Showing 1–50 of 596 results for author: Li, H

Dissipative quantum algorithms for excited-state quantum chemistry

Authors: Hao-En Li, Lin Lin

Abstract: Electronic excited states are central to a vast array of physical and chemical phenomena, yet accurate and efficient methods for preparing them on quantum devices remain challenging and comparatively underexplored. We introduce a general dissipative algorithm for selectively preparing ab initio electronic excited states. The key idea is to recast excited-state preparation as an effective ground-st… ▽ More Electronic excited states are central to a vast array of physical and chemical phenomena, yet accurate and efficient methods for preparing them on quantum devices remain challenging and comparatively underexplored. We introduce a general dissipative algorithm for selectively preparing ab initio electronic excited states. The key idea is to recast excited-state preparation as an effective ground-state problem by suitably modifying the underlying Lindblad dynamics so that the target excited state becomes the unique steady state of a designed quantum channel. We develop three complementary strategies, tailored to different types of prior information about the excited state, such as symmetry and approximate energy. We demonstrate the effectiveness and versatility of these schemes through numerical simulations of atomic and molecular spectra, including valence excitations in prototypical planar conjugated molecules and transition-metal complexes. Taken together, these results provide a new pathway for advancing quantum simulation methods for realistic strongly correlated electronic systems. △ Less

Submitted 22 December, 2025; originally announced December 2025.

Comments: 28 pages, 11 figures

Nonstabilizerness in Stark many-body localization

Authors: Han-Ze Li, Yi-Rui Zhang, Yu-Jun Zhao, Xuyang Huang, Jian-Xin Zhong

Abstract: Quantum many-body disorder-free localization can suppress transport while still allowing the buildup of computationally costly non-Clifford resources. In a transverse-field Ising chain realizing disorder-free Stark many-body localization, we show that the stabilizer Rényi entropy remains nonzero and grows slowly to a finite plateau deep in the strong Stark-field regime, with strong initial-state s… ▽ More Quantum many-body disorder-free localization can suppress transport while still allowing the buildup of computationally costly non-Clifford resources. In a transverse-field Ising chain realizing disorder-free Stark many-body localization, we show that the stabilizer Rényi entropy remains nonzero and grows slowly to a finite plateau deep in the strong Stark-field regime, with strong initial-state selectivity. As the Stark field strength increases, long-time magic and entanglement consistently signal a crossover from ergodic to constrained localized dynamics. These results establish nonstabilizerness (``magic'') as a practical complexity probe for disorder-free ergodicity breaking and constrained localization, with direct relevance to benchmarking and designing near-term quantum simulators, and fill a gap in the understanding of nonstabilizerness in disorder-free many-body localization. △ Less

Submitted 18 December, 2025; originally announced December 2025.

Characterizing entanglement shareability and distribution in $N$-partite systems

Authors: Hui Li, Ting Gao, Fengli Yan

Abstract: Exploring the shareability and distribution of entanglement possesses fundamental significance in quantum information tasks. In this paper, we demonstrate that the square of bipartite entanglement measures $G_q$-concurrence, which is the generalization of concurrence, follows a set of hierarchical monogamy relations for any $N$-qubit quantum state. On the basis of these monogamy inequalities, we r… ▽ More Exploring the shareability and distribution of entanglement possesses fundamental significance in quantum information tasks. In this paper, we demonstrate that the square of bipartite entanglement measures $G_q$-concurrence, which is the generalization of concurrence, follows a set of hierarchical monogamy relations for any $N$-qubit quantum state. On the basis of these monogamy inequalities, we render two kinds of hierarchical indicators that exhibit evident advantages in the capacity of witnessing entanglement. Moreover, we show an analytical relation between $G_q$-concurrence and concurrence in $2\otimes d$ systems. Furthermore, we rigorously prove that the monogamy property of squared $G_q$-concurrence is superior to that of squared concurrence in $2\otimes d_2\otimes d_3\otimes\cdots\otimes d_N$ systems. In addition, several concrete examples are provided to illustrate that for multilevel systems, the squared $G_q$-concurrence satisfies the monogamy relation, even if the squared concurrence does not. These results better reveal the intriguing characteristic of multilevel entanglement and provide critical insights into the entanglement distribution within multipartite quantum systems. △ Less

Submitted 16 December, 2025; originally announced December 2025.

Comments: 9 pages

Generation of mechanical cat-like states via optomagnomechanics

Authors: Hao-Tian Li, Hong-Bin Wang, Zi-Xu Lu, Jie Li

Abstract: We propose an optomagnomechanical approach for preparing a cat-like superposition state of mechanical motion. Our protocol consists of two steps and is based on the magnomechanical system where the magnetostrictively induced displacement further couples to an optical cavity mode via radiation pressure. We first prepare a squeezed mechanical state by driving the magnomechanical system with a two-to… ▽ More We propose an optomagnomechanical approach for preparing a cat-like superposition state of mechanical motion. Our protocol consists of two steps and is based on the magnomechanical system where the magnetostrictively induced displacement further couples to an optical cavity mode via radiation pressure. We first prepare a squeezed mechanical state by driving the magnomechanical system with a two-tone microwave field. We then switch off the microwave drives and send a weak red-detuned optical pulse to the optical cavity to weakly activate the optomechanical anti-Stokes scattering. We show that $k$ phonons can be subtracted from the prepared squeezed state, conditioned on the detection of $k$ anti-Stokes photons from the cavity output field, which prepares the mechanical motion in a cat-like state. The work provides a new avenue for preparing mechanical superposition states by combining opto- and magnomechanics and may find applications in the study of macroscopic quantum states and the test of collapse theories. △ Less

Submitted 11 December, 2025; originally announced December 2025.

Comments: Invited contribution to Quantum Review Letters

Entropic Uncertainty Relations with Quantum Memory in Accelerated Frames via Unruh-DeWitt Detectors

Authors: Ming-Ming Du, Hong-Wei Li, Shu-Ting Shen, Xiao-Jing Yan, Xi-Yun Li, Lan Zhou, Wei Zhong, Yu-Bo Sheng

Abstract: Quantum uncertainty is deeply linked to quantum correlations and relativistic motion. The entropic uncertainty relation with quantum memory offers a powerful way to study how shared entanglement affects measurement precision. However, under acceleration, the Unruh effect can degrade quantum correlations, raising questions about the reliability of QMA-EUR in such settings. Here, we investigate the… ▽ More Quantum uncertainty is deeply linked to quantum correlations and relativistic motion. The entropic uncertainty relation with quantum memory offers a powerful way to study how shared entanglement affects measurement precision. However, under acceleration, the Unruh effect can degrade quantum correlations, raising questions about the reliability of QMA-EUR in such settings. Here, we investigate the QMA-EUR for two uniformly accelerating Unruh-DeWitt detectors coupled to a massless scalar field. Using the Kossakowski-Lindblad master equation, we calculate the entropic uncertainty, its lower bound, and the tightness of the relation under different Unruh temperatures. We find that acceleration does not always increase the lower bound on the uncertainty relation. Depending on the initial correlations between the detectors, it may either increase or decrease. This behavior results from the interplay between quantum discord and minimal missing information. Interestingly, a higher quantum discord does not necessarily lead to lower uncertainty. △ Less

Submitted 10 December, 2025; originally announced December 2025.

Comments: 7 pages, 2 figures, Accepted for publication in Physical Review D (2025)

Quantum Mpemba effect in long-ranged U(1)-symmetric random circuits

Authors: Han-Ze Li, Ching Hua Lee, Shuo Liu, Shi-Xin Zhang, Jian-Xin Zhong

Abstract: The Mpemba effect, where a state prepared farther from equilibrium relaxes faster to equilibrium than one prepared closer, has a quantum counterpart where relaxation is resolved by conserved charge. However, the fate of the quantum Mpemba effect in systems with long-range interactions remains an open question. Here, we study the quantum Mpemba effect in long-ranged, U(1)-symmetric random unitary c… ▽ More The Mpemba effect, where a state prepared farther from equilibrium relaxes faster to equilibrium than one prepared closer, has a quantum counterpart where relaxation is resolved by conserved charge. However, the fate of the quantum Mpemba effect in systems with long-range interactions remains an open question. Here, we study the quantum Mpemba effect in long-ranged, U(1)-symmetric random unitary circuits. Using annealed Rényi-2 entanglement asymmetry computed via replica tensor networks and exact diagonalization, we track the symmetry restoration from three types of tilted product states: ferromagnetic, antiferromagnetic, and ferromagnetic with a central domain wall. The quantum Mpemba effect is present for tilted ferromagnetic states at all interaction ranges, but absent for tilted antiferromagnetic states, and occurs for the domain-wall state only in effectively short-ranged circuits, where the Mpemba time $t_{\rm M}$ is found to scale with the subsystem size $N_A$ as $t_{\rm M}\!\sim\!N_{A}^{\,z}$, with the dynamical exponent $z=\min(α-1,2)$. These results reveal how the quantum Mpemba effect is governed by the interplay between interaction range and initial-state charge bias in long-ranged chaotic systems. △ Less

Submitted 7 December, 2025; originally announced December 2025.

Fault-Tolerant Information Processing with Quantum Weak Measurement

Authors: Qi Song, Hongjing Li, Chengxi Yu, Jingzheng Huang, Ding Wang, Peng Huang, Guihua Zeng

Abstract: Noise is an important factor that influences the reliability of information acquisition, transmission, processing, and storage. In order to suppress the inevitable noise effects, a fault-tolerant information processing approach via quantum weak measurement is proposed, where pairwise orthogonal postselected measurement bases with various tiny angles and optimal compositions of measured results are… ▽ More Noise is an important factor that influences the reliability of information acquisition, transmission, processing, and storage. In order to suppress the inevitable noise effects, a fault-tolerant information processing approach via quantum weak measurement is proposed, where pairwise orthogonal postselected measurement bases with various tiny angles and optimal compositions of measured results are chosen as a decoding rule. The signal to be protected can be retrieved with a minimal distortion after having been transmitted through a noisy channel. Demonstrated by typical examples of encoding signal on two-level superposition state or Einstein-Podolsky-Rossen state transmitted through random telegraph noise and decoherence noises channel, the mean squared error distortion may be close to $0$ and the fault-tolerant capability could reach $1$ with finite quantum resources. To verify the availability of the proposed approach, classic coherent light and quantum coherent state are used for encoding information in the experiment. Potentially, the proposed approach may provide a solution for suppressing noise effects in long-distance quantum communication, high-sensitivity quantum sensing, and accurate quantum computation. △ Less

Submitted 6 December, 2025; originally announced December 2025.

