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Thursday 30 October

Quantum Physics

Single-Light-Pulse Driven Compact Atom Interferometry with Measurement Induced Large Momentum Transfer

Yinghang Jiang, Jiguo Wu, Junfan Zhu et al. (+2 more)

We propose a fundamentally new design strategy of light-pulsed atom interferometry (LPAI) with a single atomic beam splitter. A traditional $\pi/2$-pulse Raman beam is employed to render a small momentum transfer at the initial state. After a short period of evolution during which physical relevant information can be loaded, a quantum weak measurement is applied to the internal state of the atoms. The final information will be detected from the transmission spectrum of a probe light to obviate the measurement of florescence signal. An effective amplification of the order of $10^3$ about the momentum offset is achieved in our simulation employing $Cs$ atoms with current experimental condition. Our proposal offers a cost-effective, high-accuracy measurement and readout strategy for LPAI. Furthermore, the strategy makes the physical setup much simpler and more compact offering new direction towards portable sensitive LPAI.
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All authors Yinghang Jiang, Jiguo Wu, Junfan Zhu, Rongchun Ge, Zhiyou Zhang

Quantum Physics

Practical hybrid decoding scheme for parity-encoded spin systems

Yoshihiro Nambu

We propose a practical hybrid decoding scheme for the parity-encoding architecture. This architecture was first introduced by N. Sourlas as a computational technique for tackling hard optimization problems, especially those modeled by spin systems such as the Ising model and spin glasses, and reinvented by W. Lechner, P. Hauke, and P. Zoller to develop quantum annealing devices. We study the specific model, called the SLHZ model, aiming to achieve a near-term quantum annealing device implemented solely through geometrically local spin interactions. Taking account of the close connection between the SLHZ model and a classical low-density-parity-check code, two approaches can be chosen for the decoding: (1) finding the ground state of a spin Hamiltonian derived from the SLHZ model, which can be achieved via stochastic decoders such as a quantum annealer or a classical Monte Carlo sampler; (2) using deterministic decoding techniques for the classical LDPC code, such as belief propagation and bit-flip decoder. The proposed hybrid approach combines the two approaches by applying bit-flip decoding to the readout of the stochastic decoder based on the SLHZ model. We present simulations demonstrating that this approach can reveal the latent potential of the SLHZ model, realizing soft-annealing concept proposed by Sourlas.
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Quantum Physics

Quantum-coherent nonlinear interferometry using electron-phonon systems for entanglement-assisted terahertz sensing

Junya Ogiri, Hiroaki Minamide and Kunio Ishida

We present a theoretical framework for quantum-coherent nonlinear interferometry in which the nonlinear medium is modeled as active electron-phonon quantum systems rather than a passive $\chi^{(2)}$ converter. By explicitly retaining the quantum coherence of the coupled electron-phonon-photon dynamics, our model describes a two-stage buildup of entanglement - first between signal and idler photons and subsequently between idler photons mediated by material coherence. This coherent light-matter interaction imprints the internal dynamics of the medium onto the interferometer output, yielding phase-sensitive interference that enables indirect readout of terahertz-band signal modes via near-infrared detection. The results reveal a route toward entanglement-assisted terahertz sensing and establish a general framework for treating nonlinear quantum media as active components in interferometric architectures.
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Quantum Physics · Cross-listed from cond-mat.supr-con

Topological phases of the Bogoliubov de Gennes Hamiltonian

Klaus Ziegler

We investigate a two-dimensional superconducting system with a smoothly and periodically varying order parameter. The order parameter is modulated along one direction while remaining uniform in the perpendicular direction, leading to a spatially periodic superconducting phase. We show that the periodicity of the order parameter determines the winding number of the eigenfunctions, which serves as a topological characterization of the system. A topological invariant is identified that links the winding number directly with the Bloch vector. By solving the Bogoliubov-de Gennes equation, we obtain both plane-wave solutions describing bulk states and exponentially localized solutions that correspond to edge modes. The analytic bulk-edge connection is employed to identify the conditions under which the edge states emerge from the bulk spectrum. We find that the winding numbers depend on the boundary conditions, which differ between the plane-wave and exponential solutions. These results establish a direct connection between the spatial modulation of the order parameter, the topological structure of the eigenstates, and the emergence of edge modes in periodically modulated superconducting order parameters.
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Quantum Physics

Stesso: A reconfigurable decomposition of $n$-bit Toffoli gates using symmetrical logical structures and adjustable support qubits

Shanyan Chen, Ali Al-Bayaty, Xiaoyu Song et al. (+1 more)

