Showing 1–50 of 419 results for author: Liu, W

Maritime object classification with SAR imagery using quantum kernel methods

Authors: John Tanner, Nicholas Davies, Pascal Elahi, Casey R. Myers, Du Huynh, Wei Liu, Mark Reynolds, Jingbo Wang

Abstract: Illegal, unreported, and unregulated (IUU) fishing causes global economic losses of \$10-25 billion annually and undermines marine sustainability and governance. Synthetic Aperture Radar (SAR) provides reliable maritime surveillance under all weather and lighting conditions, but classifying small maritime objects in SAR imagery remains challenging. We investigate quantum machine learning for this… ▽ More Illegal, unreported, and unregulated (IUU) fishing causes global economic losses of \$10-25 billion annually and undermines marine sustainability and governance. Synthetic Aperture Radar (SAR) provides reliable maritime surveillance under all weather and lighting conditions, but classifying small maritime objects in SAR imagery remains challenging. We investigate quantum machine learning for this task, focusing on Quantum Kernel Methods (QKMs) applied to real and complex SAR chips extracted from the SARFish dataset. We tackle two binary classification problems, the first for distinguishing vessels from non-vessels, and the second for distinguishing fishing vessels from other types of vessels. We compare QKMs applied to real and complex SAR chips against classical Laplacian, RBF, and linear kernels applied to real SAR chips. Using noiseless numerical simulations of the quantum kernels, we find that QKMs are capable of obtaining equal or better performance than the classical kernel on these tasks in the best case, but do not demonstrate a clear advantage for the complex SAR data. This work presents the first application of QKMs to maritime classification in SAR imagery and offers insight into the potential and current limitations of quantum-enhanced learning for maritime surveillance. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Comments: 15 + 5 pages, 5 figures, 4 tables

LiePrune: Lie Group and Quantum Geometric Dual Representation for One-Shot Structured Pruning of Quantum Neural Networks

Authors: Haijian Shao, Bowen Yang, Wei Liu, Xing Deng, Yingtao Jiang

Abstract: Quantum neural networks (QNNs) and parameterized quantum circuits (PQCs) are key building blocks for near-term quantum machine learning. However, their scalability is constrained by excessive parameters, barren plateaus, and hardware limitations. We propose LiePrune, the first mathematically grounded one-shot structured pruning framework for QNNs that leverages Lie group structure and quantum geom… ▽ More Quantum neural networks (QNNs) and parameterized quantum circuits (PQCs) are key building blocks for near-term quantum machine learning. However, their scalability is constrained by excessive parameters, barren plateaus, and hardware limitations. We propose LiePrune, the first mathematically grounded one-shot structured pruning framework for QNNs that leverages Lie group structure and quantum geometric information. Each gate is jointly represented in a Lie group--Lie algebra dual space and a quantum geometric feature space, enabling principled redundancy detection and aggressive compression. Experiments on quantum classification (MNIST, FashionMNIST), quantum generative modeling (Bars-and-Stripes), and quantum chemistry (LiH VQE) show that LiePrune achieves over $10\times$ compression with negligible or even improved task performance, while providing provable guarantees on redundancy detection, functional approximation, and computational complexity. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Comments: 7 pages, 2 figures

$\mathcal{PT}$-symmetric cavity magnomechanics with gain-assisted transparency and amplification

Authors: Cham Oumie, Wu-Ming Liu, Kashif Ammar Yasir

Abstract: We investigate magnomechanically induced transparency in a parity-time-symmetric cavity magnomechanical system with traveling-field-induced non-Hermiticity. The setup consists of a microwave cavity mode coupled to magnons in a single-crystal yttrium iron garnet sphere, which in turn are hybridized with a vibrational mechanical mode through magnetostrictive interaction. In the Hermitian regime, str… ▽ More We investigate magnomechanically induced transparency in a parity-time-symmetric cavity magnomechanical system with traveling-field-induced non-Hermiticity. The setup consists of a microwave cavity mode coupled to magnons in a single-crystal yttrium iron garnet sphere, which in turn are hybridized with a vibrational mechanical mode through magnetostrictive interaction. In the Hermitian regime, strong photon-magnon coupling generates a single transparency window in the cavity transmission, which splits into a doublet when the magnon is coherently hybridized with the mechanical mode via magnomechanical coupling. This establishes a versatile platform in which the transparency spectrum can be engineered from single- to multi-window response using experimentally accessible, scaled magnomechanical interactions. When a non-Hermitian coupling is introduced, the system enters a parity-time-broken regime in which the transparency ceases to be purely passive and becomes gain assisted, leading to asymmetric transmission with amplification on one side of the resonance and enhanced absorption on the other. By tuning the cavity detuning, we convert magnomechanical transparency into Fano-type line shapes with strongly non-Lorentzian phase dispersion and map their deformation into asymmetric, gain-assisted Fano ridges in the joint space of probe and magnon detunings. Finally, we analyze the associated group delay and show that both slow- and fast-light behavior can be widely tuned by varying the photon-magnon and magnomechanical couplings together with the non-Hermitian strength, highlighting parity-time-symmetric cavity magnomechanics as a promising platform for reconfigurable quantum signal processing and enhanced sensing. △ Less

Submitted 9 December, 2025; originally announced December 2025.

Comments: 13 pages, 8 figures

Entanglement degradation of static black holes in effective quantum gravity

Authors: Xiaobao Liu, Wentao Liu, Shu-Min Wu

Abstract: Quantum information science has been broadly explored in Einstein gravity and in various modified gravity theories; however, its extension to quantum gravity settings remains largely unexplored. Motivated by this gap, in this paper we investigate the degradation of quantum entanglement of scalar and Dirac fields in the third-type black hole geometry arising from effective quantum gravity, which in… ▽ More Quantum information science has been broadly explored in Einstein gravity and in various modified gravity theories; however, its extension to quantum gravity settings remains largely unexplored. Motivated by this gap, in this paper we investigate the degradation of quantum entanglement of scalar and Dirac fields in the third-type black hole geometry arising from effective quantum gravity, which incorporates generic quantum gravitational corrections beyond classical general relativity. This quantum corrected spacetime is free of a Cauchy horizon and can be cast into a Rindler form in the near-horizon regime, allowing a direct identification of vacuum modes and a clear correspondence with the framework developed for uniformly accelerated observers. Within this framework, we compute the quantum entanglement and mutual information of uniformly entangled detector pairs in terms of the quantum parameter $\tildeζ$, the mode frequency $\tildeω$, and Bob's radial position $R_0$. The quantum parameter $\tildeζ$ consistently weakens the horizon-induced loss of correlations. For scalar fields this effect is pronounced, producing clear departures from the classical behavior, whereas for Dirac fields the familiar correlation pattern remains intact but its degradation is noticeably reduced. Overall, $\tildeζ$ acts as a universal protective factor against gravitational suppression of quantum correlations. The third-type effective quantum black hole therefore provides a controlled and physically transparent arena for probing how quantum-gravity corrections influence relativistic quantum information. △ Less

Submitted 28 November, 2025; v1 submitted 15 November, 2025; originally announced November 2025.

Comments: 12 pages, 7 figures

Does the survival and sudden death of quadripartite steering in curved spacetime truly depend on multi-directionality?

Authors: Xiaobao Liu, Wentao Liu, Si-Han Shang, Shu-Min Wu

Abstract: We systematically investigate the directional dependence of Gaussian quadripartite quantum steering and its redistribution among different modes in the background of a Schwarzschild black hole. For physically accessible sectors, we identify three distinct behaviors: (i) steering from non-gravitational to gravitational observers undergoes sudden death at maximal asymmetry with the Hawking temperatu… ▽ More We systematically investigate the directional dependence of Gaussian quadripartite quantum steering and its redistribution among different modes in the background of a Schwarzschild black hole. For physically accessible sectors, we identify three distinct behaviors: (i) steering from non-gravitational to gravitational observers undergoes sudden death at maximal asymmetry with the Hawking temperature, marking the crossover from two-way to one-way steerability; (ii) steering in the opposite direction decays monotonically and vanishes only in the extreme black hole limit, highlighting its directional sensitivity to spacetime curvature; (iii) steering from hybrid gravitational-non-gravitational partitions to non-gravitational mode persists at a finite asymptotic value set by the initial squeezing parameter. Moreover, all inaccessible steerings generated by the Hawking effect exhibit an intrinsic asymmetry, with their specific behavior being strongly dependent on the steering direction. △ Less

Submitted 3 November, 2025; originally announced November 2025.

Comments: 23 pages, 3 figures

Wormhole-Induced correlation: A Link Between Two Universes

Authors: Zhilong Liu, Wentao Liu, Xiaofang Liu, Jieci Wang

Abstract: Motivated by the profound connection between quantum mechanics and spacetime geometry, particularly the conjectured correspondence between wormholes and quantum entanglement as proposed in the ER=EPR framework, this study aims to investigate the influence of wormhole geometries on quantum information extraction. We examine the correlation-specifically mutual information (MI) and entanglement-extra… ▽ More Motivated by the profound connection between quantum mechanics and spacetime geometry, particularly the conjectured correspondence between wormholes and quantum entanglement as proposed in the ER=EPR framework, this study aims to investigate the influence of wormhole geometries on quantum information extraction. We examine the correlation-specifically mutual information (MI) and entanglement-extracted by two Unruh-DeWitt (UDW) detectors from the quantum vacuum field in the presence of a BTZ wormhole featuring a null-like throat, also known as an Einstein-Rosen bridge. First, we analyze how the detector's position relative to the wormhole throat and the throat's size affect the extracted MI. Our results indicate that the wormhole enhances MI extraction, with maximal MI achieved when the detectors are located at specific image-symmetric points connected by the wormhole. By analyzing the behavior of the nonlocal contribution term and the classical noise term, it is found that the correlations extracted contain genuine non-classical components. This work highlights the feasibility of extracting quantum correlations through null-like wormhole geometries and provides a novel perspective for probing the potential relationship between spacetime topology and the nonlocal characteristics of quantum mechanics. △ Less

Submitted 10 October, 2025; v1 submitted 4 October, 2025; originally announced October 2025.

Comments: 9 pages, 7 figures

Composite nonadiabatic geometric quantum gates with optimization on superconducting circuits

Authors: Cheng-Yun Ding, Wan-Fang Liu, Li-Hua Zhang, Jian Zhou, Zheng-Yuan Xue

Abstract: Due to its fast and robust characteristics, nonadiabatic geometric quantum computation with various optimized techniques has received much attention. However, these strategies either require precise pulse control or can only mitigate partial systematic errors, hindering their experimental development. Here, we propose a scheme for optimized composite nonadiabatic geometric quantum gates (OCNGQGs),… ▽ More Due to its fast and robust characteristics, nonadiabatic geometric quantum computation with various optimized techniques has received much attention. However, these strategies either require precise pulse control or can only mitigate partial systematic errors, hindering their experimental development. Here, we propose a scheme for optimized composite nonadiabatic geometric quantum gates (OCNGQGs), which can further enhance the gate performance of the composite nonadiabatic geometric scheme. Specifically, by optimizing the path parameter, our scheme effectively resists systematic errors in both directions, i.e., Rabi frequency and detuning errors, while preserving the flexibility of pulse shapes. Numerical simulations demonstrate that our scheme offers superior gate robustness against these two types of errors compared to conventional schemes. Additionally, we propose to implement our scheme on superconducting transmon qubits, where the numerical results show the robustness of universal gates remaining evident within current technology. Therefore, our proposal provides a promising approach to achieve robust quantum gates for future scalable quantum computation. △ Less

Submitted 29 September, 2025; originally announced September 2025.

