Peer Revenue Impact factor: volatile

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Quantum Physics

quant-ph Watch Quantum Physics

Tuesday 1 September

Quantum Physics

Bosonic quantum control with a weakly coupled fluxonium qubit

Anaida Ali, Shantanu R. Jha, Shoumik D. Chowdhury et al. (+4 more)

Echoed Conditional Displacement (ECD) gates constitute a fundamental building block for quantum control of harmonic oscillator modes. However, bit-flips of the auxiliary qubit remain a dominant error mechanism for this kind of bosonic control. In this work, we present a numerical case study of a bit-flip protected fluxonium operating as the control qubit and numerically implement ECD gates in a single-mode resonator-fluxonium device, demonstrating that fidelities exceeding 99.9% are possible. We systematically investigate the resonator dynamics using a combination of semiclassical trajectories and master equation simulations, numerically revealing asymptotic saturation of the dispersive shift in the strongly driven regime of the resonator. We develop an efficient technique to numerically simulate the strongly driven regime of the resonator using a semiclassical formulation that maps the full perturbation series in the dispersive expansion as order-by-order frequency shifts. This provides a compact polynomial description of the resonator which is intuitive and remains valid throughout the dispersive regime. Furthermore, we propose an improved ECD sequence that accounts for the effects of photon loss and spurious nonlinear terms on resonator trajectories.
Read the full abstract

All authors Anaida Ali, Shantanu R. Jha, Shoumik D. Chowdhury, Lev-Arcady Sellem, Max Hays, William D. Oliver, Baptiste Royer

Quantum Physics · Cross-listed from cond-mat.mes-hall

Tuning Boron-Vacancy Qubit Coherence through Layer Number in hBN

Juan M. Florez and Eric Suárez Morell

The negatively charged boron vacancy ($\VB$) in hexagonal boron nitride (\hBN{}) was the first optically addressable spin qubit identified inside a van der Waals crystal, allowing atomically defined placement relative to a target. Its coherence in bulk \hBN{} is limited by the boron nuclei of the layers flanking the defect plane, which a thin flake removes. Here, we use a generalized cluster-correlation expansion with an extended central-spin block to calculate the Hahn-echo coherence time of $\VB$ in h$^{11}$B$^{15}$N as a function of layer number. Our results show that $T_2$ rises from $199\ns$ in the bulk limit to $653\ns$ in a monolayer, a factor of $3.3$ that is already saturated at three layers and that a sublattice decomposition attributes entirely to boron. The enhancement is confined to low field, is insensitive to stacking registry and twist angle, and requires alignment to within about two degrees, an onset we reproduce with no free parameters. Under dynamical decoupling, a $1/e$ threshold returns $206\ns$ for every thickness, but this is a zero of the first-shell modulation rather than a decay: measured without a threshold, the layer contrast survives and reaches a factor of $170$. Layer number thus emerges as a design parameter for $\VB$-based sensing.
Read the full abstract

Quantum Physics

Quantum Representation Learning Beyond Pairwise Fidelity

Junpeng Hou and Changbin Lu

Quantum contrastive, metric, and self-supervised learning often expose encoded quantum states to the learner through transition probabilities, especially fidelity. Quantum states are known to possess higher-order relational invariants, but their consequences for learned representations remain unclear. Here we show that a transition-probability-only learning interface can possess exact continuous blind directions in certain quantum-state families. We recover this missing information with a batch operator, built from coherent overlap amplitudes and negative masking, where its second moment $q_-$ retains four-state interference. Moreover, $q_-$ is directly measurable through two-copy interference and can enter variational learning via methods like parameter shift. In relational quartets derived from toric-code and double-semion states, this fidelity-blind signal encodes inequivalent modular data despite identical pairwise fidelities. Finally, in a four-photon benchmark with preparation drift, augmenting all six pairwise fidelities at two orthogonal probes with the corresponding normalized $q_-$ reduces the mean out-of-distribution phase error by $86\%$ at equal total shot budget. These results establish multistate relational observables as measurable, trainable, and physically consequential signals for quantum representation learning beyond pairwise fidelity.
Read the full abstract

Quantum Physics

GadIR: A Spatial-Topology Preserving Compiler for Quantum Many-Body Systems Simulation

Xiangyu Ren, Yuexun Huang, Zhaohui Yang et al. (+5 more)

Simulating quantum many-body systems has been one of the most important applications of quantum computation. For simulation, the Hamiltonian of a physical system is compiled into quantum programs with native instructions for quantum hardware. In previous works, the Hamiltonian is represented as Pauli strings, then compiled and optimized based on the quantum circuit model. Such representation paradigm neglects the spatial topology of original physical models, which is vital information to reducing the overhead of compiling many-body systems Hamiltonians. To address such neglect, we introduce a spatial-topology preserving compiler for quantum many-body simulation. Using Pauli gadgets as the representations of the Hamiltonian, we introduce our intermediate representation – GadIR, to preserve the spatial-topology information of original physical models. Our compiler frontend performs the group reduction algorithm based on Pauli gadget model, which is a hardware-independent optimization. Our compiler backend performs trotterization and scheduling on Pauli gadgets, then synthesizes the Pauli gadgets into hardware-native quantum programs. We evaluate our compiler on all the canonical quantum many-body system models, while achieving a significant reduction on compilation overhead regarding four major quantum architectures. Overall, our spatial-topology preserving IR exploits the compilation optimization space for quantum many-body systems Hamiltonian.
Read the full abstract