An $(n+1)$-bit Toffoli gate is mainly utilized to construct other quantum gates and operators, such as Fredkin gates, arithmetical adders, and logical comparators, where $n \geq 2$. Several researchers introduced different methods to decompose $(n+1)$-bit Toffoli gates in a quantum circuit into a set of standard 3-bit Toffoli gates or a set of elementary quantum gates, such as single-qubit and two-qubit gates. However, these methods are not effectively reconfigurable for linearly connected symmetrical structures (layouts) of contemporary quantum computers, usually utilizing more ancilla qubits. This paper introduces a new structural design method to effectively decompose $(n+1)$-bit Toffoli gates by utilizing configurable ancilla qubits, which we named the “support qubits". Collectively, we call our decomposition method for symmetrical structures using support qubits the “step-decreasing structures shaped operators (Stesso)". The main advantage of Stesso is to configurable construct different decomposed operators of various polarities and intermediate sub-circuits, such as Positive Polarity-Stesso, Mixed Polarity-Stesso, and Generalized-Stesso. With Stesso, it has been experimentally proven that $(n+1)$-bit Toffoli gates always have lower quantum costs than using conventional composition methods.
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All authors Shanyan Chen, Ali Al-Bayaty, Xiaoyu Song, Marek Perkowski

Quantum Physics · Cross-listed from cs.CL

QCoder Benchmark: Bridging Language Generation and Quantum Hardware through Simulator-Based Feedback

Taku Mikuriya, Tatsuya Ishigaki, Masayuki Kawarada et al. (+9 more)

Large language models (LLMs) have increasingly been applied to automatic programming code generation. This task can be viewed as a language generation task that bridges natural language, human knowledge, and programming logic. However, it remains underexplored in domains that require interaction with hardware devices, such as quantum programming, where human coders write Python code that is executed on a quantum computer. To address this gap, we introduce QCoder Benchmark, an evaluation framework that assesses LLMs on quantum programming with feedback from simulated hardware devices. Our benchmark offers two key features. First, it supports evaluation using a quantum simulator environment beyond conventional Python execution, allowing feedback of domain-specific metrics such as circuit depth, execution time, and error classification, which can be used to guide better generation. Second, it incorporates human-written code submissions collected from real programming contests, enabling both quantitative comparisons and qualitative analyses of LLM outputs against human-written codes. Our experiments reveal that even advanced models like GPT-4o achieve only around 18.97% accuracy, highlighting the difficulty of the benchmark. In contrast, reasoning-based models such as o3 reach up to 78% accuracy, outperforming averaged success rates of human-written codes (39.98%). We release the QCoder Benchmark dataset and public evaluation API to support further research. (Codes and datasets are available at https://qcoder-bench.github.io/ )
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All authors Taku Mikuriya, Tatsuya Ishigaki, Masayuki Kawarada, Shunya Minami, Tadashi Kadowaki, Yohichi Suzuki, Soshun Naito, Shunya Takata, Takumi Kato, Tamotsu Basseda, Reo Yamada, Hiroya Takamura

Quantum Physics

Modeling of simple bandpass filters: bandwidth broadening of Josephson parametric devices due to non-Markovian coupling to dressed transmission-line modes

Rui Yang, Zheng Shi, Zhirong Lin et al. (+1 more)

Josephson parametric devices are widely used in superconducting quantum computing research but suffer from an inherent gain-bandwidth trade-off. This limitation is partly overcome by coupling the device to its input/output transmission line via a bandpass filter, leading to wider bandwidth at undiminished gain. Here we perform a non-perturbative circuit analysis in terms of dressed transmission-line modes for representative resonant coupling circuits, going beyond the weak-coupling treatment. The strong frequency dependence of the resulting coupling coefficients implies that the Markov approximation commonly employed in cQED analysis is inadequate. By retaining the full frequency dependence of the coupling, we arrive at a non-Markovian form of the quantum Langevin equation with the frequency-dependent complex-valued self-energy of the coupling in place of a single damping parameter. We also consistently generalize the input-output relations and unitarity conditions. Using the exact self-energies of elementary filter networks – a series- and parallel-LC circuit and a simple representative bandpass filter consisting of their combination – we calculate the generalized parametric gain factors. Compared with their Markovian counterpart, these gain profiles are strongly modified. We find bandwidth broadening not only in the established parameter regime, where the self-energy of the coupling is in resonance with the device and its real part has unity slope, but also within off-resonant parameter regimes where the real part of the self-energy is large. Our results offer insight for the bandwidth engineering of Josephson parametric devices using simple coupling networks.
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All authors Rui Yang, Zheng Shi, Zhirong Lin, Waltraut Wustmann

Quantum Physics

The Fast for the Curious: How to accelerate fault-tolerant quantum applications

Sam McArdle, Alexander M. Dalzell, Aleksander Kubica et al. (+1 more)