Comments: 11 pages,11 figures

Journal ref: Froniters of Physics,(2025)

Critical dynamics and superconducting state preparation in the quenched Kitaev chain with pairing imbalance

Authors: Y. B. Shi, Y. X. Zhang, S. W. Liu, Z. Song

Abstract: The dynamical balance of the pairing term plays a crucial role in the emergence of topological superconductivity in the p-wave spinless Kitaev chain, particularly in the non-Hermitian regime. In this work, we systematically investigate the effects of non-Hermitian pairing terms on both equilibrium and nonequilibrium phenomena in the Kitaev chain. Our analysis focuses on two representative forms of… ▽ More The dynamical balance of the pairing term plays a crucial role in the emergence of topological superconductivity in the p-wave spinless Kitaev chain, particularly in the non-Hermitian regime. In this work, we systematically investigate the effects of non-Hermitian pairing terms on both equilibrium and nonequilibrium phenomena in the Kitaev chain. Our analysis focuses on two representative forms of pairing imbalance: uniform and staggered. We demonstrate that a uniform imbalance induces only minor perturbations to the spectrum and dynamical properties, without significantly affecting its equilibrium phase or nonequilibrium steady behavior. In contrast, even a slight staggered imbalance leads to drastic changes. At the symmetry point, it enables the resonant generation of two distinct superconducting states through critical dynamics, with the realized state determined by the direction of the bias. Both states exhibit exact off-diagonal long-range order (ODLRO) in the thermodynamic limit. Our results emphasize the fragility of coherent dynamics in non-Hermitian topological systems and elucidate the interplay among non-Hermiticity, topology, and dynamical criticality in quench processes. △ Less

Submitted 25 September, 2025; originally announced September 2025.

Comments: 12 pages, 5 figures

Quantum Autoencoder: An efficient approach to quantum feature map generation

Authors: Shengxin Zhuang, Yusen Wu, Xavier F. Cadet, Du Q. Huynh, Wei Liu, Philippe Charton, Cedric Damour, Frederic Cadet, Jingbo B. Wang

Abstract: Quantum machine learning methods often rely on fixed, hand-crafted quantum encodings that may not capture optimal features for downstream tasks. In this work, we study the power of quantum autoencoders in learning data-driven quantum representations. We first theoretically demonstrate that the quantum autoencoder method is efficient in terms of sample complexity throughout the entire training proc… ▽ More Quantum machine learning methods often rely on fixed, hand-crafted quantum encodings that may not capture optimal features for downstream tasks. In this work, we study the power of quantum autoencoders in learning data-driven quantum representations. We first theoretically demonstrate that the quantum autoencoder method is efficient in terms of sample complexity throughout the entire training process. Then we numerically train the quantum autoencoder on 3 million peptide sequences, and evaluate their effectiveness across multiple peptide classification problems including antihypertensive peptide prediction, blood-brain barrier-penetration, and cytotoxic activity detection. The learned representations were compared against Hamiltonian-evolved baselines using a quantum kernel with support vector machines. Results show that quantum autoencoder learned representations achieve accuracy improvements ranging from 0.4\% to 8.1\% over Hamiltonian baselines across seven datasets, demonstrating effective generalization to diverse downstream datasets with pre-training enabling effective transfer learning without task-specific fine-tuning. This work establishes that quantum autoencoder architectures can effectively learn from large-scale datasets (3 million samples) with compact parameterizations ($\sim$900 parameters), demonstrating their viability for practical quantum applications. △ Less

Submitted 23 September, 2025; originally announced September 2025.

Mixed Quantum-Classical Approaches to Spin Current and Polarization Dynamics in Chiral Molecular Junctions

Authors: Yu Wang, Ruihao Bi, Wei Liu, Jiayue Han, Wenjie Dou

Abstract: Chiral molecular junctions offer a promising platform for realizing chiral-induced spin selectivity (CISS), where spin filtering occurs without external magnetic fields. Here, we investigate spin transport in such junctions by combining quantum master equation (QME) methods for purely electronic dynamics with surface hopping (SH) and mean-field Ehrenfest (MF) approaches to incorporate electron-pho… ▽ More Chiral molecular junctions offer a promising platform for realizing chiral-induced spin selectivity (CISS), where spin filtering occurs without external magnetic fields. Here, we investigate spin transport in such junctions by combining quantum master equation (QME) methods for purely electronic dynamics with surface hopping (SH) and mean-field Ehrenfest (MF) approaches to incorporate electron-phonon coupling. Our results show that transient spin polarization arises but ultimately decays to zero at long times. We find that bias voltage, molecular length, and spin-orbit coupling (SOC) strongly influence the spin current dynamics: higher bias enhances spin current but reduces polarization, while longer molecules and stronger SOC amplify transient polarization. Including electron-phonon coupling modifies current-voltage characteristics, enhancing spin currents at intermediate bias but suppressing them at high bias, while leaving the polarization dynamics largely unchanged. These findings highlight the interplay between electronic and vibrational effects in CISS and provide guidance for designing molecular spintronic devices. △ Less

Submitted 10 September, 2025; originally announced September 2025.

Comments: 30 pages, 10 figures

Above 99.9% Fidelity Single-Qubit Gates, Two-Qubit Gates, and Readout in a Single Superconducting Quantum Device

Authors: Fabian Marxer, Jakub Mrożek, Joona Andersson, Leonid Abdurakhimov, Janos Adam, Ville Bergholm, Rohit Beriwal, Chun Fai Chan, Saga Dahl, Soumya Ranjan Das, Frank Deppe, Olexiy Fedorets, Zheming Gao, Alejandro Gomez Frieiro, Daria Gusenkova, Andrew Guthrie, Tuukka Hiltunen, Hao Hsu, Eric Hyyppä, Joni Ikonen, Sinan Inel, Shan W. Jolin, Azad Karis, Seung-Goo Kim, William Kindel , et al. (42 additional authors not shown)

Abstract: Achieving high-fidelity single-qubit gates, two-qubit gates, and qubit readout is critical for building scalable, error-corrected quantum computers. However, device parameters that enhance one operation often degrade the others, making simultaneous optimization challenging. Here, we demonstrate that careful tuning of qubit-coupler coupling strengths in a superconducting circuit with two transmon q… ▽ More Achieving high-fidelity single-qubit gates, two-qubit gates, and qubit readout is critical for building scalable, error-corrected quantum computers. However, device parameters that enhance one operation often degrade the others, making simultaneous optimization challenging. Here, we demonstrate that careful tuning of qubit-coupler coupling strengths in a superconducting circuit with two transmon qubits coupled via a tunable coupler enables high-fidelity single- and two-qubit gates, without compromising readout performance. As a result, we achieve a 40h-averaged CZ gate fidelity of 99.93%, simultaneous single-qubit gate fidelities of 99.98%, and readout fidelities over 99.94% in a single device. These results are enabled by optimized coupling parameters, an efficient CZ gate calibration experiment based on our new Phased-Averaged Leakage Error Amplification (PALEA) protocol, and a readout configuration compatible with high coherence qubits. Our results demonstrate a viable path toward scaling up superconducting quantum processors while maintaining consistently high fidelities across all core operations. △ Less

Submitted 22 August, 2025; originally announced August 2025.

A hybrid-frequency on-chip programmable synthetic-dimension simulator with arbitrary couplings

Authors: Xiao-Dong Zeng, Zhao-An Wang, Jia-Ming Ren, Yi-Tao Wang, Chun Ao, Wei Liu, Nai-Jie Guo, Lin-Ke Xie, Jun-You Liu, Yu-Hang Ma, Ya-Qi Wu, Shuang Wang, Pei-Yun Li, Zong-Quan Zhou, Mu Yang, Jin-Shi Xu, Xi-Wang Luo, Jian-Shun Tang, Chuan-Feng Li, Guang-Can Guo

Abstract: High-performance photonic chips provide a powerful platform for analog computing, enabling the simulation of high-dimensional physical systems using low-dimensional devices with additional synthetic dimensions. The realization of large-scale complex simulations necessitates an architecture capable of arbitrary coupling configurations (encompassing symmetric, asymmetric and long-range coupling sche… ▽ More High-performance photonic chips provide a powerful platform for analog computing, enabling the simulation of high-dimensional physical systems using low-dimensional devices with additional synthetic dimensions. The realization of large-scale complex simulations necessitates an architecture capable of arbitrary coupling configurations (encompassing symmetric, asymmetric and long-range coupling schemes) which is also crucial for scaling up. Previous approaches rely on excessive physical components to introduce asymmetric coupling, however, are restricted in reconfiguring and scaling by the relatively complicated structures. Here, to solve this problem, we propose a hybrid-frequency synthetic-dimension simulator architecture that combines both intra-resonant and inter-resonant frequency-lattice sites, and experimentally demonstrate it using the thin-film lithium niobate (TFLN) photonic chip. Employing this hybrid programmable architecture, we are able to simulate both the regular and long-range coupled forms of diverse compound-lattice models, such as the Hall ladder, Creutz ladder (symmetric) and Su-Schrieffer-Heeger (SSH, asymmetric) model, on a single chip, simultaneously reducing the experimental requirements significantly. As results, the direct readout of the bandstructure of the SSH model is able to be achieved, to be distinguished from all previous works, and important phenomena such as spin-momentum locking, topological flat band and Aharonov-Bohm cage effect are also observed with lower experimental requirements. Furthermore, applications like piecewise-continuous optical frequency shifting can be enabled by cascading our devices. Our results offer promising insights for future large-scale complex on-chip simulators with arbitrary couplings. △ Less

Submitted 21 August, 2025; originally announced August 2025.

Comments: 11 pages, 4 figures

Can the latent signatures of quantum superposition be detected through correlation harvesting?

