Quantum Physics
Lei Zhang, Yusheng Zhao, Yimeng Cao et al. (+10 more)
Formal verification is becoming increasingly practical for
quantum computing, yet the ability of AI
agents to construct machine-checkable proofs in this domain remains unmeasured. We introduce Lean-QuantumAlg-Bench and Lean-QIT-Bench, two Lean 4
benchmarks containing 36 and 40
theorem-completion tasks for
quantum algorithms and
quantum information theory, respectively. Every task compiles in a fixed environment and is evaluated by deterministic proof checking and targeted semantic review, with difficulty weights assigned before model execution. We evaluate four models-GPT-5.5, Kimi K3, DeepSeek V4-Pro, and MiniMax M3-within a common
theorem-proving framework under two settings: a task-only baseline and library-augmented deduction (LAD), which additionally provides access to a verified domain library. The highest difficulty-weighted scores are 60.4 out of 100 on the
quantum-
algorithm benchmark and 59.6 out of 100 on the
quantum-information
benchmark. LAD improves both score and completion rate in all eight model-
benchmark comparisons, with gains of up to 15.9 points, providing evidence that verified libraries can strengthen domain-specific proof
agents. The results reveal recurring weaknesses of agentic proving in areas such as
quantum simulation,
quantum learning,
quantum information measures, and
entanglement theory. Monetary and wall-clock costs per score point also vary substantially across models, highlighting important capability-efficiency trade-offs. We expect these
benchmarks to establish a reproducible baseline for developing more capable and reliable proof
agents, and to pave the way toward self-evolving AI scientists for advancing
quantum information science.
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All authors Lei Zhang, Yusheng Zhao, Yimeng Cao, Ranyiliu Chen, Mingrui Jing, Jizhe Lai, Ziao Tang, Jingu Xie, Hongshun Yao, Xuanqiang Zhao, Guocheng Zhen, Chengkai Zhu, Xin Wang
Quantum Physics · Cross-listed from cond-mat.mes-hall
Probing the nonlocality of Landau levels in GaAs quantum wells through modified Purcell factors, Lamb shifts and dipole emitted spectra
Lara Greten, Sabrina Meyer, Christina Schröder et al. (+2 more)
In a two-dimensional electron gas, a strong perpendicular
magnetic field confines electrons to quantized cyclotron orbits, giving rise to Landau levels with discrete orbit radii. Even the smallest Landau orbit, set by the
magnetic length, spans tens of nanometers for fields of a few Tesla, imposing an intrinsic nonlocal response to electromagnetic excitations. From a microscopic theory of the nonlocal susceptibility, we derive the Green's function, the central quantity governing all electromagnetic interactions, and evaluate Purcell factors, Lamb shifts, and emission spectra from a proximal dipole emitter beyond the Markov and rotating-wave approximations. Significant nonlocal effects resulting from spatial dispersion of the Landau level response modify the response for experimentally relevant situations up to distances of hundreds of nanometers and, in particular, brighten locally dipole-forbidden transitions due to near-field gradients at multiples of the cyclotron frequency. The relevant length scales are typical of state-of-the-art nanostructured terahertz architectures, and some of our nonlocal features are consistent with recent experiments using Landau level polaritons.
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All authors Lara Greten, Sabrina Meyer, Christina Schröder, Andreas Knorr, Stephen Hughes
Quantum Physics
Unified theory of classical and quantum semiparametric efficiency
Mankei Tsang
In classical and
quantum statistics, high-dimensional unknown parameters are abundant and it is often prudent to make minimal assumptions about them using so-called semiparametric models. To attack a wide range of semiparametric problems in one broad stroke, we present a unified treatment of statistical efficiency for classical and
quantum semiparametric models, generalizing the Cramér-Rao and Helstrom bounds beyond finite-dimensional parameters. We introduce the fundamental concepts in abstract and
geometric terms before applying them to many examples, covering general classical and
quantum models as well as the paradigmatic special cases of Gaussian and Poisson fields. We give an in-depth treatment of channels in the semiparametric efficiency theory and advocate the use of the singular value decomposition to elucidate the statistical effects of channels. To demonstrate the utility of the formalism, we apply it to coherent and incoherent optical imaging problems, assuming an arbitrary field or intensity on the object plane without parametric assumptions. Our formalism enables us to compute classical and
quantum limits to coherent and incoherent imaging resolution in statistical terms. For subdiffraction incoherent imaging, we demonstrate that spatial-mode demultiplexing can be far superior to direct imaging in estimating generalized
Fourier coefficients and come closer to the
quantum limits. We envision our theory becoming an essential tool for both classical and
quantum statistics with useful applications to sensing and imaging, whenever minimal assumptions about a high-dimensional parameter should be made.
