Showing 1–50 of 227 results for author: Wu, C

Entanglement and non-local magic in a non-unitarily deformed non-Hermitian bipartite system

Authors: Chen-Huan Wu

Abstract: Non-Hermitian degeneracies are usually discussed through spectral coalescence, whereas entanglement is a property of eigenvectors and need not be fixed by the eigenvalues alone. We formulate a compact bipartite model that separates these two notions. A Hermitian operator with a degenerate eigenspace is transformed by an invertible non-unitary similarity map. The resulting Hamiltonian is non-Hermit… ▽ More Non-Hermitian degeneracies are usually discussed through spectral coalescence, whereas entanglement is a property of eigenvectors and need not be fixed by the eigenvalues alone. We formulate a compact bipartite model that separates these two notions. A Hermitian operator with a degenerate eigenspace is transformed by an invertible non-unitary similarity map. The resulting Hamiltonian is non-Hermitian and retains a non-defective degeneracy at every finite value of the non-Hermiticity parameter. For an exactly solvable two-qubit realization, the right eigenstates evolve continuously from product states to maximally entangled states although the spectrum is unchanged. We distinguish the positive right-state reduced density matrix from the generally non-positive biorthogonal reduction, for which entropy may become complex. The same two-qubit solution gives a closed partial-transpose negativity and a Schmidt-gauged non-local magic. Entanglement grows monotonically with the non-Hermiticity parameter, whereas the non-local magic vanishes for both the product and maximally entangled limits and is largest at an intermediate coupling. In larger bipartite spaces, the Page entropy and Haar-averaged purity provide reference values for eigenstate typicality. These diagnostics separate non-defective degeneracy, exceptional-point sensitivity, Haar-typical entanglement, and non-stabilizer correlations without relying on a proliferation of basis-dependent spectral quantities. △ Less

Submitted 8 August, 2026; originally announced August 2026.

A broadband, individually addressing two- and three-dimensional photonic integrated circuit for trapped-ion qubit control

Authors: Daniel Klawson, Yiyang Zhi, Bingran You, Michael Bareian, Elijah Mossman, Chun-Yuan Fan, Arkadev Roy, Ke Sun, Jason Lee, Sung Cheol Yoon, Qiming Wu, Lai Jiang, Wenjun Ke, Weiwei Wu, Sirui Tang, Zachary Wall, Jiaxiang Wang, Louis Paul Romero, Sam Vizvary, Steven Diaz, Eric R. Hudson, Wesley C. Campbell, Hartmut Haeffner, Ming C. Wu

Abstract: Trapped ions provide a high-fidelity platform for quantum information processing, yet delivery of multiple, distinct wavelengths across large networks of interaction zones remains a bottleneck. Conventional free-space light delivery lacks scalability, while on-chip grating couplers suffer from narrow operational bandwidth that increases circuit footprint and optical interfacing complexity. Here we… ▽ More Trapped ions provide a high-fidelity platform for quantum information processing, yet delivery of multiple, distinct wavelengths across large networks of interaction zones remains a bottleneck. Conventional free-space light delivery lacks scalability, while on-chip grating couplers suffer from narrow operational bandwidth that increases circuit footprint and optical interfacing complexity. Here we show a broadband photonic integrated circuit capable of addressing individual ions. The circuit combines a planar waveguide lens with a micromirror fabricated using two-photon polymerization at wafer scale. This implementation can address three individual ions from $λ$ = 405 - 880 nm with -27 dB average intensity crosstalk at $5\,μ\mathrm{m}$ pitch. We trap $^{40}\mathrm{Ca}^{+}$ and $^{138}\mathrm{Ba}^{+}$ ions above such devices, characterize optical crosstalk with barium ions, and demonstrate individual repumping of calcium ions. This monolithic photonic architecture brings broadband addressing in an on-chip modality to trapped-ion technology. More generally, integrating additive manufacturing into quantum devices is poised to unlock expanded design space for implementing novel quantum architectures. △ Less

Submitted 27 July, 2026; originally announced July 2026.

Comments: 17 pages, 5 figures

Mitigation of Measurement-Induced State Transitions via a Fast-Load and Fast-Clear Readout

Authors: Wei-En Lin, Li-Chieh Hsiao, Chen-Hsun Ma, Erh-Hsiang Yeh, Wei-Lun Peng, Hsi-Sheng Goan, Cen-Shawn Wu, Yueh-Nan Chen, Yung-Fu Chen, Chung-Ting Ke, Chii-Dong Chen

Abstract: High-fidelity and rapid qubit readout is essential for superconducting quantum processors, typically realized through the quantum non-demolition (QND) dispersive interaction within a qubit-resonator architecture. However, the achievable readout speed and fidelity are fundamentally limited by measurement-induced state transitions (MIST). For a transmon qubit, MIST is highly sensitive to the offset… ▽ More High-fidelity and rapid qubit readout is essential for superconducting quantum processors, typically realized through the quantum non-demolition (QND) dispersive interaction within a qubit-resonator architecture. However, the achievable readout speed and fidelity are fundamentally limited by measurement-induced state transitions (MIST). For a transmon qubit, MIST is highly sensitive to the offset charge $n_g$ due to the charge dispersion of its higher-lying energy levels. In this work, we systematically investigate $n_g$-dependent MIST dynamics governed by the diabaticity and symmetry of pulse shaping within a charge-sensitive transmon architecture. We engineer fast-load and fast-clear pulses that effectively suppress resonator photon overshoots, thereby demonstrating a highly practical strategy to mitigate MIST without requiring complex waveforms or real-time feedback. Utilizing active gate-voltage control and rapid feedback, the measurement-induced transition probability is precisely mapped against $n_g$ and the steady-state resonator photon number, exhibiting strong agreement with numerical Floquet branch analysis. Ultimately, we evaluate the $n_g$-averaged total error probabilities for both readout and post-readout stages, verifying that a straightforward three-step pulse scheme consistently minimizes overall readout errors. Within the framework of large-scale superconducting quantum processors, this practical, hardware-free approach inherently offers a better trade-off between the readout signal-to-noise ratio and QND preservation. △ Less

Submitted 26 July, 2026; originally announced July 2026.

Quantum Dot Moiré from Crossed MoS2 Nanoribbons

Authors: Xinting Shuai, Hao Zhang, Wenjing Wu, Chongning Wu, Maryam Amiri, T. A. M. Ragib Shahriar, Dian Pan, Zhi Kai Ng, Tymofii Pieshkov, Leeza Dutta, Yijun Zhou, Rohith Narra, Luke Van Leeuwen, Jishnu Murukeshan, Luyao Shi, Jiawei Lai, Atin Pramanik, Bipin Kumar Gupta, Edwin Hang Tong Teo, Robert Vajtai, Xiang Zhang, Hanyu Zhu, Shengxi Huang, Aditya D. Mohite, Pulickel M. Ajayan

Abstract: Twisted atomically thin layers have attracted much attention for Moiré potential and correlated quantum phenomena. However, existing Moiré superlattices have largely been limited to extensive wavefunction without lateral confinement. Here we introduce a new platform where 1D nanoribbons of 2D MoS2 grown by vapor deposition can be easily superposed at various angles from stacking and transferring,… ▽ More Twisted atomically thin layers have attracted much attention for Moiré potential and correlated quantum phenomena. However, existing Moiré superlattices have largely been limited to extensive wavefunction without lateral confinement. Here we introduce a new platform where 1D nanoribbons of 2D MoS2 grown by vapor deposition can be easily superposed at various angles from stacking and transferring, to form Moiré quantum dots at their intersections with unique exciton physics. Angle-dependent Moiré intersections show enhanced exciton emission at commensurate angle 22 deg, which demonstrates faster relaxation at the cryogenic temperature. A size-dependent study further exhibits a reduced exciton energy and soften out-of-plane interlayer coupling for smaller Moiré areas. Our results reveal exciton physics turnability via precise overlapping of 1D nanoribbons. △ Less

Submitted 8 July, 2026; originally announced July 2026.

Comments: 20 pages, 4 figures

Quantum-Optical Bound States in the Continuum

Authors: Ruo Kun Cai, Zhi Jiao Deng, Chun Wang Wu, Ping Xing Chen

Abstract: Bound states in the continuum (BICs) are counterintuitive localized states that lie within the continuum of extended states. While extensively realized and utilized in classical wave systems, it is still unclear what a close analog of BICs would be, and how to extract their experimental signature in quantum-optical settings -- where the wave field itself is quantized into bosonic excitations. Here… ▽ More Bound states in the continuum (BICs) are counterintuitive localized states that lie within the continuum of extended states. While extensively realized and utilized in classical wave systems, it is still unclear what a close analog of BICs would be, and how to extract their experimental signature in quantum-optical settings -- where the wave field itself is quantized into bosonic excitations. Here, we present a paradigmatic quantum-optical model consisting of a driven multi-level Jaynes-Cummings (JC) system, featuring few quantum degrees of freedom yet capable of hosting a BIC. Using the concept of a Fock-state lattice (FSL), this model can be mapped to an extended structure comprising two semi-infinite inhomogeneous Su-Schrieffer-Heeger (SSH) chains coupled to a common continuum. An appropriate quantum superposition of two topological zero modes from the separate chains forms a BIC that remains perfectly localized in the Fock-state dimension within the continuum spectrum, due to complete decoupling from the common continuum via destructive quantum interference. We further develop a method to extract the spectroscopic signature of the BIC -- a discrete peak embedded in a continuous background -- by Fourier-transforming the time-dependent dynamics of the system's chiral-symmetry operator. A highly feasible experimental proposal using a single trapped ion is provided. Our work bridges BIC physics with quantum optics, opening a pathway to harnessing such exotic states at the quantum limit. △ Less

Submitted 6 July, 2026; originally announced July 2026.