Authors: Yu Tang, Wentao Liu, Zhilong Liu, Jieci Wang

Abstract: In this paper, we explore correlation harvesting in quantum superposition, specifically focusing on the entanglement and mutual information extracted by two Unruh-DeWitt detectors interacting with a quantum field in a mass-superposed BTZ black hole spacetime. Our findings reveal that the superposed nature of spacetime induces constructive interference between the field modes that can significantly… ▽ More In this paper, we explore correlation harvesting in quantum superposition, specifically focusing on the entanglement and mutual information extracted by two Unruh-DeWitt detectors interacting with a quantum field in a mass-superposed BTZ black hole spacetime. Our findings reveal that the superposed nature of spacetime induces constructive interference between the field modes that can significantly enhance the entanglement harvesting relative to a single spacetime background. In contrast to entanglement, the mutual information obtained in spacetime superposition is influenced by the proper distance between the two detectors. While the mutual information harvested in a superposed spacetime remains lower than that in a single spacetime when the proper distance between detectors is small, it exceeds that in a single spacetime for specific mass ratios as the distance increases. Notably, we find that both entanglement and mutual information harvesting reach their maxima when the final spacetime superposition state is conditioned to align with the initial spacetime state. △ Less

Submitted 10 November, 2025; v1 submitted 31 July, 2025; originally announced August 2025.

Comments: 13 pages, 14 figures

Influence of dark matter on quantum entanglement and coherence in curved spacetime

Authors: Shu-Min Wu, Yu-Xuan Wang, Si-Han Shang, Wentao Liu

Abstract: Dark matter (DM) remains undetected, and developing theoretical models such as the promising perfect fluid dark matter (PFDM) is a key challenge in modern cosmology. In this work, we investigate the quantum characteristics of PFDM by analyzing the behavior of quantum entanglement and coherence for both fermionic and bosonic fields near a Schwarzschild black hole embedded in a PFDM halo. Our result… ▽ More Dark matter (DM) remains undetected, and developing theoretical models such as the promising perfect fluid dark matter (PFDM) is a key challenge in modern cosmology. In this work, we investigate the quantum characteristics of PFDM by analyzing the behavior of quantum entanglement and coherence for both fermionic and bosonic fields near a Schwarzschild black hole embedded in a PFDM halo. Our results reveal that PFDM can either enhance or degrade quantum entanglement and coherence, depending sensitively on its density. Notably, bosonic entanglement shows greater susceptibility to PFDM effects compared to fermionic entanglement, while fermionic coherence exhibits a stronger dependence on PFDM than its bosonic counterpart. These findings highlight the necessity of selecting appropriate quantum probes for DM detection based on the type of quantum resources, as different quantum fields exhibit significantly different responses to PFDM in curved spacetime. △ Less

Submitted 21 July, 2025; originally announced July 2025.

Comments: 26 pages, 4 figures

Quantum Circuit Optimization Based on Dynamic Grouping and ZX-Calculus for Reducing 2-Qubit Gate Count

Authors: Kai Chen, Wen Liu, GuoSheng Xu, Yangzhi Li, Maoduo Li, Shouli He

Abstract: In the noisy intermediate-scale quantum (NISQ) era, two-qubit gates in quantum circuits are more susceptible to noise than single-qubit gates. Therefore, reducing the number of two-qubit gates is crucial for improving circuit efficiency and reliability. As quantum circuits scale up, the optimization search space becomes increasingly complex, leading to challenges such as low efficiency and subopti… ▽ More In the noisy intermediate-scale quantum (NISQ) era, two-qubit gates in quantum circuits are more susceptible to noise than single-qubit gates. Therefore, reducing the number of two-qubit gates is crucial for improving circuit efficiency and reliability. As quantum circuits scale up, the optimization search space becomes increasingly complex, leading to challenges such as low efficiency and suboptimal solutions. To address these issues, this paper proposes a quantum circuit optimization approach based on dynamic grouping and ZX-calculus. First, a random strategy-based dynamic grouping method partitions the circuit into multiple subcircuits. Second, a ZX-calculus guided k-step lookahead search performs equivalent subcircuit filtering to minimize two-qubit gate counts. Third, a delay-aware placement method optimizes the recombined circuit to reduce the overall gate count. Finally, simulated annealing iteratively updates the grouping strategy to achieve an optimized two-qubit gate count. Experimental results on benchmark datasets demonstrate the effectiveness and superiority of the proposed method in reducing two-qubit gates. Compared to the original circuits, the approach achieves an average reduction of 18% in two-qubit gates. It outperforms classical methods with up to 25% reduction, especially on gf circuits, and shows a 4% average improvement over heuristic ZX-calculus-based methods, validating its efficiency. △ Less

Submitted 18 July, 2025; originally announced July 2025.

Quantized decay charges in non-Hermitian networks characterized by directed graphs

Authors: Wenwen Liu, Junyao Wu, Li Zhang, Oubo You, Ye Tian, Hongsheng Chen, Bumki Min, Yihao Yang, Shuang Zhang

Abstract: Non-Hermitian physics has unveiled a realm of exotic phenomena absent in Hermitian systems, with the non-Hermitian skin effect (NHSE) showcasing boundary-localized eigenstates driven by non-reciprocal interactions. Here, we introduce a new class of non-Hermitian systems exhibiting pure decay modes-eigenstates with pure, smooth exponential decay, devoid of the oscillatory wave patterns typical of t… ▽ More Non-Hermitian physics has unveiled a realm of exotic phenomena absent in Hermitian systems, with the non-Hermitian skin effect (NHSE) showcasing boundary-localized eigenstates driven by non-reciprocal interactions. Here, we introduce a new class of non-Hermitian systems exhibiting pure decay modes-eigenstates with pure, smooth exponential decay, devoid of the oscillatory wave patterns typical of traditional NHSE. Modeled as directed graphs with non-reciprocal hopping, these systems reveal quantized decay charges, defined as the sum of decay constants along edges at each node, offering a novel topological invariant. We derive universal conditions for these modes, enabling versatile configurations from one-dimensional rings, directed graphs with complicated connectivity, to higher-dimensional lattices. Experimental validation using microwave resonant circuits confirms the predicted pure decay profiles. This discovery paves the way for potential applications in photonics, signal processing, and beyond, harnessing the unique topological properties of non-Hermitian networks △ Less

Submitted 9 October, 2025; v1 submitted 15 July, 2025; originally announced July 2025.

Observation of hierarchy of Hilbert space ergodicities in the quantum dynamics of a single spin

Authors: Wenquan Liu, Zouwei Pan, Yue Fu, Wei Cheng, Wen Wei Ho, Xing Rong, Jiangfeng Du

Abstract: Ergodicity, the property that all allowed configurations are explored over time, plays a pivotal role in explaining the equilibrium behavior of classical dynamical systems. Yet, such a property is typically precluded in quantum systems owing to the presence of energy eigenstates, which are stationary states in dynamics. However, recent theoretical works have argued that ergodic explorations of the… ▽ More Ergodicity, the property that all allowed configurations are explored over time, plays a pivotal role in explaining the equilibrium behavior of classical dynamical systems. Yet, such a property is typically precluded in quantum systems owing to the presence of energy eigenstates, which are stationary states in dynamics. However, recent theoretical works have argued that ergodic explorations of the Hilbert space, occurring at varying levels as measured by statistical pseudorandomness of the time-evolved quantum states, may be exhibited for quantum systems driven by Hamiltonians with aperiodic time dependencies, which do not face such obstacles. Here, we experimentally investigate the hierarchy of Hilbert-space ergodicities (HSE) achievable in the dynamics of a single quantum spin realized by a solid-state defect in diamond, upon subjecting it to various time-dependent modulations. Through continuous monitoring of spin trajectories with full state tomography, different degrees of HSE were observed, ranging from no HSE in a time-periodic (Floquet) drive, to partial HSE in a smoothly kicked time-quasiperiodic drive, to complete HSE in a drive composed of a sequence of kicks generated by the Fibonacci word. We formulate a theoretical understanding of the increasing levels of HSE observed by attributing them to increasing levels of complexities associated with the drive sequences, whose notions we elucidate. Our work constitutes the first unambiguous experimental evidence of Hilbert space ergodicity and promotes deeper investigations into the mechanisms and fine-grained levels with which closed quantum systems reach equilibrium. △ Less

Submitted 8 July, 2025; originally announced July 2025.

Comments: 11 pages, 6 figures, research article

Temperature dependent single- and double-quantum relaxation of negatively charged boron vacancies in hexagonal boron nitride

Authors: Lin-Ke Xie, Wei Liu, Kaiyu Huang, Nai-Jie Guo, Jun-You Liu, Yu-Hang Ma, Ya-Qi Wu, Yi-Tao Wang, Zhao-an Wang, Xiao-Dong Zeng, Jia-Ming Ren, Chun Ao, Shuo Deng, Haifei Lu, Jian-Shun Tang, Chuan-Feng Li, Guang-Can Guo

Abstract: The negatively charged boron vacancy in two-dimensional hexagonal boron nitride has emerged as a promising candidate for quantum sensing. The coherence time of this defect spins which coherent quantum sensing resides in is limited spin-phonon interactions, while the underlying physical mechanism of the corresponding high-temperature behavior is still not fully understood. Here, we probe the single… ▽ More The negatively charged boron vacancy in two-dimensional hexagonal boron nitride has emerged as a promising candidate for quantum sensing. The coherence time of this defect spins which coherent quantum sensing resides in is limited spin-phonon interactions, while the underlying physical mechanism of the corresponding high-temperature behavior is still not fully understood. Here, we probe the single- and double-quantum relaxation rates on this center over the temperature range from 293 to 393 K. The results show that both relaxation rates increase with increasing temperature, and the double-quantum relaxation rate significantly increases rapidly. At high temperature (above 400 K), the double-quantum relaxation rate is much greater than single-quantum relaxation rate, and may dominate the decoherence channel of spin-phonon interactions. Using a theoretical model of second-order spin-phonon interactions, we attribute the high-temperature spin relaxation rates to interactions with higher-energy effective phonon mode, aiding the further understanding and guiding high-temperature sensing applications. △ Less

Submitted 17 June, 2025; originally announced June 2025.

Entangled Unruh-DeWitt detectors amplify quantum coherence

Authors: Shu-Min Wu, Yu-Xuan Wang, Wentao Liu

Abstract: We explore the quantum coherence between a pair of entangled Unruh-DeWitt detectors, interacting with a quantum field, using a nonperturbative approach in a (3+1)-dimensional Minkowski spacetime with instantaneous switching ($δ$-switching). It is intriguing to observe that for a maximally entangled state, increasing the coupling strength enhances the detectors' initial quantum coherence while simu… ▽ More We explore the quantum coherence between a pair of entangled Unruh-DeWitt detectors, interacting with a quantum field, using a nonperturbative approach in a (3+1)-dimensional Minkowski spacetime with instantaneous switching ($δ$-switching). It is intriguing to observe that for a maximally entangled state, increasing the coupling strength enhances the detectors' initial quantum coherence while simultaneously causing a monotonic decrease in their initial entanglement. This reveals a remarkable phenomenon: through nonperturbative interactions, entangled Unruh-DeWitt detectors can exhibit a dual effect-amplifying quantum coherence while degrading quantum entanglement. This finding stands in stark contrast to previous studies based on perturbative methods or Gaussian switching functions, which generally concluded that interactions between detectors and the field lead to a simultaneous degradation of quantum coherence and entanglement due to environmental decoherence. Notably, while initially separable detectors successfully harvest quantum coherence from the vacuum, entanglement extraction remains fundamentally prohibited. These contrasting behaviors underscore the fundamental distinction between coherence and entanglement as quantum resources, and highlight their complementary roles in field-detector interactions. △ Less

Submitted 16 June, 2025; originally announced June 2025.