All authors Xiangyu Ren, Yuexun Huang, Zhaohui Yang, Yuchen Zhu, Tsung-Wei Huang, Tsung-Yi Ho, Zhiding Liang, Antonio Barbalace

Quantum Physics

$\mathcal{N}$-bein formalism for degenerate states in the parameter space of quantum geometry

Jorge Romero, Carlos A Velasquez and J David Vergara

Recently, we introduced a geometric object analogous to an orthonormal frame in the Cartan formalism to study the parameter space of quantum systems; we called it $\mathcal{N}$-bein, with $\mathcal{N}$ being the number of parameters that characterize the quantum system. Acting as the “square root” of the quantum geometric tensor (QGT), the $\mathcal{N}$-bein allows us to define new tensors to improve our understanding of the structure beneath the parameter space of quantum mechanics. In this work, we extend this mathematical framework surrounding the $\mathcal{N}$-bein to analyze the parameter space of quantum systems with degenerate spectra. As in the non-degenerate case, we define a non-Abelian two-state QGT to identify possible transitions between degenerate states after two consecutive parameter variations. Additionally, using the Wilczek-Zee connection, we introduce a torsion-like tensor as the covariant derivative of the $\mathcal{N}$-bein. This torsion captures the noncommutativity of successive parameter variations and coincides with the antisymmetric part of the two-state QGT. We also present a geometrical formulation using differential forms and discuss the physical implications of the newly defined tensors. Furthermore, we construct several gauge-invariant observables from the $\mathcal{N}$-bein and its derivatives to highlight the utility of the new tensors. Finally, to illustrate the convenience and applications of this formalism, we apply the theoretical framework to a system of coupled harmonic oscillators immersed in an electric field. The coupling between the oscillators results in a degenerate system. Thus, using the new formalism, we found correlations among the quantum states quantified by the new invariants.
Read the full abstract

Quantum Physics

Reliable Sample-Level Quantum Error Mitigation via Dominance-Aware Clustering

Mohsen Ghodrati, Kausthubh Chandramouli and Dror Baron

Many quantum algorithms for classically difficult optimization tasks must return high-quality bitstrings from finitely many circuit executions, whereas most quantum error-mitigation methods target expectation values. We study sample-level recovery when measured probability mass is distributed around multiple latent bitstrings, called centers. Each component of the measured probability mass is called a source and we assume that each center is associated with one source. We identify dominance-at every coordinate, more than half of a retained region's probability mass comes from one source and agrees with its center-as a sufficient condition under which majority voting recovers that center with exponentially decreasing error probability. We show that nearest-center assignment, as used in clustering algorithms such as the $k$-modes algorithm, can fail to produce dominated regions even when the true centers are known. This failure motivates responsibility thresholding and a local dominance screen, whose combination we call dominance-aware (DA) refinement. Synthetic and simulated MaxCut-QAOA experiments show that DA refinement favors precision, while $k$-modes with DA refinement improves overall center recovery. All procedures are classical post-processing and require no additional quantum-circuit executions.
Read the full abstract

Quantum Physics

Non-Markovian interactions with pulses of quantum radiation

Julien Pinske and Stefan Scheel

The interaction of a traveling pulse of quantum light with a localized quantum system shows non-Markovian features when scattering takes place in a structured environment. Here, we devise a non-Markovian input-output theory by coherently coupling the scatterer to a pseudomode, which decays into a Markovian reservoir. This incorporates memory effects of a structured environment without altering the cascaded nature of the Lindblad master equation, whose solution provides the quantum state of the output field of any desired mode. We apply our theory to the stimulated emission by a two-level atom, and to transmission of a Gaussian pulse through a cavity. We observe that the non-Markovian revival of coherence in the scatterer distorts the single-mode nature of the incoming pulse, thus resulting in a multimode output field.
Read the full abstract

Quantum Physics

Bilinear correlations in Fluctuating Gaussian States with anti-unitary symmetries

Xu Zhang

We study bilinear order-parameter correlations in a general class of sign problem-free systems that are described by what we call Fluctuating Gaussian States (FGS) with anti-unitary symmetries, where the weight of each Gaussian measurement in the space-time path integral is positive-definite. Supported by Monte Carlo simulations on fluctuating Gaussian fermionic and bosonic examples, we argue that such systems generally exhibit two types of broken-symmetry phases: a saddle point phase and a non-local contraction phase, with the competition between the two determined by the stability of the fluctuation saddle point of FGS. Due to the Fermi liquid instability in fermionic FGS with anti-unitary symmetries, we also discuss the possibility of representing fermionic FGS with a particular Projected Entangled-Pair State (PEPS) ansatz, which we argue a certain construction provides an efficient description for the saddle point phase, but not for the non-local contraction phase. Finally, we discuss the potential implication of our result in non-equilibrium systems and stabilizing a target bilinear order.
Read the full abstract

Quantum Physics

Numerical simulation of D-Wave's quantum advantage experiment with time-dependent variational Monte Carlo