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Quantum Physics
Extended Single-Atom Tweezer Arrays in High-Cooperativity Cavity-QED
Thomas Picot, Clément Raphin, Marcel Kern et al. (+4 more)
A central challenge for cavity-QED-based
quantum technologies is to make high-cooperativity optical interfaces compatible with site-resolved arrays of single atoms. Here, we demonstrate optical tweezer arrays of individual $^{87}$Rb atoms inside a fiber Fabry-Perot microcavity with single-atom cooperativity $\mathcal{C} \sim 90$. We combine background-free site-resolved fluorescence imaging of extended arrays with collective coupling to a common cavity mode for arrays with a mean atom number up to $\bar{N} \simeq 36$. These results establish a high-cooperativity platform for many-body cavity-QED with site-resolved detection and control.
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All authors Thomas Picot, Clément Raphin, Marcel Kern, Pierre-Antoine Bourdel, Théo Ahamdach, Jakob Reichel, Romain Long
Quantum Physics
Flow of local sensitivity in a spin chain coupled to a bosonic bath
Marcin Płodzień
We study how local sensitivity to an encoded parameter, captured by the
quantum Fisher information, flows between a
spin chain, a coupled bosonic bath, and their
quantum correlations, where we treat the bath as a full many-body
quantum system beyond the Lindbladian approximation. We analyze how the coupling
symmetry determines the destination of the departed sensitivity directly at the level of the
Hamiltonian. We consider an excitation-exchanging Jaynes–Cummings coupling, which preserves the total number of excitations, and a
spin-excitation-conserving Holstein coupling. We find that the Holstein coupling leaves the bath with no first-order information about the phase and stores the lost sensitivity entirely in
spin–bath correlations, whereas the Jaynes–Cummings coupling passes this sensitivity to the bath, in full for a single excitation. The bath spectrum then governs whether the sensitivity ever returns to the
spins. It revives fully and periodically when the coupled-system frequencies share a common period, but when those frequencies disperse the departed share dephases across the bath modes and never returns. We note that a transported metrological register loses more sensitivity than its arrival fidelity implies.
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Quantum Physics · Cross-listed from cond-mat.mes-hall
An on-chip programmable mechano-quantum transducer
Xinrui Zhang, Wei Liu, Duanyu Ma et al. (+13 more)
Solid-state
spin defects encode local perturbations as measurable shifts in
spin-transition frequencies, but mechanical actuation and
quantum readout remain physically separated, resulting in a discrete measurement setup. Integrating these functions requires an on-site mechano-
quantum interface that programs the
lattice state of a defect host and quantitatively maps it onto the
spin Hamiltonian. Here we first report an on-chip programmable mechano-
quantum transducer (OCPMQT) that integrates voltage-defined micromechanical actuation with in situ
spin-frequency readout in a two-dimensional van der Waals
quantum-defect host. Mechanically programmed
lattice states are encoded as shifts in the axial zero-field splitting parameter and resolved by optically detected
magnetic resonance (ODMR) spectroscopy. Within a chip volume of 2.05*10^-2 cm^3, the transducer accesses ODMR-inferred strains as low as 0.0080% and delivers a volumetric force density of approximately 2.6*10^4 N*m^-3. A micromechanical-to-
spin-
Hamiltonian framework links on-chip electromechanics, interfacial strain transfer, and strain-
spin coupling, enabling the electrical control micromechanical input to be measured directly as
spin-frequency response.
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All authors Xinrui Zhang, Wei Liu, Duanyu Ma, Lin-Ke Xie, Nai-Jie Guo, Zhongtao Gou, Yifan Wang, Jianxin Xu, Xiaoguang Luo, Zhao Mu, Honglong Chang, Weizheng Yuan, Jian-Shun Tang, Chuan-Feng Li, Guangcan Guo, Tao Ye
Quantum Physics
An Optimal Analysis of the Product Test
Jacob Beckey, Fernando Granha Jeronimo and Pei Wu
Product testing, i.e., deciding whether a pure multipartite
quantum state is fully unentangled across a specified tensor decomposition, serves as a bridge between
quantum property testing, unentangled
quantum proof systems, and tensor optimization. Despite being a fundamental property testing task and having many applications, the product test's exact (worst-case) acceptance probability curve has yet to be fully determined. In this work, we determine this curve exactly. Let $\omega$ be the maximum squared overlap of the input with a product state, and let $\mathrm{PT}_n(\omega)$ be the largest possible acceptance probability of the product test over all $n$-partite pure states with product overlap $\omega$, allowing arbitrary finite local dimensions. We prove that, for every $n\ge 2 $ and every $\omega\in(0,1] $, $$ \mathrm{PT}_n(\omega)=\frac12\left(1+m\omega^2+(1-m\omega)^2\right), $$ where $m=\lfloor1/\omega\rfloor $. The formula recovers the previously known tight section of the curve for $\omega\ge 1/2 $, resolves all low-overlap regimes $\omega<1/2 $, and implies $\mathrm{PT}_n(\omega)\to 1/2 $ as $\omega\to 0$ answering an open problem in [Soleimanifar and Wright, SODA 2022]. As a complexity-theoretic application, our results improve the one-shot soundness parameter in the Harrow-Montanaro reduction from $\mathsf{QMA}(k)$ to $\mathsf{QMA}(2)$. Our techniques, built upon those of Soleimanifar and Wright, allow us to resolve these open questions while remaining surprisingly elementary.
