulation over a specified interaction space. As an example, application to energy transfer from a donor to a molecular vibration coupled to an optical cavity reveals that enhancement and suppression depend jointly on the interaction and cavity detuning, including continuous reversal of the rate response for a fixed interaction. The same approach may elucidate rate control for other golden-rule processes, including excitation-energy transfer, nonadiabatic electron transfer, nonradiative electronic transitions, vibrational and spin relaxation, and spontaneous emission.

This work revisits the debate on fractional uncertainty relations that arose a decade ago and tries to settle it. After a careful study of the position-momentum uncertainty product of the Lévy wave packet, a novel lower bound is proposed for uncertainty relations in fractional quantum mechanics. This bound is nearly linear in the Lévy index and is satisfied by exact, calculable solutions available in the literature.

In this work, we investigate the convergence rate of the quantum Blahut-Arimoto (BA) algorithm proposed for computing the coherent information of less noisy quantum channels. Previous work established exponential convergence under certain restrictive assumptions on the channel. Using a Taylor expansion around a positive definite optimizer, we show that, for an injective degradable channel whose degrading channel has a relative-entropy contraction coefficient strictly less than one, the algorithm converges at an exponential rate after sufficiently many iterations. We further verify this condition for qubit amplitude-damping (AD) channels in the relevant parameter regime. In addition, by analyzing the Bogoliubov-Kubo-Mori (BKM) metric on the Bloch ball, we derive an explicit characterization of the relative-entropy contraction coefficient of qubit AD channels. The proposed approach is further extended to calculate the relative contraction coefficient and the relative expansion coefficient of two qubit AD channels.

We present an error-controlled framework for the quantum simulation of non-Markovian open-system dynamics in Gaussian environments. For a system coupled linearly to a Gaussian environment with zero mean, the bath's influence on the reduced dynamics is completely determined by its two-time correlation kernel. This allows us to replace the microscopic environment with an equivalent bath that has the same kernel. On a finite simulation interval, a rank-$N$ approximation of the kernel yields an effective bath of $N$ bosonic modes with time-dependent couplings to the system. To encode these modes in qubits, we first truncate each mode to its lowest $d$ occupation levels. When stronger couplings lead to large occupations, we introduce coupling dilution, which replaces each mode with several more weakly coupled copies while preserving the bath correlation kernel. This distributes excitations across more modes and trades additional modes for smaller local dimensions. We derive explicit reduced-state error bounds and establish polynomial circuit width and depth in simulation time and inverse accuracy under stated spectral-decay and coupling-regularity assumptions, provided elementary unitaries admit polynomial-cost implementations.

The Fröhlich-Pizzo (FP) model is a quantum-mechanical model originally developed to describe the interaction between an atom and the electromagnetic field in the nonrelativistic limit $c\to\infty$. We show that an adaptation of the FP model based on the local algebras of a $U(1)$ chiral current captures essential features of the horizon-induced decoherence mechanism identified by Danielson, Satishchandran, and Wald (DSW) in the limit of large holding time $T$. Our analysis suggests that the effective dynamics of the system undergoing decoherence in the DSW setting retains non-Markovian features. Our approach also offers a glimpse into the possible role of quantum events in the dynamics underlying horizon-induced decoherence.

We investigate spin-resolved momentum distributions and phase vortices in multiphoton electron-positron pair production within a modified two-level model. This model retains the diagonal spinor inner-product terms neglected in the adiabatic approximation, thereby inducing spin-resolved transverse asymmetries in the momentum distribution. For a circularly polarized pulse, the handedness determines the winding direction of the quantized vortices, whereas for a linearly polarized pulse, the phase distribution exhibits nodal lines rather than quantized vortices. For two time-delayed circularly polarized pulses, the time delay introduces a relative phase that governs the multiphoton interference, which in turn drives the vortex evolution in each spin configuration. These results demonstrate that pulse polarization and time delay enable coherent control over vortex topology in pair production.

We theoretically investigate the interplay of topology and localized non-Hermiticity in a finite Su-Schrieffer-Heeger chain characterized by non-Hermitian potentials at its boundaries. By tuning the boundary gain and loss parameters, we exploit the finite-size hybridization of two mid-gap topological edge states to analytically derive the exact coordinates of boundary-induced exceptional points (EPs), $Γ_{\rm EP}=\pm i v^{N}/w^{N-1}$, at which these states undergo coalescence. We demonstrate that dynamically encircling these boundary EPs facilitates a robust, chiral edge state-transfer protocol. Depending on the orientation of the encircling loop, this protocol allows a topological edge state localized at one boundary to be either transferred to the opposite edge with perfect fidelity or returned to its starting position through a double switching process. Importantly, since the non-Hermiticity remains strictly confined to the boundaries, this chiral transport occurs without affecting the energy spectrum of the bulk bands. These results establish a minimal framework for a large-scale topological chiral switch that is experimentally verifiable and capable of being controlled through boundary non-Hermitian driving.

Dense ensembles of nitrogen-vacancy (NV$^-$) centres in nitrogen-rich diamond dephase on the electron spins of the substitutional nitrogen (P1) centres. If the paramagnetic nitrogen is instead converted into NV$^-$ centres, the laser that initializes the sensor also pumps the bath into $m_s$ = 0, a state with no moment along its own axis. Using cluster-correlation-expansion (CCE) calculations, combined with an exact solver for probe-bath exchange and with no adjustable parameter, this paper asks whether such an optically polarized NV$^-$ bath dephases a sensor more slowly than a P1 bath of the same density. The answer is set by the field. In a field along [111], three quarters of the bath centres lie off the field axis, and the moment of their $m_s$ = 0 state along the field grows from 0.04 at 25 G to 0.46 at 300 G and 0.81 at 800 G. At 25 G the polarized bath is therefore nearly silent: at $10^{17}$ cm$^{-3}$ the dephasing time $T_2^*$ of a separately addressed $^{15}$NV$^-$ probe is 112 us, six times the 18.1 us of a P1 bath, and still 2.4 times at 90 % polarization; an ensemble measurement gains a factor of two. At 300 G the advantage over P1 shrinks to 1.4, and at 800 G the polarized bath dephases faster than P1. The field dependence of every bath, P1 included, follows the mean moment of its centres along the field. For the Hahn echo, exchange with on-axis bath centres and bath relaxation ($T_1$ = 6 ms) limit the gain to 1.2 times the P1 value at 25 G. Optical polarization of an NV$^-$ bath at low field therefore offers dephasing times beyond the P1 limit of nitrogen-rich diamond.

A quantum computer could recover the key of any Ethereum account whose public key appears on chain. We prove that no sidechain or bridge that leaves Ethereum's rules unchanged can protect such accounts: their funds must move into a contract whose release condition relies only on quantum-safe primitives. We design \emph{PQ-Vault}, a custody system for unmodified Ethereum combining this vault, a quantum-safe proof-of-stake sidechain whose checkpoints carry compact certificates, and an optimistic dispute protocol. We give the first security proof of compact certificates against quantum attackers and a matching attack: with classically chosen parameters, the guarantee falls from 128 to about 60 bits, and a simple rule restores it. We show that a common seed-update rule in hash-chain proof of stake lets an attacker steer chosen slots and profit from splitting its stake, and give an election whose steering gain and inclusion delay are provably bounded against quantum attackers. Since compressing certificates with a pairing-based SNARK breaks quantum security, we use fraud proofs that need a single signature check. For 65,536 validators, a certificate is 0.8 MB, 260 times smaller than all signatures, and verifies in about 20 ms; the vault accepts a checkpoint for about 420,000 gas.

Kelvin waves carry energy along vortices, but their resonant interactions contain information that is absent from the linear spectrum. We identify a geometry that exposes this information on a vortex surface in four spatial dimensions. Perpendicular incoming waves cancel the complete local-area four-wave coupling, leaving the finite nonlocal interaction mediated by the surrounding fluid. This interaction restores conversion at generic wave-number ratios, yet changes sign and vanishes at a selected ratio while momentum and frequency remain exactly matched. Matching to Gross-Pitaevskii (GP) theory, including the microscopic core response, establishes a zero of the full coupling at every sufficiently small nonzero wave number, with ratio tending to $λ_*\simeq1.469$. Finite-grid GP coefficients exhibit a sign reversal for the same resonant quartets. Separate coherent-mixing calculations and weak-probe spectra connect the coupling sign to the generated-wave phase and the ordering of reflection-even and reflection-odd modes. The resulting suppression removes a leading channel for changing propagation directions without changing the paired wavelengths. These results isolate a nonlinear effect of the surrounding flow that local tension misses, providing a microscopic benchmark for vortex-wave theories and a starting point for studying angular redistribution beyond the Kelvin spectrum.

The solution of combinatorial optimization problems by means of quantum annealing is based on the preparation of an equally superposition state. Such superposition is crucial to the associative memory problem of correctly recalling patterns. In this paper, we study the alignment of the amplitudes of stored states in memory using the proposed auxiliary Hamiltonian, which is switched off at the end of evolution. The results of the algorithm execution were obtained both by numerical modeling and by the perturbation theory method, which made it possible to obtain the dependences on physical parameters in explicit form. As examples, systems of two and three qutrits, represented by spins S=1, are considered. Since the Hamiltonian is expressed in a univer-sal form through projectors onto states stored in memory, it can be used for other quantum sys-tems (platforms).

A circuit parameter can change measured features without changing their projected Gaussian kernel. We characterize this lost dependence and distinguish recovery by metric design from nonlinear feature expansion. With analytic feature coefficients, a fixed finite data basis affinely independent on the input domain, a fixed positive definite metric, and fixed bandwidth, the coefficient Gram matrix determines all-input kernel equivalence, global coordinate inactivity, and generic differential rank. An exact four-qubit family exhibits a sharp boundary: diagonal metrics give rank two, dense metrics reach but cannot exceed three, and no fixed affine expansion crosses this ceiling. One appended nonlinear scalar coordinate suffices for rank four and is minimal when the original features are retained. A single pairwise product achieves this with an explicit nondiagonal metric; a scalar sum of two products achieves it with a diagonal metric. Both use existing ideal local means. Exact certificates establish ranks in 54 selected circuit/readout settings. Matched finite-shot comparisons show that minimal representation size need not give the best sensitivity among the tested designs. Under a factorized measurement distribution, conditional product estimation cannot increase variance at a fixed design. Execution audits further separate kernel identifiability from compiled cost.

Selecting an effective quantum compiler configuration requires coordinated decisions over both hardware targets and compiler settings, with the ultimate goal of improving circuit execution fidelity. Existing SOTA approaches typically decompose this problem into two sequential stages: a device is chosen first, after which compiler options are tuned on that device through RL-based search. This bottom-up strategy can be fundamentally limited by its initial device decision, since a poorly matched backend may constrain the best fidelity achievable regardless of how effectively later compiler options are optimized. In contrast to classical compiler tuning, where the search space is often prohibitively large, the configuration space of quantum compilers remains manageable enough to support exhaustive search. Consequently, rather than repeatedly searching from candidate configurations, one can derive reusable configuration knowledge from offline oracle results and apply it directly to new circuits. In this paper, we introduce a top-down configuration-selection paradigm and build QuOPTBench, an exhaustively searched benchmark containing oracle configurations for 268 quantum circuits. We first study whether LLMs can directly infer suitable configurations and evaluate ten representative LLMs. The results reveal that vanilla LLMs remain far from the oracle. We then employ an LLM to extract transferable rules from sampled circuits governing configuration selection. Using these rules together with predictors trained on the enumerated configuration data of the sampled circuits, we design QuTOP, a rule-guided ML framework that performs fast configuration selection without iterative online search. Across our evaluation, the distilled rules consistently strengthen LLM-based selection, while QuTOP provides the strongest overall balance between solution quality and selection latency among the baselines.

Quantum Fisher information (QFI) is a fundamental quantity in quantum information and quantum mechanics, and evaluating it in various physical systems has become an important research topic. However, its evaluation in large systems still faces many challenges. Hereby we propose an ancilla-based protocol for evaluating the QFI of large systems and establish the conditions under which this protocol can ``perfectly'' evaluate the QFI in theory. As a demonstration, the protocol is applied to quantum circuits to evaluate the QFI of the Greenberger-Horne-Zeilinger state.

Quantum circuit optimization is a key step toward the efficient execution of quantum algorithms. Template matching has emerged as one of the dominant approaches for simplifying quantum circuits, yet it confronts the intrinsic challenge of accommodating gate commutativity. The state-of-the-art template-matching algorithm relies on a directed acyclic graph (DAG) representation. While this DAG-based technique handles gate commutativity satisfactorily, it fails to preserve the local connectivity inherent to quantum circuits, thereby leading to relatively high matching complexity. In this paper, we introduce a hypergraph representation (HG), a commutativity-aware representation that collapses commuting gates into a single super-node while retaining all local connectivity. This enables matches to be extended locally without revisiting the rest of the circuit, with incremental updates limited to the immediate neighborhood. Experimental results demonstrate that our HG matcher achieves 11--606x speed-up over the DAG-based implementation in Qiskit (Iten et al., 2022) on both random and arithmetic benchmarks, while maintaining the same optimization quality. The acceleration increases with circuit size, confirming that preserving locality and connectivity is the key to scalable quantum circuit optimisation.

We derive sufficient criteria that guarantee convergence of open quantum system dynamics to a unique long-time state independent of the initial conditions. We refer to this behavior as complete relaxation. Focusing on systems described by Gorini-Kossakowski-Sudarshan-Lindblad (GKSL) master equations on finite-dimensional Hilbert spaces, our approach uses only elementary mathematical arguments. For autonomous systems, we recover three previously derived relaxation criteria, which can be expressed as algebraic conditions on the Lindblad operators and the Hamiltonian entering the GKSL equation. For periodically driven systems, we obtain a new criterion involving a similar algebraic condition and a local continuity requirement on the time-dependent GKSL generator. This result implies an earlier criterion for complete relaxation formulated in Ref. [J. Phys. A 52, 43LT01 (2019)]. We also discuss implications of our approach for periodically modulated classical master equations, as well as extensions to driven systems without a periodicity constraint.

A ligand can adopt multiple conformations within the same binding site, and these conformations can interact differently with the surrounding protein. Multiconformer modeling must therefore determine which candidate conformations to retain and what occupancies to assign to them. An established automated approach uses mixed-integer quadratic programming (MIQP) with hard occupancy and conformer-count limits for this selection. Here, we reformulated conformer selection as a quadratic unconstrained binary optimization (QUBO) problem with finite penalties and discrete occupancies. We solved the QUBO using a quantum-classical hybrid solver. We compared this workflow with the MIQP-based qFit-ligand workflow across 83 paired X-ray ligand entries using the same experimental inputs and the same qFit-ligand processing protocol. For each entry, both final models were evaluated against the same composite-omit map generated from the common input structure before the two workflows diverged. Quantum-qFit produced higher ligand-region real-space correlation coefficients (RSCC) in 62 entries 74.7% and lower occupancy-weighted torsional strain in 66 entries 79.5%. Similar directional trends remained in the 28 entries with matched final conformer counts. The molecular Electron Density for Individual Atoms score (EDIAm) decreased in most entries. This result shows that higher regional map agreement did not necessarily correspond to stronger atom-level density support. Overall, the results show that the conformer-selection formulation can change which ligand states are represented from the same experimental data and provide a QUBO framework for studying multiconformer ligand selection.