Roeland Wiersema

Programmable quantum annealers can realize real-time dynamics of frustrated transverse-field Ising models on large, nontrivial graphs. Recent work by King et al. argued that the classical simulation of such experiments would require exponential computational resources for classical methods such as tensor networks and neural quantum states. Here, we numerically simulate the D-Wave spin-glass annealing protocol with time-dependent variational Monte Carlo (t-VMC) using a correlator state tailored to spin-glass dynamics. For the two-dimensional cylinder, three-dimensional dimer, diamond, and biclique instances considered, at annealing times of 7 and 20 ns, we show that systematically increasing the variational ansatz size enables t-VMC to approximate the final two-spin correlation errors of the quantum processing unit (QPU). We also perform an accurate large-scale simulation of a challenging biclique instance for which no other variational method is known to work, and we find close agreement with the quantum annealer. Through ablation studies, we identify poor Markov-chain mixing, high-variance local-energy estimators, and stochastic Runge-Kutta error estimates as the principal numerical failure modes. We address these numerical issues by using parallel tempering, blurred sampling and an importance-weighted differential equation solver, thereby clarifying the numerical requirements for stable, large-scale t-VMC simulations. Our results extend the frontier of classical simulation while providing a realistic assessment of the computational costs of simulating quantum dynamics at this scale.
Read the full abstract

Quantum Physics

Purification of photonic graph states

Matthias C. Löbl, Aliki A. Capatos, Ming Lai Chan et al. (+3 more)

Graph states constitute the main building block for quantum computing with photons. Quantum emitters with a hosted spin can deterministically generate photonic graph states, strongly lowering the overhead of multiplexing highly probabilistic linear-optics graph state generation. However, they generally suffer from various noise sources, resulting in reduced fidelities of the produced states. To mitigate this issue, we develop purification schemes for entangled photonic states. We first develop purification schemes to purify arbitrary photonic GHZ and other CSS states, which we generalize to all photonic graph states and stabilizer states. The proposed purification schemes have a high success probability of up to $1/2$ and require only linear optics and photon detectors. We optimize cascaded purification schemes for various graph states, taking into account phenomenological Pauli errors or physical noise in time-bin-encoded graph state generation with quantum emitters.
Read the full abstract

All authors Matthias C. Löbl, Aliki A. Capatos, Ming Lai Chan, Peter Lodahl, Anders Søndberg Sørensen, Stefano Paesani

Quantum Physics

Tunneling assisted interference in double-well levitodynamics

Yue Ma, Endre Bokor and M. S. Kim

Levitated particles trapped in double-well potentials provide a promising platform for exploring quantum dynamics beyond the harmonic regime. We show that such systems exhibit a distinctive quantum signature arising from tunneling-assisted interference. Unlike classical dynamics, where the two wells are disconnected, in the quantum case, quantum tunneling enables eigenstates to delocalize into the other well, creating nonzero overlaps between adjacent eigenstates that introduce low-frequency components into the evolution of the mean particle position. By comparing quantum and classical dynamics of particles in one-dimensional double-well potentials, we demonstrate that this interference is uniquely quantum and can be identified through the oscillation of the average position alone. We further relate the observed spectral peaks to the structure of the energy eigenvalues. The effect provides a promising probe of the quantum signature of levitated particle motion, and has fundamental importance as it predicts the demonstration of two major phenomena of quantum mechanics, quantum tunneling and quantum interference, at the same time and on the same system.
Read the full abstract

Quantum Physics · Cross-listed from physics.atom-ph

A monolithic segmented 3D ion trap fabricated from fused silica by selective laser-induced etching

Edgar Brucke, Martin Wagener, Moritz Fontboté-Schmidt et al. (+10 more)

We present the design, fabrication, and characterization of a monolithic, segmented, three-dimensional linear Paul ion trap for quantum science applications. The trap is fabricated from a single fused-silica block using selective laser-induced etching (SLE) and is subsequently metallized, forming electrodes isolated by self-shadowing trench structures without the need for layer alignment or external shadow masks. The segmented electrodes allow for shaping of the axial potential, enabling the creation of anharmonic potential wells, such as those required for equidistant ion strings. In addition, they enable shuttling and splitting of ion chains. We discuss key design choices and SLE-imposed constraints on achievable feature sizes, and evaluate electron-beam evaporation and magnetron sputtering as metallization approaches. Across two independent experimental setups, we demonstrate stable trapping and control of linear chains of up to 33 $^{40}$Ca$^+$ ions, including approximately equally spaced configurations. The measured secular frequencies in both traps agree with boundary-element simulations at the percent level, with residual deviations attributed to stray electric fields in the presence of anharmonic axial potentials, rather than fabrication imperfections. We measure axial micromotion field strengths on the order of 100 V/m along the trap axis, in approximate agreement with simulations. For radial mode frequencies near 2 MHz and an ion-electrode distance of 300 um, we measure heating rates of the order of 10 quanta/s in all but one motional mode, which is elevated by a technical noise source. The presented trap design is thus suitable for a wide range of quantum science applications and demonstrates the viability of SLE for the fabrication of finely segmented, monolithic, three-dimensional ion traps.
Read the full abstract

All authors Edgar Brucke, Martin Wagener, Moritz Fontboté-Schmidt, Philip Leindecker, Matteo Marinelli, Vlad Negnevitsky, Ilia Sergachev, Grégoire F. M. Tomassi, Paul Venetz, Stephan Welte, Jonathan Home, Daniel Kienzler, Cornelius Hempel

Quantum Physics

Comment on "Environmental memory effects and quantum resource hierarchies in polarized hyperon–antihyperon systems"