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Quantum Physics · Cross-listed from hep-th
Relational path integral, effective actions and quantum frame covariance in gravity
Sergio E. Aguilar-Gutierrez, Renata Ferrero, Philipp A. Hoehn et al. (+1 more)
We propose a relational bundle-
geometric formulation of the gravitational path integral by invoking the new tool of
quantum reference frames (QRFs), which in
gravity are gauge-covariant coordinate systems constructed from the available field content. Formulated in terms of relational (frame-dressed) observables, this yields a manifestly gauge-invariant path integral without ghosts and anomalies, and in which observables and their correlators are local to a frame. While eliminating the need for gauge fixing, it is equivalent to Faddeev-Popov versions in which the QRF is gauge-fixed, recovering certain previous proposals. A key feature is its covariance under QRF changes: it is a perspective-neutral path integral which encodes all internal QRF perspectives and the transformations between them. This leads to several qualitative predictions: local correlators and time
evolution of relational observables in one QRF perspective become fuzzy in another, and a new spectrum of relational
vacua arises. Comprised of frame-dependent no-boundary and asymptotic ground states, a
vacuum from one perspective appears generally excited in another. Finally, we construct gauge-invariant, yet frame-dependent effective actions by coupling sources exclusively to relational observables, setting the stage for a relational definition of renormalization.
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All authors Sergio E. Aguilar-Gutierrez, Renata Ferrero, Philipp A. Hoehn, Luca Marchetti
Quantum Physics
Rack-integrated quantum dot-based source of single and entangled photons at telecom C-band
Michal Vyvlecka, Raphael Joos, Benjamin Breiholz et al. (+8 more)
For
quantum light sources in everyday telecommunication networks,
quantum science needs to be fully transformed into
quantum technology. The first necessary step to move outside a well-controlled lab environment requires the use of
quantum light sources operating in the technologically relevant telecom O- and C-band. This can be provided using epitaxial
quantum dots as deterministic sources of
quantum light. Particularly intriguing is that emitters operating at telecom wavelengths are rapidly catching up with their short wavelength counterparts in terms of performances. Here, we make a decisive step forward in the development of
quantum communication networks: a state-of-the-art source of
quantum light, a
semiconductor quantum dot (QD), with record coincidence rate for entangled
photon emission in the telecom C-band, is operated inside an optimized rack-based setup. This setup includes a tunable pulsed
laser for the QD excitation (from quasi- to fully resonant excitation), all optics for the excitation filtering, and QD signal coupling into single-mode fibers. Overall, the setup allows for above $50\%$ transmission for both
exciton and biexciton
photons. These results show that
quantum dots-based telecom light sources can now be transported and integrated into existing fiber infrastructures, an important step to demonstrate the feasibility of the upcoming
quantum internet.
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All authors Michal Vyvlecka, Raphael Joos, Benjamin Breiholz, Emma Marmasse, Anna Friederike Köhler, Ponraj Vijayan, Tobias Huber-Loyola, Sven Höfling, Michael Jetter, Simone Luca Portalupi, Peter Michler
Quantum Physics
Directional telecom photons from a chirally coupled quantum dot
Kristina Bodiroga, Jacob Ewaniuk, Andrew N. Wakileh et al. (+7 more)
Chiral quantum light-matter interfaces, where the internal
spin state of a
quantum emitter determines the direction in which it emits, are essential building blocks of non-reciprocal
quantum devices, deterministic
quantum logical gates and
entanglement generation protocols. Yet, a
chiral quantum interface that operates at telecom wavelengths, and is compatible with telecommunication infrastructure and silicon photonics, does not yet exist. Here, we report on an integrated
chiral quantum interface in the original telecom band (1260-1360 nm), created by interfacing InAs
quantum dots with a waveguide-coupled InP microdisk. We tune the
quantum dot transitions through the photonic cavity using a strong
magnetic field, observing a peak cavity enhancement of 3.3 and an emission directionality of 0.985, demonstrating the near-ideal
chiral quantum coupling required for
quantum information processing on integrated photonic devices.