Quantum Multi-Programming (QMP) enables the simultaneous execution of quantum circuits from multiple users on a single quantum chip in cloud quantum computing services. However, QMP is vulnerable to crosstalk attacks, in which a malicious user deliberately induces crosstalk to disrupt other users' computations. As a countermeasure, prior work has proposed the use of buffer qubits, which remain idle and are allocated between quantum circuits to suppress the effect of crosstalk. Nevertheless, to the best of our knowledge, such countermeasures have not been publicly reported in production quantum cloud software. In this paper, we extend the QMP of OQTOPUS, open-source software that is already in production use for operating real quantum computers, with a buffer-qubit-based circuit allocation method. Experiments on a real device characterize the attack effect in terms of energy relaxation and dephasing, showing that observable degradation appears in dephasing characteristics of qubits adjacent to the attacker circuit. Based on this result, we release the proposed method as part of OQTOPUS and confirm that the buffer qubits are correctly reserved around the allocated circuits.

Reaching a degenerate ground-state manifold and sampling it uniformly are distinct properties of a quantum annealer. We quantify this distinction using an Ising ring with additional couplings between maximally separated sites. For antiferromagnetic benchmark couplings and $N \geq 5$, we derive the exact ground-state energy, degeneracy, and defect structure for each congruence class of $N$ modulo four. This classification separates ground-state hit probability from conditional sampling bias. We embed instances with up to 162 logical spins on a D-Wave Advantage processor using length-two chains and compare its output with simulated annealing on the embedded and logical problems. For a frustrated $N=83$ instance, the processor visits 164 of the 166 exact ground states, yet the conditional distributions over states and defect sectors remain nonuniform. For $N=160$, the processor has a larger ground-state hit probability than logical simulated annealing (0.869 versus 0.519), but also a larger total-variation distance from uniformity (0.317 versus 0.136). A pause during the anneal raises the ground-state hit probability from 0.42 to 0.86 without restoring uniform sampling. These results identify a relaxation window and demonstrate that optimization success and sampling quality need not improve together, providing an exactly characterized benchmark for open-system quantum annealing.

Taiyi Quantum, a Shanghai-based quantum hardware developer, has secured over ¥1 billion RMB (approx. $149.6M USD) in cumulative funding within nine months of its founding, achieving unicorn valuation status. The company specializes in Ytterbium neutral-atom arrays for fault-tolerant quantum computing and has made significant progress in hardware integration and open-sourced its LUOSHU compiler. The post Taiyi Quantum Surpasses ¥1 Billion RMB ($149.6M+ USD) in Cumulative Funding for Ytterbium Neutral-Atom Systems appeared first on Quantum Computing Report .

Insider Brief Vietnamese quantum expert Nguyen Luong Quang recommends closer EU partnerships to develop Vietnam’s quantum workforce, research infrastructure and industrial capabilities. His proposal identifies joint training, remote access to European quantum computers and participation in software, optical component and specialized chip supply chains. The recommendations build on broader EU–Vietnam cooperation but do not constitute an approved quantum agreement or funding commitment. Vietnam should make European partnerships a central part of its quantum technology development, using joint research, specialist training and access to computing infrastructure to build domestic capabilities, a Vietnamese expert has proposed. Nguyen Luong Quang, a member of the Vietnam Quantum Technology Network , or VNQuantum , outlined the approach in an interview with the Vietnam News Agency’s Brussels correspondent, according to VietnamNet Global . His recommendations would connect Vietnam’s emerging quantum sector more closely with European research institutions and technology businesses. The proposal comes as Hanoi and Brussels deepen their political and scientific relationship. The two sides upgraded relations to a Comprehensive Strategic Partnership in January, creating a broader framework for cooperation. In May, the European Commission and Vietnam’s Ministry of Science and Technology signed a letter of intent to strengthen research and innovation ties . The agreement aims to expand researcher exchanges, knowledge sharing and connections among universities, startups, industry and public institutions, according to the commission. Those arrangements provide a potential foundation, or framework for the deeper quantum cooperation that Quang advocates. Quang recommended closer ties with France, Germany, the Netherlands, Finland and Spain, including postgraduate training and pilot applications in banking, energy and cybersecurity. Connecting domestic laboratories with remotely acces

Insider Brief Finland’s Coherence Quantum raised €2.78 million in seed funding to develop cryogenic signalling and control infrastructure for scaling solid-state quantum computers. The Aalto University spinout is developing signal conditioning and higher-density interfaces to manage wiring, heat and noise as qubit counts increase. Lifeline Ventures led the round, with participation from Mårten Mickos , to fund an Espoo laboratory, product prototypes, manufacturing development, research and hiring. Image: Coherence Quantum founding team. (Provided) PRESS RELEASE &#8212; Coherence Quantum , a Finnish quantum hardware company originating from Aalto University’ s Quantum Computing and Devices (QCD) group, has raised €2.78 million in seed funding to develop a new approach to the cryogenic infrastructure surrounding solid-state quantum processors. The €2.78 million round is led by Helsinki-based early-stage investor Lifeline Ventures , with participation from technology entrepreneur Mårten Mickos . Quantum computers are being developed to tackle calculations that are beyond the practical reach of today’s computers, with potential applications ranging from discovering new materials and medicines to modelling complex physical systems. Reaching that point will require machines with far more usable qubits than today’s systems. But adding more qubits creates another scaling problem: everything needed to control them. As quantum processors grow, more control and readout signals need to reach the quantum processing unit (QPU). Conventional approaches require more wiring and signal-conditioning hardware inside a system with very limited space and cooling power. At the same time, the qubit environment has to remain protected from thermal noise and other disturbances that can affect performance. Coherence Quantum is developing an integrated cryogenic signalling and control platform to address this scaling challenge. Its first technologies focus on cryogenic signal conditioning, hel

For scientists, breakthroughs often stem from unexpected turns. A research team led by Oscar Dahlsten, an associate professor in the Department of Physics at City University of Hong Kong (CityUHK), set out to prove a theoretical limitation, only to discover a quantum solution. The finding breaks traditional physical constraints and introduces a strategy for harvesting energy from fluctuating sources.

Insider Brief Postquant Labs has launched its Quip Virtual Machine (QVM) on the Aglais testnet, providing a shared programming and execution environment for quantum and classical computing systems. The QVM supports a constraint-based programming language, a compute-credit pricing model and a verification system for results, while researchers at Monash University , the University of Notre Dame and Purdue University assess the platform. In a demonstration at Quantum.Tech World, the QVM ran 1,930 portfolio optimization comparisons in which its quantum solver matched or outperformed the classical solver under the company&#8217;s stated evaluation criteria, with both typically returning results in 0.1 to 0.3 seconds. PRESS RELEASE &#8212; Postquant Labs , developer of the quantum computing marketplace quip.network , has launched its Quip Virtual Machine (QVM) and first quantum smart contracts. The QVM is live today on the Aglais testnet at aglais.quip.network &nbsp;and provides a shared programming and execution environment for quantum and classical computing, with support for the leading quantum hardware platforms. Researchers from Monash University , the University of Notre Dame , and Purdue University are currently assessing the QVM, while SiC Systems is exploring the QVM&#8217;s potential to address complex industrial optimization problems, including applications in AI-driven manufacturing and the design, control and operation of chemical and biological processes. In a live demonstration &nbsp;at Quantum.Tech world, the QVM ran 1,930 head-to-head portfolio optimization races between quantum and classical solvers, using problems created by around 100 visitors. Results within 0.5% of each other were treated as ties. The quantum solver matched or beat the classical solver in every race, and in every race where the results differed by more than 0.5%, the quantum solver produced the better portfolio, by a median of 2.56%. Both solvers typically returned answers in 0.1 to

Insider Brief Monarch Quantum is supplying integrated photonics hardware to support Infleqtion &#8216;s work on NASA&#8217;s Quantum Gravity Gradiometer Pathfinder mission, backed by a $20 million follow-on contract. The mission, led by NASA&#8217;s Jet Propulsion Laboratory, aims to demonstrate a space-based quantum gravity gradient sensor, with the next phase focused on hardware development and testing. The technology could inform future gravity-mapping systems that measure changes in groundwater, ice, natural resources and other geophysical conditions, with instrument development targeting a 2030 launch. PRESS RELEASE &#8212; Monarch Quantum extends congratulations to Infleqtion on receiving the $20 million NASA follow-on contract supporting the Quantum Gravity Gradiometer Pathfinder (QGGPf). Led by NASA&#8217;s Jet Propulsion Laboratory in Southern California, the mission is anticipated to demonstrate the world&#8217;s first space-based Earth quantum gravity gradient sensor. The award advances the mission into its next phase of hardware development and testing. Monarch Quantum supports Infleqtion &#8216;s efforts on the mission by supplying integrated photonics hardware that delivers precise, stable light required to meet the performance of the sensor. &#8220;NASA&#8217;s continued investment in this pathfinder mission validates the progress being made to move quantum sensing beyond the laboratory and into demanding operational environments,&#8221; said Tim Day, Chief Executive Officer and Chairman of Monarch Quantum . &#8220;Space-qualified quantum systems require exceptional systems engineering paired with reliability and precision. We are proud to support Infleqtion and NASA in advancing the photonics subsystems needed to make this mission possible.&#8221; QGGPf is designed to demonstrate quantum sensor technologies that could inform future gravity-mapping instruments in low-Earth orbit. By measuring subtle variations in Earth&#8217;s gravitational field, fut

Insider Brief Project Eleven and Relm Insurance have partnered to explore how post-quantum security controls could inform digital asset insurance underwriting and risk assessments. Relm will advise on Strongpoint, Project Eleven &#8216;s institutional custody product, with a focus on key exposure, signing systems, transaction approvals, migration readiness and third-party dependencies. The collaboration is exploratory, and any future effects on insurance underwriting or premiums will require further evaluation and remain subject to Relm&#8217;s independent underwriting processes. PRESS RELEASE &#8212; Project Eleven , the post-quantum security company for digital assets, today announced Relm Insurance &nbsp;as a development partner for Strongpoint , its flagship institutional custody product. The collaboration will explore how an institution&#8217;s post-quantum security controls could be evaluated within digital asset insurance underwriting, helping both companies better understand how quantum readiness may influence future assessments of digital asset risk. As quantum computing advances, a sufficiently powerful machine could derive private keys from exposed public keys and compromise digital assets. Institutions need custody infrastructure capable of adapting its cryptography before such a machine becomes available. Strongpoint is built for that transition. The platform combines classical and post-quantum signing and separates institutional controls from the cryptography layer, enabling institutions to replace signing algorithms while preserving approval rules and audit history. &#8220;Every institution holding digital assets will eventually need to prepare for post-quantum cryptography. The open question is whether that transition happens on the institution&#8217;s schedule or under pressure,&#8221; said Alex Pruden, CEO and Co-Founder of Project Eleven . &#8220;Insurance plays a critical role in how markets assess and manage risk. We believe there is an opportun

Insider Brief Bechtle will provide the German Aerospace Center’s Quantum Computing Initiative with cloud access to IQM ’s superconducting quantum computers until June 2027, expanding its research resources and technology portfolio. The agreement enables application teams to develop and run quantum algorithms and compare superconducting systems with other quantum computing technologies. Bechtle will manage platform accounts and support, while a dedicated classical server at IQM ’s Munich data center will support hybrid quantum and classical workloads. PRESS RELEASE &#8212; Under a new framework agreement, Bechtle is providing German Aerospace Center ’s Quantum Computing Initiative (DLR QCI) with cloud-based computing time on quantum systems from IQM Quantum Computers. This expands the DLR QCI’s quantum computing resources for its application teams, complements its existing technology portfolio, and creates additional opportunities for comparison with quantum systems already in place. The IQM Resonance cloud platform supports efficient use through seamless user and group management and provides the foundation for planning, developing, running, and managing quantum algorithms across the entire development process. “ Our offering combines technological excellence with the flexibility that benefits the DLR QCI in its quantum computing applications. This is how we support the customer in expanding its research infrastructure, while also strengthening the technological sovereignty of Germany and Europe in international competition, ” says Christian Behma, Managing Director of Bechtle IT System House Bonn. The DLR QCI brings together start-ups, industry, research, and the public sector in a strong ecosystem for sovereign, competitive quantum computing. To this end, it commissions companies to develop quantum computers, quantum algorithms, and relevant use cases. The focus is on practical application scenarios, for example in materials research, aerospace, mobility, and secu

Quminex, a Quebec-based exploration technology startup, has successfully raised $1.5 million CAD (approximately $1.06 million USD) in pre-seed funding. This investment, led by Quantacet and QAI Ventures, will accelerate the commercial development and field deployment of its proprietary Quminex Discovery Platform™. The platform aims to modernize mineral discovery by using machine learning and high-performance computing to transform geological data into explainable mineral system models. The post Quminex Raises $1.5M CAD ($1.06M USD) Pre-Seed Round Led by Quantacet and QAI Ventures to Advance Mineral Discovery Platform appeared first on Quantum Computing Report .

For nearly a century, physicists have relied on the Born rule to calculate the chances of different outcomes when they measure a quantum system. Yet despite decades of effort, nobody has managed to derive the rule from more basic mathematical principles without making assumptions about probability along the way.

Light is one of the most powerful tools scientists have for probing matter. By interacting with electrons, light reveals how atoms, molecules and materials are structured and how they evolve in time. Highly energetic ultraviolet and X-ray photons are particularly attractive because they can access electrons located close to atomic nuclei, where each chemical element carries its own distinctive electronic fingerprint.

Insider Brief Arqit Quantum has made a strategic investment in Sirius Computer to support the development of quantum-safe communications for defence, government and national security users. The companies are developing Crux, a software-based connectivity platform that combines Sirius’s secure networking technology with Arqit ’s Sovereign Key Platform and NetworkSecure adaptors. The investment will support product development and integration, while the companies pursue secure networking opportunities with NATO member countries, the UK Ministry of Defence and the US Department of Defense. PRESS RELEASE &#8212; Arqit Quantum Inc. (NASDAQ: ARQQ), a global leader in quantum-safe encryption helping safeguard sensitive information from current and future cyber threats, today announced a strategic investment in Sirius Computer, Inc., a technology provider of secure computing and networking solutions for defence, intelligence and critical national infrastructure. This will accelerate the development and delivery of quantum-safe communications for defence, government and national security users. The investment builds on an existing partnership that combines Sirius’s secure networking technology with Arqit ’s Sovereign Key Platform (SKP) and NetworkSecure adaptors to deliver Crux, a software-based connectivity platform. The companies&#8217; joint offering protects sensitive communications across devices and networks, helping defence users share information securely in deployed environments, and when operating alongside allied forces. The software-based offering is designed to run on commercial devices and work alongside existing infrastructure, enabling users to extend secure communications without replacing their underlying networks. Applications include mobile devices, cloud and network systems, autonomous platforms such as Uncrewed Autonomous Vehicles (UAVs) and their associated control systems. The strategic investment will support the continued development of Crux and Sir

Transmitting electricity without losing any energy may sound impossible, yet this is precisely the promise of superconductivity. For nearly 40 years, scientists have been working to understand materials that exhibit this remarkable property at relatively high temperatures. Unlocking their secrets could one day help make power grids more efficient, enhance medical technologies and support the development of quantum computing.