Comments: 22 pages, 4 figures

Constructive interference at the edge of quantum ergodic dynamics

Authors: Dmitry A. Abanin, Rajeev Acharya, Laleh Aghababaie-Beni, Georg Aigeldinger, Ashok Ajoy, Ross Alcaraz, Igor Aleiner, Trond I. Andersen, Markus Ansmann, Frank Arute, Kunal Arya, Abraham Asfaw, Nikita Astrakhantsev, Juan Atalaya, Ryan Babbush, Dave Bacon, Brian Ballard, Joseph C. Bardin, Christian Bengs, Andreas Bengtsson, Alexander Bilmes, Sergio Boixo, Gina Bortoli, Alexandre Bourassa, Jenna Bovaird , et al. (240 additional authors not shown)

Abstract: Quantum observables in the form of few-point correlators are the key to characterizing the dynamics of quantum many-body systems. In dynamics with fast entanglement generation, quantum observables generally become insensitive to the details of the underlying dynamics at long times due to the effects of scrambling. In experimental systems, repeated time-reversal protocols have been successfully imp… ▽ More Quantum observables in the form of few-point correlators are the key to characterizing the dynamics of quantum many-body systems. In dynamics with fast entanglement generation, quantum observables generally become insensitive to the details of the underlying dynamics at long times due to the effects of scrambling. In experimental systems, repeated time-reversal protocols have been successfully implemented to restore sensitivities of quantum observables. Using a 103-qubit superconducting quantum processor, we characterize ergodic dynamics using the second-order out-of-time-order correlators, OTOC$^{(2)}$. In contrast to dynamics without time reversal, OTOC$^{(2)}$ are observed to remain sensitive to the underlying dynamics at long time scales. Furthermore, by inserting Pauli operators during quantum evolution and randomizing the phases of Pauli strings in the Heisenberg picture, we observe substantial changes in OTOC$^{(2)}$ values. This indicates that OTOC$^{(2)}$ is dominated by constructive interference between Pauli strings that form large loops in configuration space. The observed interference mechanism endows OTOC$^{(2)}$ with a high degree of classical simulation complexity, which culminates in a set of large-scale OTOC$^{(2)}$ measurements exceeding the simulation capacity of known classical algorithms. Further supported by an example of Hamiltonian learning through OTOC$^{(2)}$, our results indicate a viable path to practical quantum advantage. △ Less

Submitted 11 June, 2025; originally announced June 2025.

Comments: See following link: https://zenodo.org/records/15640503, which includes: Circuits used in Fig. 3d, Fig. 3e, Fig. 4a, Fig. 4b of the main text. In addition, OTOC (C^(2)) circuits and data with 95, 40 and 31 qubits are also provided. For system sizes <= 40 qubits, we include exact simulation results. For system sizes > 40, we include experimental data

The optical Bloch equation for the finite-temperature fluctuations

Authors: Weitao Liu

Abstract: In this work, I analyze the quantum fluctuations and the thermal fluctuations in the framework of quantum mechanics. Being recognized as incoherent perturbations with different features, fluctuations of these two types lead to dissipative terms in the optical Bloch equations. The method allows one to use the optical Bloch equation to analyze time-dependent processes in the finite-temperature fluct… ▽ More In this work, I analyze the quantum fluctuations and the thermal fluctuations in the framework of quantum mechanics. Being recognized as incoherent perturbations with different features, fluctuations of these two types lead to dissipative terms in the optical Bloch equations. The method allows one to use the optical Bloch equation to analyze time-dependent processes in the finite-temperature fluctuations. The numerical results show that the deexcitation is the limit of the equilibration at zero temperature. The impact of the fluctuations on the coherent excitations are also discussed. △ Less

Submitted 11 June, 2025; v1 submitted 4 June, 2025; originally announced June 2025.

Comments: 10 pages, 4 figures

Nonlocal Nonlinear Control of Photonic Spin Hall Effect in Strongly Interacting Rydberg Media

Authors: Wenzhang Liu, Muqaddar Abbas, Pei Zhang, Jiawei Lai

Abstract: We present a theoretical study demonstrating enhanced tunability of the photonic spin Hall effect (PSHE) using a strongly interacting Rydberg atomic medium under electromagnetically induced transparency (EIT) conditions. In contrast to conventional approaches that rely on static refractiveindex profiles or metamaterials, here the PSHE is controlled via a nonlocal third-order nonlinear susceptibili… ▽ More We present a theoretical study demonstrating enhanced tunability of the photonic spin Hall effect (PSHE) using a strongly interacting Rydberg atomic medium under electromagnetically induced transparency (EIT) conditions. In contrast to conventional approaches that rely on static refractiveindex profiles or metamaterials, here the PSHE is controlled via a nonlocal third-order nonlinear susceptibility arising from long range Rydberg-Rydberg interactions. We show that this nonlocal nonlinearity enables dynamic modulation of spin-dependent light trajectories, amplifying the normally weak PSHE into a readily observable and adjustable effect. These results pave the way for new capabilities in photonic information processing and sensing. In particular, an adjustable PSHE may enable beam steering based on photon spin, improve the sensitivity of precision measurements, and support photonic devices whose functionality can be reconfigured in real time. △ Less

Submitted 26 November, 2025; v1 submitted 31 May, 2025; originally announced June 2025.

Information-theoretically secure quantum timestamping with one-time universal hashing

Authors: Ming-Yang Li, Chen-Xun Weng, Wen-Bo Liu, Mengya Zhu, Zeng-Bing Chen

Abstract: Accurate and tamper-resistant timestamps are essential for applications demanding verifiable chronological ordering, such as legal documentation and digital intellectual property protection. Classical timestamp protocols rely on computational assumptions for security, rendering them vulnerable to quantum attacks, which is a critical limitation given the rapid progress in quantum computing. To addr… ▽ More Accurate and tamper-resistant timestamps are essential for applications demanding verifiable chronological ordering, such as legal documentation and digital intellectual property protection. Classical timestamp protocols rely on computational assumptions for security, rendering them vulnerable to quantum attacks, which is a critical limitation given the rapid progress in quantum computing. To address this, we propose an information-theoretically secure quantum timestamping protocol based on one-time universal hashing with quantum keys. Our protocol simultaneously achieves information-theoretic security and high efficiency, enabling secure timestamping for arbitrarily long documents. Simulations demonstrate a generation rate exceeding 100 timestamps per second over intercity distances. In addition, our protocol only requires weak coherent states, making it practical for large-scale deployment. This work advances the field of quantum timestamping and contributes to the broader development of quantum cryptography and the future quantum internet. △ Less

Submitted 23 July, 2025; v1 submitted 19 May, 2025; originally announced May 2025.

Comments: Minor changes for the final version

Journal ref: Sci. China-Phys. Mech. Astron. 68, 100312 (2025)

Quantum entanglement and Einstein-Podolsky-Rosen steering in ultrastrongly light-matter coupled system

Authors: Yu-qiang Liu, Shan Sun, Yi-jia Yang, Zheng Liu, Xingdong Zhao, Zunlue Zhu, Wuming Liu, Chang-shui Yu

Abstract: This work presents a scheme for engineering quantum entanglement and Einstein-Podolsky-Rosen (EPR) steering with Gaussian measurements based on the quantum Hopfield model that incorporates a common thermal reservoir. We begin by examining quantum correlations, specifically quantum entanglement and EPR steering, in the ground state. These quantum correlations primarily stem from squeezing interacti… ▽ More This work presents a scheme for engineering quantum entanglement and Einstein-Podolsky-Rosen (EPR) steering with Gaussian measurements based on the quantum Hopfield model that incorporates a common thermal reservoir. We begin by examining quantum correlations, specifically quantum entanglement and EPR steering, in the ground state. These quantum correlations primarily stem from squeezing interactions in weak and normal strong coupling regimes. As the coupling strength increases, especially upon entering the ultrastrong coupling regime, the correlations emerge from the combined effect of squeezing and mix-mode interactions. Importantly, this scenario enables the realization of two-way EPR steering. Moreover, lower optical frequencies enhance both quantum entanglement and EPR steering. Further, when considering thermal effects, the ultrastrong and deep strong coupling regimes, paired with lower optical frequencies, lead to improved entanglement. The one-way EPR steering for resonant case can be effectively controlled in the ultrastrong and deep strong coupling regimes which originates from the asymmetry of subsystem and reservoir coupling induced by the diamagnetic term. Additionally, one-way EPR steering can also be produced for nonresonant case. In this case, the asymmetry of the subsystem and reservoir originates from the combined effect of nonresonant frequencies and diamagnetic term. Our findings have the potential to inspire further research into quantum information processing that leverages light-matter entanglement and EPR steering. △ Less

Submitted 12 May, 2025; originally announced May 2025.

Comments: 13 pages, 8 figures, to be published in Physical Review A

Journal ref: Physical Review A 111, 052437 (2025)

Single-atom imaging of ${}^{173}$Yb in optical tweezers loaded by a five-beam magneto-optical trap

Authors: Omar Abdel Karim, Alessandro Muzi Falconi, Riccardo Panza, Wenliang Liu, Francesco Scazza

Abstract: We report on the trapping and imaging of individual ytterbium atoms in arrays of optical tweezers, loaded from a magneto-optical trap (MOT) formed by only five beams in an orthogonal configuration. In our five-beam MOT, operating on the narrow ${}^1$S${}_0 \rightarrow {}^3$P${}_1$ intercombination transition, gravity balances the radiation pressure of a single upward-directed beam. This approach e… ▽ More We report on the trapping and imaging of individual ytterbium atoms in arrays of optical tweezers, loaded from a magneto-optical trap (MOT) formed by only five beams in an orthogonal configuration. In our five-beam MOT, operating on the narrow ${}^1$S${}_0 \rightarrow {}^3$P${}_1$ intercombination transition, gravity balances the radiation pressure of a single upward-directed beam. This approach enables efficient trapping and cooling of the most common ytterbium isotopes (${}^{171}$Yb, ${}^{173}$Yb and ${}^{174}$Yb) to $\lesssim 20\,μ$K at densities $\sim 10^{11}$ atoms/cm$^3$ within less than one second. This configuration allows for significantly reducing the complexity of the optical setup, potentially benefiting any ytterbium-atom based quantum science platform leveraging single-atom microscopy, from quantum processors to novel optical clocks. We then demonstrate the first single-atom-resolved imaging of the fermionic, large-spin isotope ${}^{173}$Yb ($I=5/2$), employing a two-color imaging scheme that does not rely on magic-wavelength trapping. We achieve a high single-atom detection fidelity of $99.96(1)\%$ and a large survival probability of $98.5(2)\%$, despite large differential light shifts affecting all nuclear spin sublevels of the excited ${}^3$P${}_1$ state involved in the cooling transition. The demonstrated capabilities will play a key role in future quantum simulations and computing applications with ${}^{173}$Yb arrays. △ Less

Submitted 2 September, 2025; v1 submitted 12 May, 2025; originally announced May 2025.