We evaluate strategies for reducing the run time of fault-tolerant quantum computations, targeting practical utility in scientific or industrial workflows. Delivering a technology with broad impact requires scaling devices, while also maintaining acceptable run times for computations. Optimizing logical clock speed may require moving beyond current strategies, and adopting methods that trade faster run time for increased qubit counts or engineering complexity. We discuss how the co-design of hardware, fault tolerance, and algorithmic subroutines can reduce run times. We illustrate a selection of these topics with resource estimates for simulating the Fermi-Hubbard model.
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All authors Sam McArdle, Alexander M. Dalzell, Aleksander Kubica, Fernando G.S.L. Brandão

Quantum Physics · Cross-listed from cond-mat.str-el

Invariants for (2+1)D bosonic crystalline topological insulators for all 17 wallpaper groups

Vladimir Calvera, Naren Manjunath and Maissam Barkeshli

We study bosonic symmetry-protected topological (SPT) phases in (2+1) dimensions with symmetry $G = G_{\text{space}}\times K$, where $G_{\text{space}}$ is a general wallpaper group and $K=\text{U}(1),\mathbb{Z}_N, \text{SO}(3)$ is an internal symmetry. In each case we propose a set of many-body invariants that can detect all the different phases predicted from real space constructions and group cohomology classifications. They are obtained by applying partial rotations and reflections to a given ground state, combined with suitable operations in $K$. The reflection symmetry invariants that we introduce include `double partial reflections', `weak partial reflections' and their `relative' or `twisted' versions which also depend on $K$. We verify our proposal through exact calculations on ground states constructed using real space constructions. We demonstrate our method in detail for the groups p4m and p4g, and in the case of p4m also derive a topological effective action involving gauge fields for orientation-reversing symmetries. Our results provide a concrete method to fully characterize (2+1)D crystalline topological invariants in bosonic SPT ground states.
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Quantum Physics

In situ quantum verification of polarization-stabilized optical channels

Matthew L. Stevens, Noah I. Wasserbeck, Zachary Goisman et al. (+8 more)

The active stabilization of polarization channels is a task of growing importance as quantum networks move to deployed demonstrations over existing fiber infrastructure. However, the uniquely strict requirements for high-fidelity qubit transmission complicate the extent to which classical solutions may apply to future quantum networks, particularly in terms of recognizing noise sources present in low-flux, nonunitary channels. Here we introduce a novel in situ benchmarking approach that augments a classical polarization tracking system, limited to unitary correction, with simultaneously transmitted quantum light for ancilla-assisted process tomography of the full quantum map. Implemented in a local-area quantum network, our method uses the reconstructed map both to validate the classical compensation and to expose noise sources it fails to capture. A sliding measurement window that continuously updates the estimated quantum process further increases sensitivity to rapid channel fluctuations. Our results should unlock new opportunities for in situ channel characterization in quantum-classical coexistence networks.
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All authors Matthew L. Stevens, Noah I. Wasserbeck, Zachary Goisman, Arefur Rahman, John Michael Record, Taman Truong, Ariq Haqq, Muneer Alshowkan, Brian T. Kirby, Nils T. Otterstrom, Joseph M. Lukens

Wednesday 29 October

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

Path-integral Monte Carlo estimator for the dipole polarizability of quantum plasma

Juha Tiihonen, David Trejo-Garcia, Tapio T. Rantala et al. (+1 more)

We present a path-integral Monte Carlo estimator for calculating the dipole polarizability of interacting Coulomb plasma in the long-wavelength limit, i.e., the optical region. We present comprehensive details and method validation studies for our approach based on both collective and one-particle dipole autocorrelation functions in the imaginary time. The simulation of thermal equilibrium in imaginary time has exact Coulomb interactions and Boltzmann quantum statistics. For reference, we use analytically continued Drude model as the long-wavelength limit of the Lindhard response. Our collective response shows perfect match to the analytical reference. The one-particle response is used in systematic studies of physical and numerical parameters, and to discuss the phenomenological Drude scattering model.
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All authors Juha Tiihonen, David Trejo-Garcia, Tapio T. Rantala, Marco Ornigotti

Quantum Physics · Cross-listed from cs.NI

A Zero Added Loss Multiplexing (ZALM) Source Simulation

Jerry Horgan, Alexander Nico-Katz, Shelbi L. Jenkins et al. (+6 more)