Quantum machine learning for efficient reduced order modelling of turbulent flows

Authors: Han Li, Yutong Lou, Dunhui Xiao

Abstract: Accurately predicting turbulent flows remains a central challenge in fluid dynamics due to their high dimensionality and intrinsic nonlinearity. Recent developments in quantum algorithms and machine learning offer new opportunities for overcoming the computational barriers inherent in turbulence modeling. Here we present a new hybrid quantum-classical framework that enables faster-than-real-time t… ▽ More Accurately predicting turbulent flows remains a central challenge in fluid dynamics due to their high dimensionality and intrinsic nonlinearity. Recent developments in quantum algorithms and machine learning offer new opportunities for overcoming the computational barriers inherent in turbulence modeling. Here we present a new hybrid quantum-classical framework that enables faster-than-real-time turbulence prediction by integrating machine learning, quantum computation, and fluid dynamics modeling, in particular, the reduced-order modeling. The novel framework combines quantum proper orthogonal decomposition (QPOD) with a quantum-enhanced deep kernel learning (QDKL) approach. QPOD employs quantum circuits to perform efficient eigenvalue decomposition for low-rank flow reconstruction, while QDKL exploits quantum entanglement and nonlinear mappings to enhance kernel expressivity and dynamic prediction accuracy. The new method is demonstrated on three benchmark turbulent flows, our architecture achieves significantly improved predictive accuracy at reduced model ranks, with training speeds up to 10 times faster and parameter counts reduced by a factor of 1/N compared to classical counterparts, where N is the input dimensionality. Although constrained by current noisy intermediate-scale quantum (NISQ) hardware, our results demonstrate the potential of quantum machine learning to transform turbulence simulation and lay a solid foundation for scalable, real-time quantum fluid modeling in future quantum computers. △ Less

Submitted 23 November, 2025; originally announced November 2025.

Mutual Mana: Converting Local Magic into Correlations via Discrete Beamsplitters

Authors: Linshuai Zhang, Huihui Li

Abstract: Magic (non-stabilizerness) is a key resource for achieving universal fault-tolerant quantum computation beyond classical computation. While previous studies have primarily focused on magic in single systems, its interactions and distribution in multipartite settings remain largely unexplored. In this work, we introduce mutual mana as a measure of magic correlations defined in close analogy with qu… ▽ More Magic (non-stabilizerness) is a key resource for achieving universal fault-tolerant quantum computation beyond classical computation. While previous studies have primarily focused on magic in single systems, its interactions and distribution in multipartite settings remain largely unexplored. In this work, we introduce mutual mana as a measure of magic correlations defined in close analogy with quantum mutual information. Our definition builds upon mana, which is the established quantifier of magic based on discrete Wigner function negativity. We characterize magic correlations generated by discrete beamsplitters, whose Gaussian counterparts are fundamental components in quantum optics and quantum technologies. We show that coupling a magic state with a stabilizer vacuum state via a discrete beamsplitter will induce a full conversion of local magic into mutual mana, thereby establishing a mechanism for redistributing magic resources as magic correlations. We reveal the fundamental properties of mutual mana and derive its explicit expressions for several prototypical qutrit states subject to a discrete beamsplitter. We make a comparative study of mutual mana with several established quantifiers of correlations generated by the qutrit beamsplitter, including quantum mutual information, mutual $L^1$-norm magic, and mutual stabilizer 2-Rényi entropy. △ Less

Submitted 11 November, 2025; originally announced November 2025.

Comments: 16 pages,8 figures

Fock space prethermalization and time-crystalline order on a quantum processor

Authors: Zehang Bao, Zitian Zhu, Yang-Ren Liu, Zixuan Song, Feitong Jin, Xuhao Zhu, Yu Gao, Chuanyu Zhang, Ning Wang, Yiren Zou, Ziqi Tan, Aosai Zhang, Zhengyi Cui, Fanhao Shen, Jiarun Zhong, Yiyang He, Han Wang, Jia-Nan Yang, Yanzhe Wang, Jiayuan Shen, Gongyu Liu, Yihang Han, Yaozu Wu, Jinfeng Deng, Hang Dong , et al. (9 additional authors not shown)

Abstract: Periodically driven quantum many-body systems exhibit a wide variety of exotic nonequilibrium phenomena and provide a promising pathway for quantum applications. A fundamental challenge for stabilizing and harnessing these highly entangled states of matter is system heating by energy absorption from the drive. Here, we propose and demonstrate a disorder-free mechanism, dubbed Fock space prethermal… ▽ More Periodically driven quantum many-body systems exhibit a wide variety of exotic nonequilibrium phenomena and provide a promising pathway for quantum applications. A fundamental challenge for stabilizing and harnessing these highly entangled states of matter is system heating by energy absorption from the drive. Here, we propose and demonstrate a disorder-free mechanism, dubbed Fock space prethermalization (FSP), to suppress heating. This mechanism divides the Fock-space network into linearly many sparse sub-networks, thereby prolonging the thermalization timescale even for initial states at high energy densities. Using 72 superconducting qubits, we observe an FSP-based time-crystalline order that persists over 120 cycles for generic initial Fock states. The underlying kinetic constraint of approximately conserved domain wall (DW) numbers is identified by measuring site-resolved correlators. Further, we perform finite-size scaling analysis for DW and Fock-space dynamics by varying system sizes, which reveals size-independent regimes for FSP-thermalization crossover and links the dynamical behaviors to the eigenstructure of the Floquet unitary. Our work establishes FSP as a robust mechanism for breaking ergodicity, and paves the way for exploring novel nonequilibrium quantum matter and its applications. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Comments: 8 pages, 4 figures + supplementary information

Scalable protocol to coherence estimation from scarce data: Theory and experiment

Authors: Qi-Ming Ding, Ting Zhang, Hui Li, Da-Jian Zhang

Abstract: Key quantum features like coherence are the fundamental resources enabling quantum advantages and ascertaining their presence in quantum systems is crucial for developing quantum technologies. This task, however, faces severe challenges in the noisy intermediate-scale quantum era. On one hand, experimental data are typically scarce, rendering full state reconstruction infeasible. On the other hand… ▽ More Key quantum features like coherence are the fundamental resources enabling quantum advantages and ascertaining their presence in quantum systems is crucial for developing quantum technologies. This task, however, faces severe challenges in the noisy intermediate-scale quantum era. On one hand, experimental data are typically scarce, rendering full state reconstruction infeasible. On the other hand, these features are usually quantified by highly nonlinear functionals that elude efficient estimations via existing methods. In this work, we propose a scalable protocol for estimating coherence from scarce data and further experimentally demonstrate its practical utility. The key innovation here is to relax the potentially NP-hard coherence estimation problem into a computationally efficient optimization. This renders the computational cost in our protocol insensitive to the system size, in sharp contrast to the exponential growth in traditional methods. This work opens a novel route toward estimating coherence of large-scale quantum systems under data-scarce conditions. △ Less

Submitted 24 October, 2025; originally announced October 2025.

Comments: 10 pages, 6 figures

Fisher discord as a quantifier of quantum complexity

Authors: Huihui Li, Shunlong Luo, Yue Zhang

Abstract: Two classically equivalent expressions of mutual information of probability distributions (classical bipartite states) diverge when extended to quantum systems, and this difference has been employed to define quantum discord, a quantifier of quantum correlations beyond entanglement. Similarly, equivalent expressions of classical Fisher information of parameterized probability distributions diverge… ▽ More Two classically equivalent expressions of mutual information of probability distributions (classical bipartite states) diverge when extended to quantum systems, and this difference has been employed to define quantum discord, a quantifier of quantum correlations beyond entanglement. Similarly, equivalent expressions of classical Fisher information of parameterized probability distributions diverge when extended to quantum states, and this difference may be exploited to characterize the complex nature of quantum states. By complexity of quantum states, we mean some hybrid nature which intermingles the classical and quantum features. It is desirable to quantify complexity of quantum states from various perspectives. In this work, we pursue the idea of discord and introduce an information-theoretic quantifier of complexity for quantum states (relative to the Hamiltonian that drives the evolution of quantum systems) via the notion of Fisher discord, which is defined by the difference between two important versions of quantum Fisher information: the quantum Fisher information defined via the symmetric logarithmic derivatives and the Wigner-Yanase skew information defined via the square roots of quantum states. We reveal basic properties of the quantifier of complexity, and compare it with some other quantifiers of complexity. In particular, we show that equilibrium states (or stable states, which commute with the Hamiltonian of the quantum system) and all pure states exhibit zero complexity in this setting. As illustrations, we evaluate the complexity for various prototypical states in both discrete and continuous-variable quantum systems. △ Less

Submitted 17 October, 2025; originally announced October 2025.

Bayes or Heisenberg: Who(se) Rules?

Authors: Volker Tresp, Hang Li, Federico Harjes, Yunpu Ma

Abstract: Although quantum systems are generally described by quantum state vectors, we show that in certain cases their measurement processes can be reformulated as probabilistic equations expressed in terms of probabilistic state vectors. These probabilistic representations can, in turn, be approximated by the neural network dynamics of the Tensor Brain (TB) model. The Tensor Brain is a recently propose… ▽ More Although quantum systems are generally described by quantum state vectors, we show that in certain cases their measurement processes can be reformulated as probabilistic equations expressed in terms of probabilistic state vectors. These probabilistic representations can, in turn, be approximated by the neural network dynamics of the Tensor Brain (TB) model. The Tensor Brain is a recently proposed framework for modeling perception and memory in the brain, providing a biologically inspired mechanism for efficiently integrating generated symbolic representations into reasoning processes. △ Less

Submitted 23 October, 2025; v1 submitted 14 October, 2025; originally announced October 2025.