Saeed Haddadi

We comment on the recent work [Eur. Phys. J. C 86, 988 (2026)], which investigates quantum resources in polarized hyperon–antihyperon systems using correlated dephasing channels with memory. Although the use of experimentally reconstructed spin-density matrices to characterize quantum correlations in hyperon production may be a good motivation, we argue that the interpretation of the hyperon–antihyperon pair as an open quantum system undergoing correlated environmental decoherence is not physically established. In particular, no physical environment or system–environment interaction responsible for the assumed correlated dephasing channel is identified, and hadronization cannot simply be interpreted as such an environmental dephasing process. Consequently, the claimed non-Markovianity, information backflow, and memory-assisted protection of quantum resources should be regarded as properties of a phenomenological channel rather than established physical effects in hyperon–antihyperon production. We also identify several technical and conceptual issues concerning the dephasing dynamics, entanglement quantification, basis dependence of coherence, and the claimed hierarchy of quantum resources. These issues call for a substantial revision of the physical interpretation and quantitative conclusions of the work. We hope that the present Comment will help clarify the distinction between phenomenological quantum-channel modeling and physically established dynamical mechanisms in high-energy particle systems, and thereby provide useful guidance for future studies and help avoid similar conceptual and technical issues.
Read the full abstract

Quantum Physics

Observable- and state-selective prethermalization and bounds on prethermal lifetimes

C. L. Sriram, Soumya Kanti Pal and Lea F. Santos

Prethermalization describes long-lived intermediate regimes that precede equilibrium and can dominate experimentally accessible dynamics. Here, we show that a separation of spectral energy scales, despite giving rise to a hierarchy of dynamical timescales, does not by itself guarantee the appearance of a prethermal plateau. Under the same Hamiltonian, some observables may exhibit prethermal behavior, while others relax directly toward equilibrium. We uncover the mechanism governing this selectivity, showing that the emergence of a prethermal plateau depends not only on the Hamiltonian, but also on the observable and the initial state. Our results apply broadly to systems close to a fully permutation-symmetric limit and are illustrated with a long-range interacting spin model. We further prove that the Loschmidt echo provides a lower bound on the prethermal lifetime of any bounded observable whenever the prethermal and exact dynamics are unitary.
Read the full abstract

Quantum Physics

Depth-1 expanders on the unitary group and applications

Anurag Anshu, Shankar Balasubramanian, Jonas Haferkamp et al. (+2 more)

We construct a constant-degree and constant-gap quantum expander on $n$ qubits where each unitary can be implemented by a depth-$1$ and 1D circuit of Pauli or CNOT gates. We provide two applications of this expander. First, we use it to construct a family of frustration-free 1D Hamiltonians whose ground states obey the entanglement-gap relation $S = \Theta(\Delta^{-1/2})$; this is believed to be optimal, but achieving it had been open. Second, we use it to provide a streaming protocol that tests for closeness to a class of 1D volume-law entangled states. Moreover, we extend our quantum expander to a constant-degree and constant-gap expander on the unitary group where each unitary is a single $T$ gate, a single $T^{\dagger}$ gate, or a depth-$1$ Clifford circuit. This implies that a random sequence of unitaries from the expander yields a gapped walk on a dense subgroup of the unitary group. This improves upon previous work by Bourgain and Gamburd which did not control the dependence of the gap on the dimension.
Read the full abstract

All authors Anurag Anshu, Shankar Balasubramanian, Jonas Haferkamp, Aram W. Harrow, Xinyu Tan

Quantum Physics

Irreducibility and regularisation properties of Gaussian quantum Markov semigroups

Franco Fagnola and Federico Girotti

We study regularisation and irreducibility properties of Gaussian quantum Markov semigroups (GQMSs) acting on continuous-variable quantum systems. We first identify a natural notion of regularity for operators in this setting, which allows us to formulate and characterise the smoothing effects of GQMSs in terms of algebraic conditions involving the drift and quantum diffusion matrices. These conditions establish a connection with the controllability theory of quantum linear systems and with the structure of decoherence-free subsystems. We then characterise irreducibility through several equivalent algebraic criteria: one formulated in terms of the drift and quantum diffusion matrices, one in terms of the operators appearing in the generalised GKLS representation of the generator, and a third given by a quantum analogue of Hörmander's condition. A central and somewhat surprising consequence is that, in contrast with the classical case, irreducibility is strictly stronger than conditions ensuring regularisation. Our results provide an algebraic framework for analysing these properties and lay the groundwork for a broader study of reducible Gaussian quantum Markov semigroups and, more generally, more general relevant quantum Markov semigroups on continuous-variable systems.
Read the full abstract

Quantum Physics

Quantum Weighted Moving Average for Predicting Limit Order Book Trends

Matthias Kamm, Dinh-Long Vu and Patrick Rebentrost

Can quantum computers be useful for forecasting multivariate financial time series? In this work, we consider the problem of predicting price trends from limit order book (LOB) data. After identifying key components of classical models, we introduce the quantum weighted moving average (QWMA) model. The two main building blocks are, first, classically preprocessing via normalization of both feature and temporal dimensions and, second, a linear combination of unitaries-based layer for unitarily-embedded classical data. The models are evaluated on the FI-2010 benchmark dataset and a second dataset of China A-share stocks. While we do not present evidence of quantum advantage, the combined classical-quantum model demonstrates performances close to the best classical models. The quantum part of the model is expressive enough to focus on the most predictive parts of the time series. Several specializations of the QWMA model are considered, in particular a variant related to the widely-used exponential moving average (EMA). We give consideration to the limitations of the methods and the datasets.
Read the full abstract