Comments: 14 pages, 8 figures

Journal ref: Quantum Sci. Technol. 10, 045019 (2025)

Entanglement Maximization and Mirror Symmetry in Two-Higgs-Doublet Models

Authors: Marcela Carena, Guglielmo Coloretti, Wanqiang Liu, Mira Littmann, Ian Low, Carlos E. M. Wagner

Abstract: We consider 2-to-2 scatterings of Higgs bosons in a CP-conserving two-Higgs-doublet model (2HDM) and study the implication of maximizing the entanglement in the flavor space, where the two doublets $Φ_a$, $a=1,2$, can be viewed as a qubit: $Φ_1=|0\rangle$ and $Φ_2=|1\rangle$. More specifically, we compute the scattering amplitudes for $Φ_a Φ_b \to Φ_c Φ_d$ and require the outgoing flavor entanglem… ▽ More We consider 2-to-2 scatterings of Higgs bosons in a CP-conserving two-Higgs-doublet model (2HDM) and study the implication of maximizing the entanglement in the flavor space, where the two doublets $Φ_a$, $a=1,2$, can be viewed as a qubit: $Φ_1=|0\rangle$ and $Φ_2=|1\rangle$. More specifically, we compute the scattering amplitudes for $Φ_a Φ_b \to Φ_c Φ_d$ and require the outgoing flavor entanglement to be maximal for a full product basis such as the computational basis, which consists of $\{|00\rangle,|01\rangle,|10\rangle,|11\rangle\}$. In the unbroken phase and turning off the gauge interactions, entanglement maximization results in the appearance of an $U(2)\times U(2)$ global symmetry among the quartic couplings, which in general is broken softly by the mass terms. Interestingly, once the Higgs bosons acquire vacuum expectation values, maximal entanglement enforces an exact $U(2) \times U(2)$ symmetry, which is spontaneously broken to $U(1)\times U(1)$. As a byproduct, this gives rise to Higgs alignment as well as to the existence of 6 massless Nambu-Goldstone bosons. The $U(2)\times U(2)$ symmetry can be gauged to lift the massless Goldstones, while maintaining maximal entanglement demands the presence of a discrete $\mathrm{Z}_2$ symmetry interchanging the two gauge sectors. The model is custodially invariant in the scalar sector, and the inclusion of fermions requires a mirror dark sector, related to the standard one by the $\mathrm{Z}_2$ symmetry. △ Less

Submitted 1 May, 2025; originally announced May 2025.

Non-Equilibrium Probing of Topological Supersolids in Spin-Orbit-Coupled Dipolar Condensates

Authors: Biao Dong, Xiao-Fei Zhang, Wei Han, Renyuan Liao, Xue-Ying Yang, Wu-Ming Liu, Yong-Chang Zhang

Abstract: A chiral supersolid is a quantum phase that simultaneously exhibits crystalline order, superfluidity, and topological spin texture, with spontaneously broken translational, U(1) gauge, and chiral symmetries. Here, we demonstrate a chiral supersolid with tunable non-equilibrium dynamics in a spin-orbit coupled dipolar Bose-Einstein condensate. By adjusting dipolar interaction and spin-orbit couplin… ▽ More A chiral supersolid is a quantum phase that simultaneously exhibits crystalline order, superfluidity, and topological spin texture, with spontaneously broken translational, U(1) gauge, and chiral symmetries. Here, we demonstrate a chiral supersolid with tunable non-equilibrium dynamics in a spin-orbit coupled dipolar Bose-Einstein condensate. By adjusting dipolar interaction and spin-orbit coupling, we uncover two distinct quantum phase transitions: (i) a first-order transition from a single skyrmion superfluid to a triangular meron supersolid, and (ii) a second-order transition from this superfluid to a square skyrmion supersolid. These phases are characterized by their lattice symmetries, nonclassical rotational inertia, and spin textures. Under parity-time symmetric dissipation, we predict phase-dependent damping of the current oscillations, directly linked to the superfluid fraction. The predicted chiral supersolid phase can be experimentally observed in ultracold magnetic atoms with spin-orbit coupling. Our results establish dipolar quantum gases as a platform for designing topological matter with spintronic functionality. △ Less

Submitted 20 August, 2025; v1 submitted 20 April, 2025; originally announced April 2025.

Room-temperature hybrid 2D-3D quantum spin system for enhanced magnetic sensing and many-body dynamics

Authors: Haoyu Sun, Pei Yu, Xu Zhou, Xiangyu Ye, Mengqi Wang, Zhaoxin Liu, Yuhang Guo, Wenzhao Liu, You Huang, Pengfei Wang, Fazhan Shi, Kangwei Xia, Ya Wang

Abstract: Advances in hybrid quantum systems and their precise control are pivotal for developing advanced quantum technologies. Two-dimensional (2D) materials with optically accessible spin defects have emerged as a promising platform for building integrated quantum spin systems due to their exceptional flexibility and scalability. However, experimentally realizing such systems and demonstrating their supe… ▽ More Advances in hybrid quantum systems and their precise control are pivotal for developing advanced quantum technologies. Two-dimensional (2D) materials with optically accessible spin defects have emerged as a promising platform for building integrated quantum spin systems due to their exceptional flexibility and scalability. However, experimentally realizing such systems and demonstrating their superiority remains challenging. Here, we present a hybrid spin system operating under ambient conditions, integrating boron vacancy (V_B^-) spins in 2D hexagonal boron nitride flakes with a single nitrogen vacancy (NV) center in 3D single-crystal diamonds. This combined system achieves full controllability and exhibits enhanced performance for nanoscale magnetic sensing, including an improved dynamic range. Moreover, we investigate the rich many-body spin dynamics within the hybrid system, which enables us to estimate the concentration of V_B^- spins. This work provides a critical foundation for advancing the development of 2D-3D integrated quantum spin systems. △ Less

Submitted 8 December, 2025; v1 submitted 14 April, 2025; originally announced April 2025.

Comments: 15 pages, 4 figures, published to npj Quantum Information

Journal ref: npj Quantum Inf (2025)

Universal Structure of Computing Moments for Exact Quantum Dynamics: Application to Arbitrary System-Bath Couplings

Authors: Rui-Hao Bi, Wei Liu, Wenjie Dou

Abstract: We introduce a general procedure for computing higher-order moments of correlation functions in open quantum systems, extending the scope of our recent work on Memory Kernel Coupling Theory (MKCT) [W. Liu, Y. Su, Y. Wang, and W. Dou, arXiv:2407.01923 (2024)]. This approach is demonstrated for arbitrary system-bath coupling that can be expressed as polynomial,… ▽ More We introduce a general procedure for computing higher-order moments of correlation functions in open quantum systems, extending the scope of our recent work on Memory Kernel Coupling Theory (MKCT) [W. Liu, Y. Su, Y. Wang, and W. Dou, arXiv:2407.01923 (2024)]. This approach is demonstrated for arbitrary system-bath coupling that can be expressed as polynomial, $H_{SB} = \hat{V} (α_0 + α_1 \hat{q} + α_2 \hat{q}^2+ \dots)$, where we show that the recursive commutators of a system operator obey a universal hierarchy. Exploiting this structure, the higher-order moments are obtained by evaluating the expectation values of the system and bath operators separately, with bath expectation values derived from the derivatives of a generating function. We further apply MKCT to compute the dipole autocorrelation function for the spin-boson model with both linear and quadratic coupling, achieving agreement with the hierarchical equations of motion approach. Our findings suggest a promising path toward accurate dynamics for complex open quantum systems. △ Less

Submitted 13 May, 2025; v1 submitted 1 April, 2025; originally announced April 2025.

Comments: 22 pages, 6 figures

Accurate Gauge-Invariant Tensor Network Simulations for Abelian Lattice Gauge Theory in (2+1)D: ground state and real-time dynamics

Authors: Yantao Wu, Wen-Yuan Liu

Abstract: We propose a novel tensor network method to achieve accurate and efficient simulations of Abelian lattice gauge theories (LGTs) in (2+1)D for both ground state and real-time dynamics. The first key is to identify a gauge canonical form (GCF) of gauge-invariant tensor network states, which already simplifies existing algorithms for (1+1)D LGTs. The second key is to employ the GCF of projected entan… ▽ More We propose a novel tensor network method to achieve accurate and efficient simulations of Abelian lattice gauge theories (LGTs) in (2+1)D for both ground state and real-time dynamics. The first key is to identify a gauge canonical form (GCF) of gauge-invariant tensor network states, which already simplifies existing algorithms for (1+1)D LGTs. The second key is to employ the GCF of projected entangled-pair state (PEPS) combining with variational Monte Carlo (VMC), enabling efficient computations for (2+1)D LGTs. We demonstrate the versatile capability of this approach for accurate ground state simulation of pure $Z_2$, $Z_3$ and $Z_4$ gauge theory, odd-$Z_2$ gauge theories, and $Z_2$ gauge theory coupled to hard-core bosons, on square lattices up to $32 \times 32$. Furthermore, we demonstrate that it allows for accurate simulations of real-time dynamics up to long-time, exemplified by the dynamics of elementary excitations of the deconfined $Z_2$ gauge field on a $10\times10$ lattice. This is also the first example of using VMC to simulate the real-time dynamics of PEPS, whose impact may extend beyond gauge theory. △ Less

Submitted 10 August, 2025; v1 submitted 26 March, 2025; originally announced March 2025.

A Superconducting Qubit-Resonator Quantum Processor with Effective All-to-All Connectivity

Authors: Michael Renger, Jeroen Verjauw, Nicola Wurz, Amin Hosseinkhani, Caspar Ockeloen-Korppi, Wei Liu, Aniket Rath, Manish J. Thapa, Florian Vigneau, Elisabeth Wybo, Ville Bergholm, Chun Fai Chan, Bálint Csatári, Saga Dahl, Rakhim Davletkaliyev, Rakshyakar Giri, Daria Gusenkova, Hermanni Heimonen, Tuukka Hiltunen, Hao Hsu, Eric Hyyppä, Joni Ikonen, Tyler Jones, Shabeeb Khalid, Seung-Goo Kim , et al. (40 additional authors not shown)

Abstract: In this work we introduce a superconducting quantum processor architecture that uses a transmission-line resonator to implement effective all-to-all connectivity between six transmon qubits. This architecture can be used as a test-bed for algorithms that benefit from high connectivity. We show that the central resonator can be used as a computational element, which offers the flexibility to encode… ▽ More In this work we introduce a superconducting quantum processor architecture that uses a transmission-line resonator to implement effective all-to-all connectivity between six transmon qubits. This architecture can be used as a test-bed for algorithms that benefit from high connectivity. We show that the central resonator can be used as a computational element, which offers the flexibility to encode a qubit for quantum computation or to utilize its bosonic modes which further enables quantum simulation of bosonic systems. To operate the quantum processing unit (QPU), we develop and benchmark the qubit-resonator conditional Z gate and the qubit-resonator MOVE operation. The latter allows for transferring a quantum state between one of the peripheral qubits and the computational resonator. We benchmark the QPU performance and achieve a genuinely multi-qubit entangled Greenberger-Horne-Zeilinger (GHZ) state over all six qubits with a readout-error mitigated fidelity of $0.86$. △ Less

Submitted 8 December, 2025; v1 submitted 13 March, 2025; originally announced March 2025.