Tiny atoms and molecules are constantly bombarding each other all around us. While we regularly measure the large-scale effects of these interactions, measuring the effect of each individual collision is far more difficult. But now, researchers have managed to measure how tiny gas particles affect a single silica particle in the lab. In their new study, published in Physical Review Letters, the team describes how they detected the momentum transfers of individual collisions of gas particles with a nanoparticle levitated in laser light.

Insider Brief Alice &amp; Bob reported Phase 1 PROQCIMA results demonstrating core components of its cat-qubit error-correction architecture on three hardware demonstrators. Tests included protected CNOT gates, repeated error-correction cycles and a non-Clifford gate, but the measured logical error rate remained above the error-correction threshold. A digital twin identified longer, more consistent qubit coherence as a priority, while automated monitoring software tracked performance and recalibration needs. PRESS RELEASE &#8212; – Alice &amp; Bob , a leader in fault-tolerant quantum computing, today shares a summary of results from Phase 1 of PROQCIMA , the French government’s quantum computing programme. Led by the French Defense Innovation Agency (AID) and the Direction générale de l&#8217;Armement, PROQCIMA aims to develop two prototypes of universal quantum computers, each capable of supporting 1,000 logical qubits, ready for industrialisation by 2032. The programme is structured as a 10-year competition: three candidates will continue after the first four years, with two ultimately selected to continue beyond year eight.&nbsp; Five companies were selected to participate: Alice &amp; Bob , Pasqal , Quandela , Quobly and C12 . The first phase of the programme was designed to assess the technical and industrial feasibility of each company’s approach. Each candidate was required to demonstrate the expected level of technological maturity, including through the development and testing of its technology on real hardware. Alice &amp; Bob began work on Phase 1 of PROQCIMA in 2024, committing to build an integrated multi-block demonstrator with partial functional validation to demonstrate the core operations of its error-correction architecture on real hardware. Alice &amp; Bob has delivered on that commitment. The company assembled and operated three independent demonstrators, two on 6-qubit chips and one on a 12-qubit chip. The team demonstrated each building block o

Insider Brief The BIRD Foundation has approved $7.4 million in conditional grants for seven joint U.S.-Israel R&amp;D projects, with total investment expected to reach $20 million, including private-sector funding. The selected projects cover quantum computing, satellite communications, semiconductor memory, AI-driven cancer detection, precision agriculture, digital pathology and medical 3D printing. The quantum computing project pairs Israel&#8217;s Qarakal Quantum with U.S.-based Quantum Elements to develop a minimum viable product for mapping complex surface-catalysis reactions using quantum computing. PRESS RELEASE &#8212; In September 2026, the Board of Governors of the Israel-U.S. Binational Industrial Research and Development ( BIRD ) Foundation approved $7.4 million in conditional grants for seven joint R&amp;D projects between U.S. and Israeli companies. Including private-sector investment, total investment in the projects is expected to reach $20 million. The BIRD Foundation supports strategic collaborations between U.S. and Israeli companies to jointly develop innovative products and technologies for global markets. In addition to providing conditional grants of up to $1.5 million per project, the Foundation helps companies identify suitable partners and build cross-border collaborations. Projects submitted to BIRD are evaluated by BIRD staff and by expert reviewers appointed by the National Institute of Standards and Technology (NIST) of the U.S. Department of Commerce, and by the Israel Innovation Authority. The seven newly approved projects bring the total number of BIRD -supported collaborations to more than 1,200 since the Foundation&#8217;s establishment in 1977. To date, BIRD has invested approximately $470 million in joint projects, helping generate more than $10 billion in direct and indirect revenue. The newly approved projects are: Ibex Medical Analytics (Tel Aviv, Israel) and Proscia (Philadelphia, PA) will develop an AI-based precision oncolo

Insider Brief A NowSecure analysis of 136,711 iOS and Android apps found that 96.9% contained no detectable post-quantum cryptography (PQC)-related code or libraries. The analysis also identified weak encryption algorithms in more than 3,100 mobile apps, pointing to existing cryptographic weaknesses alongside future quantum-related risks. NowSecure recommends that organizations inventory cryptography in first- and third-party mobile apps, remediate vulnerable implementations and retest applications as part of a planned PQC migration. PRESS RELEASE &#8212; NowSecure today released an analysis, conducted with NowSecure Platform, of 136,711 iOS and Android apps. It found that 97% contain no detectable post-quantum cryptography (PQC), the new generation of encryption standards designed to withstand attacks from quantum computers. Even among the most popular U.S. apps, fewer than 1 in 10 showed quantum-safe code. Security teams often leave mobile apps out of their cryptographic inventories, and organizations cannot migrate what they have not inventoried.&nbsp; The risk does not wait for quantum computers. Using runtime testing, NowSecure flagged weak encryption algorithms in more than 3,100 Android and iOS apps during the same study. These checks detect legacy algorithms such as DES and RC4. The findings highlight the need to address existing encryption weaknesses while identifying and migrating public-key cryptography vulnerable to future quantum attacks.&nbsp; Q-Day Is Close, and Migration Takes Years&nbsp; According to Gartner®, Q-Day is “the moment that state actors obtain a cryptographically relevant quantum computer (CRQC),” and “Q-Day arrives as soon as 2029, but most progress on PQC migration so far is inadequate.”¹ Gartner warns that such capabilities “threaten widely used public-key cryptography” and says the business risks include “harvest now, decrypt later”.¹&nbsp; Because mobile applications transmit sensitive data over diverse public cellular and roaming n

We study the error-correction properties of multi-mode Fock-state codes under amplitude-damping (AD) noise, focusing on the asymptotic regime in which the total excitation of the code states grows without limit and the number of photon losses induced by the noise scales linearly with it. In this setting, existing code families, which correct only sublinearly many photon losses, do not protect against amplitude-damping (AD) noise with a constant loss parameter. As our main result, we address this gap by constructing asymptotically good Fock-state codes relying on random classical codes in the discrete simplex. Unlike many standard constructions of random quantum codes, our construction introduces randomness through the underlying classical indexing structure. Randomization also enables another desirable feature: bounded per-mode occupancy, which limits the number of photons in any individual mode and thereby increases the coherence lifetime of the code states. Finally, via a relation between Fock-state codes and permutation-invariant codes, our results also yield asymptotically good families of qudit permutation-invariant codes as well as codes in monolithic nuclear state spaces.

We consider the problem of testing and learning from data in the presence of resource constraints, such as limited memory or weak data access, which place limitations on the efficiency and feasibility of testing or learning. In particular, we ask the following question: Could a resource-constrained learner/tester use interaction with a resource-unconstrained but untrusted party to solve a learning or testing problem more efficiently than they could without such an interaction? In this work, we answer this question both abstractly and for concrete problems, in two complementary ways: For a wide variety of scenarios, we prove that a resource-constrained learner cannot gain any advantage through classical interaction with an untrusted prover. As a special case, we show that for the vast majority of testing and learning problems in which quantum memory is a meaningful resource, a memory-constrained quantum algorithm cannot overcome its limitations via classical communication with a memory-unconstrained quantum prover. In contrast, when quantum communication is allowed, we construct a variety of interactive proof protocols, for specific learning and testing problems, which allow memory-constrained quantum verifiers to gain significant advantages through delegation to untrusted provers. These results highlight both the limitations and potential of delegating learning and testing problems to resource-rich but untrusted third parties.

We introduce a numerical framework for reliably estimating conditional von Neumann entropies, a central quantity in device-independent quantum cryptography and randomness generation. Our method is based on semidefinite relaxations derived from the Navascués--Pironio--Acín hierarchy and provides entropy bounds directly from observed statistics, assuming only the validity of quantum mechanics. The approach builds on a recent integral representation of entropy and substantially improves efficiency: it requires about half as many support variables as existing methods, while allowing these variables to be chosen projectively, leading to a significant reduction in runtime. These advances enable the practical certification of randomness and security even in noisy conditions, while integrating seamlessly with modern entropy accumulation theorems. Consequently, our framework becomes a versatile tool for quantum cryptographic protocols, broadening the possibilities for secure communication in untrusted environments.

Matter under extreme conditions behaves as a non-equilibrium, strongly-interacting quantum system. Such systems are in the non-perturbative regime of quantum chromodynamics (QCD), where their time evolution is classically intractable. Quantum computing offers a promising alternative, but present-day devices are limited in qubit count and circuit depth, so efficient formulations and algorithms are key to scaling toward experimentally relevant QCD simulations. A scalable framework is established for simulating energy loss and hadronization in 1+1-dimensional SU(2) lattice gauge theory, in which a heavy quark traverses a lattice of light quarks. Classical lattice QCD methods are translated into physics-informed circuits to prepare the interacting ground state. The evolution is run on IBM's quantum processor ibm_pittsburgh, where the charge distribution and energy loss are measured. A further study develops the quantum simulation of the fully gauge-fixed SU(2) Hamiltonian in a mixed basis, a formulation that is expected to remain efficient at all gauge couplings. Digitizing the continuous gauge fields with as few as three qubits per plaquette reproduces low-energy observables with $10^{-3}$ precision. Scaling to larger systems is limited by resource overhead, which motivates truncations that preserve the relevant observables. Sequency Hierarchy Truncation (SeqHT) exploits the hierarchy in basis-operator contributions. Demonstrated on the adiabatic preparation of the $λφ^4$ ground state on ibm_sherbrooke, SeqHT reduces circuit depth by ~30%, suppressing hardware noise in the extracted observables. All simulations in this dissertation are validated on quantum hardware against classical benchmarks. These studies advance quantum simulations of real-time QCD dynamics.

As quantum computing moves from the noisy intermediate-scale quantum (NISQ) era toward early fault-tolerant quantum computing (EFTQC), quantum-enhanced AI is shifting from a conceptual idea to experimental research. Quantum components are expected to extend the capabilities of existing AI systems, yet it remains unclear how such components will help within large multimodal models. In this study, we try to answer that question for vision-language models (VLMs) using classically simulated quantum layers. With LLaVA-OneVision as the backbone, we evaluate 4- and 8-qubit basic-ring and strongly entangling circuits at four insertion and four replacement locations. Insertion adds quantum layers to the classical model, while replacement substitutes them for classical components. Using the same setup, we compare performance and computational cost between classical and quantum-classical hybrid models. On the Visual Spatial Reasoning dataset, inserting a quantum layer after the visual projector reaches 80.7% development accuracy, 2.28 percentage-points above classical full fine-tuning. Replacing the final decoder feed-forward sublayer retains 79.22% accuracy with 13.07 million fewer trainable parameters. Quantum insertion can thus improve accuracy, and selective replacement can reduce parameters. These benefits depend strongly on where the quantum layer is inserted or which classical component it replaces: earlier replacements lower accuracy, and fewer parameters do not reliably shorten training or reduce computation. To assess potential security benefits, we evaluated the robustness of quantum-classical hybrid models under six attack settings. Overall, our study maps where quantum layers help and hurt within VLMs, offering a starting point for hybrid VLM design; whether these gains generalize remains open. The code is available at https://github.com/TITANS-Lab-Artifacts/QuantumVLM.

This paper studies quantum spin systems: networks of spins coupled by local interactions. The Lieb-Robinson bound predicts that in these systems, information propagates at an essentially finite speed. We produce a new proof of this result. Our approach relies on a spectral bound on entries of resolvents of band matrices, the Combes-Thomas estimate, rather than on the standard path-counting argument.

We develop a method for deriving Gaussian optimality results for bosonic quantum systems from inequalities for qubit systems. Inspired by Gross's derivation of the Gaussian logarithmic Sobolev inequality from an inequality on the two-point space, we use qubits as quantum two-point spaces and lift bosonic Weyl operators to pseudo-Weyl operators on large qubit systems. By controlling weighted norms and relative entropy in the fluctuation limit, we establish two transfer theorems that convert tensorized qubit inequalities into inequalities for bosonic Gaussian channels. As a first application, we prove that the sharp $2$-logarithmic Sobolev inequality for the bosonic Ornstein--Uhlenbeck semigroup tensorizes without loss in the constant. We also establish a sharp output entropy inequality for tensor powers of a class of qubit channels. This includes a quantum Mrs.~Gerber's lemma determining the minimum output entropy of tensor powers of the qubit depolarizing channel at fixed input entropy. Applying our relative entropy transfer theorem, we obtain multimode constrained minimum output entropy bounds for Gaussian additive-noise channels and thermal attenuators in the heating range.

We design and optimize a quantum error correction (QEC) decoder for NVIDIA GPUs, combining Relay belief propagation, a state-of-the-art message-passing algorithm, with order-zero ordered statistics post-processing. Our implementation uses CUDA Graphs to control GPU execution, stops updates for converged samples, and collects unresolved samples in queues for post-processing. We optimize sparse traversal through coalesced message accesses, prefetching, and register reuse, and accelerate binary post-processing with warp-level collectives. In addition, mixed FP16-FP32 arithmetic and INT8 quantization reduce message storage and traffic while retaining accuracy using accumulators at higher precision. We evaluate surface, hypergraph product, and bivariate bicycle code workloads on NVIDIA A100 and GH200 data-center GPUs and a commodity RTX 5080. On the bivariate bicycle code at error probability 0.003, INT8 halves amortized decoding time relative to independently tuned FP32 with a negligible logical error rate increase on RTX 5080. With independent syndrome batches submitted back-to-back to concurrent decoder instances, RTX 5080 delivers 91% of GH200's highest measured throughput with an 8.9x shorter median submission-to-correction latency. The combination of performance optimization, mixed precision, INT8 quantization, and concurrent decoder instances opens a path toward QEC decoder clusters built from commodity GPUs.

Gradient-based algorithms are often applied to identify an optimal control for maximizing a quantum objective functional by following a steepest ascent path to the top of the control landscape. In contrast, this paper explores straight shots through control space where movement along such a path corresponds to a less demanding monotonic complete climb up the landscape for the optimal objective value. Existing studies of control landscapes have revealed the presence of straight shots, but identifying them required computationally intensive stochastic methods. In this paper, we introduce a non-stochastic straight-shot search algorithm (STSA) that identifies a large class of straight shots. We apply STSA to numerically generate more than 10,000 distinct straight-shot optimization paths and analyze their statistical distribution for each of the objectives of (i) state-to-state transitions, (ii) general observables, and (iii) unitary transformation generation. The results show a decrease in the nearest-neighbor distances among straight shots as the sample size increases, suggesting their prevalence in control space. We further conjecture that the starting locations of the straight-shot pathways on a landscape level set may form connected neighborhoods, motivating future investigation into their underlying topological structure. The present paper focuses on the use of STSA for locating massive numbers of straight solutions. However, the STSA is not a high-efficiency algorithm in its present form, but the discovered prevalence of control straight shots leaves open future advances to accelerate the discovery of straight shots as optimal controls.

Systems with flat bands are interesting as they potentially host many exotic quantum phenomena that would be hard to observe in usual systems with dispersive bands. Multiple approaches were developed to construct flat band systems, with most of them requiring fine-tuning and/or solving a challenging inverse-eigenvalue problem. In this article we work with an idea that uses a parent bipartite system to generate a family of flat bands by means of Hilbert space projections. This method is largely free from fine-tuning constraints and allows us to identify conditions for a Hamiltonian to guarantee flat bands at desired energies, with desired degree of degeneracy. We also show that one can control the touching points of the flat band with dispersive bands at any desirable point in the Brillouin zone. In the process, we identify perturbations that preserve the flat bands or split them controllably. This approach provides easy tunability in designing flat band systems with desired properties.