Zero Added Loss Multiplexing (ZALM) offers broadband, per channel heralded EPR pairs, with a rich parameter space that allows its performance to be tailored for specific applications. We present a modular ZALM simulator that demonstrates how design choices affect output rate and fidelity. Built in NetSquid with QSI controllers, it exposes 20+ tunable parameters, supports IDEAL and REALISTIC modes, and provides reusable components for Spontaneous Parametric Down Conversion (SPDC) sources, interference, Dense Wavelength Division Multiplexing (DWDM) filtering, fiber delay, active polarization gates, detectors, and lossy fiber. Physics based models capture Hong Ou Mandel (HOM) visibility, insertion loss, detector efficiency, gate errors, and attenuation. Using this tool, we map trade offs among fidelity, link distance, and entangled pairs per use, and show how SPDC bandwidth and DWDM grid spacing steer performance. Using the default configuration settings, average fidelity remains constant at 0.83 but the ebit rate decreases from 0.0175 at the source to 0.0 at 50 km; narrowing the SPDC degeneracy bandwidth increases the ebit rate significantly without affecting fidelity. The simulator enables codesign of source, filtering, and feedforward settings for specific quantum memories and integrates as a building block for end to end quantum network studies.
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All authors Jerry Horgan, Alexander Nico-Katz, Shelbi L. Jenkins, Ashley N. Tittelbaugh, Vivek Visan, Rohan Bali, Marco Ruffini, Boulat A. Bash, Daniel C. Kilper

Quantum Physics

Overcoming disorder in superconducting globally driven quantum computing

Riccardo Aiudi, Julien Despres, Roberto Menta et al. (+5 more)

We study the impact of static disorder on a globally-controlled superconducting quantum computing architecture based on a quasi-two-dimensional ladder geometry [R. Menta et al., Phys. Rev. Research 7, L012065 (2025)]. Specifically, we examine how fabrication-induced inhomogeneities in qubit resonant frequencies and coupling strengths affect quantum state propagation and the fidelity of fundamental quantum operations. Using numerical simulations, we quantify the degradation in performance due to disorder and identify single-qubit rotations, two-qubit entangling gates, and quantum information transport as particularly susceptible. To address this challenge, we rely on pulse optimization schemes, and, in particular, on the GRAPE (Gradient Ascent Pulse Engineering) algorithm. Our results demonstrate that, even for realistic levels of disorder, optimized pulse sequences can achieve high-fidelity operations, exceeding 99.9% for the three quantum operations, restoring reliable universal quantum logic and robust information flow. These findings highlight pulse optimization as a powerful strategy to enhance the resilience to disorder of solid-state globally-driven quantum computing platforms.
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All authors Riccardo Aiudi, Julien Despres, Roberto Menta, Ashkan Abedi, Guido Menichetti, Vittorio Giovannetti, Marco Polini, Francesco Caravelli

Quantum Physics · Cross-listed from cond-mat.str-el

Hyperbolic Fracton Model, Subsystem Symmetry and Holography III: Extension to Generic Tessellations

Yosef Shokeeb, Ludovic D.C. Jaubert and Han Yan

We generalize the Hyperbolic Fracton Model from the $\{5,4\}$ tessellation to generic tessellations, and investigate its core properties: subsystem symmetries, fracton mobility, and holographic correspondence. While the model on the original tessellation has features reminiscent of the flat-space lattice cases, the generalized tessellations exhibit a far richer and more intricate structure. The ground-state degeneracy and subsystem symmetries are generated recursively layer-by-layer, through the inflation rule, but without a simple, uniform pattern. The fracton excitations follow exponential-in-distance and algebraic-in-lattice-size growing patterns when moving outward, and depend sensitively to the tessellation geometry, differing qualitatively from both type-I or type-II fracton model on flat lattices. Despite this increased complexity, the hallmark holographic features – subregion duality via Rindler reconstruction, the Ryu-Takayanagi formula for mutual information, and effective black hole entropy scaling with horizon area – remain valid. These results demonstrate that the holographic correspondence in fracton models persists in generic tessellations, and provide a natural platform to explore more intricate subsystem symmetries and fracton physics.
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Quantum Physics

Enabling Fast and Accurate Neutral Atom Readout through Image Denoising

Chaithanya Naik Mude, Linipun Phuttitarn, Satvik Maurya et al. (+3 more)

Neutral atom quantum computers hold promise for scaling up to hundreds of thousands or more qubits, but their progress is constrained by slow qubit readout. Parallel measurement of qubit arrays currently takes milliseconds, much longer than the underlying quantum gate operations-making readout the primary bottleneck in deploying quantum error correction. Because each round of QEC depends on measurement, long readout times increase cycle duration and slow down program execution. Reducing the readout duration speeds up cycles and reduces decoherence errors that accumulate while qubits idle, but it also lowers the number of collected photons, making measurements noisier and more error-prone. This tradeoff leaves neutral atom systems stuck between slow but accurate readout and fast but unreliable readout. We show that image denoising can resolve this tension. Our framework, GANDALF, uses explicit denoising using image translation to reconstruct clear signals from short, low-photon measurements, enabling reliable classification at up to 1.6x shorter readout times. Combined with lightweight classifiers and a pipelined readout design, our approach both reduces logical error rate by up to 35x and overall QEC cycle time up to 1.77x compared to state-of-the-art convolutional neural network (CNN)-based readout for Cesium (Cs) Neutral Atom arrays.
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All authors Chaithanya Naik Mude, Linipun Phuttitarn, Satvik Maurya, Kunal Sinha, Mark Saffman, Swamit Tannu