Quantum Physics · Cross-listed from cs.FL

Behavioral Memory under Symmetry in One-Way Quantum Automata

Zeyu Chen

Under compact symmetry, observable behavior reduces to an invariant operator algebra, but its dimension is not yet classical memory: some coordinates are dynamically frozen, some invisible to threshold tests, and some already classical. We develop an operator-algebraic theory that separates these effects through three filters. For one automaton, behavior is the Hilbert–Schmidt pairing between prefix-reachable states and suffix-observable effects, whose rank equals the real Hankel rank without controllability or observability assumptions. Maximizing this invariant over a symmetry-constrained dynamical class gives a structural capacity controlled by the symmetry commutant: its center stores isotypic populations frozen by reversible dynamics, its traceless multiplicity blocks carry movable noncommutative coordinates, dissipation removes the unary spectral loss inside those blocks, and covariant mobility releases relative populations subject to component conservation. Operational realization then determines which surviving coordinates force probabilistic states. For a fixed nontrivial invariant readout, full mobility gives an exact dichotomy in worst-case state cost: a commutative invariant algebra costs exactly its dimension, whereas a noncommutative multiplicity block raises the unrestricted cost by exactly one state. Thus noncommutativity has a one-state worst-case classical price. The known four-letter quadratic-plus-one law at trivial symmetry is the fully mobile endpoint of this principle. Schur–Weyl duality further shows that different preserved symmetries on the same tensor-power Hilbert space can change the worst memory scale from polynomial to exponential, while fixed-weight modules give an exact Catalan law at half filling, with structural capacity equal to the Catalan count minus its central-sector correction.
Read the full abstract

Quantum Physics

Verifiable quantum advantage in extremely low depth

Alexandru Gheorghiu

We give a sampling problem that is solvable by shallow quantum circuits, hard for polynomial-time classical algorithms under lattice-based assumptions, and efficiently verifiable by a classical computer. The quantum sampler admits two implementations: one uses log-logarithmic-depth quantum circuits with one- and two-qubit gates, i.e., $\mathsf{QNC}^0[\log\log]$ circuits, while the other uses constant-depth quantum circuits with unbounded fan-in gates, i.e., $\mathsf{QAC}^0$ circuits. Our construction can be seen as compiling the Learning with Errors (LWE)-based single-round proof of quantumness of Arabadjieva et al. (2025) to very low depth. The price paid for this compilation is the reliance on less standard, though well-motivated, assumptions: in addition to the lattice knowledge assumption used by Arabadjieva et al. (2025), we require a strengthened variant of the adaptive-hardcore-bit property of LWE, for which we provide supporting evidence. Unlike previous low-depth proofs of quantumness, the quantum computation here requires no mid-circuit measurements or feed-forward: it consists only of running a shallow circuit and sampling from its output distribution. This shows that shallow quantum circuits have sufficient structure to solve certain classically hard tasks whose solutions can be verified efficiently.
Read the full abstract

Quantum Physics

Exact Virtual Channel Programming with Vanishing Excess Overhead

Mingrui Jing, Mengbo Guo, Hongshun Yao et al. (+1 more)

A finite-dimensional physical processor cannot exactly program a continuous family of distinct unitary channels. We show that this obstruction becomes quantitative when the target channel is stored in a normalized Choi state and its output observables are reconstructed by sampling physical channels and classically post-processing their measurement outcomes. For arbitrary $d$-dimensional channels, we construct a target-independent exact reconstruction protocol and prove the optimal one-copy sampling overhead, which grows quadratically with system dimension. We further prove the sharp fixed-$d$ law that the excess overhead vanishes inversely with the number of identical Choi programs. The upper bound combines deterministic port-based teleportation with a quasi-decomposition that corrects its depolarizing distortion. The converse maps any low-overhead reconstruction protocol to a physical learner of unknown unitaries and uses local quantum estimation to recover the same leading coefficient. These results recast the universal no-programming obstruction as a quantitative trade-off between quantum program memory and classical sampling, with a leading cost that reflects the locally learnable unitary degrees of freedom.
Read the full abstract

All authors Mingrui Jing, Mengbo Guo, Hongshun Yao, Xin Wang

Quantum Physics

Local Gaussian bounds on the non-destructive discrimination of two-mode squeezed states

Mi-Jung So, James Moran, Youngrong Lim et al. (+2 more)

Typical measurement setups in quantum systems are destructive, meaning that states are irretrievably altered after measurement. In this work, we analyse non-destructive discrimination of two two-mode squeezed vacuum states using local Gaussian measurements. We investigate a tradeoff relation between the success probability of discrimination and the fidelity of the resulting state with the initial state, and construct a protocol given by local Gaussian measurements, which is optimal within our numerically explored class. We also extend to the case where we allow for additional pre-shared entanglement, and show that this regime allows us to exceed the standard local Gaussian bound for the fidelity-success probability tradeoff. Our work provides a natural extension of the tradeoff between information gain and disturbance in entangled-state discrimination, previously established for finite-dimensional quantum systems, to infinite-dimensional continuous-variable systems.
Read the full abstract