The article outlines key topics related to deriving kinetic equations and, in general, to the relationship between the evolution equations governing quantum many-particle systems. The main issues being considered are the mathematical origin of quantum kinetic equations, novel methods for deriving kinetic equations from hierarchies of evolution equations for quantum systems, specifically focusing on kinetics within the framework of the evolution of observables, and the generalization of the quantum kinetic equation specified by non-separable initial states.

Performant classical tools for simulating quantum circuits are important for benchmarking and supporting upcoming quantum devices. Pauli propagation offers promising capabilities, but deep circuits usually cause a rapid growth in the number of Pauli strings and can quickly exhaust the available memory. In this work, we introduce a randomized protocol that combines a specialized resampling schedule, merging, and a controlled amount of bias to keep the propagating Pauli sum within any prescribed memory budget. Additional computational resources can then be spent on embarrassingly parallel repetitions that systematically improve the estimate. Building on the open-source library PauliPropagation.jl, we show that 1) increasing memory of each simulation reduces the error systematically more than outside averaging, 2) resampling just enough to apply the next gate delays variance accumulation and gives better error-per-time trade-offs than more aggressive resampling, and 3) a small, controlled bias is crucial in cutting down variance and pushing far beyond unbiased randomization. The resulting framework can reproduce deterministic calculations while requiring several orders of magnitude less memory.

Determining the symmetry of the Cooper pairing in superconductors is a central challenge in condensed matter physics. Time-reversal symmetry breaking (TRSB) is among the most distinctive symmetry-breaking pattern of a superconductor. An important subset of TRSB pairing states, including the topological $p_x+ip_y$ pairing, is expected to exhibit the optical anomalous Hall effect. However, the microscopic ingredients that enable the Hall response and their underlying organizing principle in clean superconductors remain unelucidated. Here, we develop a unified theory for TRSB multiband superconductors possessing inversion symmetry, and establish their intrinsic optical Hall response as fundamentally a quantum-geometric phenomenon. We distinguish unitary and nonunitary TRSB states. Diagrammatically, we identify two classes of processes: single-electron tunneling and Cooper-pair tunneling. Both involve at least one interband tunneling event driven by the interband velocity-which is closely tied to the interband Berry connection. We rigorously prove that interband pairing is a prerequisite for unitary states to generate intrinsic Hall response, whereas it is not absolutely needed for nonunitary states. In nonunitary states with intraband pairing alone, the Hall effect can arise through single-electron tunneling, provided spin-orbit coupling is present. An effective theory obtained by integrating out the hole degrees of freedom reproduces these results and shows how pairing may endow electrons with effective Berry curvature. Finally, through symmetry analysis, we show that intrinsic resonances near the superconducting gap edge are allowed in nonunitary states but forbidden in unitary states. Our work thus establishes quantum geometry as a unifying principle for the intrinsic Hall response in superconductors and provides a guide for distinguishing different candidate TRSB pairings.

Double-layer systems with narrow or flat electronic bands may exhibit spontaneous interlayer coherence, described by a layer-pseudospin ferromagnetic order parameter. In modern realizations of layer-pseudospin ferromagnets, the electrons carry additional valley degeneracies, endowing each layer with a valley-pseudospin degree of freedom. We study their nonequilibrium steady states driven by a static interlayer voltage bias in the presence of interlayer tunneling. While in the low-bias regime, the system is in a static state with parallel valley pseudospins between the two layers, we show that in the high-bias regime, the dynamical precession of the layer-pseudospin stabilizes the valley pseudospins in the antiparallel configuration, strongly suppressing the interlayer tunneling. This dynamical tunneling blockade leads to an absence of ac current and a sharp drop of the dc tunneling current to a tiny value, in stark contrast to conventional quantum Hall double layers.

One of the major challenges of modern foundational physics is the combination of quantum physics and general relativity into a theory of quantum gravity. A severe obstacle are the required extremely high energy scales for direct tests of quantum gravity effects. In recent years, attention has shifted towards near-future experimental predictions of effective or phenomenological models, such as gravitationally induced entanglement or interactions of linearized gravity with non-relativistic measurement devices. These developments motivate us to study the coupling between the quantized metric perturbation and an anisotropic quantum rigid rotor. The intuitive motivation for our study is that a sufficiently heavy rotor consists of a very large number of component systems. Although quantum gravitational effects are completely negligible at the scale of a single atom or molecule, the effects can get amplified by the sheer number of constituents. The resulting effective model describes the gravitational analogue of the angulon quasiparticle excitations discussed in condensed matter physics, suggesting a pathway for future analogue experiments. As a first concrete test of our model, we derive the gravitational Lamb shift for the energy eigenstates of the rotor, which become dressed by a cloud of virtual gravitons. Although the effect is very small, it could provide a concrete test for whether gravity is truly quantum.

Kerr-cat qubits offer a hardware-efficient route to fault-tolerant quantum computing by suppressing bit-flip errors exponentially, while phase-flip errors increase only linearly with the mean photon number. To maintain this protection, entangling operations must be bias-preserving, ensuring that phase-flip errors occurring during the gate do not propagate into bit-flip errors. In this paper, we propose an asymmetrically threaded SQUID (ATS) parametric coupler to implement high-fidelity, bias-preserving entangling gates between Kerr-cat qubits. By engineering a photon-number asymmetry between the control and target modes, we enable fast gate operations that suppress non-adiabatic leakage without complex pulse shaping. Through numerical simulations of the full circuit Hamiltonian, we demonstrate a bias-preserving CX gate achieving 99.69% fidelity in the absence of photon loss for a gate duration of 50 ns. Under a single-photon loss rate of 100 kHz, our protocol yields a noise bias of 9922, exceeding the noise bias of a naive non-bias-preserving CX implementation by approximately a factor of 570. These results support the ATS coupler as a valuable building block for concatenated cat-qubit architectures.

Fault-tolerant quantum computers need fast and accurate error decoding. We present CoDecoder, a small neural frontend that composes with an existing decoder to improve accuracy and reduce mean decoding time. It predicts each shot's logical outcome, retains confident predictions and routes the remaining shots to the unchanged fallback. A logical-operator-aware output head scores shifted logical operators, combining equivalent logical lines on surface codes and deciding logical qubits jointly on bivariate-bicycle (BB) codes. Fused GPU inference and efficient routing reduce the overhead paid on every shot. In registered tests under circuit-level noise, composition reduces failures by 6.4-31.4% relative to correlated matching on surface codes of distance 7-17 and by 22-50% relative to full-DEM Relay-BP on two BB codes, with 2.3-124-fold speed-ups across these comparisons. With our re-implementations of the neural decoder Cascade, composition reduces decoding time in all four settings. A joint decision of both decoders on the routed shots keeps this speed and makes the composition more accurate than Cascade in all four, with 14-18% fewer failures on the [[72,12,6]] code. On the [[72,12,6]] BB code, a conventional head with independent logical outputs fails 3.8-5.0 times as often as our joint class score under matched training conditions. Per-shot analysis shows how composition gains accuracy. On retained shots, the frontend corrects more fallback errors than it introduces, even when it is less accurate overall.

Calderbank--Shor--Steane (CSS) codes support decoding and fault-tolerant logical operations through separate pure $X$ and pure $Z$ stabilizer checks. Generator choices and single-qubit Clifford transformations can obscure this structure. We give a deterministic polynomial-time algorithm that decides whether an arbitrary stabilizer code is locally Clifford-equivalent to a CSS code and constructs the required transformation and CSS checks whenever such a form exists. For $m$ possibly redundant generator rows on $n$ qubits, the algorithm uses $O(mn^2+n^4)$ binary field operations. We reduce the problem to affine linear systems by characterizing local projectors that preserve the span of the binary stabilizer labels. The conversion preserves code parameters and check sparsity for quantum low-density parity-check (qLDPC) codes. We demonstrate CSS recovery and decoder reuse and resolve previously open LC-to-CSS classification questions for published code constructions. For graph states, LC-to-CSS equivalence corresponds to the existence of a bipartite graph in the local-complementation orbit. We derive a necessary-and-sufficient adjacency-matrix criterion for this property and construct such a graph whenever one exists. Our algorithm makes CSS decoding and fault-tolerant constructions accessible throughout the local Clifford equivalence classes of CSS codes.

We formulate quantum reference frames within the Dirac quantization of gauge theories, where physical states are obtained from a kinematical Hilbert space $\mathcal{H}_{\rm kin}$ by group averaging. We assume the gauge group $G$ is unimodular, and we define a quantum reference frame as a system of coherent states associated with a group $G_R$ of frame orientations acting on a tensor factor of $\mathcal{H}_{\rm kin}$. In direct analogy with the Faddeev-Popov procedure in path integrals, we show that the physical inner product can be written in terms of a choice of frame orientation with an appropriate operator measure, but that the physical Hilbert space is independent of this choice of frame. This yields a generalization of the Page-Wootters reduction map used to define conditional states and conditional probabilities of measurement outcomes given a frame orientation. These probabilities correspond to the expectation values of relational Dirac observables obtained from generalizations of previously considered relativization maps. Our main result is that the map that implements a change of frame is unitary, even when $G$ does not act as a tensor-product representation across a factorization of $\mathcal{H}_{\rm kin}$. The formalism therefore accommodates interactions between reference frames and the systems described relative to them. We apply this formalism to temporal frames, showing that a unitary Schrödinger equation emerges for an interacting clock and system, and that a previously reported time-nonlocal Schrödinger equation is recovered in an appropriate limit. With this, problems of non-unitarity are avoided by the use of the gauge-fixing measure in the physical inner product. We also discuss the case of interacting spatial frames, where the known correspondence between coherence in one frame and entanglement in another is shown to depend on the coupling.

Separately amplifying gate, latency, and mid-circuit measurement errors can simplify zero-noise extrapolation, but a weak interaction between amplification knobs does not establish an accurate zero-noise limit. We distinguish observable separability, response-model adequacy, and calibration of that limit, and test them in a pre-specified $2^3$ factorial experiment on three IBM dynamic circuits. For the primary echoed spectator observable, the latency-measurement coefficient is $b_{LM}=+0.0007$ with a nominal 95% bootstrap interval $[-0.0033,+0.0049]$. A separately planned follow-up meets a $\pm0.005$ equivalence criterion and recovers two injected interactions; both repeat runs nevertheless trigger the drift rule. Multi-knob extrapolations have smaller median absolute errors than the single-knob comparisons, yet all five original strategies exclude the known ideal value for three of six observables. Duration controls support a model-dependent contribution to the spectator deficit from unequal decay rates in native padding and added delay. We give an explicit construction showing why measurements at two measurement-knob levels cannot identify the extrapolated limit without response assumptions. A post-hoc precision analysis and an additive full-factorial estimator expose a further bias-variance trade-off hidden by point-error comparisons. The experiment provides a diagnostic of the implemented response surface, not a certification of physical channel independence or mitigation accuracy.

Motivated by a recent experimental work $[\href{https://arxiv.org/abs/2608.20327}{\text{arXiv:}2608.20327}]$, we theoretically investigate the nature of phase transitions in a trapped dipolar quantum gas upon tuning the contact interaction strength and dipole orientation. Using extended Gross-Pitaevskii simulations including thermal and quantum effects, we map the phase diagram comprising unmodulated superfluids, triangular droplet arrays, and stripe states. We further characterize the order of the transitions separating them through imaginary-time hysteresis analysis. The unmodulated-to-modulated transition evolves from discontinuous to continuous with increasing dipole tilt before becoming discontinuous again at large tilts. The degree of continuity is further affected by particle number, temperature, and confinement. While continuous behavior generally correlates with the emergence of stripe states, this correspondence is not systematic, and finite-size effects also influence the continuity of the transition. The triangular-to-stripe transition is found to be discontinuous at small contact interaction strengths and becomes increasingly continuous upon approaching the unmodulated-to-modulated phase boundary. Our results reveal a tunable transition order in finite dipolar quantum gases and provide guidance for its experimental investigation.

Quantum batteries can outperform their classical counterparts through collective quantum effects, yet the conditions enabling such advantage remain unclear. Using a generic class of free-fermionic chargers we prove that global operators are insufficient for scalable superextensive charging and that a cumulative hierarchy of many-body operators is required, with the structure of the battery determining the degree of advantage. This is obtained by relating the charging power to the norm of the commutator between the battery and charger Hamiltonians and deriving an upper bound only capturing noncommuting terms. Moreover, we revisit the concept of participation number and propose an effective definition that accounts for the relative strength of the contributing terms, correlating it with the charging power scaling. Not limited to quadratic Hamiltonians, our results establish cumulative locality as a key resource for quantum charging advantage.

We prove a complete modified logarithmic Sobolev inequality with a system-size-independent constant for Chen--Kastoryano--Gilyén Gibbs samplers on one-dimensional spin chain at every fixed positive temperature. The result holds for Hamiltonians with bounded finite-range interactions, including noncommuting and spatially nonuniform interactions. It yields trace and diamond mixing times of order $O(\log N+\log(1/ε))$. The proof establishes complete spatial entropy factorization and absorbs quasi-local errors as conditional relative entropy at the original joint state and reference. The static estimate also yields a system-size-independent CMLSI for the single-site Petz heat-bath and regularised heat-bath dynamics.

We study the minimum persistent memory required to distribute a graph state through a quantum switch. Specifically, consider a central switch that assists $n$ remote users in distributing a graph state, using independently generated user-switch Bell pairs. Since Bell-pair generation is probabilistic, different links generally succeed at different times. When a Bell-pair is generated, the qubits may need to be stored in memory while waiting for other links to succeed. Recently, new protocols have been proposed to reduce this storage overhead by processing and releasing some switch qubits before all Bell links are available. However, these protocols do not characterize the minimum persistent switch memory required at each stage. Moreover, the local-cover method in the state-of-the-art Piecemaker protocol is computationally expensive for general target graphs. In this work, we characterize the minimum persistent switch memory required after any subset of users' Bell links are generated and processed. We then develop an online stabilizer-transition protocol that attains this limit, which can be implemented in polynomial time in the number of qubits $n$. Remarkably, this optimal protocol can provide substantial memory reductions over existing heuristic approaches. In particular, for the path graph $P_n$ over $n$ users, Piecemaker protocol requires at least $\lfloor n/2\rfloor$ qubits of peak persistent memory for \textit{every Bell-links generation order}, whereas under the order $(1,2,\ldots,n)$, our protocol requires only one persistent switch qubit. Finally, the same stabilizer-transition framework also provides a direct forward construction for sequential graph-state generation using the minimum number of quantum emitters, equal to the maximum of the height function.