Comments: 9 pages, 4 figures

Monitoring Beam Splitter Entanglement using Quantumness

Authors: Hua-Li Chen, Hsien-Yi Hsieh, Chien-Ming Wu, Ole Steuernagel, Ray-Kuang Lee

Abstract: We report on an experiment in which two independent squeezed vacuum states get entangled by mixing them with a balanced beam splitter. We follow standard practice and use an inseparability criterion to quantify their entanglement. However, this only allows us to witness the entanglement, but not to determine the deleterious effects of experimental imperfections due to the beam splitter mixing and… ▽ More We report on an experiment in which two independent squeezed vacuum states get entangled by mixing them with a balanced beam splitter. We follow standard practice and use an inseparability criterion to quantify their entanglement. However, this only allows us to witness the entanglement, but not to determine the deleterious effects of experimental imperfections due to the beam splitter mixing and the associated mode-mismatch and detection imperfections. We therefore introduce an alternative framework suitable for continuous variable systems using the states' quantumness, $Ξ$. We show that, under ideal circumstances, $Ξ$ is a conserved quantity under beam mixing. This allows us to benchmark the experiment's performance by comparing the states' quantumness $Ξ$ after the beam splitter mixing with $Ξ$ before. Such a comparison is not possible with entanglement witnesses, as the input states are unentangled. This highlights the main strength of our approach: its ability to generally quantify the quantumness of multi-mode continuous variable states and use this to probe different stages in an experiment. △ Less

Submitted 23 June, 2026; v1 submitted 23 June, 2026; originally announced June 2026.

Comments: 9 pages, 7 figures

Suppression of Quasiparticle Poisoning to $10^{-11}$ Levels in Superconducting Qubits via Infrared Shielding

Authors: Wei-En Lin, Chen-Hsun Ma, Erh-Hsiang Yeh, Wei-Lun Peng, Yu-Sen Wei, Hsi-Sheng Goan, Cen-Shawn Wu, Chung-Ting Ke, Yung-Fu Chen, Chii-Dong Chen

Abstract: Quasiparticle poisoning bottlenecks superconducting qubits, limiting coherence and the scalability of quantum processors. In this work, we systematically investigate quasiparticle poisoning in superconducting qubits under three infrared (IR) shielding configurations, ranging from a dedicated multi-layer design to a simplified implementation. By measuring quasiparticle-induced parity switching, we… ▽ More Quasiparticle poisoning bottlenecks superconducting qubits, limiting coherence and the scalability of quantum processors. In this work, we systematically investigate quasiparticle poisoning in superconducting qubits under three infrared (IR) shielding configurations, ranging from a dedicated multi-layer design to a simplified implementation. By measuring quasiparticle-induced parity switching, we demonstrate a suppression of the switching rate by over four orders of magnitude via the implementation of improved shielding. In the best configuration, the rate decreases over time following cooldown and reaches 0.069$\,$Hz on day 34, corresponding to an anticipated quasiparticle density per Cooper pair of $1.88\times10^{-11}$. To our knowledge, this represents the lowest quasiparticle density reported in the literature to date. The remaining quasiparticle population is likely dominated by sporadic phonon bursts stemming from mechanical stress release in the on-chip films, as well as from the surrounding environment. The effective qubit temperature follows the phonon bath down to 17$\,$mK, enabling initialization errors of $\sim 0.01\%$ for 3$\,$GHz qubits. These results demonstrate that proper IR shielding and thermalization are essential for suppressing quasiparticle poisoning and enabling high-coherence, scalable superconducting qubit systems. △ Less

Submitted 5 June, 2026; originally announced June 2026.

Comments: 16 pages, 8 figures

Observation of quantum multi-Mpemba effect in a trapped-ion system

Authors: Gang Xia, Yu-Jie Zheng, Jing Huang, Chun-Wang Wu, Yi Xie, Ting Chen, Wei Wu, Weibin Li, Hui Jing, Jie Zhang, Yan-Li Zhou, Ping-Xing Chen

Abstract: The quantum Mpemba effect (ME) in Markovian systems is conventionally explained by a smaller overlap between the initial state and the slowest decay mode (SDM). Such state, initially farther away from equilibrium or steady state, relaxes faster than closer ones, resulting to a crossing of their trajectories. This picture, by neglecting the transient dynamics, holds in the long-time limit. Here we… ▽ More The quantum Mpemba effect (ME) in Markovian systems is conventionally explained by a smaller overlap between the initial state and the slowest decay mode (SDM). Such state, initially farther away from equilibrium or steady state, relaxes faster than closer ones, resulting to a crossing of their trajectories. This picture, by neglecting the transient dynamics, holds in the long-time limit. Here we experimentally observe multiple trajectory crossings (multi-ME) in the relaxation dynamics of a trapped ion. Such novel dynamics takes place in a unusual scenario where the initial state instead has a larger overlap with the SDM. We develop a theoretical framework based on relaxation speed to understand the multi-ME. We show that the initial relaxation speed is governed by the fastest decay mode, which together with the SDM overlap gives a phase diagram that reveals both the occurrence and the types of quantum ME observed in our experiment. Our study goes beyond the simple picture based on the long-time limit, tracks continuously the quantum ME dynamics, and establishes a comprehensive framework to describe the transient quantum relaxation. △ Less

Submitted 23 April, 2026; originally announced April 2026.

Collective Nuclear Polaritons with Coherent and Tunable Excitation Dynamics

Authors: Liufeng Yang, Jinling Wang, Huijun Li, Junhui Cao, Alexey Kavokin, Congjun Wu

Abstract: We propose collective nuclear polaritons formed by hybridizing a 229Th nuclear ensemble with a vacuum-ultraviolet cavity mode generated via four-wave mixing, achieving a collective light-matter coupling that scales as $\sqrt{N}$. In the strong-coupling regime the system displays vacuum Rabi oscillations, indicating the hybridization between cavity photons and nuclear excitations. In the superradia… ▽ More We propose collective nuclear polaritons formed by hybridizing a 229Th nuclear ensemble with a vacuum-ultraviolet cavity mode generated via four-wave mixing, achieving a collective light-matter coupling that scales as $\sqrt{N}$. In the strong-coupling regime the system displays vacuum Rabi oscillations, indicating the hybridization between cavity photons and nuclear excitations. In the superradiant regime, the stored excitation is released in a cooperative burst with peak intensity scaling as $N^2$. The emission lifetime shrinks from thousands of seconds to the millisecond scale and remains tunable. Detuning sweeps across the polariton avoided crossing allow adiabatic conversion of the photonic excitation into a collective nuclear excitation, enabling reversible quantum storage. Our results demonstrate that cavity-mediated nuclear polaritons enable deterministic lifetime engineering and coherent quantum storage in nuclear systems. △ Less

Submitted 14 March, 2026; originally announced March 2026.

General linear correction method for DFT+X energy: application to U-M (M=Al, Ga, In) alloys under high pressure

Authors: X. L. Pan, H. X. Song, Y. Sun, F. C. Wu, H. Wang, Y. F. Wang, Y. Chen, X. R. Chen, Hua Y. Geng

Abstract: DFT+X methods, such as DFT+U and DFT+DMFT, are important supplements to standard density functional theory when strong on-site Coulomb interactions are present. However, the involvement of external parameters in the underlying model Hamiltonian introduces intrinsic ambiguity when comparing the total energies obtained with different model parameters. This renders DFT+X approaches semi-empirical and… ▽ More DFT+X methods, such as DFT+U and DFT+DMFT, are important supplements to standard density functional theory when strong on-site Coulomb interactions are present. However, the involvement of external parameters in the underlying model Hamiltonian introduces intrinsic ambiguity when comparing the total energies obtained with different model parameters. This renders DFT+X approaches semi-empirical and severely hinders their capability to describe phase ordering and phase stability, especially when reliable experimental benchmarks are unavailable, such as under high pressure. In this work, we resolve this longstanding problem by proposing a general linear correction method that eliminates the ambiguous energy contributions introduced by the model Hamiltonian in DFT+X approaches, thereby enabling direct comparison of their energies calculated with different interaction parameters. The method is demonstrated and validated within the framework of DFT+U, an important member of the DFT+X family. It is then applied to important nuclear materials of uranium-based binaries U-M (M=Al, Ga, In) alloys. With this approach, we resolve the long-standing discrepancy between theoretical predictions and experimental observations of phase stability with unprecedented accuracy, and predict several previously unknown stable intermetallic compounds under high pressure. The broad applicability of the method is further confirmed by accurate predictions of formation enthalpies for diverse systems, including Np-Al, U-Si, and Cu-O binaries, the ternary MnSnAu compound, and oxygen adsorption on the Cu(111) surface. This work establishes linear-corrected DFT+U as a fully first-principles approach and validates the linear correction method as a robust and general scheme that can be readily extended to other DFT+X methods. △ Less

Submitted 28 February, 2026; originally announced March 2026.

Comments: 45 pages, 5 figures, with Supplementary Material

Journal ref: Acta Materialia 306, 121935 (2026)

Kaiwu-PyTorch-Plugin: Bridging Deep Learning and Photonic Quantum Computing for Energy-Based Models and Active Sample Selection

Authors: Hongdong Zhu, Qi Gao, Yin Ma, Shaobo Chen, Haixu Liu, Fengao Wang, Tinglan Wang, Chang Wu, Kai Wen

Abstract: This paper introduces the Kaiwu-PyTorch-Plugin (KPP) to bridge Deep Learning and Photonic Quantum Computing across multiple dimensions. KPP integrates the Coherent Ising Machine into the PyTorch ecosystem, addressing classical inefficiencies in Energy-Based Models. The framework facilitates quantum integration in three key aspects: accelerating Boltzmann sampling, optimizing training data via Acti… ▽ More This paper introduces the Kaiwu-PyTorch-Plugin (KPP) to bridge Deep Learning and Photonic Quantum Computing across multiple dimensions. KPP integrates the Coherent Ising Machine into the PyTorch ecosystem, addressing classical inefficiencies in Energy-Based Models. The framework facilitates quantum integration in three key aspects: accelerating Boltzmann sampling, optimizing training data via Active Sampling, and constructing hybrid architectures like QBM-VAE and Q-Diffusion. Empirical results on single-cell and OpenWebText datasets demonstrate KPPs ability to achieve SOTA performance, validating a comprehensive quantum-classical paradigm. △ Less

Submitted 22 February, 2026; originally announced February 2026.