All authors Mi-Jung So, James Moran, Youngrong Lim, Mahn-Soo Choi, Hyukjoon Kwon

Quantum Physics

Quantum phase transitions of the Cavity Heisenberg spin-chain

Lv-Ting Gong, Shao-Fan He and Fu-Quan Dou

The interplay between quantum criticality and ergodicity breaking constitutes a central challenge in complex quantum many-body systems. Here, we investigate ground-state quantum phase transitions (QPTs) and excited-state quantum phase transitions (ESQPTs), as well as ergodic-nonergodic transition in the cavity Heisenberg spin-chain (CHS) model. By combining quantum information measures with semiclassical fixed-point analysis, we identify a deformed phase that interpolates between the normal and superradiant phases, featuring a logarithmic nonanalyticity in the density of states (DoS) and two additional jump discontinuities. We further elucidate the spectral-structure mechanism underlying the connection between ESQPTs and the ergodic–nonergodic transition (ENET) via level statistics, participation ratios, and multifractal analysis. Our results provide a general framework for characterizing phase structures and spectral features in light–matter quantum many-body systems.
Read the full abstract

Quantum Physics

Fast Microwave-free State Preparation and Measurement of Superconducting Qubits

R. Abraham, F. Amet, P. Anderson et al. (+212 more)

Fast, high-fidelity, scalable state preparation and measurement is critical to the realization of a quantum computing system. The state-of-the-art methods for preparation and readout of superconducting qubits require finely tuned microwave signals and ~100 ns of measurement time, which are major obstacles to the scalability and performance of superconducting quantum computers. Here, we have demonstrated novel, microwave-free methods for both preparation and readout of superconducting qubits with >99% fidelity in only 10 ns for either operation while maintaining qubit coherence. This technology is compatible with scalable superconducting digital control systems, and using quantum flux parametrons for amplification, we demonstrated full quantum-to-digital conversion in only 15 ns, which is an order of magnitude faster than state-of-the-art microwave-based techniques.
Read the full abstract

All authors R. Abraham, F. Amet, P. Anderson, M. Arrigo, J. Arteaga, C. J. Ballard, C. Barker, T. Barnes, P. Bechmann, R. Bhatt, K. Blaine, T. M. Borman, J. Botimer, G. R. Boyd, P. Bradley, A. D. Brandon, T. K. Bristol, A. Bulkos, R. M. Burnett, D. Burrowes, D. N. Cakan, N. Carniero, T. Chamberlin, D. Chen, M. Chilcote, B. G. Christensen, I. Christie, J. Clark, D. Clarke, J. M. Cochran, J. C. Collini, K. Connolly, G. Costa, D. Cowger, B. Dalfort, R. D. Dawson, D. Davies, S. Deitemeyer, N. DeNigris, F. Densmore, S. J. Di Giacomo, S. G. Diamond, R. DiCiro, S. M. Disseler, K. Dixon, J. Donnelly, E. Donohue, M. Downing, B. Eastin, N. Edwards, M. Ehsani, S. Ellis, R. Epstein, D. Ferguson, P. Fischer, S. Friedensen, D. Gabriel, M. A. Gettelman, A. Gillam, G. Gilmore, J. Goode, E. Goodwin, M. Gottschalk, A. L. Graninger, T. Graves-Abe, J. Hackley, N. Hartman, B. Heacock, B. Heischmidt, P. Helms, R. Hinkey, B. Hong, S. T. Howard, D. Jensen, N. Johns, D. R. Johnson, J. Johnson, H. Kaplan, Z. Keane, S. Keebaugh, C. Kegerreis, K. Kelcourse-Oquendo, M. S. Khalil, D. Killeen, A. S. Knutson, T. Kohler, M. Kornecki, F. Koutsouli, A. Krick, K. L. Krycka, J. Kuan, D. Lad, J. R. Lane, N. J. Laurita, A. C. Lee, A. R. Lemmon, E. M. Leonard, L. M. D. Leonard, J. Leventis, M. P. Lilly, A. Lisiewski, L. Llano, M. Longo, C. Lostoski, Z. Lou, M. G. Loving, D. Ludwig, N. Luhrs, J. L. Lund, K. A. Maddock, R. J. Magyar, K. Mahmud, T. A. Manning, A. I. Marakov, A. D. McCreary, P. F. McLaughlin, J. R. Medford, E. Metz, A. L. Middleton, A. Miklich, R. Miller, J. Mlack, M. Mucci, N. Mungo, T. Murphy, R. E. Murray, O. Naaman, J. Nakamura, M. Noevere, S. Novikov, M. E. Nowakowski, C. Nunez, K. N. Ogg, B. Oshokoya, D. Paz, A. Pesetski, T. Pillsbury, C. Pinion, A. D. Pitcock, A. J. Przybysz, P. Quarterman, D. Queen, I. Ramos, S. L. Reed, D. Reitz, M. Rennie, S. Reza, B. Richman, K. H. Rigdon, C. Rotella, M. Rudolph, E. Sadler, T. Safford, D. Saha, A. E. Saia, D. I. Santiago, R. Schwartz, A. Schwarzkopf, M. Scott-Jones, S. L. Sendelbach, S. J. Shapiro, A. N. Sharma, M. E. Sherwin, A. Sierakowski, J. N. Sills, R. Simha, N. Siwak, J. Smith, C. Snyder, H. Solomon, N. S. Sperlein, L. St. Marie, K. Stalpes, S. F. Steers, Z. Stegen, R. M. Stein, T. I. Stephenson, M. Stoutimore, J. D. Strand, J. A. Strong, E. Swain, S. Swami, A. Tamang, I. Thompson, A. B. Tokarchik, N. Tralshawala, D. Tran, S. Tyler, L. Upton, G. Van Dyke, J. Vannucci, K. Vempati, J. S. Vogel, R. Vyas, M. Wagner, P. Warner, N. Washington, B. Way, M. A. Wayne, D. Wehella-Gamage, M. E. Weippert, T. Weitzel, J. Wenner, L. White, S. Whitsitt, A. Wilkinson, R. Willey, I. Yandow, J. Yang, L. Yu, F. Yumiceva, V. Zheng, R. Zimmerman, C. Zinn, J. Ziskind