Quantum Physics

Double categories for adaptive quantum computation

Cihan Okay, Walker Stern, Redi Haderi et al. (+1 more)

Quantum computation admits several models that emphasize different computational primitives and forms of classical control. We develop a unified double categorical framework for describing these models and the conversions between them. The syntax is provided by double port graphs, whose horizontal wires carry quantum information and whose vertical wires carry classical information and control. For each set of port labels, these graphs form a double category, and this construction is functorial in the label set. The semantics is given by the one-object double category of adaptive instruments. Its associated horizontal and vertical monoidal categories recover, respectively, quantum channels and stochastic maps. An assignment of an adaptive instrument to each primitive label therefore extends canonically to a double functor on labeled double port graphs, providing their computational semantics. We apply this framework to prominent models of quantum computation, including the circuit model, measurement-based quantum computation, quantum computation with magic states, and measurement-based Pauli computation. Gadget constructions from quantum computing that implement conversions between these models become double functors. Finally, we show that the interaction between quantum operations and affine classical control in measurement-based Pauli computation realizes every Boolean function in the vertical direction, thereby providing the non-affine classical operations required for its simulation of the circuit model.
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All authors Cihan Okay, Walker Stern, Redi Haderi, Selman Ipek

Quantum Physics

Quantum Stochastic Gradient Descent in its continuous-time limit based on the Wigner formulation of Open Quantum Systems

Jose A. Morales Escalante

The main ideas behind a research plan to use the Wigner formulation as a bridge between classical and quantum probabilistic algorithms are presented, focusing on a particular case: the Quantum analog of Stochastic Gradient Descent in its continuous-time limit based on the Wigner formulation of Open Quantum Systems.
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Quantum Physics

From Divergent Series to Geometry: Resurgence of the Quantum Metric

Marcos J. Hernández, Bogar Díaz and J. David Vergara

In this work, we analyze perturbative expansions of the quantum metric tensor (QMT) in anharmonic oscillators, focusing on quartic, sextic, and $d$-dimensional models. Using high-order perturbation theory, we show that the divergent QMT series exhibit factorial growth. Our analysis identifies universal non-perturbative scales, with coefficients displaying large-order behavior consistent with resurgence theory. Then, we apply resurgence and Borel–Padé resummation to the QMT. Comparisons with exact diagonalization confirm that Borel–Padé resummations yield accurate results, especially for the ground state. For completeness, we also present the analysis of the energy eigenvalues in the examples. Our findings extend resurgent techniques from energies to the QMT, highlighting the interplay between quantum geometry and non-perturbative physics.
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Quantum Physics

Control of memory effects in a spin-boson system by periodic driving

Pietro Follia, Bassano Vacchini and Heinz-Peter Breuer

We study the emergence of quantum memory effects in a spin-boson system at finite temperature driven by an external time-periodic force. Quantifying memory effects by the trace-distance based measure for non-Markovianity and performing numerical simulations employing the hierarchical equations of motion approach, we find a pronounced peak structure when plotting the non-Markovianity measure as a function of the driving amplitude. This distinctive feature is interpreted using Floquet theory and the Floquet-Lindblad master equation, associating the peaks with the degeneracies of the quasienergy spectrum which lead to a strong enhancement of the relaxation times of the system. These results suggest strategies for the efficient control of non-Markovianity in open quantum systems by periodic driving.
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Quantum Physics

Optimal Displacement Sensing with Spin-Dependent Squeezed States

Liam J. Bond, Christophe H. Valahu, Athreya Shankar et al. (+2 more)

Displacement sensing is a fundamental task in metrology. However, the development of quantum-enhanced sensors that fully utilize the available degrees of freedom in many-body quantum systems remains an outstanding challenge. We propose many-body displacement sensing schemes that use spin-dependent squeezed (SDS) states – hybrid spin-boson states whose bosonic squeezed quadrature is conditioned on an auxiliary spin. We prove that SDS states are optimal, i.e. their quantum Cramér-Rao bound saturates the Heisenberg limit. We propose explicit measurement sequences that can be readily implemented in systems such as trapped ions. We also introduce a scalable state-preparation protocol and numerically demonstrate the preparation of $8.7$~dB of spin-dependent squeezing $15$ times faster than the standard approach using second-order sidebands in trapped ions. The potential applications of our sensing protocols range from measuring single-photon scattering to searches for dark matter.
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All authors Liam J. Bond, Christophe H. Valahu, Athreya Shankar, Ting Rei Tan, Arghavan Safavi-Naini