Near-single-domain superconducting aluminum films on GaAs(111)A with exceptional crystalline quality for scalable quantum circuits

Authors: Hsien-Wen Wan, Yi-Ting Cheng, Chao-Kai Cheng, Jui-Min Chia, Chien-Ting Wu, Sheng-Shiuan Yeh, Chia-Hung Hsu, Jueinai Kwo, Minghwei Hong

Abstract: We have reproducibly grown near-single-domain superconducting aluminum (Al) films on GaAs(111)A wafers using molecular beam epitaxy. Synchrotron X-ray diffraction revealed twin-domain ratios of 0.00005 and 0.0003 for 19.4-nm- and 9.6-nm-thick films, respectively-the lowest reported for Al on any substrate and long considered unattainable for practical device platforms. Azimuthal scans across off-n… ▽ More We have reproducibly grown near-single-domain superconducting aluminum (Al) films on GaAs(111)A wafers using molecular beam epitaxy. Synchrotron X-ray diffraction revealed twin-domain ratios of 0.00005 and 0.0003 for 19.4-nm- and 9.6-nm-thick films, respectively-the lowest reported for Al on any substrate and long considered unattainable for practical device platforms. Azimuthal scans across off-normal Al{$11\bar{1}$} reflections exhibit narrow full width at half maximum (FWHM) values down to $0.55^\circ$, unmatched by epi-Al grown by any other method. Normal scans showed a well-defined (111) orientation with pronounced Pendellösung fringes, and $θ$-rocking-curve FWHM values down to $0.018^\circ$; the former indicates abrupt film-substrate and oxide-film interfaces. Electron backscatter diffraction mapping confirms macroscopic in-plane uniformity and the absence of $Σ$3 twin domains. Atomic force microscopy and scanning transmission electron microscopy confirmed atomically smooth surfaces and abrupt heterointerfaces. The films exhibit critical temperatures approaching bulk values, establishing a materials platform for scalable, high-coherence superconducting qubits. △ Less

Submitted 19 February, 2026; originally announced February 2026.

Comments: 19 pages, 4 figures, 1 table

QASMTrans: An End-to-End QASM Compilation Framework with Pulse Generation for Near-Term Quantum Devices

Authors: Aaron Hoyt, Meng Wang, Fei Hua, Chunshu Wu, Chenxu Liu, Muqing Zheng, Samuel Stein, Drew Rebar, Yufei Ding, Travis S. Humble, Ang Li

Abstract: QASMTrans is a lightweight, high-performance, C++-based quantum compiler that bridges abstract quantum algorithms to device-level control and is designed for just-in-time (JIT) deployment on QPU testbeds with tightly integrated FPGAs or CPUs. We focus on achieving fast transpilation times on circuits of interest, we find more than 100x faster compilation than Qiskit in some circuits with similar c… ▽ More QASMTrans is a lightweight, high-performance, C++-based quantum compiler that bridges abstract quantum algorithms to device-level control and is designed for just-in-time (JIT) deployment on QPU testbeds with tightly integrated FPGAs or CPUs. We focus on achieving fast transpilation times on circuits of interest, we find more than 100x faster compilation than Qiskit in some circuits with similar circuit quality, enabling transpilation of large, high-depth circuits in seconds. Unlike existing tools, QASMTrans offers end-to-end device-pulse compilation and direct quantum control integration with QICK, closing the gap between logical circuits and hardware control enabling closed-loop optimization. QASMTrans supports latency-aware Application-tailored Gate Sets (AGS) at the pulse level, identifying high-impact gate sequences on the circuit critical path and synthesizing optimized pulse schedules using pre-defined robust circuit ansatz. Validated through integrated QuTiP pulse-level simulation, this is found to significantly reduce execution latency and can improve final-state fidelity by up to 12% in some tested circuits. QASMTrans further implements device-aware, noise-adaptive transpilation that uses device calibration data for circuit placement on high-quality qubits and can focus on the circuit critical path to reduce transpilation-pass time while maintaining comparable fidelity. Additionally, it introduces circuit space sharing via calibration-aware device partitioning, enabling concurrent execution of multiple circuits or shots on a single QPU. Moreover, QASMTrans is entirely self-contained and has no external library dependencies, making it easy for practical deployment. By combining fast compilation, pulse-level control, and noise-aware optimization, QASMTrans enables real-time adaptive algorithms such as ADAPT-VQE and ADAPT-QAOA. △ Less

Submitted 4 February, 2026; originally announced February 2026.

Comments: arXiv admin note: substantial text overlap with arXiv:2308.07581

Confined non-Hermitian skin effect in a semi-infinite Fock-state lattice

Authors: Zhi Jiao Deng, Xing Yao Mi, Ruo Kun Cai, Chun Wang Wu, Ping Xing Chen

Abstract: In this paper, we investigate the non-Hermitian skin effect in a semi-infinite Fock-state lattice, where the inherent coupling scales as \sqrt{n}. By analytically solving a non-uniform, non-reciprocal SSH model, we demonstrate that the intrinsic inhomogeneous coupling, in combination with nonreciprocity, fundamentally modifies the conventional skin effect. Instead of accumulating at the physical b… ▽ More In this paper, we investigate the non-Hermitian skin effect in a semi-infinite Fock-state lattice, where the inherent coupling scales as \sqrt{n}. By analytically solving a non-uniform, non-reciprocal SSH model, we demonstrate that the intrinsic inhomogeneous coupling, in combination with nonreciprocity, fundamentally modifies the conventional skin effect. Instead of accumulating at the physical boundary, all eigenmodes become compressed and skewed within a finite spatial range determined by the inhomogeneous profile-a phenomenon we term the confined non-Hermitian skin effect. Consequently, the evolution of the probability distribution on the lattice starting from a single site is doubly confined: it is spatially bounded to a finite range by the inhomogeneous coupling, and further restricted to a one-sided trajectory at the edge of this range by the non-reciprocity. Moreover, a feasible experimental scheme based on a single trapped ion is also proposed. This work reveals how engineered coupling profiles in synthetic dimensions can reshape non-Hermitian properties and enable new protocols for quantum state manipulation. △ Less

Submitted 19 January, 2026; originally announced January 2026.

Comments: 7 pages, 6 figures

A scalable gallium-phosphide-on-diamond spin-photon interface

Authors: Nicholas S. Yama, Chun-Chi Wu, Fariba Hatami, Kai-Mei C. Fu

Abstract: The efficient interfacing of quantum emitters and photons is fundamental to quantum networking. Quantum defects embedded in integrated nanophotonic circuits are promising for such applications due to the deterministic light-matter interactions of high-cooperativity ($C>1$) cavity quantum electrodynamics and potential for scalable integration with active photonic processing. Silicon-vacancy (SiV) c… ▽ More The efficient interfacing of quantum emitters and photons is fundamental to quantum networking. Quantum defects embedded in integrated nanophotonic circuits are promising for such applications due to the deterministic light-matter interactions of high-cooperativity ($C>1$) cavity quantum electrodynamics and potential for scalable integration with active photonic processing. Silicon-vacancy (SiV) centers embedded in diamond nanophotonic cavities are a leading approach due to their excellent optical and spin coherence, however their long-term scalability is limited by the diamond itself, as its suspended geometry and weak nonlinearity necessitates coupling to a second processing chip. Here we realize the first high-cooperativity coupling of quantum defects to hybrid-integrated nanophotonics in a scalable, planar platform. We integrate more than 600 gallium phosphide (GaP) nanophotonic cavities on a diamond substrate with near-surface SiV centers. We examine a particular device with two strongly coupled SiV centers in detail, confirming above-unity cooperativity via multiple independent measurements. Application of an external magnetic field via a permanent magnet enables optical resolution of the SiV spin transitions from which we determine a spin-relaxation time $T_1>0.4$ ms at 4 K. We utilize the high cooperativity coupling to observe spin-dependent transmission switching and the quantum jumps of the SiV spin via single-shot readout. These results, coupled with GaP's strong nonlinear properties, establish GaP-on-diamond as a scalable planar platform for quantum network applications. △ Less

Submitted 8 January, 2026; originally announced January 2026.

Vector spin polarization evolution determined in an entangled muon-fluorine system under pulsed excitation

Authors: Dipranjan Chatterjee, Benjamin M. Huddart, Hank C. H. Wu, Dharmalingam Prabhakaran, Alex Louat, Stephen P. Cottrell, Stephen J. Blundell

Abstract: A spin-polarized muon implanted into a fluoride forms a coupled F--$μ$--F complex in which the muon spin and neighbouring fluorine nuclear spins become entangled. Here we apply radio-frequency (RF) excitation to this coupled system and use the three-dimensional distribution of emitted positrons to reconstruct the time-dependent evolution of the muon spin polarization. This three-dimensional readou… ▽ More A spin-polarized muon implanted into a fluoride forms a coupled F--$μ$--F complex in which the muon spin and neighbouring fluorine nuclear spins become entangled. Here we apply radio-frequency (RF) excitation to this coupled system and use the three-dimensional distribution of emitted positrons to reconstruct the time-dependent evolution of the muon spin polarization. This three-dimensional readout, using single spin detection, is not possible in a single NMR experiment and demonstrates significant advantages that are achieved by using RF muon techniques. We demonstrate the application of this vector-readout method to the experimental observation of a muon spin echo signal that is controlled by the dipolar coupling to fluorine, as well as to a double resonance experiment, in which we use pulses tuned to separate frequencies to address both the muon and fluorine spins. This targeted approach, in which selective RF pulses can control the muon spin and other spins to which it is coupled, provides a novel route for probing systems of entangled spins. △ Less

Submitted 21 October, 2025; originally announced October 2025.