Quantum low-density parity-check codes now reach encoding rates up to 50% at useful distances. Their checks however are long-range group actions, not local neighbourhoods, and that connectivity has so far been supplied by neutral atoms. Silicon spin qubits offer the same primitive --- coherent transport of qubit blocks --- through electron shuttling, and on microsecond rather than millisecond timescales. They however travel along fabricated tracks rather than free space: permutations an atom array obtains by moving tweezers must here become collision-free motions on a physical lattice. We here present the first code and spin-qubit hardware co-design. We build an architecture whose geometry mimics that of a family of non-abelian groups, broad enough to host codes of excellent parameters: a hierarchy of nested conveyor-belt loops on a plain square lattice of shuttling tracks, in which every group multiplication becomes a rigid, globally controlled motion of whole qubit trains. We call it NeST, for Nested Shuttling Tracks. A code search over the family returns rate-20% mitten codes up to $[[1400,280,\leq 28]]$, and circuit-level simulations including shuttling dephasing give thresholds above $10^{-3}$ with sub-$50μ$s stabiliser cycles, two to three orders of magnitude faster than neutral-atom implementations. Via extrapolations, we estimate that this largest code may reach a logical error probability per qubit per round of $10^{-14}$, assuming a ten-fold improvement on early shuttling demonstrations, with other physical errors at p=0.1%. Logic is compatible with NeST too: for the [[150,30,10]] code we build a code-surgery gadget in which every qubit again moves only by rigid belt motions, at no qubit cost and a 29% increase in gate layers. This demonstrates that ultra-low-overhead fault tolerance and a fast clock speed are not competing goals, and that silicon spin qubits can supply both.

We demonstrate a hybrid quantum-classical approach for exploring ground-state manifolds of maximum independent set problems, in which quantum hardware supplies the initial solutions and an entirely classical post-processing algorithm expands them, increasing the solution diversity of quantum hardware measurements by up to several orders of magnitude. Quantum optimization devices, while capable of generating high-quality solutions, can suffer from fundamental sampling limitations. This is particularly problematic for applications that strongly depend on a large variety of uncorrelated optimal solutions. We apply the Houdayer cluster update algorithm to systematically expand quantum-generated solution sets through classical post-processing. We validate our approach on a test bed of 43 problem instances from QuEra's Aquila analog annealing device, achieving diversity amplification factors, defined as the increase in the number of distinct solutions at a given set size, of up to 11923x with a median of 24.3x across different problem scales and hardness parameters. Because exact ground-state degeneracies are known for these instances, the recovered fraction of the manifold can be measured rather than bounded: post-processing recovers a median of 21% of the ground-state manifold, and provably all of it for six instances. We also demonstrate that, in some cases, the classical post-processing can discover independent sets larger than those found by the quantum hardware, thus improving on solution quality and not just diversity. While the method is non-ergodic and cannot guarantee complete manifold coverage, it consistently discovers a larger number of high-quality, and in some cases strictly better, configurations than quantum sampling alone. This work demonstrates how simple classical post-processing can enhance the utility of quantum optimization results.

Long-range interactions in many-body quantum systems give rise to a wide range of dynamical phenomena, from collective dynamics well described by integrable mean-field models with symmetric all-to-all couplings, to fast scrambling of quantum information from disordered long-range interactions. Here, we investigate scenarios in which both regimes emerge within a single deterministic, translation-invariant XY spin model with long-range couplings. We consider a sparse powers-of-two (PWR2) graph, where each spin interacts with a logarithmic number of neighbors, and a power-law-decaying model. By altering the initial state via local perturbations on a completely symmetric state, we show that the dynamics changes from collective to scrambling as witnessed by bipartite and multipartite entanglement measures. We characterize this collective-to-scrambling crossover using Lyapunov exponents in the semiclassical regime, and show that the spectral properties of the coupling graph adjacency matrix provide a very efficient tool to predict the onset of fast scrambling. Our results offer a unified framework for controlling the switch between collective and scrambling dynamics in a setup accessible in experiments with neutral atoms in cavities or in tweezer arrays.

Trapped-ion, neutral-atom, and circuit QED quantum computers naturally enable coupled qubit-boson simulations. Boson-fermion interactions arise in quantum field theory, where renormalization is required to obtain finite results. We study one of the simplest examples of a coupled fermion-boson system, the static Yukawa model, on the QSCOUT trapped-ion system. We use similarity renormalization to express the same physics in terms of effective particles described by different values of the renormalization parameter $s$. This enables us to map data taken in the window of bosonic occupancy that is experimentally accessible to larger occupancies of distinct effective particles. We use this to study strongly coupled, high-occupancy regimes despite limited readout ranges. Using a trapped-ion qubit-boson device on Sandia National Laboratories' QSCOUT platform, we demonstrate the time evolution of the static Yukawa model.

We evaluate the electron scattering properties in CoSi thin films having either twin (heterochiral) or non-twin (homochiral) grain boundaries using first-principles quantum transport calculations. We find that scattering across a twin grain boundary is more resistive than scattering across a non-twin grain boundary and that non-twin grain boundaries have a greater percentage of surface conduction than twin grain boundaries. This is corroborated by the transmission eigenstate profiles, which show that the surface Fermi-arc electrons can transmit past the non-twin grain boundaries between homochiral domains on the same surface without significant backscattering. In contrast, these surface electrons get scattered along the twin grain boundaries between heterochiral domains to the opposite surface, resulting in partial forward transmission and partial backscattering that yields higher grain-boundary resistivity. This work helps elucidate the complexities of electron transport in chiral topological semimetals for potential application in next-generation nano-interconnects.

Identifying the quantum signatures of classical chaos remains a central question in quantum physics, and quantum scrambling provides a new perspective on this correspondence. We study two distinct limits of the same model to examine how the correspondence between chaos and scrambling changes across different regimes. The thermodynamic-limit anisotropic Dicke model exhibits a close correspondence between chaos and scrambling, whereas this correspondence breaks down in the large-frequency-ratio limit of the anisotropic Rabi model (ARM). The contrasting chaotic behavior in the two limits originates from the different numbers of classical degrees of freedom, whereas their similar scrambling behavior stems from eigenstate delocalization. This implies that, in the large-frequency-ratio limit, eigenstate delocalization alone is insufficient to qualify the ARM as a classically chaotic model. This finding suggests that identifying chaos in quantum systems requires jointly considering the classical degrees of freedom and eigenstate delocalization.

Early studies on the Dicke model linked superradiance to quantum chaos, whereas later anisotropic Dicke and Rabi studies reached apparently conflicting conclusions. We resolve this tension by distinguishing global chaos from local instability. Along the isotropic Dicke path, a sweep at fixed low excitation energy crosses both the superradiant boundary and a nearby chaotic window, explaining the reported correlation. However, the anisotropic Dicke model can be chaotic in the normal phase and regular in the superradiant phase, making superradiance neither necessary nor sufficient for global chaos. A fidelity out-of-time-order correlator (FOTOC), in contrast, probes the local stability of the stationary point selected by the initial wave packet. The superradiant transition destabilizes the origin, whereas a change in anisotropy can restore its stability and create displaced saddles. Wave packets centered at these saddles exhibit exponential FOTOC growth even on a classically regular Dicke energy shell with Poisson statistics. This local sensitivity also enables quantitative spectroscopy: combined with the topology of stationary points and local density of states relations, FOTOC dynamics reconstructs the absolute amplitudes of spectral singularities in both models without fitting the density of states.

We present a fully quantum formulation of the spinterface model for the chirality-induced spin selectivity (CISS) effect, implemented within the non-equilibrium Green's function (NEGF) formalism. The model consists of a gold atom hosting a localised magnetic moment, coupled to a chiral molecular chain with Rashba spin-orbit coupling, and contacted by two non-magnetic leads. The magnetic moment is determined self-consistently from the non-equilibrium electronic distribution, and the spin-resolved transmission is computed from the mean-field Hamiltonian. We show that the interfacial magnetic moment and the chiral Rashba term cooperate to produce large current polarisations that reproduce the key experimental signatures of CISS: high polarisation, a threshold emergence at four total sites followed by interference-modulated growth with chain length, thermal suppression, and sign reversal upon chirality inversion. The central new result of this work is a clean separation of the CISS effect into an even (achiral) and an odd (chiral) contribution to the spin current, $I_{S_z}(φ) = I_{S_z}^{\rm even}(φ) + I_{S_z}^{\rm odd}(φ)$. We demonstrate that $I_{S_z}^{\rm odd}$ vanishes exactly at fixed $m_z$ for chains of fewer than four sites and becomes non-zero for chains of four or more sites, with the smallest junction exhibiting a non-zero odd part being the four-site geometry (one gold atom plus three molecular sites). The odd part arises from reciprocity breaking in a device that is simultaneously chiral, magnetically asymmetric (moment on the gold end only), and long enough to support two or more Rashba-active bonds. This provides a direct, parameter-free test of whether an observed spin signal is genuinely chiral or arises from an achiral spin-valve mechanism.

Structured light provides a route to controlling quantum materials not only through its polarization, but also through its spatial profile and orbital angular momentum (OAM). We develop real space theories of a Weyl semimetal driven by a vortex beam and show that optical OAM generates highly localized Floquet vortex states with pronounced circulating photocurrents. Exploiting cylindrical symmetry, we derive a Bogoliubov-de Gennes-like radial equation that resolves the states by angular momentum and reveals their evolution between the light-dressed Weyl cones. For Laguerre-Gaussian beams, the spatially varying drive produces strong hybridization between localized vortex states and bulk states. We complement this continuum description with a Wilson-lattice formulation that retains the full two-dimensional spatial structure and enables direct calculation of local photocurrents. Both approaches consistently identify OAM-induced vortex states localized around the beam axis. The lattice calculation further shows that these states support substantially stronger circulating current densities than the more extended surface states, with the largest current densities associated with the most strongly localized, low-angular-momentum vortex modes. Our results establish optical OAM as a tunable control parameter for creating and manipulating localized current-carrying states in Weyl systems and provide a real-space framework for studying photocurrents generated by spatially structured light.

Phase transitions (PTs) in quantum many-body systems offer a powerful route to manipulate the performance of quantum batteries (QBs). Here, we investigate an anisotropic Dicke QB with Kerr nonlinearity, focusing on the role of PTs in the charging process of the QB system. By analyzing how the Kerr nonlinearity reshapes the cavity level-spacing structure, we find that multiple near-degeneracies emerge at specific nonlinearity strengths. Away from the region of multiple near-degeneracies, the stable stored energy is governed primarily by the ergodic-nonergodic transition (ENET), whereas within this region it is controlled by first- and second-order dissipative phase transitions (DPTs). We employ Liouvillian spectral theory to quantify the critical slowing down associated with the DPTs, and use the Wigner function to characterize the properties of the cavity field in the vicinity of criticality. We optimize the charging process via reinforcement learning (RL) and reveal the physical mechanism underlying performance enhancement from the perspective of ergodic and nonergodic phase dynamics. Our results offer a feasible pathway for manipulating and optimizing quantum battery performance based on intrinsic PT behaviors.

We give a bounded-error quantum polynomial-time algorithm for finding hidden parabolic subgroups of $\mathrm{GL}_n(R)$ over any effectively presented finite chain ring $R$. We call auxiliary group elements or subgroups used to extract information through oracle queries \emph{probes}. For chain length at least two, elementary abelian socle probes first recover the complete flag modulo the maximal ideal. When the residue field has size $q\ge3$, we reconstruct the flag recursively, lifting rank-one terminal members one digit at a time. The intermediate digits reduce to abelian hidden subgroup problems, while the final digit is a finite-field multiple-shift problem solved using learning from subset and Fourier sampling. For $q=2$, where distinct flags can have the same stabilizer, we instead lift the conjugate parabolic subgroup through the congruence filtration. A final linear system determines it modulo normalizer directions. The algorithm outputs generators with probability at least $1-ε$ in time $\mathrm{poly}(n,\log|R|,\log(1/ε))$. Consequences include $\mathrm{GL}_n(\mathbb{Z}/N\mathbb{Z})$ for every $N\ge2$ and, with an explicit maximal-order presentation, $\mathrm{GL}_n(\mathcal{O_K}/N\mathcal{O_K})$ for number fields $K$.

We advance the compact dressed Hamiltonian (CDH) framework to simulate the dynamics of open quantum systems strongly coupled to structured bosonic environments. The CDH approach combines reaction-coordinate mapping with a polaron transformation, incorporating strong system-environment hybridization into a dressed representation before truncating the collective bosonic mode. As a result of this truncation, dynamical features are captured with substantially fewer states than in the original representation. The residual environment is treated using a weak-coupling Markovian quantum master equation. We benchmark the method for spin-boson-type models including a single spin, coupled spins, and spin ensembles, considering both resonant and off-resonant regimes and weak to strong system-bath coupling. Comparisons with hierarchical equations of motion and converged reaction-coordinate calculations demonstrate that the CDH representation systematically approaches the reference dynamics with a compact Hilbert space, accurately reproducing oscillation frequencies, relaxation behavior, and long-time populations over a broad parameter regime. The method further captures cooperative phenomena, including bath-mediated interactions, synchronization between spins, and signatures for collective emission. Beyond efficient time propagation, the CDH framework provides direct access to the spectrum and eigenmodes of the Liouvillian. We demonstrate that slow dynamical modes converge rapidly in the CDH representation, enabling identification of relaxation timescales without fitting time-dependent observables. As a whole, the CDH framework provides an efficient and physical description of strongly coupled open quantum-system dynamics.

Photonic and qubit-based (digital) approaches to quantum computing are largely regarded as separate paradigms. This article aims to bridge these paradigms by developing a method for mapping quantum-optical systems onto qubit-based quantum circuits. The key ingredient enabling this mapping is the introduction of a truncation of the Fock space describing single-mode optical states. Within this framework, representations of basic photonic operations are developed, including the phase-rotation operator, the displacement operator, the squeezing operator, and the beam splitter. Explicit quantum circuit constructions are provided for Fock-space truncations of dimension $N=2$ and $N=4$. We discuss benchmarking of the implemented operations and identify the regime of applicability and the limitations of the proposed method. The presented results can be used to simulate quantum optical circuits on qubit-based quantum computers, with special relevance to Gaussian Boson Sampling in the low-photon-number regime. To demonstrate the practical applicability of this approach, we complement the theoretical framework with a Python-based quantum programming tool CO$Φ$ that compiles Blackbird quantum-optics programs into qubit-based OpenQASM circuits using a truncated Fock-space encoding. The compiler is available on GitHub at https://github.com/Quantum-Cosmos-Lab/cophi.

Cloud-accessible quantum computing has made heterogeneous Quantum Processing Units (QPUs) available through provider platforms that differ in qubit technology, calibration state, queueing behavior, and pricing model. This heterogeneity makes execution management a quantum-engineering concern: a quantum circuit may be executable on several backends, but the resulting cost, latency, fidelity, and reproducibility depend on backend selection and on how measurement shots are allocated. This paper presents the Quantum Broker, an open-source and provider-agnostic framework for Quality-of-Service-aware quantum execution management. The framework operationalizes shot-wise distribution by exploiting the statistical independence of quantum measurement shots to dispatch a single circuit across multiple heterogeneous QPUs according to user-defined constraints and optimization objectives. It combines a modular execution architecture, interchangeable backend-profiling strategies, and the Quantum QoS Specification Language (QQSpec), a declarative language for expressing QoS requirements. Dispatch planning is supported by two solver backends: a mixed-integer linear-programming (MILP) solver, and a nonlinear dual-annealing solver. Experiments on benchmark quantum circuits and noisy simulator backends show that the Quantum Broker can produce feasible QoS-aware dispatch plans under heterogeneous backend conditions and can improve QoS satisfaction with respect to single-backend and naive multi-backend baselines. The results also expose a practical trade-off between planning time and dispatch quality, with the nonlinear solver producing higher-quality allocations at increased computational cost. Overall, the Quantum Broker provides an extensible execution-management layer for engineering portable, reproducible, and QoS-aware quantum software over fragmented quantum cloud infrastructures.