Basis-independent Coherence in Noninertial Frames

Authors: Ming-Ming Du Yi-Hao Fan, Hong-Wei Li, Shu-Ting Shen, Xiao-Jing Yan, Xi-Yun Li, Wei Zhong, Yu-Bo Sheng, Lan Zhou

Abstract: We investigate the behavior of basis-independent quantum coherence between two modes of a free Dirac field as observed by relatively accelerated observers. Our findings reveal three key results: (i) the basis-independent coherence between modes A and BI decreases with increasing acceleration but remains finite even in the limit of infinite acceleration; (ii) at zero acceleration, the coherence bet… ▽ More We investigate the behavior of basis-independent quantum coherence between two modes of a free Dirac field as observed by relatively accelerated observers. Our findings reveal three key results: (i) the basis-independent coherence between modes A and BI decreases with increasing acceleration but remains finite even in the limit of infinite acceleration; (ii) at zero acceleration, the coherence between modes $A$ and $B_II$ is nonzero contrasting with the behavior of basis-dependent coherence, which typically vanishes in this case; and (iii) the basis-independent coherence between modes BI and BII remains constant regardless of acceleration, exhibiting a freezing phenomenon. These results demonstrate the intrinsic robustness of basis-independent coherence under Unruh effects. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Comments: 4 pages, 1 figures

Journal ref: European Physical Journal C (2025)

Non-Hermitian many-body localization in asymmetric chains with long-range interaction

Authors: Wen Wang, Han-Ze Li, Jian-Xin Zhong

Abstract: Understanding the relationship between many-body localization and spectra in non-Hermitian many-body systems is crucial. In a one-dimensional clean, long-range interaction-induced non-Hermitian many-body localization system, we have discovered the coexistence of static and dynamic spectral real-complex phase transitions, along with many-body ergodic-localized phase transitions. The phase diagrams… ▽ More Understanding the relationship between many-body localization and spectra in non-Hermitian many-body systems is crucial. In a one-dimensional clean, long-range interaction-induced non-Hermitian many-body localization system, we have discovered the coexistence of static and dynamic spectral real-complex phase transitions, along with many-body ergodic-localized phase transitions. The phase diagrams of these two types of transitions show similar non-monotonic boundary trends but do not overlap, highlighting properties distinct from conventional disorder-induced non-Hermitian many-body localization. We also propose a potential experimental realization of this model in cold-atom systems. Our findings provide valuable insights for further understanding the relationship between non-Hermitian many-body localization and non-Hermitian spectra in long-range interacting systems. △ Less

Submitted 9 October, 2025; originally announced October 2025.

Comments: Any comments are welcome

A Quantum Walk-Enabled Blockchain with Weighted Quantum Voting Consensus

Authors: Chong-Qiang Ye, Heng-Ji Li, Jian Li, Xiao-Yu Chen

Abstract: Quantum blockchains provide inherent resilience against quantum adversaries and represent a promising alternative to classical blockchain systems in the quantum era. However, existing quantum blockchain architectures largely depend on entanglement to maintain inter-block connections, facing challenges in stability, consensus efficiency, and system verification. To address these issues, this work p… ▽ More Quantum blockchains provide inherent resilience against quantum adversaries and represent a promising alternative to classical blockchain systems in the quantum era. However, existing quantum blockchain architectures largely depend on entanglement to maintain inter-block connections, facing challenges in stability, consensus efficiency, and system verification. To address these issues, this work proposes a novel quantum blockchain framework based on quantum walks, which reduces reliance on entanglement while improving stability and connection efficiency. We further propose a quantum consensus mechanism based on a weighted quantum voting protocol, which enables a fairer voting process while reflecting the weights of different nodes. To validate the proposed framework, we conduct circuit simulations to evaluate the correctness and effectiveness of both the quantum walk-based block construction and the quantum voting consensus mechanism. Compared with existing entanglement-dependent approaches, our framework achieves stronger stability and enables simpler verification of block integrity, making it a practical candidate for quantum-era blockchain applications. △ Less

Submitted 12 October, 2025; v1 submitted 9 October, 2025; originally announced October 2025.

Comments: 13 pages, 10 figures

CLASS: A Controller-Centric Layout Synthesizer for Dynamic Quantum Circuits

Authors: Yu Chen, Yilun Zhao, Bing Li, He Li, Mengdi Wang, Yinhe Han, Ying Wang

Abstract: Layout Synthesis for Quantum Computing (LSQC) is a critical component of quantum design tools. Traditional LSQC studies primarily focus on optimizing for reduced circuit depth by adopting a device-centric design methodology. However, these approaches overlook the impact of classical processing and communication time, thereby being insufficient for Dynamic Quantum Circuits (DQC). To address this,… ▽ More Layout Synthesis for Quantum Computing (LSQC) is a critical component of quantum design tools. Traditional LSQC studies primarily focus on optimizing for reduced circuit depth by adopting a device-centric design methodology. However, these approaches overlook the impact of classical processing and communication time, thereby being insufficient for Dynamic Quantum Circuits (DQC). To address this, we introduce CLASS, a controller-centric layout synthesizer designed to reduce inter-controller communication latency in a distributed control system. It consists of a two-stage framework featuring a hypergraph-based modeling and a heuristic-based graph partitioning algorithm. Evaluations demonstrate that CLASS effectively reduces communication latency by up to 100% with only a 2.10% average increase in the number of additional operations. △ Less

Submitted 19 September, 2025; originally announced September 2025.

Combinatorial optimization enhanced by shallow quantum circuits with 104 superconducting qubits

Authors: Xuhao Zhu, Zuoheng Zou, Feitong Jin, Pavel Mosharev, Maolin Luo, Yaozu Wu, Jiachen Chen, Chuanyu Zhang, Yu Gao, Ning Wang, Yiren Zou, Aosai Zhang, Fanhao Shen, Zehang Bao, Zitian Zhu, Jiarun Zhong, Zhengyi Cui, Yihang Han, Yiyang He, Han Wang, Jia-Nan Yang, Yanzhe Wang, Jiayuan Shen, Gongyu Liu, Zixuan Song , et al. (9 additional authors not shown)

Abstract: A pivotal task for quantum computing is to speed up solving problems that are both classically intractable and practically valuable. Among these, combinatorial optimization problems have attracted tremendous attention due to their broad applicability and natural fitness to Ising Hamiltonians. Here we propose a quantum sampling strategy, based on which we design an algorithm for accelerating solvin… ▽ More A pivotal task for quantum computing is to speed up solving problems that are both classically intractable and practically valuable. Among these, combinatorial optimization problems have attracted tremendous attention due to their broad applicability and natural fitness to Ising Hamiltonians. Here we propose a quantum sampling strategy, based on which we design an algorithm for accelerating solving the ground states of Ising model, a class of NP-hard problems in combinatorial optimization. The algorithm employs a hybrid quantum-classical workflow, with a shallow-circuit quantum sampling subroutine dedicated to navigating the energy landscape. Using up to 104 superconducting qubits, we demonstrate that this algorithm outputs favorable solutions against even a highly-optimized classical simulated annealing (SA) algorithm. Furthermore, we illustrate the path toward quantum speedup based on the time-to-solution metric against SA running on a single-core CPU with just 100 qubits. Our results indicate a promising alternative to classical heuristics for combinatorial optimization, a paradigm where quantum advantage might become possible on near-term superconducting quantum processors with thousands of qubits and without the assistance of error correction. △ Less

Submitted 14 September, 2025; originally announced September 2025.

Entanglement phases and phase transitions in monitored free fermion system due to localizations

Authors: Yu-Jun Zhao, Xuyang Huang, Yi-Rui Zhang, Han-Ze Li, Jian-Xin Zhong

Abstract: In recent years, the presence of local potentials has significantly enriched and diversified the entanglement patterns in monitored free fermion systems. In our approach, we employ the stochastic Schrödinger equation to simulate a one-dimensional spinless fermion system under continuous measurement and local potentials. By averaging the steady-state entanglement entropy over many quantum trajector… ▽ More In recent years, the presence of local potentials has significantly enriched and diversified the entanglement patterns in monitored free fermion systems. In our approach, we employ the stochastic Schrödinger equation to simulate a one-dimensional spinless fermion system under continuous measurement and local potentials. By averaging the steady-state entanglement entropy over many quantum trajectories, we investigate its dependence on measurement and localization parameters. We used a phenomenological model to interpret the numerical results, and the results show that the introduction of local potentials does not destroy the universality class of the entanglement phase transition, and that the phase boundary is jointly characterized by the measurement process and the localization mechanism. This work offers a new perspective on the characterization of the entanglement phase boundary arising from the combined effects of measurement and localization, and provides criteria for detecting this novel phase transition in cold atom systems, trapped ions, and quantum dot arrays. △ Less

Submitted 15 September, 2025; v1 submitted 11 September, 2025; originally announced September 2025.

Comments: Any comments are welcome

Topology and criticality in non-Hermitian multimodal optical resonators through engineered losses

Authors: Elizabeth Louis Pereira, Hongwei Li, Andrea Blanco-Redondo, Jose L. Lado

Abstract: Non-Hermitian topological matter provides a platform for engineering phenomena that go beyond the capabilities of Hermitian systems, enabling the use of losses to engineer topological phenomena. Non-Hermitian models often rely on artificial platforms made of engineered lattices because controlling losses in natural compounds is challenging. Although typical models for non-Hermitian photonic matter… ▽ More Non-Hermitian topological matter provides a platform for engineering phenomena that go beyond the capabilities of Hermitian systems, enabling the use of losses to engineer topological phenomena. Non-Hermitian models often rely on artificial platforms made of engineered lattices because controlling losses in natural compounds is challenging. Although typical models for non-Hermitian photonic matter are often single mode, photonic systems are often multimodal, producing mixing between different normal modes in each site. In this work, we explore a generalized family of multimodal non-Hermitian lattices, featuring multiple resonant modes. We show that these multimodal models are capable of featuring topological modes and criticality, similar to the artificial single-mode models often considered. We analyze the robustness of these non-Hermitian topological modes to fluctuation of local losses, disorder, and artificial gauge field. We show that these effects can be captured via both a full microscopic model and effective multiorbital models. Specifically, we show that due to their multiorbital nature, the localization properties of non-Hermitian multiorbital models can be controlled by an external gauge field. Our results demonstrate that internal orbital degrees of freedom provide a promising strategy to engineer controllable non-Hermitian topology and criticality. △ Less

Submitted 5 September, 2025; originally announced September 2025.

Optimizing digital quantum simulation of open quantum lattice models

Authors: Xie-Hang Yu, Hongchao Li, J. Ignacio Cirac, Rahul Trivedi

Abstract: Many-body systems arising in condensed matter physics and quantum optics inevitably couple to the environment and need to be modelled as open quantum systems. While near-optimal algorithms have been developed for simulating many-body quantum dynamics, algorithms for their open system counterparts remain less well investigated. We address the problem of simulating geometrically local many-body open… ▽ More Many-body systems arising in condensed matter physics and quantum optics inevitably couple to the environment and need to be modelled as open quantum systems. While near-optimal algorithms have been developed for simulating many-body quantum dynamics, algorithms for their open system counterparts remain less well investigated. We address the problem of simulating geometrically local many-body open quantum systems interacting with a stationary Gaussian environment. Under a smoothness assumption on the system-environment interaction, we develop near-optimal algorithms that, for a model with $N$ spins and evolution time $t$, attain a simulation error $δ$ in the system-state with $\mathcal{O}(Nt(Nt/δ)^{o(1)})$ gates, $\mathcal{O}(t(Nt/δ)^{o(1)})$ parallelized circuit depth and $\tilde{\mathcal{O}}(N(Nt/δ)^{o(1)})$ ancillas. We additionally show that, if only simulating local observables is of interest, then the circuit depth of the digital algorithm can be chosen to be independent of the system size $N$. This provides theoretical evidence for the utility of these algorithms for simulating physically relevant models, where typically local observables are of interest, on pre-fault tolerant devices. Finally, for the limiting case of Markovian dynamics with commuting jump operators, we propose two algorithms based on sampling a Wiener process and on a locally dilated Hamiltonian construction, respectively. These algorithms reduce the asymptotic gate complexity on $N$ compared to currently available algorithms in terms of the required number of geometrically local gates. △ Less

Submitted 7 September, 2025; v1 submitted 2 September, 2025; originally announced September 2025.