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All authors Kristina Bodiroga, Jacob Ewaniuk, Andrew N. Wakileh, Lucas Rantz, Ivanna M. Boras Vazquez, Dan Dalacu, Philip J. Poole, Robin L. Williams, Xiao-Liu Chu, Nir Rotenberg
Quantum Physics
QuantumChain: Blockchain-Backed Quantum Federated Learning for Financial Fraud Detection
Epameinondas Douros, Konstantinos Dalampekis, Nouhaila Innan et al. (+2 more)
Financial fraud detection is challenged by decentralized data, severe class imbalance, and
privacy constraints. This paper presents QuantumChain, a secure
Quantum Federated Learning (QFL) framework that combines hybrid
quantum-classical neural networks, encrypted
federated aggregation, blockchain-based auditability, and
quantum-secure communication. Each client trains a local hybrid model in which a variational
quantum circuit is embedded between classical neural layers, while model updates are protected through homomorphic encryption, threshold secret sharing, and QKD-based keying. A permissioned blockchain records aggregation events and supports reputation-weighted trust among participants. We evaluate QuantumChain on financial transaction data using a compact, size-matched classical baseline to isolate the effect of the
quantum layer. Results show that the HQNN achieves comparable accuracy while improving fraud-class recall in most settings, reaching 94.6% recall compared with 93.2% for the classical model. The Deep QLayer improves performance in full-data settings, suggesting that added
circuit depth helps recover representational capacity when the shallow
circuit becomes limited. Mixed-state simulations further show that the recall trend persists under non-ideal
quantum evolution. In
federated deployment with 10 heterogeneous clients, global accuracy increases from 97.7% to 98.8% over five rounds before stabilizing. These results show that QuantumChain can integrate depth-aware hybrid
quantum models into a secure
federated fraud-detection pipeline while maintaining stable global convergence.
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All authors Epameinondas Douros, Konstantinos Dalampekis, Nouhaila Innan, Ioannis Theodonis, Muhammad Shafique
Quantum Physics
Exponentially enhanced two-mode multiboson entanglement via phase-modulated tunneling
Pritam Chattopadhyay, A. G. Kofman and Gershon Kurizki
The
entanglement of
quantum systems is commonly restricted by their coupling
Hamiltonian and initial state properties. Here, we prove by exact analysis of tunnel-coupled bosonic field modes, that factorized multi-
boson two-mode states can become fully entangled via stroboscopic sign flips of the two-mode coupling. Their
entanglement can exponentially grow with the number of flips. With the exception of specific prohibitive states that are invariant under such sign-flip control, this effect universally applies to two-mode state preparation. Remarkably, this linear control may provide
entanglement resources for diverse
quantum technological applications by readily available means.
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Quantum Physics
QSTAR: Quantum Selective Transfer with Adaptive Routing
Saim Rehman, Nouhaila Innan and Muhammad Shafique
Quantum transfer learning (QTL) is often evaluated by replacing a classical classifier with a fixed variational
quantum head, but this hides a key question: when is the
quantum branch actually useful? We propose QSTAR:
Quantum Selective Transfer with Adaptive Routing, a selective QTL framework that keeps high-confidence classical predictions and routes only low-confidence samples to a fallback branch. Using a frozen ResNet18 backbone on Fashion-MNIST, we compare manually designed QTL heads, KetGPT-designed
quantum heads, and parameter-matched classical baselines under a common data split and optimization schedule. Standard QTL heads reach at most 57.0% accuracy, while the strongest KetGPT head in the main filtered sweep reaches 78.5% accuracy and 0.785 F1-score. Although the strongest fixed classical head remains higher at 81.6%, selective routing gives the
quantum branch a clearer role. On low-confidence samples, KetGPT #180 improves accuracy over a parameter-matched MLP fallback by 6.82, 4.31, and 3.03 percentage points at thresholds of 0.70, 0.80, and 0.90. At the full-system level, Adaptive KetGPT-QTL reaches 80.9% accuracy and 0.807 F1-score, outperforming the adaptive classical baseline. A separate compact-
circuit ablation identifies KetGPT #160 as a stronger fixed-head candidate, reaching 81.9% accuracy with only 10
quantum parameters and 9 gates. These results suggest that architecture-searched
quantum heads are most useful as targeted fallback branches for uncertain inputs rather than uniform replacements for classical classifiers.
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Quantum Physics
Cautious optimism for deep parameterized quantum circuits
Marie Kempkes, Elies Gil-Fuster, Carlos Bravo-Prieto et al. (+5 more)
A central challenge in
quantum machine learning is understanding the scaling behavior of parameterized
quantum circuits (PQCs). In particular, it remains unclear how their performance on unseen data changes as the number of trainable parameters increases. Prior works have derived formal generalization guarantees for
quantum models, but it is well-known that many such results do not fully characterize generalization behavior in practice. In this work, we show that gradient-based PQCs can exhibit improved performance on unseen data as model size increases, displaying the phenomenon of double descent. This contrasts with the traditional view that larger models lead to degraded generalization. We provide analytical results rigorously underpinning this behavior by leveraging add-one-in perturbation techniques and spectral properties of random
matrices. We support these results with numerical experiments on re-uploading PQCs across several data sets and training set sizes, consistently observing the predicted double descent behavior. While other obstacles on the path toward practical
quantum machine learning remain, our finding that deeper parameterized
quantum circuits do not necessarily exhibit degraded performance provides reasons for cautious optimism.