Clean, interacting, periodically driven systems are believed to thermalize to featureless, infinite-temperature states that preclude the formation of stable ordered states. Here, we show stable quantum order, distinct from prethermal order, and its phase transitions in the ground state of the average-energy operator. Decomposing the time evolution into geometric and average-energy dynamics, we apply Geometric Floquet theory to identify the Floquet ground state. We derive a general variational principle to compute the Floquet ground state in large interacting periodically driven systems, and use it to develop a matrix product state algorithm. In driven nonintegrable chains of more than 100 interacting spins, our numerical simulations exhibit a gapped, area-law entangled Floquet ground state in extended parameter regimes; the ground-state manifold can support both dressed equilibrium order (e.g., Floquet antiferromagnets) and inherently nonequilibrium order (e.g., ground-state time crystals). This quantum order is protected by a finite average-energy gap, which closes at phase transition points upon changing model parameters. We decompose Floquet phases of matter into their equilibrium and nonequilibrium elements: whereas the Floquet ground state at any fixed time is a representative of an equilibrium phase of matter, the nonequilibrium content is entirely produced by the drive holonomy and is geometric. Finally, we identify quasilocal counterdiabatic driving as a mechanism for the stability against heating of gapped Floquet ground states in nonintegrable quantum systems, and argue why Floquet ground states evade the Eigenstate Thermalization Hypothesis. Our work enables the study of interacting nonequilibrium matter deep into the many-body regime, and lays the foundations for the engineering of strongly correlated ordered quantum states.

The resource theory of coherence quantifies the quantum properties of states and their role in quantum information processing. Extending coherence theory to ensembles, the natural objects in quantum communication, remains an active research direction, with their operational potential still being explored. In this work, we establish a maximally coherent ensemble in every finite dimension: the continuous ensemble of pure states distributed according to the normalized Haar measure attains the tight upper bound on basis-free relative entropy ensemble coherence. We then prove that ensemble coherence bounds the effective informational advantage of postselective measurements over the Holevo quantity for two equiprobable pure states. Finally, for the qubit B92 QKD protocol, we show that the coherence of Alice's ensemble upper-bounds the secret key rate in the asymptotic regime. These results give ensemble coherence a quantitative operational meaning in quantum communication and cryptography

We theoretically investigate electronic driving of a torsional mode in a suspended carbon nanotube quantum dot. The valley states in a nanotube carry opposite orbital magnetic moments along the tube axis, and intervalley mixing forms valley-mixed eigenstates whose splitting can be controlled by an axial magnetic field. We formulate an orbital-rotation coupling between the torsional angular velocity and the valley orbital angular momentum. Using a master equation for sequential tunneling through normal-metal electrodes, we calculate the steady-state current and the phonon distribution of the torsional mode. When the valley-state splitting matches the torsional phonon energy, orbital transitions can drive the mode out of equilibrium. The contacts control both phonon pumping and its electrical readout, allowing substantial excitation with a positive, vanishing, or negative current response. The mechanism requires no intrinsic spin or valley polarization of the electrodes, but uses state-dependent tunneling at the contacts.

When an ensemble of emitters is confined within an optical wavelength, its radiation can become correlated, leading to cooperative emission. In two-dimensional (2D) transition metal dichalcogenide (TMD) electron-hole bilayers, strong light-matter coupling enables the formation of interlayer excitons (IXs), long-lived dipolar excitations that provide an ideal setting for emergent collective phenomena. Here, we engineer an atomically thin light-emitting diode (LED) that generates electroluminescence (EL) from electrically injected IXs that are confined near the sample edges by an edge-enhanced fringing electric field. By measuring Hanbury-Brown-Twiss photon-photon correlations, we find pronounced signatures of collective decay in the form of large photon bunching followed by finite delay antibunching and bunching revivals. These emitter correlation signatures disappear when free charge carriers are doped to form a degenerate Fermi sea but are enhanced by the introduction of localized electrons. The results are consistent with a many-body quantum master equation that models the steady-state superradiant photon statistics of incoherently injected IXs. Our work establishes steady-state cooperative emission in a 2D TMD LED as a platform for studying strong light-matter interactions in electrically driven, non-equilibrium phases of Bose-Fermi mixtures.

We investigate the dynamics of two bosons in a tilted one-dimensional optical lattice with both standard and density-assisted tunnelling. The relative sign of the two tunnelling processes strongly affects the Bloch dynamics, leading to distinct reinforcing and competing regimes. We examine how the tunnelling processes generate correlations and find that, in the absence of onsite interactions, the early-time entanglement growth follows the same scaling with the density-assisted tunnelling amplitude. Finite onsite interaction changes this picture by breaking the symmetry between the reinforcing and competing regimes and enhancing the correlation differently in two regimes. This shows how the interplay between the two tunnelling mechanisms can change dyanmics and entanglement in a controlled few-body setting. Particularly, at equal tunnelling amplitudes, the doublon and singlon sectors decouple completely for arbitrary onsite interaction, lattice tilting, and initial state.

Practical security analysis of Coherent-One-Way (COW) quantum key distribution requires optical-device modeling, finite experimental statistics, and security inference to be treated consistently without conflating assumptions. We present a modular observable-level simulation framework organized through the pipeline θ_phys -> p -> O -> S_j(O), in which physical source, channel, receiver, and detector parameters determine detector-resolved event probabilities, a finite-block layer applies an effective dead-time treatment and generates aggregate detector counts, and interchangeable security evaluators act on the same observable record. The framework is verified against analytical optical, virtual-state, and finite-key relations and evaluated against reported experimental COW-QKD operating points. The Kato finite-key calculation reproduces the refined experimentally reported secure-key rates most closely at intermediate distances, with deviations of -1.5% at 50 km and -10.3% at 75 km. Monitoring bright-port decoy counts agree within 0.9-2.4%, while remaining distance-dependent dark-port residual identifies the principal model-sensitive observable of the present physical description. Applying Kato and Azuma-Hoeffding concentration treatments to identical detector records isolates the effect of finite-key statistical inference and shows substantially tighter Kato phase-error bounds for rare-event monitoring records studied here. Holding the Kato evaluator fixed, joint optimization of coherent-state mean photon number mu and receiver splitting fraction t_B increases model-predicted secure-key rate by 7.4-20.2% relative to optimization of mu alone with t_B = 0.3. The framework therefore provides a common computational interface for experimental reproduction, controlled security-model comparison, model-based protocol optimization, and modular adversarial stress testing in COW-QKD.

We design a hybrid quantum-classical computational workflow, combining density functional theory and dynamical mean-field theory, to investigate the electronic properties of CaCuO2, a parent structure of high-temperature cuprate superconductors. Our approach uses a quantum algorithm as an impurity solver that is based on variational quantum compressed time evolution to compute the time-dependent Greens function on an IBM Heron quantum device. Utilizing error mitigation techniques and a Lehmann representation fitting procedure, we extract the density of states from the signal in the accessible time regime. Despite the significant challenges rooted in the residual imprecision of currently accessible NISQ devices, we successfully resolve the characteristic features of the spectral function. However, we find that the required numerical accuracy for full DMFT self-consistency exceeds current hardware capabilities, indicating that practical real-material DMFT applications will necessitate post-NISQ hardware developments.

Geometric phase gates with addressed laser radiation are widely used in trapped-ion quantum computers to drive high-fidelity entangling gates on an arbitrary qubit pair of a larger ion chain. Such programmable connectivity exploits the collective phonons to mediate the desired interaction, while simultaneously achieving robustness to their thermal fluctuations by a careful calibration of the gate time with respect to the laser and vibrational-mode frequencies. Crosstalk errors can arise when the spectator qubits, which should ideally remain idle during the gate, are partially driven by the laser fields. The minimal crosstalk, which is set by the laser beam size on the spectator ions, can be achieved when the addressing beams propagate perpendicular to the ion chain. However, this results in exciting the radial phonons, and can complicate achieving high-fidelities as the ion chain grows due to the so-called spectral mode crowding. In this work, we present the theoretical description of a scheme recently implemented by Faorlin et $al.$. This scheme overcomes these complications by engineering addressable state-dependent forces along the ion-chain with laser beams that propagate perpendicular to it through the use of structured light gradients. In this way, one can excite the axial phonons and avoid the spectral mode crowding, while simultaneously minimizing the crosstalk. We present a detailed derivation of the entangling gate scheme, together with analytical closed-form expressions for the leading contribution to the gate error caused by thermal motional fluctuations and dephasing noise. Our results confirm that such fluctuations account for up to 93$\%$ of the error budget under the operating conditions of the gate implemented by Faorlin et $al.$. We identify target parameters to reduce the motional error from the reported $10^{-3}$ to the $10^{-5}$ level.

The five-qubit Absolutely Maximally Entangled AME$(5,2)$ state, whose every pair of qubits is maximally mixed so that all its information lives in non-local correlations, could in principle serve as a single shared quantum networking resource for teleporting two unknown qubits in parallel (each via its own Bell measurement and Pauli correction). Nonetheless, its hardware implementations remain scarce despite its theoretical importance. Here, we demonstrate parallel teleportation based on a five-qubit absolutely maximally entangled state, AME$(5,2)$, on the superconducting processor ibm_pittsburgh. We construct three-qubit Clifford decoders that extract two Bell pairs using three logical two-qubit gates for each of 60 inequivalent sender-receiver assignments. Using parallelization and classical Pauli frame post-processing, we retain reference-receiver entanglement on both channels after three teleportation rounds. With XY4 dynamical decoupling and the lowest-cost decoder, the final entanglement fidelities are $0.704\pm0.028$ and $0.680\pm0.022$, where uncertainties are pointwise $99\%$ confidence-interval half-widths over eight trials. Their lower bounds exceed the separability threshold of $1/2$. The decoder with lower circuit depth generally retains higher mean fidelity, and XY4 generally improves on XX. These results establish a hardware demonstration of two-channel entanglement transmission through repeated AME-assisted teleportation and provide compact decoding circuits for reconfigurable multipartite communication.

We review and analyse quantum information-theoretic approaches to black hole evaporation that purport to bring us closer to a resolution of the black hole information paradox. Our focus is on the Page-time paradox and on the contribution of the Hayden-Preskill model to understanding information release under the assumption of unitary evaporation. In this model, the black hole is taken to be a finite-dimensional quantum system whose dynamics can be represented by a quantum circuit, and its information-processing and communication abilities are studied. We identify the assumptions underlying this modelling and highlight two key features, fast scrambling dynamics and entanglement as a resource, that underpin the information release in the model. We argue that this reasoning exemplifies a broader change in how information is used in black hole physics, in which quantum information theory now provides a useful operational modelling framework. This application avoids earlier philosophical objections insofar as it is not based on epistemic ignorance and does not regard information as a substance. This line of reasoning has become central to the debate and, as such, warrants greater attention from the philosophy of physics community.

The quantum marginal problem, concerned with the compatibility of local and global properties of a multipartite quantum system, is arguably one of the fundamental questions in quantum theory. In this article we introduce a novel family of inequalities bounding the allowed local spectra of a pure tripartite state. The number of inequalities in this family grows with the dimension of the system. Most importantly, the inequalities hold for arbitrary dimensions. For equal local dimension at most 4, they generate the complete set of eigenvalue inequalities.

The growing demand for high-capacity, fast-charging, and durable rechargeable batteries has intensified the search for advanced electrode materials, with two-dimensional materials offering large surface-to-mass ratios and short ion-diffusion pathways. Here, pristine and Co-doped Janus HfSSe monolayers were investigated as anode materials for Li-ion and Na-ion batteries using first-principles density functional theory. Pristine HfSSe was found to be dynamically stable and exhibited a 0.85 eV band gap, while Co substitution shifted the Fermi level toward the valence-band region. Adsorption of the first Li or Na layer induced metallic behavior, thereby improving charge transport. Co doping strengthened alkali-metal binding, with the most favorable Li and Na adsorption energies changing from -2.6125 and -1.9800 eV to -3.7405 and -3.0529 eV, respectively. Co doping created electron-deficient sites that enhanced Li/Na binding. Co-doped HfSSe accommodated up to four Li layers and three Na layers, increasing the theoretical capacities from 555.43 to 776.19 mAh/g for Li and from 370.29 to 582.14 mAh/g for Na. The average open-circuit voltages were 0.62 V for Li and 0.29-0.30 V for Na, with minimum migration barriers of 0.2153 and 0.1044 eV, respectively. These results identified Co-doped Janus HfSSe as a promising anode material for Li-ion and Na-ion batteries.

We investigate photon-to-axion-like-particle (ALP) conversion in a finite, linearly polarized laser pulse for a single ALP field with simultaneous scalar-type and pseudoscalar-type couplings to photons. Varying the collision angle between the strong pulse and the probe provides a continuous kinematic scan of the resonant ALP mass. For fixed kinematics in this setting, the scalar-type and pseudoscalar-type ALP conversion amplitudes interfere coherently, making both the photon-to-ALP conversion probability and the polarization rotation depend on the difference between the probe polarization angle $α$ and the coupling angle $θ_g$. Conversion is maximal at $|α-θ_g|=90^\circ$, where the polarization rotation vanishes, while the rotation magnitude peaks at $α-θ_g=45^\circ$ modulo $90^\circ$, where conversion is half-maximal. These complementary polarization-angle dependences provide polarization-resolved signatures of mixed scalar--pseudoscalar photon couplings.

We show that several potential-energy functions based on the exponential function $e^{-αr}$, $α> 0$, are either equivalent or identical to the Tietz potential. Some of those potentials exhibit redundant parameters that can be removed without affecting their performance for the description of the vibration-rotation spectra of diatomic molecules.

Neural network fractional quantum Hall (FQH) states offer a promising alternative for capturing Landau level (LL) mixing and for understanding FQH physics, yet the incorporation of physical priors has so far been limited to the minimal exact constraints built into the ansatz. Working in spherical geometry, we show that the network's flexibility suffers both when only minimal additional physical priors are supplied and when priors such as flux attachment are imposed rigidly. In the former case, the monopole harmonic product orbital (MHPO) ansatz is difficult to optimize, whereas in the latter, the expressivity of the neural network is restricted. We therefore propose the orbital pair matrix factor MHPO (MHPO-M) ansatz, which balances physical priors against flexibility by not only replacing the fixed Laughlin structure with learnable pair factors but also making them dependent on both the electron configurations and the orbitals. Across $ν=1/5$, $1/3$, and $2/5$, MHPO-M achieves the lowest variational energy among the tested variants, and a factorized orbital readout based on it enables scaling to 35 electrons, with energies competitive with trends inferred from three-LL exact-diagonalization results. These results demonstrate that physical priors can be appropriately incorporated without sacrificing the flexibility of neural network wavefunctions, opening a promising path toward accurate, scalable modeling of FQH systems with LL mixing.

In single-shot Bayesian multiparameter quantum estimation, measurement incompatibility can increase the minimum joint quadratic loss by at most a factor of two relative to the bound obtained by optimising each parameter separately. Using the generalised Barnum--Knill inequality, we establish the same bound for a wider class of additive losses generated by positive score functions, showing that this limitation extends beyond the standard quadratic setting. To illustrate this result, we consider a broad family of periodic losses, including the sine loss sometimes employed in interferometry, and derive the corresponding incompatibility bound for Bayesian multiphase estimation with arbitrary prior knowledge. We further extend the framework to unbounded losses, such as absolute losses; this also recovers the case of quadratic losses.