Comments: 61 pages, 6 figures

Observing Two-Particle Correlation Dynamics in Tunable Superconducting Bose-Hubbard Simulators

Authors: Z. T. Wang, Si-Yun Zhou, Yun-Hao Shi, Kaixuan Huang, Z. H. Yang, Jingning Zhang, Kui Zhao, Yueshan Xu, Hao Li, S. K. Zhao, Yulong Feng, Guangming Xue, Yu Liu, Wei-Guo Ma, Cai-Ping Fang, Hao-Tian Liu, Yong-Yi Wang, Kai Xu, Haifeng Yu, Heng Fan, S. P. Zhao

Abstract: The generation and propagation of quantum correlations are central to understanding many dynamical properties of quantum systems, yet their precise experimental control and characterization remain a key challenge. Here we experimentally study the two-particle correlation dynamics via quantum walks in superconducting Bose-Hubbard qutrit arrays, with tunable on-site interaction $U$ realized by Floqu… ▽ More The generation and propagation of quantum correlations are central to understanding many dynamical properties of quantum systems, yet their precise experimental control and characterization remain a key challenge. Here we experimentally study the two-particle correlation dynamics via quantum walks in superconducting Bose-Hubbard qutrit arrays, with tunable on-site interaction $U$ realized by Floquet engineering. Quantum walks show the characteristic change from bosonic bunching to fermionic antibunching with increasing $U$. The two-particle entanglement and quantum correlation dynamics, as measured by negativity and quantum discord, are investigated. We find that depending on the initial state, the propagation of entanglement can be strongly suppressed with increasing $U$, while that of quantum discord exhibits considerably larger amplitude; or both of them appear insensitive to $U$. Furthermore, the forms of entanglement are found to persist throughout particle walks for $U =$ 0 and it is generally not the case when $U$ increases. Our work highlights the role of interaction in shaping quantum dynamics and extends the realm of simulating correlated quantum systems with superconducting circuits. △ Less

Submitted 2 September, 2025; originally announced September 2025.

Observation of Inelastic Meson Scattering in a Floquet System using a Digital Quantum Simulator

Authors: Ziting Wang, Zi-Yong Ge, Yun-Hao Shi, Zheng-An Wang, Si-Yun Zhou, Hao Li, Kui Zhao, Yue-Shan Xu, Wei-Guo Ma, Hao-Tian Liu, Cai-Ping Fang, Jia-Cheng Song, Tian-Ming Li, Jia-Chi Zhang, Yu Liu, Cheng-Lin Deng, Guangming Xue, Haifeng Yu, Kai Xu, Kaixuan Huang, Franco Nori, Heng Fan

Abstract: Lattice gauge theories provide a non-perturbative framework for understanding confinement and hadronic physics, but their real-time dynamics remain challenging for classical computations. However, quantum simulators offer a promising alternative for exploring such dynamics beyond classical capabilities. Here, we experimentally investigate meson scattering using a superconducting quantum processor.… ▽ More Lattice gauge theories provide a non-perturbative framework for understanding confinement and hadronic physics, but their real-time dynamics remain challenging for classical computations. However, quantum simulators offer a promising alternative for exploring such dynamics beyond classical capabilities. Here, we experimentally investigate meson scattering using a superconducting quantum processor. Employing a digital protocol, we realize a Floquet spin chain equivalent to a one-dimensional Floquet $\mathbb{Z}_2$ lattice gauge theory. We observe Bloch oscillations of single kinks and strong binding between adjacent kinks, signaling confinement and the formation of stable mesons in this Floquet system. Using full-system joint readout, we resolve meson populations by string length, enabling identification of meson scattering channels. Our results reveal the fragmentation of a long-string meson into multiple short-string mesons, which is also an experimental signature of string breaking. Moreover, we directly observe inelastic meson scattering, where two short-string mesons can merge into a longer one. Our results pave the way for studying interacting gauge particles and composite excitations on digital quantum simulators. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Comments: 7+3 pages, 4+2 figures

Photo-Thermally Tunable Photon-Pair Generation in Dielectric Metasurfaces

Authors: Omer Can Karaman, Hua Li, Elif Nur Dayi, Christophe Galland, Giulia Tagliabue

Abstract: Photon-pair sources based on spontaneous four-wave mixing (SFWM) in integrated photonics are often spectrally static. We demonstrate and model a fundamental thermo-optical mechanism that modulates photon-pair generation in amorphous silicon (a-Si) thin films and metasurfaces via SFWM. Femtosecond-pulsed excitation yields g2(0) higher than 400 in unpatterned a-Si, confirming high-purity nonclassica… ▽ More Photon-pair sources based on spontaneous four-wave mixing (SFWM) in integrated photonics are often spectrally static. We demonstrate and model a fundamental thermo-optical mechanism that modulates photon-pair generation in amorphous silicon (a-Si) thin films and metasurfaces via SFWM. Femtosecond-pulsed excitation yields g2(0) higher than 400 in unpatterned a-Si, confirming high-purity nonclassical emission. Resonant a-Si metasurfaces produce photon pairs at rates exceeding 3.8 kHz under 0.6 mW pump power through Mie-type modes. Pump absorption induces localized heating that redshifts resonances, altering modal overlap and SFWM efficiency, leading to deviations from the quadratic power scaling expected in the undepleted regime. Coupled electromagnetic and heat-transfer simulations quantitatively reproduce these trends. Polarization-resolved measurements show nearly isotropic nonlinear responses, with 3 times higher third-order susceptibility of a-Si compared to poly-Si. This work positions a-Si as a bright, CMOS-compatible quantum photonics platform and identifies thermo-optical detuning as a key mechanism that should be considered-and potentially harnessed-in integrated photon-pair sources. △ Less

Submitted 26 August, 2025; originally announced August 2025.

Non-Equilibrium Criticality-Enhanced Quantum Sensing with Superconducting Qubits

Authors: Hao Li, Yaoling Yang, Yun-Hao Shi, Zheng-An Wang, Ziting Wang, Jintao Li, Yipeng Zhang, Kui Zhao, Yue-Shan Xu, Cheng-Lin Deng, Yu Liu, Wei-Guo Ma, Tian-Ming Li, Jia-Chi Zhang, Cai-Ping Fang, Jia-Cheng Song, Hao-Tian Liu, Si-Yun Zhou, Zheng-He Liu, Bing-Jie Chen, Gui-Han Liang, Xiaohui Song, Zhongcheng Xiang, Kai Xu, Kaixuan Huang , et al. (2 additional authors not shown)

Abstract: Exploiting quantum features allows for estimating external parameters with precisions well beyond the capacity of classical sensors, a phenomenon known as quantum-enhanced precision. Quantum criticality has been identified as a resource for achieving such enhancements with respect to the probe size. However, they demand complex probe preparation and measurement and the achievable enhancement is ul… ▽ More Exploiting quantum features allows for estimating external parameters with precisions well beyond the capacity of classical sensors, a phenomenon known as quantum-enhanced precision. Quantum criticality has been identified as a resource for achieving such enhancements with respect to the probe size. However, they demand complex probe preparation and measurement and the achievable enhancement is ultimately restricted to narrow parameter regimes. On the other hand, non-equilibrium probes harness dynamics, enabling quantum-enhanced precision with respect to time over a wide range of parameters through simple probe initialization. Here, we unify these approaches through a Stark-Wannier localization platform, where competition between a linear gradient field and particle tunneling enables quantum-enhanced sensitivity across an extended parameter regime. The probe is implemented on a 9-qubit superconducting quantum device, in both single- and double-excitation subspaces, where we explore its performance in the extended phase, the critical point and the localized phase. Despite employing only computational-basis measurements we have been able to achieve near-Heisenberg-limited precision by combining outcomes at distinct evolution times. In addition, we demonstrate that the performance of the probe in the entire extended phase is significantly outperforming the performance in the localized regime. Our results highlight Stark-Wannier systems as versatile platforms for quantum sensing, where the combination of criticality and non-equilibrium dynamics enhances precision over a wide range of parameters without stringent measurement requirements. △ Less

Submitted 20 August, 2025; originally announced August 2025.

Comments: 22 pages, 15 figures, 1 table

Generation of a CW anti-bunched photon field from a thin-film PPLN waveguide by two-photon interference with a weak coherent state

Authors: Yue Li, Haochuan Li, Yuhang Lei, Xiaoting Li, Jianmin Wang, Xuan Tang, Mu Ku Chen, E. Y. B. Pun, Cheng Wang, Z. Y. Ou

Abstract: An anti-bunched photon field is produced from a thin-film ppln waveguide by mixing the on-chip two-photon state with a weak but matched coherent state. This is achieved by taking out the two-photon part of the coherent state via a destructive two-photon interference with the on-chip two-photon state. We achieve a photon rate of 100 kHz with a g2-value of 0.35. This anti-bunched light field will ha… ▽ More An anti-bunched photon field is produced from a thin-film ppln waveguide by mixing the on-chip two-photon state with a weak but matched coherent state. This is achieved by taking out the two-photon part of the coherent state via a destructive two-photon interference with the on-chip two-photon state. We achieve a photon rate of 100 kHz with a g2-value of 0.35. This anti-bunched light field will have applications in high-resolution quantum imaging such as long baseline quantum telescopy for enhancing the signal-to-noise ratio. △ Less

Submitted 13 August, 2025; originally announced August 2025.