Quantum Physics

Completing or Refusing Low-Dimensional Records of Structured Quantum Circuits: Measurement Loss, Compression Loss, and Hardware Drift

Gunhee Cho and Juhee Lee

Structured quantum circuits are often represented by low-dimensional records such as occupation numbers or constraint feasibility rather than by full outcome distributions. A record loses control-dependent information when it merges outcomes whose probabilities respond differently to circuit parameters. We assess this loss without assuming a parametric hardware-noise model. Quantum Fisher information bounds premeasurement sensitivity; Fisher metrics of measurements and recorded statistics describe device-attainable sensitivity. For finite control changes, a Hellinger residual measures the response removed by a record, while its local quadratic term is the conditional covariance of the full-outcome score. Simultaneous confidence bounds support approval, refusal, or deferral. We prove a finite-library completion theorem: executable augmentations terminate either with a record preserving every declared response or with proof that no library augmentation removes the loss. For an analytic control germ, integral closures characterize preservation along every analytic control arc, and finitely many Rees valuations detect failure. This connects the state–measurement–record chain to an executable completion-or-refusal procedure, an attainable-Fisher kernel criterion, and finite-sample decisions. A three-qubit calculation separates measurement loss from record loss. Prospectively fixed IBM Kingston and Marrakesh experiments test decisions in four-qubit fixed-particle-number and GHZ families, including negative controls. In two-epoch IQM Garnet data, median record-level drift is 0.0797 times full-distribution drift, but a significant residual remains in 35 of 36 settings. On these circuits, the rules detect loss and approve records only within stated tolerances; they do not establish universal compression performance or device quantum Fisher information.
Read the full abstract

Quantum Physics

Emerging Personas and Tools for Hybrid Quantum-HPC Systems

Eun-Kyung Lee, Jessie Yu, Claudio Carvalho et al. (+4 more)

Quantum computing is entering an era where quantum processing units (QPUs) with tens to hundreds of qubits are increasingly integrated with high-performance computing (HPC) systems to support hybrid quantum-classical workloads. This paradigm, often referred to as Quantum-Centric SuperComputing (QCSC), introduces new operational, software, and infrastructure challenges. In this paper, we identify and characterize six distinct personas involved in QCSC environments. Particular attention is given to emerging roles that arise at the interface between quantum and HPC systems. We analyze the responsibilities and tools associated with each persona and examine their differing requirements for operational data. Consistent data representations and analytics frameworks will be required to support diverse users across the quantum-HPC ecosystem. By defining personas and their data needs, we provide a foundation for future discussions in this critical area.
Read the full abstract

All authors Eun-Kyung Lee, Jessie Yu, Claudio Carvalho, Yoonho Park, Marcelo Amaral, Tim Osborne, Woong Shin

Quantum Physics

A Scalable Multi-Protocol Platform for Quantum Key Distribution Simulation with Rigorous Statistical Evaluation

Anuj Rathore and Kartick Sutradhar

Quantum Key Distribution (QKD) offers information- theoretically secure key establishment grounded in the laws of quantum physics, yet its practical reach is limited by the prohibitive cost of photonic hardware and the fragmented nature of existing simulation tools. Most simulators support only a single protocol and report results from individual stochastic runs, making systematic protocol comparison and reproducible statistical inference difficult. This paper presents a unified QKD simulation platform that implements four foundational protocols BB84, B92, E91, and BBM92 within a single Python/Qiskit engine. A shared impairment model covers fiber attenuation, source and detector losses, po- larization drift, and configurable intercept-resend eavesdropping. The platform is accessible through two independent interfaces that share the same backend: a desktop application (Tkinter, Matplotlib) for local experimentation and a browser-based web client (React, Node.js/Express) for zero-install remote access. All reported results are drawn from repeated-run studies (20 independent runs, 10000 qubits each), with mean, standard deviation, and 95% confidence intervals stated throughout. At a 25 km fiber link, BB84 achieves the highest mean key-rate of 160,045 Hz, followed by BBM92 (80023 Hz), E91 (52815 Hz), and B92 (40011 Hz) ordering that tracks simulation-derived sifting efficiencies precisely. Under the E91 protocol, the CHSH S-statistic averages 2.12 at baseline and falls to 1.58 when an eavesdropper is activated, demonstrating Bell-inequality-based intrusion detection independent of QBER
Read the full abstract