Quantum Physics · Cross-listed from cond-mat.stat-mech

Spatially Structured Entanglement from Nonequilibrium Thermal Pure States

Chen Bai, Mao Tian Tan, Bastien Lapierre et al. (+1 more)

We study quantum quench dynamics in (1+1)-dimensional critical systems, starting from thermal pure states called crosscap states, and evolving them under spatially inhomogeneous Hamiltonians. The spatial inhomogeneity is introduced through a deformation of the Hamiltonian, expressed as linear combinations of the generators of the $SL^{(q)}(2,\mathbb{R})$ subalgebra of the Virasoro algebra. We analyze the free massless Dirac fermion theory and holographic conformal field theory as prototypical examples of integrable and non-integrable dynamics. Consistent with general expectations, "Möbius-type" deformations lead to thermalization in the non-integrable case, and to periodic revivals in the integrable one. In contrast, "sine-square-type" and "displacement-type" deformations prevent both thermalization and scrambling, instead producing late-time, graph-like entanglement patterns. These patterns emerge from the interplay between the deformed Hamiltonian and the crosscap initial state and appear to be universal: they are determined solely by the deformation profile while remaining largely insensitive to microscopic details. Finally, we perform a holographic calculation in three-dimensional gravity using AdS$_3$/CFT$_2$, which reproduces the main features of our (1+1)-dimensional study.
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All authors Chen Bai, Mao Tian Tan, Bastien Lapierre, Shinsei Ryu

Quantum Physics · Cross-listed from cond-mat.supr-con

Theories of Superconducting Diode Effects

Daniel Shaffer and Alex Levchenko

Superconducting diode effects (SDE), both in bulk superconductors and in Josephson junctions, have garnered a lot of attention due to potential applications in classical and quantum computing, as well as superconducting sensors. Here we review various mechanisms that have been theoretically proposed for their realization. We first provide a brief historical overview and discuss the basic but subtle phenomenological Ginzburg-Landau theory of SDE, emphasizing the need to the simultaneous breaking of time-reversal and inversion symmetries. We then proceed to more microscopic treatments, focusing especially on implementations in noncentrosymmetric materials described by the Rashba-Zeeman model. Finally, we review proposals based on other condensed matter systems such as altermagnets, valley polarized and topological materials, and systems out of equilibrium.
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Quantum Physics

GHZ-Preserving Gates and Optimized Distillation Circuits

Mingyuan Wang, Guus Avis and Stefan Krastanov

Greenberger-Horne-Zeilinger (GHZ) states play a central role in quantum computing and communication protocols, as a typical multipartite entanglement resource. This work introduces an efficient enumeration and simulation method for circuits that preserve and distill noisy GHZ states, significantly reducing the simulation complexity of a gate on $n$ qubits, from exponential $O(2^n)$ for standard state-vector methods or $O(n)$ for Clifford circuits, to a constant $O(1)$ for the method presented here. This method has profound implications for the design of quantum networks, where preservation and purification of entanglement with minimal resource overhead is critical. In particular, we demonstrate the use of the new method in an optimization procedure enabled by the fast simulation, that discovers GHZ distillation circuits far outperforming the state of the art. Fine-tuning to arbitrary noise models is possible as well. We also show that the method naturally extends to graph states that are local Clifford equivalent to GHZ states.
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Quantum Physics

Establishing Baselines for Photonic Quantum Machine Learning: Insights from an Open, Collaborative Initiative

Cassandre Notton, Vassilis Apostolou, Agathe Senellart et al. (+28 more)