Harvesting correlations from BTZ black hole coupled to a Lorentz-violating vector field

Authors: Xiaofang Liu, Wentao Liu, Zhilong Liu, Jieci Wang

Abstract: In this paper, we investigate the effects of Lorentz violation on correlations harvesting, specifically focusing on the harvested entanglement and harvested mutual information between two Unruh-DeWitt detectors interacting with a quantum field in the Lorentz-violating BTZ-like black hole spacetime. Our findings reveal that Lorentz symmetry breaking has contrasting impacts on entanglement harvestin… ▽ More In this paper, we investigate the effects of Lorentz violation on correlations harvesting, specifically focusing on the harvested entanglement and harvested mutual information between two Unruh-DeWitt detectors interacting with a quantum field in the Lorentz-violating BTZ-like black hole spacetime. Our findings reveal that Lorentz symmetry breaking has contrasting impacts on entanglement harvesting and mutual information harvesting in BTZ backgrounds: it enhances mutual information harvesting while suppressing entanglement harvesting. This phenomenon suggests that the increase in total correlations in Lorentz-violating vector field backgrounds with gravitational coupling is predominantly driven by classical components, with quantum correlations contributing less to the overall mutual information. These results indicate that Lorentz violation, as a quantum property of spacetime, may impose intrinsic constraints on the quantum information capacity encoded in spacetime due to competition among quantum degrees of freedom for resources. Furthermore, Lorentz symmetry breaking expands the \textit{entanglement shadow} region, further demonstrating its disruptive effect on quantum correlations. △ Less

Submitted 16 June, 2025; v1 submitted 8 March, 2025; originally announced March 2025.

Comments: 14 pages, 31 figures

Deterministic generation of multi-qubit entangled states among distant parties using indefinite causal order

Authors: Wen-Qiang Liu, Hai-Rui Wei

Abstract: Quantum entanglement plays an irreplaceable role in various remote quantum information processing tasks. Here we present protocols for generating deterministic and heralded $N$-qubit entangled states across multiple network nodes. By utilizing a pre-shared maximally entangled state and single-qubit operations within an indefinite causal order framework, the multi-qubit entangled state between dist… ▽ More Quantum entanglement plays an irreplaceable role in various remote quantum information processing tasks. Here we present protocols for generating deterministic and heralded $N$-qubit entangled states across multiple network nodes. By utilizing a pre-shared maximally entangled state and single-qubit operations within an indefinite causal order framework, the multi-qubit entangled state between distant parties can be generated deterministically. The complex entangled state measurements and multiple pre-shared entangled states, are essential in conventional entanglement swapping technique, but are not required in our approach. This greatly reduces the complexity of the quantum circuit and makes it more experimentally feasible. Furthermore, we develop optical architectures to implement these protocols by encoding qubits in polarization degree of freedom. The results indicate that our protocols significantly improve the efficiency of long-distance entanglement generation and provide a practical framework for establishing large-scale quantum networks. △ Less

Submitted 27 May, 2025; v1 submitted 5 March, 2025; originally announced March 2025.

Comments: 12 pages, 7 figures

Journal ref: Physical Review Applied 23, 054075 (2025)

Microwave-coupled optical bistability in driven and interacting Rydberg gases

Authors: Zhehua Zhang, Zeyan Zhang, Shaoxing Han, Yuqing Zhang, Guoqing Zhang, Jizhou Wu, Vladimir B. Sovkov, Wenliang Liu, Yuqing Li, Linjie Zhang, Liantuan Xiao, Suotang Jia, Weibin Li, Jie Ma

Abstract: Nonequilibrium dynamics are closely related to various fields of research, in which vastly different phases emerge when parameters are changed. However, it is difficult to construct nonequilibrium systems that have sufficiently tunable controllable parameters. Using microwave field coupling induced optical bistability, Rydberg gases exhibit a range of significantly different optical responses. In… ▽ More Nonequilibrium dynamics are closely related to various fields of research, in which vastly different phases emerge when parameters are changed. However, it is difficult to construct nonequilibrium systems that have sufficiently tunable controllable parameters. Using microwave field coupling induced optical bistability, Rydberg gases exhibit a range of significantly different optical responses. In conjunction with electromagnetically induced transparency, the microwave coupling can create versatile nonequilibrium dynamics. In particular, the microwave coupling of two Rydberg states provides an additional handle for controlling the dynamics. And the microwave-controlled nonequilibrium phase transition has the potential to be applied in microwave field measurement. This study opens a new avenue to exploring bistable dynamics using microwave-coupled Rydberg gases, and developing quantum technological applications. △ Less

Submitted 27 February, 2025; originally announced February 2025.

Comments: 10 page,5 figure

Journal ref: npj Quantum Inf (2025)

Accurate Simulation of the Hubbard Model with Finite Fermionic Projected Entangled Pair States

Authors: Wen-Yuan Liu, Huanchen Zhai, Ruojing Peng, Zheng-Cheng Gu, Garnet Kin-Lic Chan

Abstract: We demonstrate the use of finite-size fermionic projected entangled pair states, in conjunction with variational Monte Carlo, to perform accurate simulations of the ground-state of the 2D Hubbard model. Using bond dimensions of up to $D=28$, we show that we can surpass state-of-the-art DMRG energies that use up to $m=32000$ SU(2) multiplets on 8-leg ladders. We further apply our methodology to… ▽ More We demonstrate the use of finite-size fermionic projected entangled pair states, in conjunction with variational Monte Carlo, to perform accurate simulations of the ground-state of the 2D Hubbard model. Using bond dimensions of up to $D=28$, we show that we can surpass state-of-the-art DMRG energies that use up to $m=32000$ SU(2) multiplets on 8-leg ladders. We further apply our methodology to $10\times 16$, $12\times 16$ and $16 \times 16$ lattices at $1/8$ hole doping and observe the dimensional crossover between stripe orientations. Our work shows the power of finite-size fermionic tensor networks to resolve the physics of the 2D Hubbard model and related problems. △ Less

Submitted 31 May, 2025; v1 submitted 19 February, 2025; originally announced February 2025.

Comments: main text: 5pages, 5 figures

Journal ref: Phys. Rev. Lett. 134, 256502 (2025), Editor's Suggestion

Efficient Implementation of Arbitrary Two-Qubit Gates via Unified Control

Authors: Zhen Chen, Weiyang Liu, Yanjun Ma, Weijie Sun, Ruixia Wang, He Wang, Huikai Xu, Guangming Xue, Haisheng Yan, Zhen Yang, Jiayu Ding, Yang Gao, Feiyu Li, Yujia Zhang, Zikang Zhang, Yirong Jin, Haifeng Yu, Jianxin Chen, Fei Yan

Abstract: The native gate set is fundamental to the performance of quantum devices, as it governs the accuracy of basic quantum operations and dictates the complexity of implementing quantum algorithms. Traditional approaches to extending gate sets often require accessing multiple transitions within an extended Hilbert space, leading to increased control complexity while offering only a limited set of gates… ▽ More The native gate set is fundamental to the performance of quantum devices, as it governs the accuracy of basic quantum operations and dictates the complexity of implementing quantum algorithms. Traditional approaches to extending gate sets often require accessing multiple transitions within an extended Hilbert space, leading to increased control complexity while offering only a limited set of gates. Here, we experimentally demonstrate a unified and highly versatile gate scheme capable of natively generating arbitrary two-qubit gates using only exchange interaction and qubit driving on a superconducting quantum processor, achieving maximum expressivity. Using a state-of-the-art transmon-coupler-transmon architecture, we achieve high fidelities averaging $99.37 \pm 0.07\%$ across a wide range of commonly used two-qubit unitaries. This outstanding performance, combined with reduced complexity, enables precise multipartite entangled state preparation, as demonstrated. To further enhance its applicability, we also show the high-fidelity realization of the unique B gate, which efficiently synthesizes the entire family of two-qubit gates. Our results highlight that fully exploiting the capabilities of a single interaction can yield a comprehensive and highly accurate gate set. With maximum expressivity, gate-time optimality, demonstrated high fidelity, and easy adaptability to other quantum platforms, our unified control scheme paves the way for optimal performance in quantum devices, offering exciting prospects for advancing quantum hardware and algorithm development. △ Less

Submitted 5 February, 2025; originally announced February 2025.

Observational signature of Lorentz violation in acceleration radiation

Authors: Yu Tang, Wentao Liu, Jieci Wang

Abstract: In recent years, Lorentz violation (LV) has emerged as a vibrant area of research in fundamental physics. Despite predictions from quantum gravity theories that Lorentz symmetry may break down at Planck-scale energies, which are currently beyond experimental reach, its low-energy signatures could still be detectable through alternative methods. In this paper, we propose a quantum optical approach… ▽ More In recent years, Lorentz violation (LV) has emerged as a vibrant area of research in fundamental physics. Despite predictions from quantum gravity theories that Lorentz symmetry may break down at Planck-scale energies, which are currently beyond experimental reach, its low-energy signatures could still be detectable through alternative methods. In this paper, we propose a quantum optical approach to investigate potential LV effects on the acceleration radiation of a freely falling atom within a black hole spacetime coupled to a Lorentz-violating vector field. Our proposed experimental setup employs a Casimir-type apparatus, wherein a two-level atom serves as a dipole detector, enabling its interaction with the field to be modeled using principles from quantum optics. We demonstrate that LV can introduce distinct quantum signatures into the radiation flux, thereby significantly modulating particle emission rates. It is found that while LV effects are negligible at high mode frequencies, they become increasingly pronounced at lower frequencies. This suggests that detecting LV at low-energy scales may depend on advancements in low-frequency observational techniques or detectors. △ Less

Submitted 5 February, 2025; originally announced February 2025.