Observation and Modulation of the Quantum Mpemba Effect on a Superconducting Quantum Processor

Authors: Yueshan Xu, Cai-Ping Fang, Bing-Jie Chen, Ming-Chuan Wang, Zi-Yong Ge, Yun-Hao Shi, Yu Liu, Cheng-Lin Deng, Kui Zhao, Zheng-He Liu, Tian-Ming Li, Hao Li, Ziting Wang, Gui-Han Liang, Da'er Feng, Xueyi Guo, Xu-Yang Gu, Yang He, Hao-Tian Liu, Zheng-Yang Mei, Yongxi Xiao, Yu Yan, Yi-Han Yu, Wei-Ping Yuan, Jia-Chi Zhang , et al. (11 additional authors not shown)

Abstract: In non-equilibrium quantum many-body systems, the quantum Mpemba effect (QME) emerges as a counterintuitive phenomenon: systems exhibiting greater initial symmetry breaking restore symmetry faster than those with less. While theoretical exploration of QME has surged, experimental studies on its multidimensional modulation remain limited. Here, we report the observation and control of QME using a s… ▽ More In non-equilibrium quantum many-body systems, the quantum Mpemba effect (QME) emerges as a counterintuitive phenomenon: systems exhibiting greater initial symmetry breaking restore symmetry faster than those with less. While theoretical exploration of QME has surged, experimental studies on its multidimensional modulation remain limited. Here, we report the observation and control of QME using a superconducting processor featuring a unique fully connected, tunable-coupling architecture that enables precise modulation from short- to long-range interactions. This platform allows independent manipulation of coupling regimes, on-site potentials, and initial states, elucidating their roles in QME. To quantify symmetry restoration, we employ entanglement asymmetry (EA) -- the relative entropy between a subsystem reduced density matrix and its symmetric projection -- as a sensitive probe of symmetry breaking. In strong short-range coupling regimes, EA crossovers during quenches from tilted Néel states confirm the presence of QME. In contrast, in intermediate coupling regimes, synchronized EA and entanglement entropy dynamics reveal the suppression of QME. Remarkably, QME reemerges with the introduction of on-site linear potentials or quenches from tilted ferromagnetic states, the latter proving robust against on-site disorder. Our study provides the first demonstration of flexible QME modulation on a superconducting platform with multiple controllable parameters, shedding light on quantum many-body non-equilibrium dynamics and opening avenues for quantum information applications. △ Less

Submitted 11 August, 2025; originally announced August 2025.

Magic Entropy in Hybrid Spin-Boson Systems

Authors: Samuel Crew, Ying-Lin Li, Heng-Hsi Li, Po-Yao Chang

Abstract: We introduce entropic measures to quantify non-classical resource in hybrid spin-boson systems. We discuss the stabilizer Rényi entropy in the framework of phase space quantisation and define an analogous hybrid magic entropy and a mutual magic entropy that capture the distribution of quantum magic across spin and bosonic subsystems. We use these entropic measures to demonstrate two key phenomena:… ▽ More We introduce entropic measures to quantify non-classical resource in hybrid spin-boson systems. We discuss the stabilizer Rényi entropy in the framework of phase space quantisation and define an analogous hybrid magic entropy and a mutual magic entropy that capture the distribution of quantum magic across spin and bosonic subsystems. We use these entropic measures to demonstrate two key phenomena: the detection of the superradiant phase transition in the Dicke model and the dynamics of magic in the Jaynes-Cummings model following a quench. We develop a Monte Carlo numerical scheme to enable practical computation in many-body examples. △ Less

Submitted 8 August, 2025; originally announced August 2025.

Comments: 15 pages, 3 figures

Long-distance free-space quantum key distribution with continuous variables

Authors: Tianxiang Zhan, Huasheng Li, Peng Huang, Haoze Chen, Jiaqi Han, Zijing Wu, Hao Fang, Hanwen Yin, Zehao Zhou, Huiting Fu, Feiyu Ji, Piao Tan, Yingming Zhou, Xueqin Jiang, Tao Wang, Jincai Wu, Cheng Ye, Yajun Miao, Wei Qi, Guihua Zeng

Abstract: Continuous-variable quantum key distribution (CVQKD) enables remote users to share high-rate and unconditionally secure secret keys while maintaining compatibility with classical optical communication networks and effective resistance against background noise. However, CVQKD experiments have only been demonstrated indoors or over short outdoor distances. Here, by developing channel-fluctuation-ind… ▽ More Continuous-variable quantum key distribution (CVQKD) enables remote users to share high-rate and unconditionally secure secret keys while maintaining compatibility with classical optical communication networks and effective resistance against background noise. However, CVQKD experiments have only been demonstrated indoors or over short outdoor distances. Here, by developing channel-fluctuation-independent high-precision manipulation of continuous-variable quantum states, high-accuracy quantum signal acquisition and processing, and high-efficiency free-space acquisition, tracking, and pointing technology, we overcome the excess noise due to atmospheric effects especially in daylight without extra wavelength conversion and spectral filtering, and demonstrate for the first time long-distance free-space quantum key distribution over 7-km inland and 9.6-km maritime atmospheric channels with Gaussian-modulated coherent states. This achieved distribution distance of secure quantum secret keys is well beyond the atmosphere's effective thickness, offering a promising alternative for realizing satellite-based quantum cryptography communication in daylight. Moreover, given that the CVQKD system is naturally compatible with existing ground fiber telecommunication networks, it marks an essential step for realizing integrated air-ground quantum access networks with cross-domain applications. △ Less

Submitted 29 July, 2025; originally announced July 2025.

Preselection-Free Fiber-Optic Weak Measurement Sensing Framework with High-sensitivity

Authors: Zifu Su, Weiqian Zhao, Wanshou Sun, Hexiang Li, Yafei Yu, Jindong Wang

Abstract: A preselection-free fiber-optic weak measurement sensing framework is proposed and experimentally verified in this paper. In view of the limitation that fiber-optic weak measurement require specific preselection, this scheme innovates theoretically and achieves high sensitivity sensing by optimizing the post-selection when single-mode optical fiber is used to generate random polarization state. Th… ▽ More A preselection-free fiber-optic weak measurement sensing framework is proposed and experimentally verified in this paper. In view of the limitation that fiber-optic weak measurement require specific preselection, this scheme innovates theoretically and achieves high sensitivity sensing by optimizing the post-selection when single-mode optical fiber is used to generate random polarization state. The experimental results show that the sensing performance is two to three orders of magnitude higher than that of traditional optical fiber sensing technology. △ Less

Submitted 24 July, 2025; originally announced July 2025.

Many-body delocalization with a two-dimensional 70-qubit superconducting quantum simulator

Authors: Tian-Ming Li, Zheng-Hang Sun, Yun-Hao Shi, Zhen-Ting Bao, Yong-Yi Wang, Jia-Chi Zhang, Yu Liu, Cheng-Lin Deng, Yi-Han Yu, Zheng-He Liu, Chi-Tong Chen, Li Li, Hao Li, Hao-Tian Liu, Si-Yun Zhou, Zhen-Yu Peng, Yan-Jun Liu, Ziting Wang, Yue-Shan Xu, Kui Zhao, Yang He, Da'er Feng, Jia-Cheng Song, Cai-Ping Fang, Junrui Deng , et al. (13 additional authors not shown)

Abstract: Quantum many-body systems with sufficiently strong disorder can exhibit a non-equilibrium phenomenon, known as the many-body localization (MBL), which is distinct from conventional thermalization. While the MBL regime has been extensively studied in one dimension, its existence in higher dimensions remains elusive, challenged by the avalanche instability. Here, using a 70-qubit two-dimensional (2D… ▽ More Quantum many-body systems with sufficiently strong disorder can exhibit a non-equilibrium phenomenon, known as the many-body localization (MBL), which is distinct from conventional thermalization. While the MBL regime has been extensively studied in one dimension, its existence in higher dimensions remains elusive, challenged by the avalanche instability. Here, using a 70-qubit two-dimensional (2D) superconducting quantum simulator, we experimentally explore the robustness of the MBL regime in controlled finite-size 2D systems. We observe that the decay of imbalance becomes more pronounced with increasing system sizes, scaling up from 21, 42 to 70 qubits, with a relatively large disorder strength, and for the first time, provide an evidence for the many-body delocalization in 2D disordered systems. Our experimental results are consistent with the avalanche theory that predicts the instability of MBL regime beyond one spatial dimension. This work establishes a scalable platform for probing high-dimensional non-equilibrium phases of matter and their finite-size effects using superconducting quantum circuits. △ Less

Submitted 22 July, 2025; originally announced July 2025.

Comments: main text: 7 pages, 3 figures; supplementary information: 19 pages, 17 figures

Enhancing Photon Indistinguishability of Spectrally Mismatched Single Photons by Cavity Floquet Engineering

Authors: J. W. Yu, X. Q. Zhou, Z. B. Ni, X. T. Cheng, Y. Zhao, H. H. Zhu, C. H. Li, F. Liu, C. Y. Jin

Abstract: We theoretically propose a scheme to enhance the photon indistinguishability of spectrally mismatched single photons via Floquet-engineered optical frequency combs (OFCs) in cavity quantum electrodynamic systems. By periodically modulating two distinct single-photon states under a modulation frequency which is exactly equal to the spectral mismatch of two cavity modes, a pair of single-photon freq… ▽ More We theoretically propose a scheme to enhance the photon indistinguishability of spectrally mismatched single photons via Floquet-engineered optical frequency combs (OFCs) in cavity quantum electrodynamic systems. By periodically modulating two distinct single-photon states under a modulation frequency which is exactly equal to the spectral mismatch of two cavity modes, a pair of single-photon frequency-comb (SPFC) states is prepared energy-conservatively based on full unitary operations. The two states show high indistinguishability with an ideal $g^{(2)}_\mathrm{HOM}(0)$ down to zero due to the superposition of intensity-matched single-photon states coherently distributed across the teeth of the combs. △ Less

Submitted 3 July, 2025; originally announced July 2025.