The Perceval Challenge is an open, reproducible benchmark designed to assess the potential of photonic quantum computing for machine learning. Focusing on a reduced and hardware-feasible version of the MNIST digit classification task or near-term photonic processors, it offers a concrete framework to evaluate how photonic quantum circuits learn and generalize from limited data. Conducted over more than three months, the challenge attracted 64 teams worldwide in its first phase. After an initial selection, 11 finalist teams were granted access to GPU resources for large-scale simulation and photonic hardware execution through cloud service. The results establish the first unified baseline of photonic machine-learning performance, revealing complementary strengths between variational, hardware-native, and hybrid approaches. This challenge also underscores the importance of open, reproducible experimentation and interdisciplinary collaboration, highlighting how shared benchmarks can accelerate progress in quantum-enhanced learning. All implementations are publicly available in a single shared repository (https://github.com/Quandela/HybridAIQuantum-Challenge), supporting transparent benchmarking and cumulative research. Beyond this specific task, the Perceval Challenge illustrates how systematic, collaborative experimentation can map the current landscape of photonic quantum machine learning and pave the way toward hybrid, quantum-augmented AI workflows.
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All authors Cassandre Notton, Vassilis Apostolou, Agathe Senellart, Anthony Walsh, Daphne Wang, Yichen Xie, Songqinghao Yang, Ilyass Mejdoub, Oussama Zouhry, Kuan-Cheng Chen, Chen-Yu Liu, Ankit Sharma, Edara Yaswanth Balaji, Soham Prithviraj Pawar, Ludovic Le Frioux, Valentin Macheret, Antoine Radet, Valentin Deumier, Ashesh Kumar Gupta, Gabriele Intoccia, Dimitri Jordan Kenne, Chiara Marullo, Giovanni Massafra, Nicolas Reinaldet, Vincenzo Schiano Di Cola, Danylo Kolesnyk, Yelyzaveta Vodovozova, Rawad Mezher, Pierre-Emmanuel Emeriau, Alexia Salavrakos, Jean Senellart

Quantum Physics

Heuristic Quantum Advantage with Peaked Circuits

Hrant Gharibyan, Mohammed Zuhair Mullath, Nicholas E. Sherman et al. (+3 more)

We design and demonstrate heuristic quantum advantage with peaked circuits (HQAP circuits) on Quantinuum's System Model H2 quantum processor. Through extensive experimentation with state-of-the-art classical simulation strategies, we identify a clear gap between classical and quantum runtimes. Our largest instance involves all-to-all connectivity with 2000 two-qubit gates, which H2 can produce the target peaked bitstring directly in under 2 hours. Our extrapolations from leading classical simulation techniques such as tensor networks with belief propagation and Pauli path simulators indicate the same instance would take years on exascale systems (Frontier, Summit), suggesting a potentially exponential separation. This work marks an important milestone toward verifiable quantum advantage, as well as providing a useful benchmarking protocol for current utility-scale quantum hardware. We sketch our protocol for designing these circuits and provide extensive numerical results leading to our extrapolation estimates. Separate from our constructed HQAP circuits, we prove hardness on a decision problem involving generic peaked circuits. When both the input and output bitstrings of a peaked circuit are unknown, determining whether the circuit is peaked constitutes a QCMA-complete problem, meaning the problem remains hard even for a quantum polynomial-time machine under commonly accepted complexity assumptions. Inspired by this observation, we propose an application of the peaked circuits as a potentially quantum-safe encryption scheme~\cite{chen2016report,kumar2020post,joseph2022transitioning,dam2023survey}. We make our peaked circuits publicly available and invite the community to try additional methods to solve these circuits to see if this gap persists even with novel classical techniques.
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All authors Hrant Gharibyan, Mohammed Zuhair Mullath, Nicholas E. Sherman, Vincent P. Su, Hayk Tepanyan, Yuxuan Zhang

Quantum Physics

Nonlinear quantum evolution of a dissipative superconducting qubit

Orion Lee, Qian Cao, Yogesh N. Joglekar et al. (+1 more)

Unitary and dissipative models of quantum dynamics are linear maps on the space of states or density matrices. This linearity encodes the superposition principle, a key feature of quantum theory. However, this principle can break down in effective non-Hermitian dynamics arising from postselected quantum evolution. We theoretically characterize and experimentally investigate this breakdown in a dissipative superconducting transmon circuit. Within the circuit's three-level manifold, no-jump postselection generates an effective non-Hermitian Hamiltonian governing the excited two-level subspace and an anti-Hermitian nonlinearity. We prepare different initial states and use quantum state tomography to track their evolution under this effective, nonlinear Hamiltonian. By comparing the evolution of a superposition-state to a superposition of individually-evolved basis states, we test linearity and observe clear violations which we quantify across the exceptional-point (EP) degeneracy of the non-Hermitian Hamiltonian. We extend the analysis to density matrices, revealing a breakdown in linearity for the two-level subspace while demonstrating that linearity is preserved in the full three-level system. These results provide direct evidence of nonlinearity in non-Hermitian quantum evolution, highlighting unique features that are absent in classical non-Hermitian systems.
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All authors Orion Lee, Qian Cao, Yogesh N. Joglekar, Kater Murch