Electrons in graphene move like massless relativistic particles, making them exceptionally mobile but difficult to trap because Klein tunnelling permits unimpeded passage through electrostatic barriers. This challenge extends to atomic collapse and hadron confinement. Twisted trilayers form Bernal and rhombohedral domains joined by smooth boundaries, bringing their carriers into contact. Here we show that a new mechanism, distinct from established approaches, confines massless fermions in equilateral triangular Bernal domains without mass barriers, bulk gaps or physical edges. Simulations and analytical modeling reveal that massless carriers have no adiabatic continuation into rhombohedral domains, while escape through nonadiabatic coupling to massive carriers is exponentially suppressed by smooth stacking variation. Perfect reflection in the adiabatic limit turns Bernal domains into quantum cavities in a gapless, edgeless metal. Striking density-of-states oscillations encode Eisenstein-integer arithmetic, linking energies and degeneracies to norms and prime factorizations. These findings bring relativistic confinement and number theory into experimentally accessible electronic spectra.

We study how the one-dimensional deformation suggested by nonadditive $q$-calculus can be extended to a rotationally covariant quantum model and what observable consequences follow from this extension. We choose a radial extension about a distinguished center in which only the radial derivative is deformed, while tangential derivatives retain their ordinary form. Within this model, we construct self-adjoint frame-momentum operators and derive a rotationally invariant uncertainty bound with a correction proportional to the mean distance from the center. We then adopt a non-negative kinetic Hamiltonian built from these momenta and derive the leading harmonic-oscillator energy shifts for weak deformation. The energy corrections split the levels with different orbital angular momenta that are degenerate in the undeformed oscillator, while preserving the degeneracy associated with rotational symmetry.

We theoretically introduce a quantum-circuit synthesis protocol to realize any $n$-qubit transformation $U\in U(2^n)$, up to a diagonal. The resulting circuit is directly native to and optimal in gate count and depth for systems where bitstring-conditioned rotations with tunable angle and axis, $C^{(n-1)}R(θ,φ)$, form the set of native operations. Subsequently, we suggest how this protocol can be implemented in a few-mode superconducting circuit, and experimentally demonstrate the method for the smallest nontrivial case, i.e., for two qubits. We report an average gate fidelity of 97.6 % for Haar-random two-qubit unitaries up to phase shifts in the computational basis. Importantly, these results suggest that multimode devices, such as those in the multimon or multiunimon families may become competitive with qubit-array networks for general-unitary implementations for qubit counts as low as three.

The exact multi-resolvent hierarchy of dense many-body spectra encodes higher-order spectral-weight correlations, but closing it predictively for interacting Hamiltonians remains a challenge. We introduce the multi-resolvent self-consistency (MRSC) equations, which separate an exact algebraic hierarchy from an approximate finite-parameter closure. The exact Feshbach geometric identity organizes r-resolvent cumulants into a ladder over irreducible vertices Gamma^(r), and the projected hierarchy expresses those vertices as functionals of the cumulants. The closure works in finite parameters: a connectivity basis organizes a general Hamiltonian's seed into class amplitudes, and a causal r-fold Stieltjes representation with a moment-field identity reduce moment matching to a finite-dimensional problem closed at a predictive fixed point. On the free-fermion benchmark the tested exact identities are reproduced and the Faddeeva closure is recovered at r=1. In a blind test on the interacting Ising chain, with the exact two-resolvent data withheld, the Hamiltonian-derived closure predicts the tested probes to 0.35%-0.97%. At the observable level the exact two-resolvent sector supplies a sign-correct, energy-resolved correction to the single-resolvent baseline for the off-diagonal eigenstate-thermalization-hypothesis (ETH) variance, of order one relative to it. Closure errors organize hierarchically: a level-by-level deficit decomposition, anchor measurements of the isolatable terms, and an explicit propagation bound. The same moments further yield a diagnostic chain for the window conditions of local rotational invariance -- an exact drift-kernel identity, a proven single-state identifiability boundary, and a transferability census over couplings and realizations -- a finite-order framework, not a proof of universal emergence.

Thin-film spontaneous parametric down-conversion, due to the relaxed phase-matching condition, generates photon pairs that are extremely broadband in frequency and angle and highly entangled in time/frequency and position/momentum. Here we show that it also provides a very broad orbital angular momentum (OAM) spectrum, which, in contrast to the case of bulk crystals, is decoupled from the frequency spectrum. To demonstrate it experimentally, we generate photon pairs in a $7~μ\mathrm{m}$-thick lithium niobate film and compare them with those from a $500~μ\mathrm{m}$-thick periodically poled lithium niobate crystal under identical pump conditions. The thin-film source exhibits a substantially broader OAM spectrum, with the azimuthal Schmidt number almost 9 times larger than that of the bulk source. On this highly entangled state, we perform quantum-state tomography in selected two- and four-dimensional OAM subspaces, demonstrating high-purity maximally entangled states. These results highlight thin nonlinear films as a promising platform for high-dimensional quantum-state generation with weak spatial--spectral coupling.

The Unruh effect links acceleration to thermalization, providing a relativistic setting for anomalous quantum relaxation. We demonstrate a {\it relativistic} strong quantum Mpemba effect in the Unruh thermalization of a two-level detector coupled to a massless scalar field. For a fixed pair of isospectral initial states, relaxation curves that never cross in inertial motion exhibit a Mpemba crossing above a threshold acceleration. At a higher, precisely tuned acceleration, the initially farther state has zero overlap with the slowest decay mode and relaxes with a faster asymptotic exponential rate. We identify how competition between transition and dephasing channels governs the relaxation spectrum, where sufficiently strong longitudinal coupling enables acceleration to switch the relaxation bottleneck between population and coherence modes. We derive the spectral-switching condition and construct isospectral preparation protocols that eliminate slow-mode contributions within their physical domains. These protocols reveal how coherence can suppress or enhance slow-mode overlap at fixed purity, depending on the underlying spectral structure. Our results establish acceleration as a control parameter for anomalous quantum relaxation, connecting relativistic quantum dynamics with nonequilibrium thermodynamics.

Optimal approximate state conversion is a fundamental task in quantum resource theories, yet existing solutions are largely tailored to specific distinguishability measures and resource theories. We show that every optimal approximate-conversion problem in the three paradigmatic majorization-based quantum resource theories of non-uniformity, bipartite pure-state entanglement, and pure-state coherence reduces exactly to one of only four elementary taut-string constructions. This holds for problems generated by Schur-convex spectral distances and by a broad family of quantum divergences satisfying a natural reduction property with respect to the corresponding equivalence group. The resulting framework encompasses a broad class of physically relevant distinguishability measures, including the trace distance, all unitarily invariant norms, quantum relative entropy, maximal quantum $f$-divergences, and the $α$-$z$ Rényi relative entropies. The increment vector of the corresponding taut string completely determines both the optimal approximation error and a canonical optimal state. Our results establish a common geometric framework for approximate quantum resource conversion, revealing that a broad class of seemingly different optimization problems is governed by the same taut-string geometric principle.

The measured logical error rate of a quantum low-density parity-check (QLDPC) code depends on the decoding algorithm. We develop a framework that certifies non-degenerate maximum-likelihood (ML) decoding outcomes on individual sampled shots under circuit-level noise, providing a common reference for comparing decoders and codes. Upper and lower bounds on the minimum correction cost in the true and competing logical classes establish success, failure, or an undecided outcome. Branch-and-bound search refines these intervals while retaining valid bounds under resource limits. Counting the outcomes bounds the empirical ML logical error rate, with interval width equal to the undecided fraction. Results for two bivariate bicycle codes show that best-first ordered statistics decoding (BF-OSD) tracks the non-degenerate ML benchmark closely while leaving some ML-correctable shots.

Ions possess both center-of-mass motion and internal states, rendering trapped-ion optical clocks susceptible to perturbations of both degrees of freedom, which results in systematic shifts and fluctuations with motional and relativistic origins. We develop a quantum theory that connects these effects to filter functions determined by the employed pulse sequences and show how the interrogation can be tailored to suppress or enhance specific perturbations. Our treatment includes laser frequency noise and motional effects such as recoil and Doppler shifts, micromotion and excess micromotion, as well as state-dependent trap imperfections and accelerations, e.g., caused by Stark shifts. We further account for relativistic effects including time dilation and the mass defect, and show how the same framework can be applied to hypothetical dark-matter signals. By considering ensemble-averaged phases and their variances, we characterize both systematic shifts and fluctuations, while asynchronous operation relative to the Paul-trap drive allows motional fluctuations to average down between runs. Our results provide a unified framework for characterizing and controlling the systematic and statistical contributions that determine the trueness and precision of trapped-ion optical clocks.

The Fer expansion writes the propagator of a driven quantum system as an ordered product of exponentials, each generated by the time integral of an effective Hamiltonian that governs the evolution left over by the previous factors. It can be stopped after finitely many factors whenever this leftover evolution is known in closed form, for instance when the effective Hamiltonian commutes with itself at all times, or precesses about a fixed axis with constant angular velocity. For $\mathfrak{su}(2)$, in any representation, from a qubit to a spin of any size, we resum the Fer recursion into a closed map on curves in $\mathbb{R}^3$. We prove that, for a real-analytic drive, in both cases the expansion stops beyond the first factor only trivially, when the first exponential is already exact.

We show that, starting from the same state, optimal driving can sometimes reach a colder (or hotter) target in the same amount of time while dissipating less energy, or equivalently dissipate the same amount of energy in a shorter time. We study this counterintuitive phenomenon in the slow-driving regime of an open quantum system, where we name it Near-Equilibrium Anomalous Tradeoff (NEAT). We establish necessary conditions for its occurrence and show its underlying geometric origin. While NEAT is reminiscent of the well-known Mpemba effect, the two phenomena are distinct in general. We demonstrate NEAT in an exactly solvable qutrit model, as well as for d-dimensional birth-death dynamics with independently controlled energy levels. Finally, we show how NEAT can improve the performance of Carnot engines.

We establish sufficient conditions for two-way local quantum-channel stability in classical $\mathbb Z_2$ lattice gauge models with spins on $m$-dimensional cells of a $d$-dimensional lattice. Each interaction multiplies the spins on the boundary of an $(m+1)$-cell. This family, defined on the full spin Hilbert space without a Gauss-law constraint, includes the Ising model at $m=0$ and the magnetic sector of the toric code at $m=1$. The low-temperature proof combines two ingredients: locally indistinguishable flat sectors and extended magnetic defects of dimension $d-m-1$. For $1\le m\le d-2$, sufficiently weak local classical perturbations at sufficiently low positive temperature preserve equivalence to the canonical flat ensemble. No internal or gauge symmetry is required of the perturbation. For weak noncommuting perturbations, we prove the same conclusion in a smaller sufficient window by reducing the diagonal probabilities to a weak classical interaction and recovering the coherences with a local channel. The conversion channels use product ancillary inputs, have polylogarithmic causal radius, and achieve any prescribed inverse-power whole-system trace-norm error. Sufficiently high-temperature states are instead two-way equivalent to a product state. Independent finite-dimensional onsite systems can be included with weak local couplings. An optimized covariance between two distant neighborhoods of parallel $m$-tori is nonincreasing under one-way local conversion and invariant under two-way conversion. Its values $\mathcal F_m=1$ and $0$ distinguish the proved low- and high-temperature domains without a protecting symmetry. These sufficient domains do not determine the full phase diagram.

Quantum amplitude estimation offers a theoretical quadratic speedup over classical Monte Carlo methods for financial derivative pricing. However, extending gate-based algorithms to path-dependent barrier options has historically been hampered by sequential path discretization, where tracking price paths across $d$ monitoring dates incurs a linear escalation in qubit footprint and gate depth ($\mathcal{O}(d)$), posing severe coherence challenges for near-term quantum processors. In this work, we present a constant-depth quantum pricing framework that fundamentally eliminates the temporal dependency of barrier monitoring. Leveraging the Brownian reflection principle and Girsanov theorem, we project the continuous supremum dynamics onto a static bivariate joint distribution of the terminal price $S_T$ and running supremum $M_T$. This allows decoupling dynamic boundary checks into a static bivariate oracle comprising two parallel comparators and a dual-controlled rotation gate. We prove this architecture reduces circuit depth and comparator complexity from $\mathcal{O}(d)$ to an invariant $\mathcal{O}(1)$, while supporting discrete monitoring via zero-quantum-cost boundary corrections. Transpilation benchmarks for daily monitoring ($d = 252$) show our framework slashes physical CNOT count by 98.59% (from 2262 to 32) and compresses two-qubit depth by 98.02% (from 1514 to 30 layers). Under a realistic 127-qubit IBM Eagle noise model, the shallow circuit achieves a 7.84% relative valuation error with M3 readout mitigation. Finally, the framework seamlessly extends to nonlinear exotic payoffs lacking analytical solutions, establishing a noise-resilient pathway toward practical quantum advantage in computational finance.

Unstructured meshes are widely used in modelling and simulation in Computational Fluid Dynamics (CFD) due to their geometric flexibility. However, they require an efficient block encoding circuit describing the system. Here, we present a new block encoding methodology for unstructured mesh solvers based on decomposing the system matrix into a sum of 1-sparse matrices. This block encoding is engineered to reduce subnormalisation even in the absence of structure by hiding the contribution of large matrix elements behind others. We investigate three methods of 1-sparse decomposition. Our circuit constructions can optionally take advantage of limited matrix bandwidth and repeated values. For example we consider digitisation (reduced precision), where the number of multiplexed rotation gates is equal to the number of non-unique matrix entries. We evaluate our methodologies using 2D and 3D CFD matrices for unstructured aerofoil meshes, structured cavity, and duct meshes, with and without matrix preconditioning. Our results show that we are able to achieve a block encoding with a near constant subnormalisation factor as the number of matrix preconditioning infill levels increases. This significantly reduces the subnormalised condition number and, in one case, reduces the degree of the QSP polynomial approximation to $1/x$ by 100,000. Reduced precision digitisation is shown to become more effective as the number of preconditioning infill levels is increased and, in one case, reduces the number of multiplexed rotations from 2,785,576 to 546 whilst maintaining an infidelity of $2.6\times10^{-5}$ relative to the classical solution. The effect of digitisation on QSVT solutions is demonstrated using 2D and 3D unstructured mesh aerofoil cases. Due to its flexibility and automatic applicability, we believe our 1-sparse decomposition block encoding can offer benefits to other quantum applications.