Analytical Control of Quantum Coherence: Markovian Revival via Basis Engineering and Exact Non-Markovian Criteria

Authors: Na-Na Zhang, Chao-Yi Wu, Ming Li, Wei-Xuan Cao, Jun-Hao Zhang, Yong-Rui Guo, Ren-Pu Li

Abstract: The preservation of quantum coherence is besieged by a fundamental dogma: its revival necessitates non-Markovian memory effects from structured environments. This paradigm has constrained quantum control strategies and obscured simpler paths to coherence protection. Here, we shatter this belief by demonstrating unambiguous coherence revival even in strictly Markovian regimes, achieved solely throu… ▽ More The preservation of quantum coherence is besieged by a fundamental dogma: its revival necessitates non-Markovian memory effects from structured environments. This paradigm has constrained quantum control strategies and obscured simpler paths to coherence protection. Here, we shatter this belief by demonstrating unambiguous coherence revival even in strictly Markovian regimes, achieved solely through basis engineering in the $σ_x/σ_y$ bases. We establish a comprehensive analytical framework for predictive coherence control, delivering three universal design principles. First, we derive a minimum critical noise based frequency, $ω_{0}^{c} = 1.57/(0.4996 \cdot t_{\max})$, serving as a universal criterion for engineering non-Markovian dynamics over any interval $[0, t_{\max}]$. Crucially, we show that Markovian environments ($ω_0 < ω_0^c$) can exhibit coherence revival when the Zeeman energy satisfies $ω_k > π/(2t_{\max})$, decoupling revival from environmental memory. Furthermore, for non-Markovian environments, we provide exact conditions for periodic and complete revival: setting $ω_0 = n \cdot 6.285/t_{\max}$ guarantees revival in the $σ_z$ basis, while combining it with $ω_k = πω_0 / 6.285$ ensures perfect revival in the $σ_x/σ_y$ bases. Our results, validated by rigorous quantum simulations, provide a predictive toolkit for coherence control, offering immediate strategies for enhancing quantum memory, sensing, and error mitigation. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Machine Learning for Quantum State Tomography: Robust Covariance Matrix Estimation for Squeezed Vacuum States with Thermal Noise

Authors: Juan Camilo Rodrıguez, Hsien-Yi Hsieh, Hua-Li Chen, Ole Steuernagel, Chien-Ming Wu, Ray-Kuang Lee

Abstract: We present a supervised machine learning-based method using convolutional neural networks to estimate the covariance matrix of Gaussian quantum states in the presence of thermal noise. Unlike computationally intensive density matrix reconstructions, our machine learning-based method allows for the reconstruction of impure squeezed vacuum states using sparse measurements of quadrature sequences bas… ▽ More We present a supervised machine learning-based method using convolutional neural networks to estimate the covariance matrix of Gaussian quantum states in the presence of thermal noise. Unlike computationally intensive density matrix reconstructions, our machine learning-based method allows for the reconstruction of impure squeezed vacuum states using sparse measurements of quadrature sequences based on a model employing a two-component state mixed together from thermal and squeezed thermal states. The method achieves high fidelity and precision, notably also at high squeezing levels, while offering an effective characterization of physical quantities and accurately estimating the covariance matrix. We benchmark our machine against experimental data of single-mode squeezed vacuum states, demonstrating its accuracy and capability to quantify experimental degradation to squeezing and purity. We experimentally verify that our covariance matrix estimation exhibits robustness to state degradation induced by thermal state admixtures. We provide a method for lightweight, compact, and complete representation of lab-generated Gaussian states and lay the foundation for extending real-time quantum state tomography for thermal multi-component Gaussian states to multi-mode systems. △ Less

Submitted 25 September, 2025; originally announced September 2025.

Comments: 5 figures

Spontaneous formation of subsystem and bath under accordion-type driving

Authors: Suyang Lin, Ming Gong, Congjun Wu

Abstract: Floquet modulations often yield effective Hamiltonians not easily accessible in traditional time-dependent systems, which brings opportunities for exploring novel physics of quantum dynamics. We investigate a Floquet system exhibiting translational symmetry at any fixed time but the spatial periodicity is time-dependent. Such a system is a natural platform for studying thermalization and novel dyn… ▽ More Floquet modulations often yield effective Hamiltonians not easily accessible in traditional time-dependent systems, which brings opportunities for exploring novel physics of quantum dynamics. We investigate a Floquet system exhibiting translational symmetry at any fixed time but the spatial periodicity is time-dependent. Such a system is a natural platform for studying thermalization and novel dynamical structures. We find that the single-particle Hilbert space spontaneously develops a structure of a two-level subsystem and the rest part forms a bath. The dynamic process is analyzed perturbatively within the two-level subsystem as well as numerical solutions, exhibiting stable time-evolutions. These results enrich our understanding of Floquet thermalization without definite spatial periodicity, which brings hints for exploring many-body physics such as scar states. △ Less

Submitted 16 September, 2025; originally announced September 2025.

High-efficiency Weak-trace-free Counterfactual Communication via Quantum Zeno Effect

Authors: Tianyi Xing, Anqi Huang, Yizhi Wang, Chao Wu, Yaxuan Wang, Pingyu Zhu, Jiangfang Ding, Dongyang Wang, Yingwen Liu, Xiaogang Qiang, Sheng Ma, Ping Xu, Junjie Wu

Abstract: The quantum Zeno effect, which inhibits quantum state evolution via repeated weak measurements, significantly enhances the efficiency of interaction-free measurement (IFM). This fundamental mechanism facilitates high-efficiency counterfactual quantum communication, enabling information delivery without particle transmission through the channel. However, the transmission time of the counterfactual… ▽ More The quantum Zeno effect, which inhibits quantum state evolution via repeated weak measurements, significantly enhances the efficiency of interaction-free measurement (IFM). This fundamental mechanism facilitates high-efficiency counterfactual quantum communication, enabling information delivery without particle transmission through the channel. However, the transmission time of the counterfactual communication requires minutes for bit and suffers the bit error when transmitting an image. Applying the quantum Zeno effect, we experimentally demonstrate high-efficiency weak-trace-free counterfactual communication on a quantum photonic chip, achieving a transmission probability of 74.2 $\pm$ 1.6\% for bit 0 and 85.1 $\pm$ 1.3\% for bit 1. Furthermore, we successfully transmit our group's logo -- Quanta -- through counterfactual communication, and reduce the time cost from minutes to seconds for bit, with zero bit errors after information processing. Our study provides a promising approach for secure and efficient communication using integrated silicon quantum photonics. △ Less

Submitted 18 March, 2026; v1 submitted 31 August, 2025; originally announced September 2025.

MiqroForge: An Intelligent Workflow Platform for Quantum-Enhanced Computational Chemistry

Authors: Jianan Wang, Wenbo Guo, Xin Yue, Minjie Xu, Yueqiang Zheng, Jingxiang Dong, Jiarui Hu, Jian Xia, Chuixiong Wu

Abstract: The connect-fill-run workflow paradigm, widely adopted in mature software engineering, accelerates collaborative development. However, computational chemistry, computational materials science, and computational biology face persistent demands for multi-scale simulations constrained by simplistic platform designs. We present MiqroForge, an intelligent cross-scale platform integrating quantum comput… ▽ More The connect-fill-run workflow paradigm, widely adopted in mature software engineering, accelerates collaborative development. However, computational chemistry, computational materials science, and computational biology face persistent demands for multi-scale simulations constrained by simplistic platform designs. We present MiqroForge, an intelligent cross-scale platform integrating quantum computing capabilities. By combining AI-driven dynamic resource scheduling with an intuitive visual interface, MiqroForge significantly lowers entry barriers while optimizing computational efficiency. The platform fosters a collaborative ecosystem through shared node libraries and data repositories, thereby bridging practitioners across classical and quantum computational domains. △ Less

Submitted 10 August, 2025; originally announced August 2025.

Quantum Estimation with State Symmetry-Induced Optimal Measurements

Authors: Jia-Xuan Liu, Hai-Long Shi, Chunfeng Wu, Sixia Yu

Abstract: A central challenge in quantum metrology is identifying optimal measurements that saturate the quantum Cramer-Rao bound under realistic constraints, e.g., local measurements. We show that symmetries of the probe state provide a general principle for identifying optimal measurement strategies. Building on this idea, we demonstrate that when a parameter is encoded in the real coefficients of a fixed… ▽ More A central challenge in quantum metrology is identifying optimal measurements that saturate the quantum Cramer-Rao bound under realistic constraints, e.g., local measurements. We show that symmetries of the probe state provide a general principle for identifying optimal measurement strategies. Building on this idea, we demonstrate that when a parameter is encoded in the real coefficients of a fixed-basis expansion, the optimal measurement reduces to projection in that basis, with an application to critical metrology. Under local-measurement constraints, we show that local state symmetries provide a systematic route to constructing optimal local measurements. We illustrate this framework using graph states, explicitly constructing optimal local measurements from their local symmetries. Furthermore, weak and strong connection rules are introduced to generate broader classes of graph states that achieve Heisenberg-scaling precision using local measurements. By relaxing the number of stabilizer generators, graph states are extended to a stabilizer-code subspace. Analytical and numerical results show that coherent states in these subspaces offer multiple metrological advantages: high precision, partial noise resilience, local-measurement accessibility, and built-in error correction. These findings advance the theory of optimal measurements in quantum metrology and underscore the central role of state symmetry. △ Less

Submitted 9 March, 2026; v1 submitted 9 August, 2025; originally announced August 2025.