Quantum Physics

Inverse-free quantum state estimation with Heisenberg scaling

Kean Chen

In this paper, we present an inverse-free pure quantum state estimation protocol that achieves Heisenberg scaling. Specifically, let $\mathcal{H}\cong \mathbb{C}^d$ be a $d$-dimensional Hilbert space with an orthonormal basis $\{|1\rangle,\ldots,|d\rangle\}$ and $U$ be an unknown unitary on $\mathcal{H}$. Our protocol estimates $U|d\rangle$ to within trace distance error $\varepsilon$ using $O(\min\{d^{3/2}/\varepsilon,d/\varepsilon^2\})$ forward queries to $U$. This complements the previous result $O(d\log(d)/\varepsilon)$ by van Apeldoorn, Cornelissen, Gilyén, and Nannicini (SODA 2023), which requires both forward and inverse queries. Moreover, our result implies a query upper bound $O(\min\{d^{3/2}/\varepsilon,1/\varepsilon^2\})$ for inverse-free amplitude estimation, improving the previous best upper bound $O(\min\{d^{2}/\varepsilon,1/\varepsilon^2\})$ based on optimal unitary estimation by Haah, Kothari, O'Donnell, and Tang (FOCS 2023), and disproving a conjecture posed in Tang and Wright (2025).
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Quantum Physics · Cross-listed from cond-mat.quant-gas

Universal Random Matrix Behavior of a Fermionic Quantum Gas

Maxime Dixmerias, Giuseppe Del Vecchio Del Vecchio, Cyprien Daix et al. (+6 more)

The pursuit of universal governing principles is a foundational endeavor in physics, driving breakthroughs from thermodynamics to general relativity and quantum mechanics. In 1951, Wigner introduced the concept of a statistical description of energy levels of heavy atoms, which led to the rise of Random Matrix Theory (RMT) in physics. The theory successfully captured spectral properties across a wide range of atomic systems, circumventing the complexities of quantum many-body interactions. Rooted in the fundamental principles of stochasticity and symmetry, RMT has since found applications and revealed universal laws in diverse physical contexts, from quantum field theory to disordered systems and wireless communications. A particularly compelling application arises in describing the mathematical structure of the many-body wavefunction of non-interacting Fermi gases, which underpins a complex spatial organization driven by Pauli's exclusion principle. However, experimental validation of the counting statistics predicted in such systems has remained elusive. Here, we probe at the single-atom level ultracold atomic Fermi gases made of two interacting spin states, obtaining direct access to their counting statistics in situ. Our measurements show that, while the system is strongly attractive, each spin-component is extremely well described by RMT predictions based on Fredholm determinants. Our results constitutes the first experimental validation of the Fermi-sphere point process through the lens of RMT, and establishes its relevance for strongly-interacting systems.
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All authors Maxime Dixmerias, Giuseppe Del Vecchio Del Vecchio, Cyprien Daix, Joris Verstraten, Tim de Jongh, Bruno Peaudecerf, Pierre Le Doussal, Grégory Schehr, Tarik Yefsah

Quantum Physics

Symmetry and Asymmetry in Bosonic Gaussian Systems: A Resource-Theoretic Framework

Nikolaos Koukoulekidis and Iman Marvian

We study the interplay of symmetries and Gaussianity in bosonic systems, under closed and open dynamics, and develop a resource theory of Gaussian asymmetry. Specifically, we focus on Gaussian symmetry-respecting (covariant) operations, which serve as the free operations in this framework. We prove that any such operation can be realized via Gaussian Hamiltonians that respect the symmetry under consideration, coupled to an environment prepared in a symmetry-respecting pure Gaussian state. We further identify a family of tractable monotone functions of states that remain non-increasing under Gaussian symmetry-respecting dynamics, and are exactly conserved in closed systems. We demonstrate that these monotones are not generally respected under non-Gaussian symmetry-respecting dynamics. Along the way, we provide several technical results of independent interest to the quantum information and optics communities, including a new approach to the Stinespring dilation theorem, and an extension of Williamson's theorem for the simultaneous normal mode decomposition of Gaussian systems and conserved charges.
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Quantum Physics · Cross-listed from cond-mat.stat-mech

Monotonicity of eigenstate thermalization hypothesis in two-dimensional systems

Nilakash Sorokhaibam and Anjan Daimari

We study numerically the enveloping $f$-function of the fluctuation term in eigenstate thermalization hypothesis (ETH) statement. We concentrate on the energy (or entropy) dependence of this function in two-dimensional systems. Our numerical results show that it is, in general, a monotonically increasing function of the entropy. This is in agreement with the general expectation that fluctuations increase with increasing entropy. We show that the $f$-function locally flattens with increasing system-size. The flattening rate is directly proportional to the system size. We also show that the flattening rate is directly proportional to the particle number for systems of same spatial size. This variation of the $f$-function is important for physics at subleading order of the system-size. So, it is relevant for intermediate-size systems (upto a few hundred qubits) which are experimentally accessible. One exception we found is that the $f$-function of the order parameter of a thermal phase transition defy the monotonic behaviour.
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