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All authors Marie Kempkes, Elies Gil-Fuster, Carlos Bravo-Prieto, Aroosa Ijaz, Alissa Wilms, Jens Eisert, Evert van Nieuwenburg, Vedran Dunjko
Quantum Physics · Cross-listed from physics.chem-ph
Towards more accurate natural orbital functional approximations: including 4-index cumulant contributions
Valerii Chuiko, Paul W. Ayers and Eduard Matito
Accurate modeling of bond breaking remains a central challenge for reduced density
matrix functional theory (RDMFT). Although some modern functionals can yield reasonably accurate dissociation energies, they often fail to reproduce key properties of the dissociated fragments, such as a vanishing fragment population covariance (also known as the delocalization index) and the correct total
spin angular momentum of each fragment (local
spin). In this work, we revisit the construction of natural orbital functionals by correcting the cumulant contribution produced by the PNOF5 functional. Our method enforces known contributions of the cumulant to local
spin fragments and the delocalization index at the dissociation limit. We obtain the closest cumulant consistent with these physically motivated constraints and subsequently purify the corresponding one- and two-electron reduced density
matrices by imposing the standard $P, Q, \text{and } G$ $N$-representability conditions. The resulting functional yields improved behavior in strongly correlated regimes. Benchmarking on the dissociation of the singlet states of \ce{N2}, \ce{NO+}, \ce{O2}, \ce{S2}, and \ce{CO} shows that in the dissociation regime the energies computed from the updated cumulant exactly reproduce the complete active space self-consistent field (CASSCF) energies. We further analyze the limitations of the approach and identify scenarios in which the current approach performs poorly. This work provides a pathway for systematically improving natural orbital functionals to achieve reliable bond-breaking calculations within RDMFT.
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Quantum Physics
A solution to 2-copy distillability of Werner states
Jinshi Fu, Li Gao and Sang-Jun Park
Entanglement distillation is a fundamental task in
quantum information theory. In this work, we prove that Werner states in arbitrary dimension are $2$-copy distillable if and only if they are $1$-copy distillable. This answers the longstanding open question of the $2$-copy distillability of Werner states. This is an important step on determining whether every non-positive partial transpose (NPT) state is distillable, which remains one of the central open problems in the field of
entanglement distillation.
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Quantum Physics
Floquet Reservoir Engineering for Remote Logical Entanglement
Mingxing Yao and Aashish A. Clerk
Implementing controlled dissipative dynamics is a powerful approach for state preparation in a variety of contexts, including the preparation of remote entangled states. Here, we show that by going beyond the standard setting of time-independent dissipative dynamics, one can realize even more powerful non-
unitary protocols. We introduce dissipative Floquet protocols for stabilizing remote
entanglement of logical
qubits, where continuously-running dissipation is interleaved with a periodic sequence of
unitary gates. These protocols harness existing experimental capabilities, and overcome time-
entanglement limits that constrain standard approaches. They also implement an autonomous form of
entanglement distillation. We show how these protocols give enhanced protection against waveguide loss, and as an example, analyze a specific implementation using cat-
qubits and transmons in a superconducting
circuit.
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Quantum Physics
Efficient classical simulation of large-scale unitary cluster Jastrow circuits
Hrishikesh Belagali, Thomas Van Camp, R. Pradeep et al. (+3 more)
Recent experiments on
quantum computers have challenged the limits of classical computation in chemistry, simulating ground states of strongly correlated molecules. Many of these experiments have utilized the
unitary cluster Jastrow ansatz, a
quantum circuit inspired by the
unitary coupled cluster ansatz that can be tailored to current
quantum hardware. Notably, the largest experiment in Sci. Adv. 11, 25 (2025) executed a
quantum circuit with 77
qubits and 10,570 gates on an IBM
quantum computer and performed classical post-processing with up to 6400 nodes on Fugaku to compute ground state energies better than Hartree-Fock. In this work, we present a
polynomial time classical
algorithm to compute the energy of any single-layer
unitary cluster Jastrow
circuit, independent of locality constraints for
quantum hardware. Our
algorithm can reproduce the largest experiment from Sci. Adv. 11, 25 (2025) in less than a minute on a laptop, and through
circuit optimization enabled by fast simulation we achieve a lower ground state energy than the experiment.
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All authors Hrishikesh Belagali, Thomas Van Camp, R. Pradeep, Sourin Das, Namit Anand, Ryan LaRose
Quantum Physics
Quasiparticle-induced transitions in a fluxonium qubit
Maksim Litskevich, Kesavan Manivannan, Benjamin Byrd et al. (+4 more)
Quasiparticles are a prominent decoherence source in superconducting
qubits, but their effects are notoriously difficult to isolate in fluxonium. Unlike the transmon, fluxonium is insensitive to offset charge, precluding charge-parity detection of quasiparticle tunneling. We address this challenge by measuring the excitation and de-excitation rates in a fluxonium
qubit under controlled on-chip quasiparticle injection and isolating the quasiparticle-induced contribution by subtracting the background transition rates. We show that to accurately model the external
magnetic flux dependence of the quasiparticle-induced transition rates, it is necessary to account for the superconducting gap asymmetry across the Josephson junctions. A comparison between theory and experiment constrains the relative quasiparticle densities in the small junction and the junction array and helps explain previously reported discrepancies between the bounds on the quasiparticle densities inferred for these two
circuit elements.