Dipolar Bose--Einstein condensates (BECs), i.e., BECs with long-range dipole-dipole interactions (DDI), exhibit extraordinarily rich physics and serve as a versatile experimental platform for exploring exotic quantum states of matter. Within the mean-field framework, a dipolar BEC can be described by the Gross--Pitaevskii (GP) model with a DDI term. Its stationary states consist of the ground state, which minimizes the GP energy functional under the normalization constraint, and excited states, which are higher-energy critical points that typically correspond to constrained saddle points. Excited states encode collective excitation modes and play a key role in the dynamical stability and quantum phase transitions of cold-atom systems. However, in contrast to the extensively studied ground state, they remain far less explored numerically, especially in dipolar systems. In this work, we develop a numerical method based on the constrained gentlest ascent dynamics (CGAD) that systematically computes excited states of dipolar BECs by stably targeting constrained saddle points with any prescribed Morse index. Specifically, a semi-implicit sine-pseudospectral discretization with an orthonormalization correction step is adopted, and the nonlocal DDI terms are evaluated efficiently and accurately via the nonuniform fast Fourier transform (NUFFT). The resulting scheme is applied to one-, two-, and three-dimensional dipolar BECs, enabling a detailed numerical investigation of their excited states. Remarkably, our simulations reveal that excited states can persist even in regimes where the ground state of the condensate becomes mean-field unstable. This work provides a computational framework for studying excited states in dipolar quantum gases and offers insights for future theoretical and experimental investigations.

Using contour-integral representations of the permanent and of the Hafnian, we turn the computation of their moments for random matrices into a replica calculation, analogous to that of the moments of the partition function of a mean-field spin glass. For the $2k$-th moment of $N\times N$ matrices with independent entries, the dominant saddle point is replica symmetric for $k>2$, and we obtain in closed form the exponential growth rate, the prefactor and the first $1/N$ correction, in agreement with exact enumerations. The growth rate depends only on whether the entries are real or complex; higher cumulants affect only the prefactor and the $1/N$ term. At $k=2$ the replica-symmetric solution becomes unstable, separating a power-law bulk of the distribution from a large-deviation tail, which we compute. The results apply to boson sampling with single photons and with squeezed light.

Atmospheric turbulence and channel loss represent the primary limiting factors in ground-to-satellite quantum communication systems, yet their joint impact remains insufficiently characterized across diverse operational conditions. In this work, we develop a comprehensive and open atmospheric channel model for quantum optical links along ground-to-satellite paths, integrating altitude-dependent molecular and aerosol absorptions. The model is validated with available data from missions such as Micius and Hispasat, including a secondary viability assessment for a hypothetical Starlink-based quantum communication network, where we evaluate the predicted channel behavior in terms of single-photon transmittance and power balance, alongside the channel capacity of the link for uplink and downlink exclusively. Our comparative analysis demonstrates the ability of our channel model to predict real data under simple atmospheric behavior assumptions, which offer practical guidelines for the design and optimization of future quantum satellite missions.

Concatenation of quantum repeater nodes has been proposed as a means to distribute entanglement efficiently across future long-distance networks. Here, we demonstrate a trapped-ion repeater node that establishes photonic entanglement over a 17 km fiber traversing a city, moving beyond laboratory-only prototypes. The node comprises two atomic ions coupled to an optical cavity. First, a detailed characterization is performed of the long fiber channel and of ion-photon entanglement distributed across it. Next, a repeater-node protocol is implemented, achieving entanglement between a local photon and a remote photon with a Bell-state fidelity of $81.6^{+1.9}_{-1.4}\%$. These results demonstrate that trapped-ion repeater-node technology can operate over existing city-scale fiber infrastructure and represent a step toward distributed quantum repeater networks.

High-fidelity entangling gates are essential for quantum information processing. In transmon circuits, higher excited states provide additional pathways for engineering interactions within the computational subspace. Here we demonstrate controlled-Z (CZ) gates that exploit two noncomputational states, $\ket{02}$ and $\ket{20}$, through selective Floquet coupling. The nontrivial parametric modulation can activate both auxiliary transitions from $\ket{11}$ while suppressing the leading exchange between $\ket{01}$ and $\ket{10}$. Based on this approach, we develop two gate protocols: a nonadiabatic round trip through a bright auxiliary superposition and adiabatic evolution along a zero-energy dark state, both achieving average gate fidelities above $99.99\%$ in numerical simulations. Control of the modulation phase further extends the bright-state protocol to conventional and unconventional geometric CZ gates. Effective-model simulations show that unconventional control improves tolerance to residual $ZZ$ coupling and static qubit-frequency offsets relative to conventional control over the parameter ranges examined. Simulations including neighboring spectator qubits show that the original nonadiabatic bright-state and adiabatic dark-state CZ protocols retain high gate fidelities. This framework offers new routes toward the experimental realization of CZ gates and their geometric implementations.

Understanding the three-dimensional (3D) quantum Hall effect, characterized by a Chern vector rather than a single Chern number, has been a central pursuit in topological physics. While quantized Hall transport is established for the special case with one nonzero Chern component, recent realizations of more general Chern-vector states raise a fundamental question: how does such topology protect quantized transport? Here, we predict a distinct 3D quantized Hall effect protected by $\mathbf{C}=(0,m,n)$. For samples with dimensions $L_y$ and $L_z$, global topology enforces collective quantization of $mL_y+nL_z$, despite the fragility of individual edge modes to disorder. This reveals a novel transport regime in which robust quantization emerges as a holistic property of a unified chiral network,rather than of its constituent modes. Crucially, this collective response manifests as a quantized Hall conductance $G_{xy}=\pm(mL_y+nL_z)e^2/h$, with a distinctive dependence on both Chern-vector components and sample dimensions. We propose candidate materials to facilitate experimental observation.

We theoretically investigate narrowband nonreciprocal transmission in a Doppler-broadened five-level M-type atomic medium. After Doppler averaging, the M-type system retains a narrow near-resonant electromagnetically induced transparency window that is narrower than that of a standard three-level $Λ$ system. This spectral narrowing is associated with the decreasing separation between the two inner dressed states as atomic velocity increases. The transparency window exhibits pronounced direction-dependent transmission, with high forward transmission and strong suppression in the reverse direction. The transparency linewidth and forward-backward probe transmission can be controlled via two independent driving fields, while the central transparency frequency is kept essentially unchanged. The resulting narrowband nonreciprocity supports high forward transmission together with strong suppression in the reverse direction, which is suitable for frequency-selective optical filtering and nonreciprocal optical transmission in thermal atomic media. Our scheme with these specific features is geared towards enabling compact vapor-cell-based nonreciprocal devices for quantum network applications.

Symmetry-protected ground-state crossings can produce exact first-order transitions (FOTs) even at finite $N$, in contrast to continuous transitions governed by soft-mode criticality. We establish exact Juddian ground-state crossings for arbitrary finite $N$ in the one- and two-photon anisotropic Dicke models and identify a common two-channel structure: the eigenvalues of the coupling matrix set the local normal-state instability thresholds, whereas its determinant fixes the exact crossing. Despite this common structure, the resulting FOTs have distinct fates determined by the bosonic response. In the one-photon model, the overlap between coherent Juddian branches vanishes in the thermodynamic or infinite frequency-ratio limits, asymptotically suppressing the FOT cusp. In the two-photon model, squeezed Juddian states lose normalizability at spectral collapse, thereby terminating the physical FOT line at finite $N$. Although the cusp strength tends to zero as the endpoint is approached, the terminating FOT retains a collective spectral signature: the different-parity gap is predicted to close with an $N$-dependent exponent $μ_N=(2N+3)/4$, one greater than the cusp termination exponent. By contrast, the same-parity soft mode retains $N$-independent square-root scaling and governs the critical response. Thus spectral collapse can terminate an exact finite-$N$ FOT while preserving its collective imprint in the parity-resolved spectrum.

We propose an approximate classical algorithm for estimating quantum circuits' transition amplitudes, $\langle Ψ_f | \hat{U} | Ψ_0 \rangle$, based on Monte Carlo sums over bidirectionally sampled Feynman paths. The algorithm generates Feynman paths, i.e., sequences of intermediate computational basis states, by combining information from random walks initiated at both the input and output states, $Ψ_0$ and $Ψ_f$, respectively. It further combines this bidirectional approach with Multiple Importance Sampling, a powerful variance reduction technique that avoids variance peaks caused by divisions by the very low sampling probabilities associated with hard to reach paths. Empirical data demonstrate the superior convergence rate exhibited by the bidirectional algorithm over a unidirectional, forward-only sampling approach. This superiority is due to the effectiveness of the proposed algorithm in finding and weighting paths with non-zero amplitude in an extremely sparse path space. Sum of paths algorithms exhibit very favourable space complexity. Monte Carlo replaces exhaustive enumeration of the exponentially large path space by stochastic sampling, the computational cost being determined by the variance of the estimator. This work demonstrates these two features by presenting results on very large quantum circuits, with up to 4096 qubits.

Axions are a compelling dark matter candidate suggested by theories beyond the Standard Model. The predicted axion-electron coupling and the resulting pseudomagnetic field allow for laboratory axion searches. Here we report an experimental axion search via a superconductor-spin hybrid magnetometer. A state-of-the-art broadband magnetometer with a sensitivity of sub-100 aT/Hz$^{1/2}$ at tens of kHz has been realized by coupling a ferrite spin sensor to a readout system based on a superconducting quantum interference device. The most stringent terrestrial constraints on the axion-electron coupling have been established in the frequency range 5$\sim$60 kHz. In the future, an improvement on the constraints of more than 4 orders of magnitude is foreseeable through arrays of superconductor-spin hybrid magnetometers with optimized designs. This work demonstrates the potential of superconductor-spin hybrid magnetometers in high-precision magnetic field sensing and the study of fundamental physics.

We demonstrate K-band nondegenerate three-wave-mixing amplification in a multimode resonator comprising an array of 500 SNAILs. Pairing K-band signal modes with lower-frequency internal idler modes enables 20 dB of gain continuously from 19.6 to 25.6 GHz with pump frequencies below 32.2 GHz. At 20 dB gain, the 3-dB bandwidth ranges from 2.6 to 11.7 MHz, and the input-referred 1-dB compression power reaches -100.9 dBm. In the 20-22 GHz band, the average added noise is 0.73 quanta. A two-mode nondegenerate parametric amplification model describes the measured gain response and gain-bandwidth behavior, while a multimode Kerr model captures the overall compression scale. Our amplifier provides a practical solution for implementing a state-of-the-art readout of superconducting qubits in the K-band.

The detection of axion dark matter poses a significant challenge due to its exceptionally weak coupling to standard-model particles. Here we develop a noise-tolerant quantum-metrology scheme based on coupled $^{129}$Xe spin ensembles to search for such weakly interacting particles. Within an experimentally accessible parameter regime, our scheme achieves an ideal exclusion limit on the axion coupling constant that is several orders of magnitude more stringent than that of conventional detection methods. We further investigate the performance of our scheme under dissipative noise and find that its robustness is fundamentally governed by the energy-spectrum structure of the composite spin-environment system. Remarkably, when a bound state emerges in the spectrum, the exclusion limit asymptotically recovers its ideal value in the non-Markovian dynamics, whereas under the Markovian approximation the limit deteriorates significantly due to noise. Our results establish a universal mechanism for noise-resilient exploration of beyond-standard-model physics, which can be practically implemented by engineering bound-state formation via tuning the Larmor frequency of the spin ensembles.

Treating the arrow of time as a controllable quantum variable rather than a fixed external parameter is a central challenge in quantum physics. Recently, Bloch~\cite{Bloch2025} proposed the theoretical concept of a \emph{time qubit}, a two-level control space $\mathcal{H}_T=\mathrm{span}\{\ket{+},\ket{-}\}$ that selects between opposite Hamiltonian evolutions $\hat{H}_{\pm}=\hat{H}_0\pm\hat{V}$, but this paradigm has remained experimentally unrealized. Here we formulate the quantum-optical theory of a single-photon time qubit---uncovering quantum-vacuum control and complementarity of the arrow of time---and experimentally probe and validate its predictions using phase-resolved single-photon interferometry from two coherently seeded entangled nonlinear biphoton sources~\cite{Lee2018,Yoon2021}. First, we show theoretically and verify experimentally that a controlled $π$ pump--seed phase inversion during pair creation from the quantum vacuum flips the stimulated displacement generator $\hat{V}\to -\hat{V}$ on top of the spontaneous two-mode squeezing background $\hat{H}_0$, reversing the stimulated evolution time [$\hat{U}_{\mathrm{stim},-}(t)=\hat{U}_{\mathrm{stim},+}(-t)$] and enabling universal single-qubit $\mathrm{SU}(2)$ control and postselection-free first-order tomography on the temporal Bloch sphere. Second, we prove that spontaneous idler vacuum fluctuations record complete which-branch (temporal-direction) information whereas the shared coherent seed erases it without cascading or aligning the idler beams, establishing an exact wave--particle complementarity law $|\bm{r}|=\mathcal{V}=|α|^2/(1+|α|^2)$ for the purity of the arrow of time and enabling direct first-order measurement of the Loschmidt time-reversal echo.

How macroscopic definite outcomes and nonlocal correlations emerge from entangled superpositions across spacelike-separated regions without superluminal action or {\it ad hoc} wavefunction collapse remains a defining open question in the foundations of quantum mechanics. Here, we resolve this century-long paradox within \textit{linear} relativistic quantum electrodynamics by developing an open-system and measurement-defined framework realized in dual, spacelike-separated nonlinear crystals driven synchronously by a multi-mode optical frequency comb and seeded by an ultra-narrow coherent laser. Expanding the transverse electromagnetic vector potential into discrete single-photon frequency-comb supermodes, we show that tracing out the unmeasured continuous-wave idler field yields an exact spatial dephasing Lindblad master equation whose decoherence rate is governed by the non-orthogonal state overlap of single-photon-added coherent states. Connecting this open-system map to free-vector-space quotient measurement theory, we demonstrate that single-particle interference arises from the geometric projection of the composite state onto detector-defined conditional cosets rather than remote collapse, establishing strict operational equivalence across pump, seed, and signal phase scans. The resulting wave-particle-entanglement triality equality $P^2 + E^2 + V^2 = 1$ is saturated across the complete parameter space, while the atomic-clock-referenced comb structure anchors continuous-variable time-frequency displacement stabilizers directly at the hardware layer. Our work unifies induced coherence, Bohr's complementarity, and quotient measurement theory, providing a microscopic pathway toward fault-tolerant bosonic quantum information processing.

Stabilizer Rényi moments depend on a choice of operator basis and need not be determined by entanglement spectra. In this paper, we study their spatial decay in critical quantum chains described by two-dimensional conformal field theories. We derive an exact entanglement baseline for reductions of pure stabilizer states and a symmetry selection rule for the charged contribution at fixed support. An exact Ising example shows that an on-site rotation changes the full decay exponent while preserving every subsystem entanglement spectrum. For growing Ising intervals at index two, we obtain an exact Pfaffian representation and compare the charged amplitude with a candidate conformal boundary calculation. The data support this prediction, but its identification with the lattice limit still requires endpoint matching and control of the order of limits.

It has been shown that Discrete Time Crystal (DTC) behavior may arise in the periodically driven, open Dicke model in the thermodynamic limit ($N \rightarrow \infty$). In this work, we demonstrate that finite $N$ non-mean-field fluctuations in this model can lead to decay rates and amplitudes of transient DTCs that display a non-trivial non-monotonic behavior with an increasing number of atoms. We show that the second-order cumulant expansion fails to capture the finite-size dynamics, while a stochastic version of the Truncated Wigner Approximation (TWA) is remarkably accurate, particularly in the large atom ensemble limit. Using the TWA and the Monte Carlo Wave Function (MCWF) approach, we identify three distinct dynamical regimes of transient DTC behavior in the finite-size Dicke model. We outline the mechanism behind the non-monotonic finite size dynamical decay of DTC order and discuss the implications for experiments performed on finite-sized atomic assemblies.