Comments: 16 pages, 6 figures

LLM-based Multi-Agent Copilot for Quantum Sensor

Authors: Rong Sha, Binglin Wang, Jun Yang, Xiaoxiao Ma, Chengkun Wu, Liang Yan, Chao Zhou, Jixun Liu, Guochao Wang, Shuhua Yan, Lingxiao Zhu

Abstract: Large language models (LLM) exhibit broad utility but face limitations in quantum sensor development, stemming from interdisciplinary knowledge barriers and involving complex optimization processes. Here we present QCopilot, an LLM-based multi-agent framework integrating external knowledge access, active learning, and uncertainty quantification for quantum sensor design and diagnosis. Comprising c… ▽ More Large language models (LLM) exhibit broad utility but face limitations in quantum sensor development, stemming from interdisciplinary knowledge barriers and involving complex optimization processes. Here we present QCopilot, an LLM-based multi-agent framework integrating external knowledge access, active learning, and uncertainty quantification for quantum sensor design and diagnosis. Comprising commercial LLMs with few-shot prompt engineering and vector knowledge base, QCopilot employs specialized agents to adaptively select optimization methods, automate modeling analysis, and independently perform problem diagnosis. Applying QCopilot to atom cooling experiments, we generated 10${}^{\rm{8}}$ sub-$\rmμ$K atoms without any human intervention within a few hours, representing $\sim$100$\times$ speedup over manual experimentation. Notably, by continuously accumulating prior knowledge and enabling dynamic modeling, QCopilot can autonomously identify anomalous parameters in multi-parameter experimental settings. Our work reduces barriers to large-scale quantum sensor deployment and readily extends to other quantum information systems. △ Less

Submitted 7 August, 2025; originally announced August 2025.

Comments: 13 pages,4 figures

Characterizing and Mitigating Flux Crosstalk in Superconducting Qubits-Couplers System

Authors: Myrron Albert Callera Aguila, Nien-Yu Li, Chen-Hsun Ma, Li-Chieh Hsiao, Yi-Shiang Huang, Yen-Chun Chen, Teik-Hui Lee, Chin-Chia Chang, Jyh-Yang Wang, Ssu-Yen Huang, Hsi-Sheng Goan, Chiao-Hsuan Wang, Cen-Shawn Wu, Chii-Dong Chen, Chung-Ting Ke

Abstract: Superconducting qubits have achieved exceptional gate fidelities, exceeding the error-correction threshold in recent years. One key ingredient of such improvement is the introduction of tunable couplers to control the qubit-to-qubit coupling through frequency tuning. Moving toward fault-tolerant quantum computation, increasing the number of physical qubits is another step toward effective error co… ▽ More Superconducting qubits have achieved exceptional gate fidelities, exceeding the error-correction threshold in recent years. One key ingredient of such improvement is the introduction of tunable couplers to control the qubit-to-qubit coupling through frequency tuning. Moving toward fault-tolerant quantum computation, increasing the number of physical qubits is another step toward effective error correction codes. Under a multiqubit architecture, flux control (Z) lines are crucial in tuning the frequency of the qubits and couplers. However, dense flux lines result in magnetic flux crosstalk, wherein magnetic flux applied to one element inadvertently affects neighboring qubits or couplers. This crosstalk obscures the idle frequency of the qubit when flux bias is applied, which degrades gate performance and calibration accuracy. In this study, we characterize flux crosstalk and suppress it in a multiqubit-coupler chip with multi-Z lines without adding additional readout for couplers. By quantifying the mutual flux-induced frequency shifts of qubits and couplers, we construct a cancellation matrix that enables precise compensation of non-local flux, demonstrating a substantial reduction in Z-line crosstalk from 56.5$\,$permille$\,$to 0.13$\,$permille$\,$ which is close to statistical error. Flux compensation corrects the CZ SWAP measurement, leading to a symmetric map with respect to flux bias. Compared with a crosstalk-free calculated CZ SWAP map, the measured map indicates that our approach provides a near-zero crosstalk for the coupler-transmon system. These results highlight the effectiveness of our approach in enhancing flux crosstalk-free control and supporting its potential for scaling superconducting quantum processors. △ Less

Submitted 19 December, 2025; v1 submitted 5 August, 2025; originally announced August 2025.

Comments: v3: 25 pages, 11 figures, 6 tables. Revisions include: revised several arguments in main text in main text and supplemental material; corrected mislabeled methods in Table S4; key results unchanged; updated references in main text and SI; minor typographical corrections

A Solvable Semi-infinite Fock-state-lattice SSH Model: the Stable Topological Zero Mode and the Non-Hermitian Bound Effect

Authors: Xing Yao Mi, Yong-Chun Liu, Zhi Jiao Deng, Chun Wang Wu, Ping Xing Chen

Abstract: Fock-state lattice (FSL) offers a powerful quantum simulator for topological phenomena due to the unbounded scalability and ease of implementation. Nevertheless, the unique topological properties induced by its site-dependent coupling have remained elusive, mainly due to the challenge of handling an infinite state space without translational symmetry. Here, we rigorously analyze the topological fe… ▽ More Fock-state lattice (FSL) offers a powerful quantum simulator for topological phenomena due to the unbounded scalability and ease of implementation. Nevertheless, the unique topological properties induced by its site-dependent coupling have remained elusive, mainly due to the challenge of handling an infinite state space without translational symmetry. Here, we rigorously analyze the topological features of a semi-infinite FSL-based Su-Schrieffer-Heeger (SSH) model, in both Hermitian and non-Hermitian realms, by mapping it to the solvable Jaynes-Cummings (JC) model via a unitary displacement transformation. We find a more stable topological zero mode than the conventional SSH model, originating from the bound state at the inherent domain wall under anisotropic conditions. With gain and loss introduced, we predict a non-Hermitian bound effect (NHBE), i. e., any state overlapping with the bound state will quickly stabilize to the domain wall, with the minimal stabilization time occurring in the vicinity of exceptional point (EP). The paritytime (PT ) phase transition can be observed by the oscillating-to-steady crossover of dynamics in the subspace orthogonal to the bound state. Furthermore, a concrete experimental proposal based on the trapped-ion setup is provided. △ Less

Submitted 10 October, 2025; v1 submitted 21 June, 2025; originally announced June 2025.

Comments: 17 pages, 6figures

Two imaginarity monotones induced by unified $(α,β)$-relative entropy

Authors: Chuanfa Wu, Zhaoqi Wu

Abstract: Complex numbers play a pivotal role in both mathematics and physics, particularly in quantum mechanics, and are extensively utilized to depict the behavior of microscopic particles. Recognizing the significance of complex numbers, a framework of imaginarity resource theory has recently been established. In this work, we propose two types of imaginarity monotones induced by the unified $(α,β)$-rela… ▽ More Complex numbers play a pivotal role in both mathematics and physics, particularly in quantum mechanics, and are extensively utilized to depict the behavior of microscopic particles. Recognizing the significance of complex numbers, a framework of imaginarity resource theory has recently been established. In this work, we propose two types of imaginarity monotones induced by the unified $(α,β)$-relative entropy and investigate their properties. Moreover, we give explicit examples to illustrate our results. △ Less

Submitted 11 June, 2025; originally announced June 2025.

Comments: 22 pages

Journal ref: Commun. Theor. Phys. 77 (2025) 095101

Quantifying imaginarity of quantum operations

Authors: Chuanfa Wu, Zhaoqi Wu

Abstract: Complex numbers are theoretically proved and experimentally confirmed as necessary in quantum mechanics and quantum information, and a resource theory of imaginarity of quantum states has been established. In this work, we establish a framework to quantify the imaginarity of quantum operations from the perspective of the ability to create or detect imaginarity, following the idea by Theurer {\it e… ▽ More Complex numbers are theoretically proved and experimentally confirmed as necessary in quantum mechanics and quantum information, and a resource theory of imaginarity of quantum states has been established. In this work, we establish a framework to quantify the imaginarity of quantum operations from the perspective of the ability to create or detect imaginarity, following the idea by Theurer {\it et al.} [Phys. Rev. Lett. \textbf{122}, 190405 (2019)] used in coherence theory. We present two types of imaginarity measures of quantum operations based on the norm and the weight, investigate their properties and relations, and derive the analytical formulas of the measure under the trace norm for qubit unitary operations. The results provide new insights into imaginarity of operations and deepen our understanding of dynamical imaginarity. △ Less

Submitted 7 April, 2026; v1 submitted 11 June, 2025; originally announced June 2025.

Comments: 32 pages

Journal ref: Sci. China-Phys. Mech. Astron. 2026, 69(3): 230316

Clock Synchronization for Drone-Based Entanglement Quantum Key Distribution

Authors: Jinquan Huang, Bangying Tang, Hui Han, JianJi Yi, Bo Xu, Chunqing Wu, Xiangwei Zhu, Wanrong Yu, Huicun Yu, Jiahao Li, Shihai Sun, Bo Liu

Abstract: Drone-based entanglement distribution provides full spatiotemporal coverage for quantum networks, enabling quantum key distribution (QKD) in dynamic environments. The security of QKD fundamentally depends on high-fidelity quantum state measurements, for which high-precision clock synchronization is indispensable, as timing jitter is inversely correlated with quantum state fidelity. However, drone-… ▽ More Drone-based entanglement distribution provides full spatiotemporal coverage for quantum networks, enabling quantum key distribution (QKD) in dynamic environments. The security of QKD fundamentally depends on high-fidelity quantum state measurements, for which high-precision clock synchronization is indispensable, as timing jitter is inversely correlated with quantum state fidelity. However, drone-based clock synchronization is constrained by SWaP (Size, Weight, and Power) limitations and dynamic mobility effects. Here, we propose a synchronization protocol for drone-based entanglement distribution, leveraging nanosecond-accurate Global Navigation Satellite System (GNSS) timing and entanglement-based timing correction to overcome SWaP constraints. Experimental results demonstrate 24 ps RMS synchronization in simulated free-space quantum channels with distance dynamics, without requiring precision reference clock. Our protocol enables drone-based entanglement distribution, paving the way for seamless wide-area and local-area quantum internet. △ Less

Submitted 9 June, 2025; originally announced June 2025.