Comments: 9 pages, 8 figures

Steering Non-Equilibrium Molecular Dynamics in Optical Cavities

Authors: Mingxuan Xiao, Wei Wang, Wenjing Liu, Zheng Li, Shui-Jing Tang, Yun-Feng Xiao

Abstract: Optical resonators have shown outstanding abilities to tailor chemical landscapes through enhanced light-matter interaction between confined optical modes and molecule vibrations. We propose a theoretical model to study cooperative vibrational strong coupling in an open quantum system. The non-equilibrium stochastic molecular dynamics in an optical cavity with an auxiliary ensemble is investigated… ▽ More Optical resonators have shown outstanding abilities to tailor chemical landscapes through enhanced light-matter interaction between confined optical modes and molecule vibrations. We propose a theoretical model to study cooperative vibrational strong coupling in an open quantum system. The non-equilibrium stochastic molecular dynamics in an optical cavity with an auxiliary ensemble is investigated. It shows that coupling with a cavity mode introduces an additional colored noise and a negative feedback, both of which enable control over thermalization rates (i.e. the lifetime of excitation) of reactive molecules. Our work offers a pathway to steer stability of chemical bonds for chemical reactivity under cooperative vibrational strong coupling. △ Less

Submitted 10 December, 2024; originally announced December 2024.

Orbital Optical Raman Lattice

Authors: Zhi-Hao Huang, Kou-Han Ma, Bao-Zong Wang, W. Vincent Liu, Xiong-Jun Liu

Abstract: Spin and orbital are two basic degrees of freedom that play significant roles in exploring exotic quantum phases in optical lattices with synthetic spin-orbit coupling (SOC) and high orbital bands, respectively. Here, we combine these two crucial ingredients for the first time by proposing a completely new orbital optical Raman lattice scheme to explore exotic high-orbital Bose condensates with Ra… ▽ More Spin and orbital are two basic degrees of freedom that play significant roles in exploring exotic quantum phases in optical lattices with synthetic spin-orbit coupling (SOC) and high orbital bands, respectively. Here, we combine these two crucial ingredients for the first time by proposing a completely new orbital optical Raman lattice scheme to explore exotic high-orbital Bose condensates with Raman-induced SOC in a square lattice. We find that both the SOC and p-orbital interactions influence the condensed state of bosons. Their interplay results in two novel high-orbital many-body quantum phases: the uniform angular momentum superfluid phase, which exhibits a global topological chiral orbital current characterized by a uniform Chern number, and the two-dimensional topological spin-orbital supersolid phase, which is characterized by the spin and orbital angular momentum density wave patterns and topological excitations with opposite Chern numbers, respectively protecting the chiral and antichiral edge modes in the neighboring supersolid clusters. Our scheme may open a new avenue for exploring exotic SOC and high-orbital physics in optical lattices, and is expected to advance the experimental realization of novel supersolids in higher dimensions. △ Less

Submitted 28 July, 2025; v1 submitted 5 December, 2024; originally announced December 2024.

Comments: 6+10 pages, 4+4 figures. Discussions are updated. References are updated

Versatile photonic frequency synthetic dimensions using a single Mach-Zehnder-interferometer-assisted device on thin-film lithium niobate

Authors: Zhao-An Wang, Xiao-Dong Zeng, Yi-Tao Wang, Jia-Ming Ren, Chun Ao, Zhi-Peng Li, Wei Liu, Nai-Jie Guo, Lin-Ke Xie, Jun-You Liu, Yu-Hang Ma, Ya-Qi Wu, Shuang Wang, Jian-Shun Tang, Chuan-Feng Li, Guang-Can Guo

Abstract: Investigating physical models with photonic synthetic dimensions has been generating great interest in vast fields of science. The rapid developing thin-film lithium niobate (TFLN) platform, for its numerous advantages including high electro-optic coefficient and scalability, is well compatible with the realization of synthetic dimensions in the frequency together with spatial domain. While coupli… ▽ More Investigating physical models with photonic synthetic dimensions has been generating great interest in vast fields of science. The rapid developing thin-film lithium niobate (TFLN) platform, for its numerous advantages including high electro-optic coefficient and scalability, is well compatible with the realization of synthetic dimensions in the frequency together with spatial domain. While coupling resonators with fixed beam splitters is a common experimental approach, it often lacks tunability and limits coupling between adjacent lattices to sites occupying the same frequency domain positions. Here, on the contrary, we conceive the resonator arrays connected by electro-optic tunable Mach-Zehnder interferometers in our configuration instead of fixed beam splitters. By applying bias voltage and RF modulation on the interferometers, our design extends such coupling to long-range scenario and allows for continuous tuning on each coupling strength and synthetic effective magnetic flux. Therefore, our design enriches controllable coupling types that are essential for building programmable lattice networks and significantly increases versatility. As the example, we experimentally fabricate a two-resonator prototype on the TFLN platform, and on this single chip we realize well-known models including tight-binding lattices, topological Hall ladder and Creutz ladder. We directly observe the band structures in the quasi-momentum space and important phenomena such as spin-momentum locking and the Aharonov-Bohm cage effect. These results demonstrate the potential for convenient simulations of more complex models in our configuration. △ Less

Submitted 19 August, 2025; v1 submitted 20 November, 2024; originally announced November 2024.

Multiplexed readout of Superconductor--Normal-Conductor--Superconductor bolometers

Authors: Priyank Singh, András Gunyhó, Heikki Suominen, Giacomo Catto, Florian Blanchet, Qi-Ming Chen, Arman Alizadeh, Aarne Keränen, Jian Ma, Timm Mörstedt, Wei Liu, Mikko Möttonen

Abstract: Recently, ultrasensitive calorimeters have been proposed as a resource-efficient solution for multiplexed qubit readout in superconducting large-scale quantum processors. However, experiments demonstrating frequency multiplexing of these superconductor--normal--conductor--superconductor (SNS) sensors are are lacking in the literature. To this end, we present the design, fabrication, and operation… ▽ More Recently, ultrasensitive calorimeters have been proposed as a resource-efficient solution for multiplexed qubit readout in superconducting large-scale quantum processors. However, experiments demonstrating frequency multiplexing of these superconductor--normal--conductor--superconductor (SNS) sensors are are lacking in the literature. To this end, we present the design, fabrication, and operation of three SNS sensors with frequency-multiplexed input and probe circuits, all on a single chip. These devices have their probe frequencies in the range 150 MHz--200 MHz, which is well detuned from the heater frequencies of 4.4 GHz--7.6 GHz compatible with typical readout frequencies of superconducting qubits. Importantly, we show on-demand triggering of both individual and multiple low-noise SNS bolometers with very low cross talk. These experiments pave the way for multiplexed bolometric characterization and calorimetric readout of multiple qubits, a promising step in minimizing related resources such as the number of readout lines and microwave isolators in large-scale superconducting quantum computers. △ Less

Submitted 11 March, 2025; v1 submitted 19 November, 2024; originally announced November 2024.

Comments: 8 pages, 4 figures

Observation of freezing phenomenon in high-dimensional quantum correlation dynamics

Authors: Yue Fu, Wenquan Liu, Yunhan Wang, Chang-Kui Duan, Bo Zhang, Yeliang Wang, Xing Rong

Abstract: Quantum information processing (QIP) based on high-dimensional quantum systems provides unique advantages and new potentials where high-dimensional quantum correlations (QCs) play vital roles. Exploring the resistance of QCs against noises is crucial as QCs are fragile due to complex and unavoidable system-environment interactions. In this study, we investigate the performance of high-dimensional… ▽ More Quantum information processing (QIP) based on high-dimensional quantum systems provides unique advantages and new potentials where high-dimensional quantum correlations (QCs) play vital roles. Exploring the resistance of QCs against noises is crucial as QCs are fragile due to complex and unavoidable system-environment interactions. In this study, we investigate the performance of high-dimensional QCs under local dephasing noise using a single nitrogen-vacancy center in diamond. A freezing phenomenon in the high-dimensional quantum discord dynamics was observed, showing discord is robust against local dephasing noise. Utilizing a robustness metric known as freezing index, we found that the discord of qutrits outperforms their qubits counterpart when confronted with dephasing noise. Furthermore, we developed a geometric picture to explain this intriguing freezing phenomenon phenomenon. Our findings highlight the potential of utilizing discord as a physical resource for advancing QIP in high-dimensional quantum settings. △ Less

Submitted 3 November, 2024; originally announced November 2024.

Lorentz violation alleviates gravitationally induced entanglement degradation

Authors: Wentao Liu, Cuihong Wen, Jieci Wang

Abstract: Lorentz violation is a significant phenomenon in the framework of quantum physics, with implications for fundamental symmetries. In this paper, we explore the effects of Lorentz violation on quantum entanglement through a black hole spacetime that is coupled with a Lorentz-violating field. We establish the relationship between the Hartle-Hawking vacuum state and the Boulware number states for this… ▽ More Lorentz violation is a significant phenomenon in the framework of quantum physics, with implications for fundamental symmetries. In this paper, we explore the effects of Lorentz violation on quantum entanglement through a black hole spacetime that is coupled with a Lorentz-violating field. We establish the relationship between the Hartle-Hawking vacuum state and the Boulware number states for this case, and employ the near horizon approximation in an appropriate form to rewrite the black hole metric into a Rindler-like form. Subsequently, using this revised metric, the analytical forms of logarithmic negativity and mutual information are derived and plotted as functions of Rob's distance from the $ r=0 $ point. Based on the results, we find that the coupling between spacetime and the Lorentz-violating vector field alleviates gravity-induced entanglement degradation. At high mode frequencies, the effects of Lorentz violation are negligible, but they become significant at low frequencies. This suggests that investigating Lorentz violation at astrophysical scales requires low-frequency detectors, as the low energy of these fields enhances the significance of the Lorentz-violating field's non-zero vacuum expectation value. △ Less

Submitted 27 December, 2024; v1 submitted 28 October, 2024; originally announced October 2024.

Comments: 10 pages, 17 figures

Journal ref: JHEP 01 (2025) 184

Experimental observation of spin defects in van der Waals material GeS$_2$

Authors: W. Liu, S. Li, N. -J. Guo, X. -D. Zeng, L. -K. Xie, J. -Y. Liu, Y. -H. Ma, Y. -Q. Wu, Y. -T. Wang, Z. -A. Wang, J. -M. Ren, C. Ao, J. -S. Xu, J. -S. Tang, A. Gali, C. -F. Li, G. -C. Guo

Abstract: Spin defects in atomically thin two-dimensional (2D) materials such as hexagonal boron nitride (hBN) attract significant attention for their potential quantum applications. The layered host materials not only facilitate seamless integration with optoelectronic devices but also enable the formation of heterostructures with on-demand functionality. Furthermore, their atomic thickness renders them pa… ▽ More Spin defects in atomically thin two-dimensional (2D) materials such as hexagonal boron nitride (hBN) attract significant attention for their potential quantum applications. The layered host materials not only facilitate seamless integration with optoelectronic devices but also enable the formation of heterostructures with on-demand functionality. Furthermore, their atomic thickness renders them particularly suitable for sensing applications. However, the short coherence times of the spin defects in hBN limit them in quantum applications that require extended coherence time. One primary reason is that both boron and nitrogen atoms have non-zero nuclear spins. Here, we present another 2D material germanium disulfide ($β$-GeS$_2$) characterized by a wide bandgap and potential nuclear-spin-free lattice. This makes it as a promising host material for spin defects that possess long-coherence time. Our findings reveal the presence of more than two distinct types of spin defects in single-crystal $β$-GeS$_2$. Coherent control of one type defect has been successfully demonstrated at both 5 K and room temperature, and the coherence time $T_2$ can achieve tens of microseconds, 100-folds of that of negatively charged boron vacancy (V$_{\text{B}}^-$) in hBN, satisfying the minimal threshold required for metropolitan quantum networks--one of the important applications of spins. We entatively assign the observed optical signals come from substitution defects. Together with previous theoretical prediction, we believe the coherence time can be further improved with optimized lattice quality, indicating $β$-GeS$_2$ as a promising host material for long-coherence-time spins. △ Less

Submitted 24 October, 2024; originally announced October 2024.