Quantum Physics

Dynamical regimes of QAOA gradient response

Zarin Shakibaei and Alexander Schnell

Characterizing the trainability of the Quantum Approximate Optimization Algorithm (QAOA) requires understanding how its gradient landscape changes across circuit parameters and problem size. Yet these gradients are usually described in terms of the native QAOA angles, making it difficult to distinguish parameter specific features from broader changes in the underlying circuit dynamics. Here we introduce a dynamical representation of the QAOA parameter space based on a norm-weighted layer strength and a cost–mixer imbalance, separating the overall scale of the evolution from the relative contribution of the two generators. Using exact-state simulations of MaxCut, we find that the gradient landscape exhibits a coarse organization in these dynamical variables that persists across changes in circuit depth and schedule structure, while the finer interference pattern remains schedule dependent. Near-optimal solutions do not simply coincide with the largest local gradients, but instead occupy a distinct intermediate dynamical regime. Uniform schedules recover the broad location of this regime, whereas nonuniform schedules mainly reorganize its fine structure. Across the system sizes studied, near-optimal solution regions remain extended in the dynamical representation while their preimages in the native QAOA angles become substantially compressed at larger sizes. These results separate the persistence of useful QAOA dynamics from their accessibility in the native parameterization, and provide a dynamical framework for interpreting QAOA trainability across circuit and problem scales.
Read the full abstract

Quantum Physics

A nonabelian anyon violates Haag duality

Daniel Wallick and Henrik Wilming

We show that a superselction sector describing a single nonabelian anyon violates Haag duality, which is equivalent to the fundamental quantum-information theoretic principle of uniqueness of purifications. We provide a simple physics argument as well as a rigorous proof using sector theory, and instantiate our result concretely in Levin-Wen models. We also show that the associated ground state does not allow for quantum steering despite being a pure state. Finally, we show that this ground state violates approximate Haag duality, disproving the conjecture that all gapped ground states satisfy this condition. Our result implies that there are gapped phases of matter where Haag duality fails at every point in the phase.
Read the full abstract

Quantum Physics

DF-SQD: Deterministic Fields for Sampling-Based Quantum Diagonalization

Kushagra Agarwal and Anupama Ray

Sampling-based quantum diagonalization method exploits Quantum-centric supercomputing platforms to sample bitstrings for Hamiltonian projection on a quantum computer, and then classically diagonalize the Hamiltonian to estimate the eigenvalues and eigenvectors. In current quantum devices an algorithm is useful when shallow quantum circuits with error mitigation support can discover better results while having either a proof of convergence or some method to explain trust in experiment. In this paper, we introduce DF-SQD, a hybrid algorithm that derives deterministic auxiliary-field circuits from selected double-factorization leaves of the two-electron tensor. The circuits propose occupation-number configurations, while selected configuration interaction evaluates the original active-space Hamiltonian and can recentre subsequent proposal rounds. On N2 (32 qubits; 6-31G basis) and a 40-qubit [Fe2S2(SCH3)4]2- active-space Hamiltonian, we show that DF-SQD improves the energy obtained from sampled determinant spaces while using shallow number-preserving circuits in both simulator and hardware runs. For N2, DF-SQD is 45x more accurate with a 11.23% smaller subspace, and due to its ability to sample better bitstrings at lesser shots it is 2.93x faster than SQD in quantum devices. For the iron-sulfur cluster, DF-SQD generated a subspace dimension of 221M with 400K shots, while SQD needed 1.5M shots to generate a 238M subspace, thus we have better subspace recovery evident from the hardware at 3.75x reduced shots. At a matched 50M subspace dimension, DF-SQD is 1.32x more accurate (achieves a 24.5% relative error reduction over standard SQD). So overall, our method is able to discover better results with shallower circuits, is sample efficient, uses configuration recovery (so has targeted error mitigation) and we have empirical convergence observation.
Read the full abstract

Quantum Physics

A Backend-Agnostic MWIS Kernel for Stochastic Unit Commitment with Neutral-Atom Hardware Validation

Jiying Chen, Min Lin, Jingwei Wen et al. (+2 more)

Quantum hardware is beginning to address structured combinatorial optimisation, but two steps still block practical use: mapping real operational models onto hardware-compatible instances, and converting noisy hardware output back into feasible decisions. Here we introduce a backend-agnostic computational interface that compiles the discrete decision layer of stochastic unit commitment into a move-based maximum-weight independent set (MWIS) problem, while retaining continuous dispatch and feasibility recovery in the classical computational layer. We validate the approach in a green hydrogen scheduling setting and deploy it on the QuEra Aquila neutral-atom quantum processor. This is the first end-to-end industrial scheduling workflow that connects real operational decisions to programmable neutral-atom hardware through a solver-agnostic MWIS representation. Across a 15-day hardware campaign on 50-node instances, hardware-generated solutions after classical refinement match or exceed the dispatch margins obtained from exact MWIS on every day. When scaling to 144 nodes, encoding quality remains stable, while the probability that the full atom array survives, rather than graph embedding, emerges as the dominant bottleneck to further scaling. Together, these results establish a hardware-compatible computational pathway toward larger problem scales, and lay the groundwork for exploring regimes in which exact classical optimisation may no longer scale efficiently.
Read the full abstract

All authors Jiying Chen, Min Lin, Jingwei Wen, Zhihong Zhang, Chuixiong Wu