Comments: 16 pages,6 figures

Magnonic entanglement in a chiral cavity-magnon coupling system

Authors: Yuxin Kang, Xin Zeng, Wuji Zhang, Chunfang Sun, Chunfeng Wu, Gangcheng Wang

Abstract: The generation of magnon entanglement and squeezing plays a crucial role in quantum information processing. In this study, we propose a scheme based on a chiral cavity-magnon system, which consists of a torus-shaped cavity and two yttrium iron garnet spheres. The magnon mode of each yttrium iron garnet sphere is selectively coupled to one of the two degenerate rotating microwave modes of the toroi… ▽ More The generation of magnon entanglement and squeezing plays a crucial role in quantum information processing. In this study, we propose a scheme based on a chiral cavity-magnon system, which consists of a torus-shaped cavity and two yttrium iron garnet spheres. The magnon mode of each yttrium iron garnet sphere is selectively coupled to one of the two degenerate rotating microwave modes of the toroidal cavity. The system aims to achieve entangled and squeezed magnon states through the mediation of the cavity. We further show that bipartite entanglement can be achieved by tuning external driving parameters. Additionally, our scheme does not rely on the magnon Kerr nonlinearity, which is usually extremely weak in yttrium iron garnet spheres. This work provides insights and methods for the research of quantum states in cavity-magnon systems. △ Less

Submitted 22 May, 2025; originally announced May 2025.

Holstein mechanism in single-site model with unitary evolution

Authors: Chen-Huan Wu

Abstract: We investigate the Holstein mechanism in a single-electron (one-site) system, where unitary evolution intrinsically involves both fermion and boson operators under nonadiabatic conditions. The resulting unitary dynamics and boson-frequency dependence reveal a quantum phase transition, evidenced by distinct short-time (power-law decay) and long-time (exponential decay) behaviors, which are manifest… ▽ More We investigate the Holstein mechanism in a single-electron (one-site) system, where unitary evolution intrinsically involves both fermion and boson operators under nonadiabatic conditions. The resulting unitary dynamics and boson-frequency dependence reveal a quantum phase transition, evidenced by distinct short-time (power-law decay) and long-time (exponential decay) behaviors, which are manifested in the polaronic shift, bosonic energy, and dynamics of reduced density matrix. This observation is consistent with a non-Markovian to Markovian transition. △ Less

Submitted 28 November, 2025; v1 submitted 21 May, 2025; originally announced May 2025.

Stark-induced tunable phase transition in the two-photon Dicke-Stark model

Authors: Cui-Lu Zhai, Wei Wu, Chun-Wang Wu, Ping-Xing Chen

Abstract: We theoretically investigate the superradiant phase transition (SPT) in the two-photon Dicke-Stark model, which incorporates both Rabi and Stark coupling. By introducing a Stark coupling term, we significantly reduce the critical Rabi coupling strength required to achieve the SPT, enabling it to occur even in strong coupling regimes. Using mean-field theory, we derive the conditions for the SPT an… ▽ More We theoretically investigate the superradiant phase transition (SPT) in the two-photon Dicke-Stark model, which incorporates both Rabi and Stark coupling. By introducing a Stark coupling term, we significantly reduce the critical Rabi coupling strength required to achieve the SPT, enabling it to occur even in strong coupling regimes. Using mean-field theory, we derive the conditions for the SPT and show that it exhibits a second-order phase transition. Surprisingly, we demonstrate that the transition point can be widely tuned by the Stark coupling strength. The signatures of these Stark-tunable SPT points are manifested through atomic averages. When quantum fluctuations are included, the spin-squeezing distributions also reveal the effects of Stark-tunable SPT points. In addition, we propose an experimentally feasible realization using an ion trap system driven by three lasers. Our scheme enables optical switching between normal and superradiant phases through pump field intensity modulation, where the Stark coupling coefficient serves as the optically tunable parameter. Our results offer a new approach to engineer the SPT, extending superradiance-based quantum technologies beyond the ultrastrong coupling regime. △ Less

Submitted 13 April, 2025; originally announced April 2025.

Journal ref: Phys. Rev. A 112, 013720 (2025)

Anomalous current-electric field characteristics in transport through a nanoelectromechanical systems

Authors: Chengjie Wu, Yi Ding, Yiying Yan, Yuguo Su, Elijah Omollo Ayieta, Slobodan Radošević, Georg Engelhardt, Gernot Schaller, JunYan Luo

Abstract: A deep understanding of the correlation between electronic and mechanical degrees of freedom is crucial to the development of quantum devices in a nanoelectromechanical system (NEMS). In this work, we first establish a fully quantum mechanical approach for transport through a NEMS device, which is valid for arbitrary bias voltages, temperatures, and electro-mechanical couplings. We find an anomalo… ▽ More A deep understanding of the correlation between electronic and mechanical degrees of freedom is crucial to the development of quantum devices in a nanoelectromechanical system (NEMS). In this work, we first establish a fully quantum mechanical approach for transport through a NEMS device, which is valid for arbitrary bias voltages, temperatures, and electro-mechanical couplings. We find an anomalous current-electric field characteristics at a low bias, where the current decreases with a rising electric field, associated with the backward tunneling of electrons for a weak mechanical damping. We reveal that this intriguing behavior arises from a combined effect of mechanical motion and Coulomb blockade, where the rapid increase of backward tunneling events at a large oscillation amplitude suppresses the forward current due to prohibition of double occupation. In the opposite limit of strong damping, the oscillator dissipates its energy to the environment and relaxes to the ground state rapidly. Electrons then transport via the lowest vibrational state such that the net current and its corresponding noise have a vanishing dependence on the electric field. △ Less

Submitted 13 May, 2025; v1 submitted 15 March, 2025; originally announced March 2025.

Scaffold-Assisted Window Junctions for Superconducting Qubit Fabrication

Authors: Chung-Ting Ke, Jun-Yi Tsai, Yen-Chun Chen, Zhen-Wei Xu, Elam Blackwell, Matthew A. Snyder, Spencer Weeden, Peng-Sheng Chen, Chih-Ming Lai, Shyh-Shyuan Sheu, Zihao Yang, Cen-Shawn Wu, Alan Ho, R. McDermott, John Martinis, Chii-Dong Chen

Abstract: The superconducting qubit is one of the promising directions in realizing fault-tolerant quantum computing (FTQC), which requires many high-quality qubits. To achieve this, it is desirable to leverage modern semiconductor industry technology to ensure quality, uniformity, and reproducibility. However, conventional Josephson junction fabrication relies mainly on resist-assistant double-angle evapor… ▽ More The superconducting qubit is one of the promising directions in realizing fault-tolerant quantum computing (FTQC), which requires many high-quality qubits. To achieve this, it is desirable to leverage modern semiconductor industry technology to ensure quality, uniformity, and reproducibility. However, conventional Josephson junction fabrication relies mainly on resist-assistant double-angle evaporation, posing integration challenges. Here, we demonstrate a lift-off-free qubit fabrication that integrates seamlessly with existing industrial technologies. This method employs a silicon oxide (SiO$_2$) scaffold to define an etched window with a well-controlled size to form a Josephson junction. The SiO$_2$, which has a large dielectric loss, is etched away in the final step using vapor HF leaving little residue. This Window junction (WJ) process mitigates the degradation of qubit quality during fabrication and allows clean removal of the scaffold. The WJ process is validated by inspection and Josephson junction measurement. The scaffold removal process is verified by measuring the quality factor of the resonators. Furthermore, compared to scaffolds fabricated by plasma-enhanced chemical vapor deposition (PECVD), qubits made by WJ through physical vapor deposition (PVD) achieve relaxation time up to $57\,μ\text{s}$. Our results pave the way for a lift-off-free qubit fabrication process, designed to be compatible with modern foundry tools and capable of minimizing damage to the substrate and material surfaces. △ Less

Submitted 13 March, 2025; originally announced March 2025.