Architectural mechanisms of a universal fault-tolerant quantum computer

Authors: Dolev Bluvstein, Alexandra A. Geim, Sophie H. Li, Simon J. Evered, J. Pablo Bonilla Ataides, Gefen Baranes, Andi Gu, Tom Manovitz, Muqing Xu, Marcin Kalinowski, Shayan Majidy, Christian Kokail, Nishad Maskara, Elias C. Trapp, Luke M. Stewart, Simon Hollerith, Hengyun Zhou, Michael J. Gullans, Susanne F. Yelin, Markus Greiner, Vladan Vuletic, Madelyn Cain, Mikhail D. Lukin

Abstract: Quantum error correction (QEC) is believed to be essential for the realization of large-scale quantum computers. However, due to the complexity of operating on the encoded `logical' qubits, understanding the physical principles for building fault-tolerant quantum devices and combining them into efficient architectures is an outstanding scientific challenge. Here we utilize reconfigurable arrays of… ▽ More Quantum error correction (QEC) is believed to be essential for the realization of large-scale quantum computers. However, due to the complexity of operating on the encoded `logical' qubits, understanding the physical principles for building fault-tolerant quantum devices and combining them into efficient architectures is an outstanding scientific challenge. Here we utilize reconfigurable arrays of up to 448 neutral atoms to implement all key elements of a universal, fault-tolerant quantum processing architecture and experimentally explore their underlying working mechanisms. We first employ surface codes to study how repeated QEC suppresses errors, demonstrating 2.14(13)x below-threshold performance in a four-round characterization circuit by leveraging atom loss detection and machine learning decoding. We then investigate logical entanglement using transversal gates and lattice surgery, and extend it to universal logic through transversal teleportation with 3D [[15,1,3]] codes, enabling arbitrary-angle synthesis with logarithmic overhead. Finally, we develop mid-circuit qubit re-use, increasing experimental cycle rates by two orders of magnitude and enabling deep-circuit protocols with dozens of logical qubits and hundreds of logical teleportations with [[7,1,3]] and high-rate [[16,6,4]] codes while maintaining constant internal entropy. Our experiments reveal key principles for efficient architecture design, involving the interplay between quantum logic and entropy removal, judiciously using physical entanglement in logic gates and magic state generation, and leveraging teleportations for universality and physical qubit reset. These results establish foundations for scalable, universal error-corrected processing and its practical implementation with neutral atom systems. △ Less

Submitted 25 June, 2025; originally announced June 2025.

Comments: Main text + Methods. Ancillary files: 3 movies, error model, raw experimental commands

Continuous operation of a coherent 3,000-qubit system

Authors: Neng-Chun Chiu, Elias C. Trapp, Jinen Guo, Mohamed H. Abobeih, Luke M. Stewart, Simon Hollerith, Pavel Stroganov, Marcin Kalinowski, Alexandra A. Geim, Simon J. Evered, Sophie H. Li, Lisa M. Peters, Dolev Bluvstein, Tout T. Wang, Markus Greiner, Vladan Vuletić, Mikhail D. Lukin

Abstract: Neutral atoms are a promising platform for quantum science, enabling advances in areas ranging from quantum simulations and computation to metrology, atomic clocks and quantum networking. While atom losses typically limit these systems to a pulsed mode, continuous operation could significantly enhance cycle rates, remove bottlenecks in metrology, and enable deep-circuit quantum evolution through q… ▽ More Neutral atoms are a promising platform for quantum science, enabling advances in areas ranging from quantum simulations and computation to metrology, atomic clocks and quantum networking. While atom losses typically limit these systems to a pulsed mode, continuous operation could significantly enhance cycle rates, remove bottlenecks in metrology, and enable deep-circuit quantum evolution through quantum error correction. Here we demonstrate an experimental architecture for high-rate, continuous reloading and operation of a large-scale atom array system while realizing coherent storage and manipulation of quantum information. Our approach utilizes a series of two optical lattice conveyor belts to transport atom reservoirs into the science region, where atoms are repeatedly extracted into optical tweezers without affecting the coherence of qubits stored nearby. Using a reloading rate of 300,000 atoms in tweezers per second, we create over 30,000 initialized qubits per second, which we leverage to assemble and maintain an array of over 3,000 atoms for more than two hours. Furthermore, we demonstrate persistent refilling of the array with atomic qubits in either a spin-polarized or a coherent superposition state while preserving the quantum state of stored qubits. Our results pave the way for realization of large-scale continuously operated atomic clocks, sensors, and fault-tolerant quantum computers. △ Less

Submitted 25 June, 2025; originally announced June 2025.

Comments: Main text: 8 pages, 4 figures. Methods: 7 pages, 10 figures. Ancillary files: one supplementary movie and caption

Journal ref: Nature (2025)

Experimental realization of the bucket-brigade quantum random access memory

Authors: Fanhao Shen, Yujie Ji, Debin Xiang, Yanzhe Wang, Ke Wang, Chuanyu Zhang, Aosai Zhang, Yiren Zou, Yu Gao, Zhengyi Cui, Gongyu Liu, Jianan Yang, Yihang Han, Jinfeng Deng, Anbang Wang, Zhihong Zhang, Hekang Li, Qiujiang Guo, Pengfei Zhang, Chao Song, Liqiang Lu, Zhen Wang, Jianwei Yin

Abstract: Quantum random access memory (QRAM) enables efficient classical data access for quantum computers -- a prerequisite for many quantum algorithms to achieve quantum speedup. Despite various proposals, the experimental realization of QRAM remains largely unexplored. Here, we experimentally investigate the circuit-based bucket-brigade QRAM with a superconducting quantum processor. To facilitate the ex… ▽ More Quantum random access memory (QRAM) enables efficient classical data access for quantum computers -- a prerequisite for many quantum algorithms to achieve quantum speedup. Despite various proposals, the experimental realization of QRAM remains largely unexplored. Here, we experimentally investigate the circuit-based bucket-brigade QRAM with a superconducting quantum processor. To facilitate the experimental implementation, we introduce a hardware-efficient gate decomposition scheme for quantum routers, which effectively reduces the depth of the QRAM circuit by more than 30% compared to the conventional controlled-SWAP-based implementation. We further propose an error mitigation method to boost the QRAM query fidelity. With these techniques, we are able to experimentally implement the QRAM architectures with two and three layers, achieving query fidelities up to 0.800 $\pm$ 0.026 and 0.604$\pm$0.005, respectively. Additionally, we study the error propagation mechanism and the scalability of our QRAM implementation, providing experimental evidence for the noise resilience nature of the bucket-brigade QRAM architecture. Our results highlight the potential of superconducting quantum processors for realizing a scalable QRAM architecture. △ Less

Submitted 19 June, 2025; originally announced June 2025.

Comments: 10 pages, 5 figures + 13 pages, 7 figures

The impact of parameter spread of high-temperature superconducting Josephson junctions on the performance of quantum-based voltage standards

Authors: Guanghong Wen, Yi Zhu, Yingxiang Zheng, Shuhe Cui, Ji Wang, Yanyun Ren, Hao Li, Guofeng Zhang, Lixing You

Abstract: Quantum metrology based on Josephson junction array reproduces the most accurate desired voltage by far, therefore being introduced to provide voltage standards worldwide. In this work, we quantitatively analyzed the dependence of the first Shapiro step height of the junction array at 50 GHz on the parameter spread of 10,000 Josephson junctions by numerical simulation with resistively shunted junc… ▽ More Quantum metrology based on Josephson junction array reproduces the most accurate desired voltage by far, therefore being introduced to provide voltage standards worldwide. In this work, we quantitatively analyzed the dependence of the first Shapiro step height of the junction array at 50 GHz on the parameter spread of 10,000 Josephson junctions by numerical simulation with resistively shunted junction model. The results indicate an upper limit spread of the critical current and resistance of the Josephson junctions. Specifically, to keep the maximum first Shapiro step above 0.88 mA, the critical current standard deviation, $σ$, should not exceed 25%, and for it to stay above 0.6 mA, the resistance standard deviation should not exceed 1.5%. △ Less

Submitted 15 June, 2025; originally announced June 2025.

Cavity-Mediated Gas-Liquid Transition

Authors: Fan Zhang, Haowei Li, Wei Yi

Abstract: We study the gas-liquid transition in a binary Bose-Einstein condensate, where the two Zeeman-shifted hyperfine spin components are coupled by cavity-assisted Raman processes. Below a critical Zeeman field, the cavity becomes superradiant for an infinitesimally small pumping strength, where the enhanced superradiance is facilitated by the simultaneous formation of quantum droplet, a self-bound liq… ▽ More We study the gas-liquid transition in a binary Bose-Einstein condensate, where the two Zeeman-shifted hyperfine spin components are coupled by cavity-assisted Raman processes. Below a critical Zeeman field, the cavity becomes superradiant for an infinitesimally small pumping strength, where the enhanced superradiance is facilitated by the simultaneous formation of quantum droplet, a self-bound liquid phase stabilized by quantum fluctuations. Above the critical Zeeman field, the gas-liquid transition only takes place at a finite pumping strength after the system becomes superradiant. As the back action of the gas-liquid transition, the superradiant cavity field undergoes an abrupt jump at the first-order transition point. Furthermore, as a result of the fixed density ratio of the quantum droplet, the cavity field exhibits a linear scaling with the pumping strength in the liquid phase. These features serve as prominent signals for the cavity-mediated gas-liquid transition and coexistence, which derive from the interplay of Zeeman field, cavity-assisted spin mixing, and quantum fluctuations. △ Less

Submitted 22 June, 2025; v1 submitted 10 June, 2025; originally announced June 2025.

Experimental Detection of Dissipative Quantum Chaos

Authors: Kristian Wold, Zitian Zhu, Feitong Jin, Xuhao Zhu, Zehang Bao, Jiarun Zhong, Fanhao Shen, Pengfei Zhang, Hekang Li, Zhen Wang, Chao Song, Qiujiang Guo, Sergey Denisov, Lucas Sá, H. Wang, Pedro Ribeiro

Abstract: More than four decades of research on chaos in isolated quantum systems have led to the identification of universal signatures -- such as level repulsion and eigenstate thermalization -- that serve as cornerstones in our understanding of complex quantum dynamics. The emerging field of dissipative quantum chaos explores how these properties manifest in open quantum systems, where interactions with… ▽ More More than four decades of research on chaos in isolated quantum systems have led to the identification of universal signatures -- such as level repulsion and eigenstate thermalization -- that serve as cornerstones in our understanding of complex quantum dynamics. The emerging field of dissipative quantum chaos explores how these properties manifest in open quantum systems, where interactions with the environment play an essential role. We report the first experimental detection of dissipative quantum chaos and integrability by measuring the complex spacing ratios (CSRs) of open many-body quantum systems implemented on a high-fidelity superconducting quantum processor. Employing gradient-based tomography, we retrieve a ``donut-shaped'' CSR distribution for chaotic dissipative circuits, a hallmark of level repulsion in open quantum systems. For an integrable circuit, spectral correlations vanish, evidenced by a sharp peak at the origin in the CSR distribution. As we increase the depth of the integrable dissipative circuit, the CSR distribution undergoes an integrability-to-chaos crossover, demonstrating that intrinsic noise in the quantum processor is a dissipative chaotic process. Our results reveal the universal spectral features of dissipative many-body systems and establish present-day quantum computation platforms, which are predominantly used to run unitary simulations, as testbeds to explore dissipative many-body phenomena. △ Less

Submitted 4 June, 2025; originally announced June 2025.