Comments: 8 pages, 5 figures

Observation of disorder-free localization using a (2+1)D lattice gauge theory on a quantum processor

Authors: Gaurav Gyawali, Shashwat Kumar, Yuri D. Lensky, Eliott Rosenberg, Aaron Szasz, Tyler Cochran, Renyi Chen, Amir H. Karamlou, Kostyantyn Kechedzhi, Julia Berndtsson, Tom Westerhout, Abraham Asfaw, Dmitry Abanin, Rajeev Acharya, Laleh Aghababaie Beni, Trond I. Andersen, Markus Ansmann, Frank Arute, Kunal Arya, Nikita Astrakhantsev, Juan Atalaya, Ryan Babbush, Brian Ballard, Joseph C. Bardin, Andreas Bengtsson , et al. (197 additional authors not shown)

Abstract: Disorder-induced phenomena in quantum many-body systems pose significant challenges for analytical methods and numerical simulations at relevant time and system scales. To reduce the cost of disorder-sampling, we investigate quantum circuits initialized in states tunable to superpositions over all disorder configurations. In a translationally-invariant lattice gauge theory (LGT), these states can… ▽ More Disorder-induced phenomena in quantum many-body systems pose significant challenges for analytical methods and numerical simulations at relevant time and system scales. To reduce the cost of disorder-sampling, we investigate quantum circuits initialized in states tunable to superpositions over all disorder configurations. In a translationally-invariant lattice gauge theory (LGT), these states can be interpreted as a superposition over gauge sectors. We observe localization in this LGT in the absence of disorder in one and two dimensions: perturbations fail to diffuse despite fully disorder-free evolution and initial states. However, Rényi entropy measurements reveal that superposition-prepared states fundamentally differ from those obtained by direct disorder sampling. Leveraging superposition, we propose an algorithm with a polynomial speedup in sampling disorder configurations, a longstanding challenge in many-body localization studies. △ Less

Submitted 6 July, 2025; v1 submitted 9 October, 2024; originally announced October 2024.

Fermionic tensor network contraction for arbitrary geometries

Authors: Yang Gao, Huanchen Zhai, Johnnie Gray, Ruojing Peng, Gunhee Park, Wen-Yuan Liu, Eirik F. Kjønstad, Garnet Kin-Lic Chan

Abstract: We describe our implementation of fermionic tensor network contraction on arbitrary lattices within both a globally ordered and locally ordered formalism. We provide a pedagogical description of these two conventions as implemented for the quimb library. Using hyperoptimized approximate contraction strategies, we present benchmark fermionic projected entangled pair states simulations of finite Hub… ▽ More We describe our implementation of fermionic tensor network contraction on arbitrary lattices within both a globally ordered and locally ordered formalism. We provide a pedagogical description of these two conventions as implemented for the quimb library. Using hyperoptimized approximate contraction strategies, we present benchmark fermionic projected entangled pair states simulations of finite Hubbard models defined on the three-dimensional diamond lattice and random regular graphs. △ Less

Submitted 24 October, 2025; v1 submitted 3 October, 2024; originally announced October 2024.

Comments: 9 pages, 9 figures

Journal ref: Phys. Rev. Research 7, 023193 (2025)

Squeezing atomic $p$-orbital condensates for detecting gravitational waves

Authors: Xinyang Yu, W. Vincent Liu, Xiaopeng Li

Abstract: Detecting the faint signal of continuous gravitational waves (CWs) stands as a major frontier in gravitational-wave astronomy, pushing the need for detectors whose sensitivity exceeds the standard quantum limit (SQL). Here, we propose an orbital optomechanical (OOM) sensor that exploits the sensitive coupling of an orbitally squeezed $p$-orbital Bose-Einstein condensate to spacetime distortions, e… ▽ More Detecting the faint signal of continuous gravitational waves (CWs) stands as a major frontier in gravitational-wave astronomy, pushing the need for detectors whose sensitivity exceeds the standard quantum limit (SQL). Here, we propose an orbital optomechanical (OOM) sensor that exploits the sensitive coupling of an orbitally squeezed $p$-orbital Bose-Einstein condensate to spacetime distortions, enabling the detection of interferometer phase shifts induced by CWs. This sensor achieves a theoretical quantum-noise-limited sensitivity 16 dB below the SQL while reducing the required laser power by five orders of magnitude. The performance arises from a novel noise trade-off: a counter-propagating readout scheme suppresses photonic shot noise, while orbital squeezing minimizes the remaining atomic projection noise. By leveraging quantum control over atomic orbital degrees of freedom, this approach establishes a new framework for interferometric sensing with direct applications to the search for CWs and ultralight dark matter. △ Less

Submitted 15 September, 2025; v1 submitted 1 October, 2024; originally announced October 2024.

Comments: 4.5+77 pages, 4+21 figures, 0+3 tables

Exotic localization for the bound states in the non-reciprocal two-particle Hubbard model

Authors: Huan-Yu Wang, Ji Li, Wu-Ming Liu, Lin Wen, Xiao-Fei Zhang

Abstract: We investigate the localization behavior of two-particle Hubbard model in the presence of non-reciprocal tunneling and non-Hermitian bound states can be obtained with strong repulsive interaction. Remarkably, the interaction induced bound state localization (BSL) can compete with non-Hermitian skin effect (NHSE) and give rise to diverse density profiles. Via the quantum scattering methods in the c… ▽ More We investigate the localization behavior of two-particle Hubbard model in the presence of non-reciprocal tunneling and non-Hermitian bound states can be obtained with strong repulsive interaction. Remarkably, the interaction induced bound state localization (BSL) can compete with non-Hermitian skin effect (NHSE) and give rise to diverse density profiles. Via the quantum scattering methods in the center of mass frame, the system can be mapped to an effective two dimensional (2D) lattice with the two-particle interaction contributing to a defective line. For the bound states of the largest eigen-energy, in contrast to the Hermitian cases, where the maximal localization center is pinned around the center of lattice, NHSE can lead to a faded diagonal line localization. For the unbound scattering states, unlike the single corner localization in the 2D Hatano-Nelson model, interaction can force the total localization to split into multiple centers. To make the system topological nontrivial, we further include terms taking the form of two-photon tunneling and the non-Hermitian photon bound pairs are also observed, which demonstrates a competition among NHSE, BSL and edge localization. Finally, we propose the experimental simulations via the platforms of electrical circuits. Our works shed light on the crossover study of quantum optics and non-Hermitian many body physics. △ Less

Submitted 7 February, 2025; v1 submitted 12 September, 2024; originally announced September 2024.

Demonstrating two-particle interference with a one-dimensional delta potential well

Authors: Zhi Jiao Deng, Xin Zhang, Yong Shen, Wei Tao Liu, Ping Xing Chen

Abstract: In quantum mechanics, the exchange symmetry of wave functions for identical particles has observable effects, including the widely studied Hong-Ou-Mandel (HOM) effect. A theoretical description using second quantization is elegant but abstract. In contrast, this paper describes a simple model of two-particle interference using a one-dimensional delta potential well as a beam splitter. The conditio… ▽ More In quantum mechanics, the exchange symmetry of wave functions for identical particles has observable effects, including the widely studied Hong-Ou-Mandel (HOM) effect. A theoretical description using second quantization is elegant but abstract. In contrast, this paper describes a simple model of two-particle interference using a one-dimensional delta potential well as a beam splitter. The conditions for the HOM effect are derived from the perspective of wave packet evolution. Furthermore, the interference processes of bosons, fermions and distinguishable particles are demonstrated and compared in detail. The method presented here is concrete, easy to visualize, and can help students to better understand the effects arising from the exchange symmetry of wave functions. The main results can be animated for classroom teaching or developed into an undergraduate seminar topic. △ Less

Submitted 28 August, 2024; originally announced August 2024.

Quantum error correction below the surface code threshold

Authors: Rajeev Acharya, Laleh Aghababaie-Beni, Igor Aleiner, Trond I. Andersen, Markus Ansmann, Frank Arute, Kunal Arya, Abraham Asfaw, Nikita Astrakhantsev, Juan Atalaya, Ryan Babbush, Dave Bacon, Brian Ballard, Joseph C. Bardin, Johannes Bausch, Andreas Bengtsson, Alexander Bilmes, Sam Blackwell, Sergio Boixo, Gina Bortoli, Alexandre Bourassa, Jenna Bovaird, Leon Brill, Michael Broughton, David A. Browne , et al. (224 additional authors not shown)

Abstract: Quantum error correction provides a path to reach practical quantum computing by combining multiple physical qubits into a logical qubit, where the logical error rate is suppressed exponentially as more qubits are added. However, this exponential suppression only occurs if the physical error rate is below a critical threshold. In this work, we present two surface code memories operating below this… ▽ More Quantum error correction provides a path to reach practical quantum computing by combining multiple physical qubits into a logical qubit, where the logical error rate is suppressed exponentially as more qubits are added. However, this exponential suppression only occurs if the physical error rate is below a critical threshold. In this work, we present two surface code memories operating below this threshold: a distance-7 code and a distance-5 code integrated with a real-time decoder. The logical error rate of our larger quantum memory is suppressed by a factor of $Λ$ = 2.14 $\pm$ 0.02 when increasing the code distance by two, culminating in a 101-qubit distance-7 code with 0.143% $\pm$ 0.003% error per cycle of error correction. This logical memory is also beyond break-even, exceeding its best physical qubit's lifetime by a factor of 2.4 $\pm$ 0.3. We maintain below-threshold performance when decoding in real time, achieving an average decoder latency of 63 $μ$s at distance-5 up to a million cycles, with a cycle time of 1.1 $μ$s. To probe the limits of our error-correction performance, we run repetition codes up to distance-29 and find that logical performance is limited by rare correlated error events occurring approximately once every hour, or 3 $\times$ 10$^9$ cycles. Our results present device performance that, if scaled, could realize the operational requirements of large scale fault-tolerant quantum algorithms. △ Less

Submitted 24 August, 2024; originally announced August 2024.

Comments: 10 pages, 4 figures, Supplementary Information

Journal ref: Nature 638 (2025) 920-926