Exploring the boundary of quantum network states from inside out

Authors: Xiang Zhou, Zhen-Peng Xu, Liang-Liang Sun, Chunfeng Wu, Sixia Yu

Abstract: Quantum networks with bipartite resources and shared randomness present the simplest infrastructure for implementing a future quantum internet. Here, we shall investigate which kinds of entanglement can or cannot be generated from this kind of quantum network by examining their fidelity with different graph states. On the one hand, based on a standard form of graph states under local complementati… ▽ More Quantum networks with bipartite resources and shared randomness present the simplest infrastructure for implementing a future quantum internet. Here, we shall investigate which kinds of entanglement can or cannot be generated from this kind of quantum network by examining their fidelity with different graph states. On the one hand, based on a standard form of graph states under local complementation and a fine-grained uncertainty relation between two projections, we establish upper bounds of fidelity that improve over previous results by at least $25\%$ as the dimension of local systems tends to infinity. On the other hand, in the triangle network, we propose efficient protocols to generate genuine multipartite entangled states from the network, providing significant nontrivial lower bounds of fidelity with high dimensional GHZ states. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Comments: 5+8 page, 10 figures. See also the related work by Justus Neumann et al. in today's arXiv listing

Singularity and universality from von Neumann to Rényi entanglement entropy and disorder operator in Motzkin chains

Authors: Jianyu Wang, Zenan Liu, Zheng Yan, Congjun Wu

Abstract: The Rényi entanglement entropy is widely used in studying quantum entanglement properties in strongly correlated systems, whose analytic continuation as the Rényi index $n \to 1$ is often believed to yield the von Neumann entanglement entropy. However, earlier findings indicate that this process exhibits a singularity for the colored Motzkin spin chain problem, leading to different scaling behavio… ▽ More The Rényi entanglement entropy is widely used in studying quantum entanglement properties in strongly correlated systems, whose analytic continuation as the Rényi index $n \to 1$ is often believed to yield the von Neumann entanglement entropy. However, earlier findings indicate that this process exhibits a singularity for the colored Motzkin spin chain problem, leading to different scaling behaviors of $\sim \sqrt{l}$ and $\sim \log{l}$ for the von Neumann and Rényi entropies, respectively. Our analytical and numerical calculations confirm this transition, which can be explained by the exponentially increasing density of states in the entanglement spectrum that we extract numerically. Disorder operators are further employed under various symmetries to study such a system. Both analytical and numerical results demonstrate that the scaling of the disorder operators also follows $\log{l}$ as the leading behavior, matching that of the Rényi entropy. We propose that the coefficient of the term $\log{l}$ is a universal constant shared by both the Rényi entropies and disorder operators. This universal constant could potentially help capture the underlying constraint physics of Motzkin walks. △ Less

Submitted 18 February, 2025; v1 submitted 28 January, 2025; originally announced January 2025.

Observation of Subnatural-Linewidth Biphotons In a Two-Level Atomic Ensemble

Authors: Jyun-Kai Lin, Tzu-Hsiang Chien, Chin-Te Wu, Ravikumar Chinnarasu, Shengwang Du, Ite A. Yu, Chih-Sung Chuu

Abstract: Biphotons and single photons with narrow bandwidths and long coherence times are essential to the realization of long-distance quantum communication (LDQC) and linear optical quantum computing (LOQC). In this Letter, we manipulate the biphoton wave functions of the spontaneous four-wave mixing in a two-level atomic ensemble with a single-laser pump scheme. Our innovative experimental approach enab… ▽ More Biphotons and single photons with narrow bandwidths and long coherence times are essential to the realization of long-distance quantum communication (LDQC) and linear optical quantum computing (LOQC). In this Letter, we manipulate the biphoton wave functions of the spontaneous four-wave mixing in a two-level atomic ensemble with a single-laser pump scheme. Our innovative experimental approach enables the generation of biphotons with a sub-MHz bandwidth of 0.36 MHz, a record spectral brightness of $2.28\times10^7$${\rm s}^{-1}{\rm mW}^{-1}{\rm MHz}^{-1}$, and a temporally symmetric wave packet at moderate optical depth. The strong non-classical cross-correlation of the biphotons also enables the observation of heralded sub-MHz-linewidth single photons with a pronounced single-photon nature. The generation of sub-MHz-linewidth biphotons and single photons with a two-level atomic ensembles not only finds applications in quantum repeaters and large cluster states for LDQC and LOQC but also opens up the opportunity to miniaturize the biphoton or single-photon sources for chip-scale quantum technologies. △ Less

Submitted 21 January, 2025; originally announced January 2025.

Machine Learning Enhanced Quantum State Tomography on FPGA

Authors: Hsun-Chung Wu, Hsien-Yi Hsieh, Zhi-Kai Xu, Hua Li Chen, Zi-Hao Shi, Po-Han Wang, Popo Yang, Ole Steuernagel, Chien-Ming Wu, Ray-Kuang Lee

Abstract: Machine learning techniques have opened new avenues for real-time quantum state tomography (QST). In this work, we demonstrate the deployment of machine learning-based QST onto edge devices, specifically utilizing field programmable gate arrays (FPGAs). This implementation is realized using the {\it Vitis AI Integrated Development Environment} provided by AMD\textsuperscript \textregistered~Inc. C… ▽ More Machine learning techniques have opened new avenues for real-time quantum state tomography (QST). In this work, we demonstrate the deployment of machine learning-based QST onto edge devices, specifically utilizing field programmable gate arrays (FPGAs). This implementation is realized using the {\it Vitis AI Integrated Development Environment} provided by AMD\textsuperscript \textregistered~Inc. Compared to the Graphics Processing Unit (GPU)-based machine learning QST, our FPGA-based one reduces the average inference time by an order of magnitude, from 38 ms to 2.94 ms, but only sacrifices the average fidelity about $1\% $ reduction (from 0.99 to 0.98). The FPGA-based QST offers a highly efficient and precise tool for diagnosing quantum states, marking a significant advancement in the practical applications for quantum information processing and quantum sensing. △ Less

Submitted 8 January, 2025; originally announced January 2025.

Comments: 6 pages, 5 figures

Generation of high-fidelity Greenberger-Horne-Zeilinger states in a driven hybrid quantum system

Authors: Xin Zeng, Yuxin Kang, Chunfang Sun, Chunfeng Wu, Gangcheng Wang

Abstract: In this study, we propose a theoretical scheme for achieving long-distance Greenberger-Horne-Zeilinger states in a driven hybrid quantum system. By applying a microwave field to the YIG sphere, we utilize the Kerr effect to induce the squeezing of the magnon, thereby achieving an exponential enhancement of the coupling strength between the magnonic mode and spins, and we also discuss in detail the… ▽ More In this study, we propose a theoretical scheme for achieving long-distance Greenberger-Horne-Zeilinger states in a driven hybrid quantum system. By applying a microwave field to the YIG sphere, we utilize the Kerr effect to induce the squeezing of the magnon, thereby achieving an exponential enhancement of the coupling strength between the magnonic mode and spins, and we also discuss in detail the relationship between the squeezing parameter and the external microwave field. By means of the Schrieffer-Wolff transformation, the magnonic mode can be adiabatically eliminated under the large detuning condition, thereby establishing a robust effective interaction between spins essential for realizing the desired entangled state. Numerical simulations indicate that the squeezing parameter can be effectively increased by adjusting the driving field, and our proposal can generate high-fidelity Greenberger-Horne-Zeilinger states even in dissipative systems. Additionally, we extensively discuss the influence of inhomogeneous broadening on the entangled states, and the experimental feasibility shows that our results provide possibilities in the realms of quantum networking and quantum computing. △ Less

Submitted 4 November, 2024; originally announced November 2024.

Comments: 11 pages, 5 fighres

Quantum Phonon Dynamics Induced Spontaneous Spin-Orbit Coupling

Authors: Xiangyu Zhang, Da Wang, Congjun Wu

Abstract: Spin-orbit coupling in solids is typically a single-body effect arising from relativity. In this work, we propose a spontaneous generation of spin-orbit coupling from symmetry breaking. A spin-dependent electron-phonon coupling model is investigated on a half-filled square lattice, which is solved by sign-problem-free quantum Monte Carlo simulations. The phase diagram as function of phonon frequen… ▽ More Spin-orbit coupling in solids is typically a single-body effect arising from relativity. In this work, we propose a spontaneous generation of spin-orbit coupling from symmetry breaking. A spin-dependent electron-phonon coupling model is investigated on a half-filled square lattice, which is solved by sign-problem-free quantum Monte Carlo simulations. The phase diagram as function of phonon frequency $ω$ and coupling constant $λ$ is fully investigated. The spin-orbit coupling emerges as an order in the ground state for any $λ$ in the adiabatic limit, accompanied by a breathing mode of lattice distortion and a staggered loop spin-current. This phase dominates in the entire range of $ω$ with $λ< λ_{\infty}$, a critical value in the $ω\to \infty$ limit. With increasing $ω$ and $λ> λ_{\infty}$, the emergent spin-orbit coupling is suppressed and a phase transition occurs leading to charge-density-wave degenerate with superconductivity order. Our work opens up the possibility of hidden spin-orbit coupling in materials where it is otherwise forbidden by lattice symmetry and paves the way to explore new usable materials or devices in spintronics. △ Less

Submitted 22 October, 2024; originally announced October 2024.

Comments: 5 pages, 7 figures

Quantum Stirling heat engine based on Two-qubit Quantum Rabi Model with Spin-Spin Coupling

Authors: Luxin Xu, Chunfeng Wu, Changliang Ren

Abstract: Enhancing the efficiency of quantum heat engines (QHEs) is crucial for advancing fundamental research and quantum technology.We here we explore a quantum Stirling cycle using a twoqubit quantum Rabi model with spin-spin coupling as a working medium. We propose parameter optimization strategies to maximize the efficiency of the heat engine, as there are multiple ways for the effective coupling cons… ▽ More Enhancing the efficiency of quantum heat engines (QHEs) is crucial for advancing fundamental research and quantum technology.We here we explore a quantum Stirling cycle using a twoqubit quantum Rabi model with spin-spin coupling as a working medium. We propose parameter optimization strategies to maximize the efficiency of the heat engine, as there are multiple ways for the effective coupling constant to move toward its critical value. In the normal phase of the system, the efficiency can be improved by increasing the temperature ratio of hot-to-cold reservoirs and enhancing spin-mode coupling strength. However, increasing spin-spin coupling strength inhibits the improvement of the efficiency. As the system goes to its critical point, QHE efficiency under low-temperature conditions tends to the Carnot limit. In the superradiant phase, the efficiency approaches the Carnot limit more closely as the cold reservoir's temperature decreases given a constant temperature ratio. Conversely, when the cold reservoir's temperature rises, the efficiency increases due to a higher ratio of spin-mode coupling strength to mode frequency. If the spinspin coupling strength is constant, increasing the hot-to-cold reservoir temperature ratio requires a corresponding increase in spin-mode coupling strength to achieve the Carnot efficiency. Our work deepens the understanding of QHE performance under various conditions and provides operative methods for optimizing the efficiency of QHE. △ Less

Submitted 5 October, 2024; originally announced October 2024.