Comments: 7 pages, 3 figures + Supplementary Information

Non-adiabatically driven quantum interference effects in the ultracold K + KRb $\longrightarrow$ Rb + K$_{2}$ chemical reaction

Authors: H. da Silva Jr., B. K. Kendrick, H. Li, S. Kotochigova, N. Balakrishnan

Abstract: The K + KRb $\longrightarrow$ Rb + K$_{2}$ chemical reaction is the first ultracold atom-diatom chemical reaction for which experimental results have been reported for temperatures below 1 $μ$K more than a decade ago. The reaction occurs through coupling with an excited electronic state that is accessible even in the ultracold limit. A previous quantum dynamics study, excluding non-adiabatic effec… ▽ More The K + KRb $\longrightarrow$ Rb + K$_{2}$ chemical reaction is the first ultracold atom-diatom chemical reaction for which experimental results have been reported for temperatures below 1 $μ$K more than a decade ago. The reaction occurs through coupling with an excited electronic state that is accessible even in the ultracold limit. A previous quantum dynamics study, excluding non-adiabatic effects, has reported a rate coefficient that is about 35\% below the experimental value. Here, we report the first non-adiabatic quantum dynamics study of this reaction and obtain rate coefficients in better agreement with experiments. Our results show that short-range dynamics mediated by coupling with the excited electronic state introduces quantum interference effects that influence both the state-to-state rate coefficients and the overall reaction rates. △ Less

Submitted 2 June, 2025; originally announced June 2025.

hqQUBO: A Hybrid-querying Quantum Optimization Model Validated with 16-qubits on an Ion Trap Quantum Computer for Life Science Applications

Authors: Rong Chen, Quan-Xin Mei, Wen-Ding Zhao, Lin Yao, Hao-Xiang Yang, Shun-Yao Zhang, Jiao Chen, Hong-Lin Li

Abstract: AlphaFold has achieved groundbreaking advancements in protein structure prediction, exerting profound influence across biology, medicine, and drug discovery. However, its reliance on multiple sequence alignment (MSA) is inherently time-consuming due to the NP-hard nature of constructing MSAs. Quantum computing emerges as a promising alternative, compared to classical computers, offering the potent… ▽ More AlphaFold has achieved groundbreaking advancements in protein structure prediction, exerting profound influence across biology, medicine, and drug discovery. However, its reliance on multiple sequence alignment (MSA) is inherently time-consuming due to the NP-hard nature of constructing MSAs. Quantum computing emerges as a promising alternative, compared to classical computers, offering the potentials for exponential speedup and improved accuracy on such complex optimization challenges. This work bridges the gap between quantum computing and MSA task efficiently and successfully, where we compared classical and quantum computational scaling as the number of qubits increases, and assessed the role of quantum entanglement in model performance. Furthermore, we proposed an innovative hybrid query encoding approach hyQUBO to avoid redundancy, and thereby the quantum resources significantly reduced to a scaling of $\mathcal{O}(NL)$. Additionally, coupling of VQE and the quenched CVaR scheme was utilized to enhance the robustness and convergence. The integration of multiple strategies facilitates the robust deployment of the quantum algorithm from idealized simulators (on CPU and GPU) to real-world, noisy quantum devices (HYQ-A37). To the best of our knowledge, our work represented the largest-scale implementation of digital simulation using up to 16 qubits on a trapped-ion quantum computer for life science problem, which achieved state of the art performance in both simulation and experimental results. Our work paves the way towards large-scale simulations of life science tasks on real quantum processors. △ Less

Submitted 2 June, 2025; originally announced June 2025.

Experimental demonstration of generalized quantum fluctuation theorems in the presence of coherence

Authors: Hui Li, Jie Xie, Hyukjoon Kwon, Yixin Zhao, M. S. Kim, Lijian Zhang

Abstract: Fluctuation theorems have elevated the second law of thermodynamics to a statistical realm by establishing a connection between time-forward and time-reversal probabilities, providing invaluable insight into nonequilibrium dynamics. While well established in classical systems, their quantum generalization, incorporating coherence and the diversity of quantum noise, remains open. We report the expe… ▽ More Fluctuation theorems have elevated the second law of thermodynamics to a statistical realm by establishing a connection between time-forward and time-reversal probabilities, providing invaluable insight into nonequilibrium dynamics. While well established in classical systems, their quantum generalization, incorporating coherence and the diversity of quantum noise, remains open. We report the experimental validation of a quantum fluctuation theorem (QFT) in a photonic system, applicable to general quantum processes with nonclassical characteristics, including quasi-probabilistic descriptions of entropy production and multiple time-reversal processes. Our experiment confirms that the ratio between the quasi-probabilities of the time-forward and any multiple time-reversal processes obeys a generalized Crooks QFT. Moreover, coherence induced by a quantum process leads to the imaginary components of quantum entropy production, governing the phase factor in the QFT. These findings underscore the fundamental symmetry between a general quantum process and its time reversal, providing an elementary toolkit to explore noisy quantum information processing. △ Less

Submitted 31 May, 2025; originally announced June 2025.

Journal ref: Sci. Adv. 11, eadq6014(2025)

Energy-Embedded Neural Solvers for One-Dimensional Quantum Systems

Authors: Yi-Qiang Wu, Xuan Liu, Hanlin Li, Fuqiang Wang

Abstract: Physics-informed neural networks (PINN) have been widely used in computational physics to solve partial differential equations (PDEs). In this study, we propose an energy-embedding-based physics-informed neural network method for solving the one-dimensional time-independent Schrödinger equation to obtain ground- and excited-state wave functions, as well as energy eigenvalues by incorporating an em… ▽ More Physics-informed neural networks (PINN) have been widely used in computational physics to solve partial differential equations (PDEs). In this study, we propose an energy-embedding-based physics-informed neural network method for solving the one-dimensional time-independent Schrödinger equation to obtain ground- and excited-state wave functions, as well as energy eigenvalues by incorporating an embedding layer to generate process-driven data. The method demonstrates high accuracy for several well-known potentials, such as the infinite potential well, harmonic oscillator potential, Woods-Saxon potential, and double-well potential. Further validation shows that the method also performs well in solving the radial Coulomb potential equation, showcasing its adaptability and extensibility. The proposed approach can be extended to solve other partial differential equations beyond the Schrödinger equation and holds promise for applications in high-dimensional quantum systems. △ Less

Submitted 30 May, 2025; originally announced May 2025.

Comments: 27 pages, 7figures

Bridging the classical and quantum regimes in a dissipative Ising chain

Authors: Zhenming Zhang, Haowei Li, Wei Yi

Abstract: We study the long-time dynamics of a dissipative Ising chain with varying quantum correlation. Invoking an ensemble-average formalism, and assuming spatial translation symmetry, we show that the dynamics can be described by a Lindblad master equation with an interpolated coherent Hamiltonian. In the classical limit, the interpolation Hamiltonian leads to a set of nonlinear equations of motion, whe… ▽ More We study the long-time dynamics of a dissipative Ising chain with varying quantum correlation. Invoking an ensemble-average formalism, and assuming spatial translation symmetry, we show that the dynamics can be described by a Lindblad master equation with an interpolated coherent Hamiltonian. In the classical limit, the interpolation Hamiltonian leads to a set of nonlinear equations of motion, where limit cycles can emerge in the long-time dynamics. In the quantum limit, by contrast, the system approaches a ferromagnetic steady state at long times. In between the two extremes, the discrete spatial translation symmetry can be spontaneously broken, as an antiferromagnetic steady state emerges, bridging the classical and quantum regimes. In particular, we illustrate how the classical limit-cycle behavior gradually disappears with the increase of quantum correlation. Since our model in the two extremes respectively applies to a dissipative Rydberg gas in the high- and zero-temperature limits, we expect it to provide a qualitatively correct description of dissipative Rydberg gases at interim temperatures, and shed light on the fate of limit cycles in a quantum open system. △ Less

Submitted 10 September, 2025; v1 submitted 29 May, 2025; originally announced May 2025.

Comments: 8 pages, 4 figures. Published in Phys. Rev. A

Journal ref: Phys. Rev. A 112, 033310 (2025)

Microwave Engineering of Tunable Spin Interactions with Superconducting Qubits

Authors: Kui Zhao, Ziting Wang, Yu Liu, Gui - Han Liang, Cai - Ping Fang, Yun - Hao Shi, Lv Zhang, Jia - Chi Zhang, Tian - Ming Li, Hao Li, Yueshan Xu, Wei - Guo Ma, Hao - Tian Liu, Jia - Cheng Song, Zhen - Ting Bao, Yong - Xi Xiao, Bing - Jie Chen, Cheng - Lin Deng, Zheng - He Liu, Yang He, Si - Yun Zhou, Xiaohui Song, Zhongcheng Xiang, Dongning Zheng, Kaixuan Huang , et al. (2 additional authors not shown)

Abstract: Quantum simulation has emerged as a powerful framework for investigating complex many - body phenomena. A key requirement for emulating these dynamics is the realization of fully controllable quantum systems enabling various spin interactions. Yet, quantum simulators remain constrained in the types of attainable interactions. Here we demonstrate experimental realization of multiple microwave - eng… ▽ More Quantum simulation has emerged as a powerful framework for investigating complex many - body phenomena. A key requirement for emulating these dynamics is the realization of fully controllable quantum systems enabling various spin interactions. Yet, quantum simulators remain constrained in the types of attainable interactions. Here we demonstrate experimental realization of multiple microwave - engineered spin interactions in superconducting quantum circuits. By precisely controlling the native XY interaction and microwave drives, we achieve tunable spin Hamiltonians including: (i) XYZ spin models with continuously adjustable parameters, (ii) transverse - field Ising systems, and (iii) Dzyaloshinskii - Moriya interacting systems. Our work expands the toolbox for analogue - digital quantum simulation, enabling exploration of a wide range of exotic quantum spin models. △ Less

Submitted 13 August, 2025; v1 submitted 22 May, 2025; originally announced May 2025.