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All authors Maksim Litskevich, Kesavan Manivannan, Benjamin Byrd, Pavel D. Kurilovich, Vladislav D. Kurilovich, Gianluigi Catelani, Ivan V. Pechenezhskiy
Quantum Physics
Classifying Topology via Edge-State Pure Thermalization
Fatih Ozaydin, Haydar Sahin, Armando Perez-Leija et al. (+4 more)
Repeated-interaction machines distinguish heat-like from work-like resources through the steady states they generate, but whether
topology can control this distinction remains unknown. Here we reveal the role of
topology in the process by showing that topological edge states can act as pure-thermalization fuels. For an open Su-Schrieffer-Heeger chain used as the fuel source of a micromaser, edge eigenstates suppress both displacement and squeezing and drive the cavity to a Gibbs state, whereas bulk eigenstates activate coherent channels and yield thermo-mechanical operation. This edge-bulk thermodynamic dichotomy remains robust under realistic decoherence, cavity loss, bond disorder, and moderate onsite disorder. We further design a superconducting implementation in which a sixteen-site SSH eigenstate is deterministically compressed into a four-
qubit fuel register. The resulting cavity response provides a transport-free classifier of
topology and identifies a
topology-thermodynamics link that extends beyond cavity-QED to repeated-interaction settings more generally.
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All authors Fatih Ozaydin, Haydar Sahin, Armando Perez-Leija, Azmi Ali Altintas, Cihan Bayindir, Ozgur E. Mustecaplioglu, Sahin K. Ozdemir
Quantum Physics · Cross-listed from cond-mat.quant-gas
Fluctuation-Induced Bistability in the Dissipative Dynamics of Generic Cavity-Matter Quantum Systems
Luisa Tolle, Simon B. Jäger, Ameneh Sheikhan et al. (+2 more)
We demonstrate that fluctuation-induced bistability is a robust and generic phenomenon in strongly interacting many-body systems with strong light-matter coupling. We identify a common microscopic mechanism based on resonances between photonic transitions and many-body energy scales, unifying the emergence of fluctuation-induced bistability across a broad class of models, including interacting
spins,
fermions, and
bosons coupled to cavity modes. We develop complementary methods to study both the steady-state properties of fluctuation-induced bistability and its dynamical formation at finite times. In particular, we introduce the dressed-state rate equation approach, which reveals rich metastable dynamics and enables the investigation of its system-size dependence. By comparing its predictions with numerically-exact tensor-network simulations, we identify signatures of fluctuation-induced bistability already in small systems on finite timescales. Our results establish fluctuation-induced bistability as a universal feature of dissipative cavity-coupled many-body systems and provide a general framework for the investigation of its non-
equilibrium dynamics across a wide range of hybrid
quantum platforms.
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All authors Luisa Tolle, Simon B. Jäger, Ameneh Sheikhan, Corinna Kollath, Catalin-Mihai Halati
Quantum Physics
Device-Independent Self-Testing of the Three-Qubit CCZ Hypergraph State
Yunguang Han, Xin Kuang, Xingyuan Bu et al. (+1 more)
The three-
qubit CCZ state is the smallest rank-three hypergraph state and an elementary entangled magic resource. Its cubic phase is governed by generalized stabilizers that are not Pauli strings, so standard graph-state self-testing arguments do not apply directly. We show that twenty correlators, all obtainable from five of the eight global input triples in the tripartite two-input, two-output scenario, determine this state and the action of the Pauli $X/Z$ measurements up to local isometries. The proof fixes eight equally weighted computational branches and propagates conditional $X$-flip relations across the branch cube, recovering the minus sign of the $111$ amplitude. These five-context correlations are nonlocal, but the canonical Pauli measurements cannot attain the largest
quantum value of any Bell inequality that they violate: whenever they maximize a Bell expression, its local bound has the same value. Introducing an independent third measurement makes self-testing from maximal Bell violation possible. We construct an explicit Bell inequality whose maximal
quantum violation self-tests the CCZ state and all three local measurements. An exact sum-of-squares decomposition proves the
quantum bound, and its equality conditions yield an analytic SWAP extraction. Together, these results give two explicit device-independent self-tests of the CCZ state and demonstrate that determining a state and its measurements from several correlator equalities is distinct from identifying them through the maximal violation of a single Bell inequality.