Comments: 13 pages, 4 figures

Journal ref: Appl. Phys. Lett. 127, 064001 (2025)

Digital quantum simulation of squeezed states via enhanced bosonic encoding in a superconducting quantum processor

Authors: Hengyue Li, Yusheng Yang, Zhe-Hui Wang, Shuxin Xie, Zilong Zha, Hantao Sun, Jie Chen, Jian Sun, Shenggang Ying

Abstract: We present a fully digital approach for simulating single-mode squeezed states on a superconducting quantum processor using an enhanced bosonic encoding strategy. By mapping up to 2^{n} photonic Fock states onto n qubits, our framework leverages Gray-code-based encodings to reduce gate overhead compared to conventional one-hot or binary mappings. We further optimize resource usage by restricting t… ▽ More We present a fully digital approach for simulating single-mode squeezed states on a superconducting quantum processor using an enhanced bosonic encoding strategy. By mapping up to 2^{n} photonic Fock states onto n qubits, our framework leverages Gray-code-based encodings to reduce gate overhead compared to conventional one-hot or binary mappings. We further optimize resource usage by restricting the simulation on Fock states with even number of photons only, effectively doubling the range of photon numbers that can be represented for a given number of qubits. To overcome noise and finite coherence in current hardware, we employ a variational quantum simulation protocol, which adapts shallow, parameterized circuits through iterative optimization. Implemented on the Zuchongzhi-2 superconducting platform, our method demonstrates squeezed-state dynamics across a parameter sweep from vacuum state preparation (r=0) to squeezing levels exceeding the Fock space truncation limit (r>1.63). Experimental results, corroborated by quantum state tomography and Wigner-function analysis, confirm high-fidelity state preparation and demonstrate the potential of Gray-code-inspired techniques for realizing continuous-variable physics on near-term, qubit-based quantum processors. △ Less

Submitted 11 June, 2025; v1 submitted 16 May, 2025; originally announced May 2025.

Security Analysis of Mode-Pairing Quantum Key Distribution with Flexible Pairing Strategy

Authors: Yi-Fei Lu, Yang Wang, Yan-Yang Zhou, Yu Zhou, Xiao-Lei Jiang, Xin-Hang Li, Hai-Tao Wang, Jia-Ji Li, Chun Zhou, Hong-Wei Li, Yu-Yao Guo, Lin-Jie Zhou, Wan-Su Bao

Abstract: Mode-pairing quantum key distribution (MP-QKD) is advantageous for long-distance secure communication, leveraging its simple implementation and quadratic scaling capacity. The post-measurement pairing in MP-QKD alleviates the photon-coincidence demands, which is essential for surpassing the fundamental limit to the key-rate transmission. In this work, we propose an improved decoy-state MP-QKD prot… ▽ More Mode-pairing quantum key distribution (MP-QKD) is advantageous for long-distance secure communication, leveraging its simple implementation and quadratic scaling capacity. The post-measurement pairing in MP-QKD alleviates the photon-coincidence demands, which is essential for surpassing the fundamental limit to the key-rate transmission. In this work, we propose an improved decoy-state MP-QKD protocol featuring a flexible and efficient pairing strategy. We prove the security of the proposed scheme by presenting an entanglement model for decoy-state MP-QKD. The simulation results show that the secret key rate (SKR) can be enhanced among all distances. Notably, compared with the original scheme [Nature Communication 13, 3903 (2022)], the improvement of SKR is greater than 65\% within 375 km in the asymptotic case and greater than 50\% within 400 km in the finite case. And the achievable distance can be extended in the finite case, especially with a small block length. The simulation results demonstrate the high efficiency of the proposed scheme, which is expected to promote the practical applicability of MP-QKD. Furthermore, the entanglement model could provide a theoretical framework for further security and performance analysis of decoy-state MP-QKD. △ Less

Submitted 16 May, 2025; originally announced May 2025.

Comments: 26 pages, 8 figures

Demonstration of low-overhead quantum error correction codes

Authors: Ke Wang, Zhide Lu, Chuanyu Zhang, Gongyu Liu, Jiachen Chen, Yanzhe Wang, Yaozu Wu, Shibo Xu, Xuhao Zhu, Feitong Jin, Yu Gao, Ziqi Tan, Zhengyi Cui, Ning Wang, Yiren Zou, Aosai Zhang, Tingting Li, Fanhao Shen, Jiarun Zhong, Zehang Bao, Zitian Zhu, Yihang Han, Yiyang He, Jiayuan Shen, Han Wang , et al. (17 additional authors not shown)

Abstract: Quantum computers hold the potential to surpass classical computers in solving complex computational problems. However, the fragility of quantum information and the error-prone nature of quantum operations make building large-scale, fault-tolerant quantum computers a prominent challenge. To combat errors, pioneering experiments have demonstrated a variety of quantum error correction codes. Yet, mo… ▽ More Quantum computers hold the potential to surpass classical computers in solving complex computational problems. However, the fragility of quantum information and the error-prone nature of quantum operations make building large-scale, fault-tolerant quantum computers a prominent challenge. To combat errors, pioneering experiments have demonstrated a variety of quantum error correction codes. Yet, most of these codes suffer from low encoding efficiency, and their scalability is hindered by prohibitively high resource overheads. Here, we report the demonstration of two low-overhead quantum low-density parity-check (qLDPC) codes, a distance-4 bivariate bicycle code and a distance-3 qLDPC code, on our latest superconducting processor, Kunlun, featuring 32 long-range-coupled transmon qubits. Utilizing a two-dimensional architecture with overlapping long-range couplers, we demonstrate simultaneous measurements of all nonlocal weight-6 stabilizers via the periodic execution of an efficient syndrome extraction circuit. We achieve a logical error rate per logical qubit per cycle of $(8.91 \pm 0.17)\%$ for the distance-4 bivariate bicycle code with four logical qubits and $(7.77 \pm 0.12)\%$ for the distance-3 qLDPC code with six logical qubits. Our results establish the feasibility of implementing various qLDPC codes with long-range coupled superconducting processors, marking a crucial step towards large-scale low-overhead quantum error correction. △ Less

Submitted 14 May, 2025; originally announced May 2025.

Experimental Frequency-Comb-Based Mode-Pairing Quantum Key Distribution Beyond the Rate-Loss Limit

Authors: Yi-Fei Lu, Yan-Yang Zhou, Yu-Yao Guo, Xin-Hang Li, Xiao-Lei Jiang, Yang Wang, Yu Zhou, Jia-Ji Li, Chun Zhou, Hong-Wei Li, Lin-Jie Zhou, Wan-Su Bao

Abstract: Mode-pairing quantum key distribution (MP-QKD) offers significant potential for long-distance secure communication, benefiting from its quadratic scaling capacity and phase compensation-free characteristic. However, MP-QKD still requires stringent wavelength consistency between remote lasers, which is impractical with commercial lasers without locking. In this work, we develop a simple optical-fre… ▽ More Mode-pairing quantum key distribution (MP-QKD) offers significant potential for long-distance secure communication, benefiting from its quadratic scaling capacity and phase compensation-free characteristic. However, MP-QKD still requires stringent wavelength consistency between remote lasers, which is impractical with commercial lasers without locking. In this work, we develop a simple optical-frequency-comb-based MP-QKD system to simultaneously establish coherence and distribute keys with free-running commercial lasers. We implement the experiment over standard single-mode fiber with a loss coefficient of 0.2 dB/km. The system achieves finite-size secret key rates (SKRs) of 561.26, 113.59, and 10.20 bits per second over 303.37, 354.62, and 404.25 km, which are 1.0267, 2.5230, and 2.1033 times of the rate-loss limit. Besides, the SKR over 202.31 km is 8695.34 bits per second, which is sufficient to support practical cryptographic applications. These results validate the practicality and robustness of our method, offering a simplified yet high-performance framework for long-distance secure communication. △ Less

Submitted 14 May, 2025; originally announced May 2025.

Comments: 22 pages, 10 figures

Quantum Annealing Algorithms for Estimating Ising Partition Functions

Authors: Haowei Li, Zhiyuan Yao, Xingze Qiu

Abstract: Estimating partition functions of Ising spin glasses is crucial in statistical physics, optimization, and machine learning, yet remains classically intractable due to its #P-hard complexity. While Jarzynski's equality offers a theoretical approach, it becomes unreliable at low temperatures due to rare divergent statistical fluctuations. Here, we present a protocol that overcomes this limitation by… ▽ More Estimating partition functions of Ising spin glasses is crucial in statistical physics, optimization, and machine learning, yet remains classically intractable due to its #P-hard complexity. While Jarzynski's equality offers a theoretical approach, it becomes unreliable at low temperatures due to rare divergent statistical fluctuations. Here, we present a protocol that overcomes this limitation by synergizing reverse quantum annealing with tailored nonequilibrium initial distributions. Our method can dramatically suppress the estimator variance, achieving saturation in the low-temperature regime. Numerical benchmarks on the Sherrington-Kirkpatrick spin glass and the 3-SAT problem demonstrate that our protocol reduces scaling exponents by over an order of magnitude (e.g., from ~8.5 to ~0.5), despite retaining exponential system-size dependences. Crucially, our protocol circumvents stringent adiabatic constraints, making it feasible for near-term quantum devices like superconducting qubits, trapped ions, and Rydberg atom arrays. This work bridges quantum dynamics with computational complexity, offering a practical pathway to quantum advantage in spin glass thermodynamics and beyond. △ Less

Submitted 30 April, 2025; originally announced April 2025.

Comments: 6+8 pages, 3+3 figures

Microwave-activated high-fidelity three-qubit gate scheme for fixed-frequency superconducting qubits

Authors: Kui Zhao, Wei-Guo Ma, Ziting Wang, Hao Li, Kaixuan Huang, Yun-Hao Shi, Kai Xu, Heng Fan

Abstract: Scalable superconducting quantum processors require balancing critical constraints in coherence, control complexity, and spectral crowding. Fixed-frequency architectures suppress flux noise and simplify control via all-microwave operations but remain limited by residual ZZ crosstalk. Here we propose a microwave-activated three-qubit gate protocol for fixed-frequency transmon qubits in the large-de… ▽ More Scalable superconducting quantum processors require balancing critical constraints in coherence, control complexity, and spectral crowding. Fixed-frequency architectures suppress flux noise and simplify control via all-microwave operations but remain limited by residual ZZ crosstalk. Here we propose a microwave-activated three-qubit gate protocol for fixed-frequency transmon qubits in the large-detuning regime ($|Δ| \gg g$), leveraging the third-order nonlinear interaction to coherently exchange $\ket{001} \leftrightarrow \ket{110}$ states. By incorporating a phase-compensated optimization protocol, numerical simulations demonstrate a high average gate fidelity exceeding $99.9\%$. Systematic error analysis identifies static long-range ZZ coupling as the dominant error source in multi-qubit systems, which can be suppressed via operations in the large-detuning regime ($\sim 1$ GHz). The protocol maintains process fidelities exceeding $98\%$ under decoherence, while demonstrating intrinsic robustness to fabrication-induced parameter variations and compatibility with existing all-microwave two-qubit gate architectures. This hardware-efficient strategy advances scalable quantum computing systems by improving coherence properties, reducing spectral congestion, and expanding the experimental toolkit for error-resilient quantum operations in the noisy intermediate-scale quantum era. △ Less

Submitted 16 October, 2025; v1 submitted 30 April, 2025; originally announced April 2025.

Comments: 16 pages, 11 figures

Journal ref: Phys. Rev. Applied 24, 034064 (2025)