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All authors Yunguang Han, Xin Kuang, Xingyuan Bu, Yukun Wang
Quantum Physics
QUBO Sampling for Mixed Binary Quadratic Programming without Continuous Variable Binarization
Taisei Takabayashi and Masayuki Ohzeki
Quantum annealing and related combinatorial optimization methods typically accept quadratic unconstrained binary optimization (QUBO) problems as input, whereas many practical models include constraints and continuous variables. Standard QUBO conversions discretize continuous variables, increasing the binary dimension and often making feasible low-energy states harder to sample. We develop a Lagrange-multiplier method for a separable class of mixed-binary quadratic programs (MBQPs) without discretizing continuous variables. The method is based on a finite-temperature free-energy formulation and uses QUBO sampling for the binary sector. At fixed Lagrange multipliers, the continuous sector is integrated out analytically and enters only the multiplier update, leaving a QUBO over the original binary variables. We evaluate the method on the continuous relaxation of the quadratic $p$-median problem. Compared with a penalty-based QUBO formulation, it generates feasible solutions more reliably. At an appropriate inverse temperature, its conditional relative error is comparable to that of local search for small instances and often lower for the larger tested instances. In the time-to-target comparisons, the proposed method maintains high target-reached rates for stringent fixed-accuracy targets. For the larger instances within the tested range, it also reaches the prescribed targets faster than a commercial mixed-integer optimization solver.
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Quantum Physics · Cross-listed from math-ph
Representation of the causal logic for the Dirac system and the electron
Domenico P.L. Castrigiano, Carmine De Rosa and Valter Moretti
We construct a covariant representation of the causal logic for the Dirac system and the electron, based on the conserved Dirac probability current and a general current-to-localization procedure for achronal regions. A
polynomial decay estimate, derived by a non-stationary phase argument, verifies the conditions required to define covariant achronal localization for the full Dirac system. Extending this localization to complete spacetime regions yields the corresponding causal-logic representation; restriction to the positive-energy invariant subspace gives the analogous construction for the electron. We establish several structural properties. On Euclidean space, Dirac localization agrees with canonical projection-valued localization, while its position operator differs from the Newton–Wigner operator by an explicitly determined bounded self-adjoint correction. Full Dirac achronal localization is projection valued and represents achronal separateness by orthogonality, thus satisfying microscopic causality. After compression to the electron subspace, it becomes positive-operator valued while preserving causality. We further extend known results from spatial to general achronal regions, prove separation and norm-one criteria, and analyze the high-boost limit, obtaining Lorentz contraction in a precise probabilistic sense. Finally, we discuss the electron–positron decomposition and the state transformation induced by position measurements, showing that measurement-induced positron production is universal and independent of the specific measuring device.
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Quantum Physics
Space-division multiplexed quantum key distribution exploiting multi-plane light conversion for few-mode fibers
Qian Zhang, Stefan Krause, Felix Kunzmann et al. (+1 more)
As
quantum key distribution (QKD) progresses from laboratory demonstrations toward practical deployment,
quantum communi- cation networks increasingly require higher key rates and the ability to distribute independent secret keys among multiple users and network nodes. In this paper we present a promsing approach with multi-plane light conversion (MPLC) for demultiplexing entangled
photons, transmitted through a few-mode fiber (FMF). We experimentally demonstrated a spatially multiplexed BBM92 QKD scheme. The modes are selectively excited through separate single-mode-fibers and subsequently separated by MPLC into distinct output ports. Unlike high-dimensional QKD based on coherent modal superpositions, our approach exploits distinguishable guided modes as parallel channels while preserving the
entanglement required for QKD. For the multiplexed links, we obtain
quantum bit error rates of $1.9 \pm 0.4\%$ for the channel 1 and $6.8 \pm 0.8\%$ for the channel 2. These results are relevant for scalable
quantum-secured networks, space-division-multiplexed QKD systems, multi-user
entanglement distribution, and future
quantum internet architectures, where parallel
quantum channels must be implemented without compromising the
quantum correlations required for security.
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All authors Qian Zhang, Stefan Krause, Felix Kunzmann, Juergen W Czarske
Quantum Physics
Tailoring optical Schrödinger cat states via orientation-dependent high-harmonic generation in $\rm{H}_2^+$
Ziyang Gan, Ahai Chen and Yuhai Jiang
We theoretically demonstrate that the molecular orientation angle $\theta$ provides a structurally intrinsic, continuously tunable control parameter for engineering optical Schrödinger cat states via high-harmonic generation (HHG) in H$_2^+$. Coupling time-dependent Schrödinger equation simulations to the fully quantized HHG framework, we evaluate the Wigner functions of the post-selected harmonic-mode states under two complementary conditioning strategies. Conditioning on resonance-enhanced low-order harmonics exploits the complementary dipole selection rules of the $1\sigma_g\to1\sigma_u$ and $1\sigma_g\to1\pi_u$ transitions, driving a kitten-cat crossover whose direction is opposite in the two channels as $\theta$ is varied. Conditioning on plateau harmonics instead exploits two-center destructive interference, producing a reentrant cat$\to$kitten$\to$cat transition controlled by the order-dependent interference angle $\theta^*(q)$. In both cases the crossover is decoupled from the
laser intensity, focal geometry, and molecular density, offering a degree of control with no counterpart in atomic targets.
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Quantum Physics
Approximate Virtual Quantum Recovery
Yuan Liu, Linhan Lin and Ke-Mi Xu
The recovery of
quantum information after subsystem loss is a central challenge in
quantum information processing. However, some states remain beyond the reach of any recovery strategies. Here we identify the algebraic origin of virtual irrecoverability, the ghost information—correlations encoded in the global state that leave no trace on any accessible subsystem. We introduce a scalar measure quantifying its magnitude and prove a universal error floor below which no virtual recovery map can operate, irrespective of resource investment. In such cases only approximate virtual recovery is available. We study the sampling cost when approaching the minimal attainable recovery error, and find it bounded when the underlying linear map exhibits a spectrum gap, and divergent in the gapless regime, respectively. Together with the universal error floor, this dichotomy partitions all multipartite
quantum states into four classes. Moreover, we show that conditional mutual information, the standard entropic diagnostic, does not constrain virtual recoverability. As an implication, we show that the error floor imposes a detection threshold for loss-tolerant
quantum metrology.
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Quantum Physics · Cross-listed from cond-mat.stat-mech
Entanglement asymmetry and quantum Mpemba effect for Kramers-Wannier duality
Milo Vescovo, Pasquale Calabrese and Filiberto Ares
The Kramers-Wannier duality is the prototypical example of a non-invertible
symmetry, yet little is known about its fate away from criticality and out of
equilibrium. We introduce the Kramers-Wannier
entanglement asymmetry, a
quantum-information measure that quantifies the breaking of this non-invertible
symmetry in the transverse-field Ising chain. We first investigate its
equilibrium properties, showing that it exhibits a striking crossover between the ordered and disordered phases together with a pronounced dip at the critical point that becomes increasingly sharp with subsystem size. We then study
quantum quenches from both gapped phases to criticality and show that the Kramers-Wannier
entanglement asymmetry decays to zero, signaling the dynamical restoration of the non-invertible
symmetry. Remarkably, we uncover the emergence of a
quantum Mpemba effect: under suitable conditions, states initially farther from
equilibrium restore the Kramers-Wannier
symmetry faster than states prepared closer to it. We provide both analytical and numerical evidence for this phenomenon and identify the mechanism responsible for its occurrence. Our work establishes
entanglement asymmetry as a powerful probe of non-invertible
symmetries beyond
equilibrium and opens new perspectives on the dynamics of dualities in
quantum many-body systems.
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Quantum Physics · Cross-listed from cs.ET
ARGON: A GNN-Empowered Compilation Framework for Scalable Neutral Atom Computing
Wenjie Sun, Xiaoyu Li, Zhigang Wang et al. (+3 more)
Neutral atom
quantum systems offer a promising pathway to large-scale
quantum computing due to high
qubit uniformity and flexible connectivity. To exploit this architecture, compilers must coordinate dynamic atom transport alongside highly parallel entangling gates. As
circuits scale, the interplay between these operations becomes a system bottleneck, introducing denser logical interactions and longer temporal dependencies. Compilers must simultaneously satisfy rigid spatial constraints and complex movement schedules. Existing joint spatiotemporal compilation methods face an exponentially expanding search space, incurring substantial overheads or compromising fidelity as
circuit size grows. In this work, we propose ARGON, a scalable compilation framework that introduces a spatiotemporal decoupling paradigm for neutral atom processors. Our key novelty is offloading static
geometric conflict resolution to an offline phase, precomputing a library of hardware-certified, high-parallelism spatial layouts. To guide temporal routing, we deploy a Graph Neural Network (GNN) predictor to evaluate candidate layouts against deep temporal horizons, proactively evading downstream kinematic bottlenecks. Finally, a heuristic router translates the selected sequence into collision-free physical transport. Evaluations show ARGON completes compilation in under 10 seconds, delivering up to a >10^4x and 600x average speedup over state-of-the-art baselines. ARGON also minimizes routing decoherence and reduces Rydberg stages, improving execution fidelity by up to 10^2x on dense
circuits.
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All authors Wenjie Sun, Xiaoyu Li, Zhigang Wang, Lianhui Yu, Geng Chen, Guowu Yang
Quantum Physics
Quantum Circuit Fragments and Link Products in Continuous Variables
Amalina Lai, Graeme D. Berk, Minjeong Song et al. (+1 more)
Quantum circuits are often drawn as complete processes, with fixed inputs and outputs. In many
quantum-information tasks, however, the natural object is only a fragment of such a
circuit: an unknown source of non-Markovian noise to be probed, a subroutine to be inserted into a larger
algorithm, or an
agent implementing an adaptive strategy. In finite dimensions, the link product provides a systematic means to analyze how such
circuit fragments interact and compose. Here, we develop the corresponding framework for continuous-variable systems. We introduce continuous-variable
circuit fragments and associated link products that stitch such fragments together into larger processes. We show that the formalism simplifies substantially in the Gaussian regime, where link products can be evaluated efficiently using covariance-
matrix representations. We use the formalism to construct non-Markovian processes and adaptive
agent-environment interactions from modular components. This extends the
quantum-comb toolkit to continuous variables, providing systematic methods for adaptive sensing, non-Markovian noise mitigation, and higher-order
quantum circuit design.
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All authors Amalina Lai, Graeme D. Berk, Minjeong Song, Mile Gu