An Explicit Wavefunction of the Interacting Non-Hermitian Spin-1/2 1D System

Authors: Yue Wang, Xiangyu Zhang, Zhesen Yang, Congjun Wu

Abstract: We present an explicit Bethe-ansatz wavefunction to a 1D spin-$\frac{1}{2}$ interacting fermion system, manifesting a many-body resonance resulting from the interplay between interaction and non-Hermitian spin-orbit coupling. In the dilute limit, the Bethe-ansatz wavefunction is factorized into Slater determinants and a Jastrow factor. An effective thermodynamic distribution is constructed with an… ▽ More We present an explicit Bethe-ansatz wavefunction to a 1D spin-$\frac{1}{2}$ interacting fermion system, manifesting a many-body resonance resulting from the interplay between interaction and non-Hermitian spin-orbit coupling. In the dilute limit, the Bethe-ansatz wavefunction is factorized into Slater determinants and a Jastrow factor. An effective thermodynamic distribution is constructed with an effective Hamiltonian including a repulsion resulting from Pauli's exclusion principle and a distinctive zigzag potential arising from the resonance. The competition between these effects leads to a transition from a uniformly distributed configuration to a phase separation. Clustering of particles with identical spins is observed in the latter phase, demonstrating that the many-body resonance effect is enhanced by the repulsive interaction. △ Less

Submitted 20 January, 2026; v1 submitted 6 September, 2024; originally announced September 2024.

Comments: 7+6 pages, 3+4 figures

Journal ref: Phys. Rev. Lett. 136, 036501 (2026)

Microsatellite-based real-time quantum key distribution

Authors: Yang Li, Wen-Qi Cai, Ji-Gang Ren, Chao-Ze Wang, Meng Yang, Liang Zhang, Hui-Ying Wu, Liang Chang, Jin-Cai Wu, Biao Jin, Hua-Jian Xue, Xue-Jiao Li, Hui Liu, Guang-Wen Yu, Xue-Ying Tao, Ting Chen, Chong-Fei Liu, Wen-Bin Luo, Jie Zhou, Hai-Lin Yong, Yu-Huai Li, Feng-Zhi Li, Cong Jiang, Hao-Ze Chen, Chao Wu , et al. (16 additional authors not shown)

Abstract: A quantum network provides an infrastructure connecting quantum devices with revolutionary computing, sensing, and communication capabilities. As the best-known application of a quantum network, quantum key distribution (QKD) shares secure keys guaranteed by the laws of quantum mechanics. A quantum satellite constellation offers a solution to facilitate the quantum network on a global scale. The M… ▽ More A quantum network provides an infrastructure connecting quantum devices with revolutionary computing, sensing, and communication capabilities. As the best-known application of a quantum network, quantum key distribution (QKD) shares secure keys guaranteed by the laws of quantum mechanics. A quantum satellite constellation offers a solution to facilitate the quantum network on a global scale. The Micius satellite has verified the feasibility of satellite quantum communications, however, scaling up quantum satellite constellations is challenging, requiring small lightweight satellites, portable ground stations and real-time secure key exchange. Here we tackle these challenges and report the development of a quantum microsatellite capable of performing space-to-ground QKD using portable ground stations. The quantum microsatellite features a payload weighing approximately 23 kg, while the portable ground station weighs about 100 kg. These weights represent reductions by more than an order and two orders of magnitude, respectively, compared to the Micius satellite. Additionally, we multiplex bidirectional satellite-ground optical communication with quantum communication, enabling key distillation and secure communication in real-time. Using the microsatellite and the portable ground stations, we demonstrate satellite-based QKD with multiple ground stations and achieve the sharing of up to 0.59 million bits of secure keys during a single satellite pass. The compact quantum payload can be readily assembled on existing space stations or small satellites, paving the way for a satellite-constellation-based quantum and classical network for widespread real-life applications. △ Less

Submitted 20 August, 2024; originally announced August 2024.

Comments: 40 pages, 8 figures

Journal ref: Nature 640, 47-54 (2025)

From Maximum Cut to Maximum Independent Set

Authors: Chuixiong Wu, Jianan Wang, Fen Zuo

Abstract: The Maximum Cut (Max-Cut) problem could be naturally expressed either in a Quadratic Unconstrained Binary Optimization (QUBO) formulation, or as an Ising model. It has long been known that the Maximum Independent Set (MIS) problem could also be related to a specific Ising model. Therefore, it would be natural to attack MIS with various Max-Cut/Ising solvers. It turns out that this strategy greatly… ▽ More The Maximum Cut (Max-Cut) problem could be naturally expressed either in a Quadratic Unconstrained Binary Optimization (QUBO) formulation, or as an Ising model. It has long been known that the Maximum Independent Set (MIS) problem could also be related to a specific Ising model. Therefore, it would be natural to attack MIS with various Max-Cut/Ising solvers. It turns out that this strategy greatly improves the approximation for the independence number of random Erdős-Rényi graphs. It also exhibits perfect performance on a benchmark arising from coding theory. These results pave the way for further development of approximate quantum algorithms on MIS, and specifically on the corresponding coding problems. △ Less

Submitted 18 September, 2024; v1 submitted 13 August, 2024; originally announced August 2024.

Comments: Independence number of 1dc.2048 updated, new results for 1dc.4096 included, references added; 22 pages, 5 figures

Dynamical resource theory of incompatibility preservability

Authors: Chung-Yun Hsieh, Benjamin Stratton, Chao-Hsien Wu, Huan-Yu Ku

Abstract: The uncertainty principle is one of quantum theory's most foundational features. It underpins a quantum phenomenon called measurement incompatibility -- two physical observables of a single quantum system may not always be measured simultaneously. Apart from being fundamentally important, measurement incompatibility is also a powerful resource in the broad quantum science and technologies, with wi… ▽ More The uncertainty principle is one of quantum theory's most foundational features. It underpins a quantum phenomenon called measurement incompatibility -- two physical observables of a single quantum system may not always be measured simultaneously. Apart from being fundamentally important, measurement incompatibility is also a powerful resource in the broad quantum science and technologies, with wide applications to cryptography, communication, random number generation, and device-independent tasks. Since every physical system is unavoidably subject to noise, an important, yet still open, question is how to characterise the ability of noisy quantum dynamics to preserve measurement incompatibility. This work fills this gap by providing the first resource theory of this ability, termed incompatibility preservability. We quantify incompatibility preservability by a robustness measure. Then, we introduce an operational task, entanglement-assisted filter game, to completely characterise both the robustness measure and the conversion of incompatibility preservability. Our results provide a general framework to describe how noisy dynamics affect the uncertainty principle's signature. △ Less

Submitted 23 January, 2025; v1 submitted 12 August, 2024; originally announced August 2024.

Comments: 5+5 pages; 4 figures

Quantum thermalization and Floquet engineering in a spin ensemble with a clock transition

Authors: Mi Lei, Rikuto Fukumori, Chun-Ju Wu, Edwin Barnes, Sophia Economou, Joonhee Choi, Andrei Faraon

Abstract: Studying and controlling quantum many-body interactions is fundamentally important for quantum science and related emerging technologies. Optically addressable solid-state spins offer a promising platform for exploring various quantum many-body phenomena due to their scalability to a large Hilbert space. However, it is often challenging to probe many-body dynamics in solid-state spin systems due t… ▽ More Studying and controlling quantum many-body interactions is fundamentally important for quantum science and related emerging technologies. Optically addressable solid-state spins offer a promising platform for exploring various quantum many-body phenomena due to their scalability to a large Hilbert space. However, it is often challenging to probe many-body dynamics in solid-state spin systems due to large on-site disorder and undesired coupling to the environment. Here, we investigate an optically addressable solid-state spin system comprising a strongly interacting ensemble of millions of ytterbium-171 ions in a crystal. Notably, this platform features a clock transition that gives rise to pure long-range spin-exchange interactions, termed the dipolar XY model. Leveraging this unique feature, we investigate quantum thermalization by varying the relative ratio of interaction strength to disorder, dynamically engineering the XY model into other many-body Hamiltonian models, and realizing a time-crystalline phase of matter through periodic driving. Our findings indicate that an ensemble of rare-earth ions serves as a versatile testbed for many-body physics and offers valuable insights for advancing quantum technologies. △ Less

Submitted 31 July, 2024; originally announced August 2024.

Thermometry of Trapped Ions Based on Bichromatic Driving

Authors: Xie-Qian Li, Yi Tao, Ting Chen, Wei Wu, Yi Xie, Chun-Wang Wu, Ping-Xing Chen

Abstract: Accurate thermometry of laser-cooled ions is crucial for the performance of the trapped-ions quantum computing platform. However, most existing methods face a computational exponential bottleneck. Recently, a thermometry method based on bichromatic driving was theoretically proposed by Ivan Vybornyi et al. to overcome this obstacle, which allows the computational complexity to remain constant with… ▽ More Accurate thermometry of laser-cooled ions is crucial for the performance of the trapped-ions quantum computing platform. However, most existing methods face a computational exponential bottleneck. Recently, a thermometry method based on bichromatic driving was theoretically proposed by Ivan Vybornyi et al. to overcome this obstacle, which allows the computational complexity to remain constant with the increase of ion numbers. In this paper, we provide a detailed statistical analysis of this method and prove its robustness to several imperfect experimental conditions using Floquet theory. We then experimentally verify its good performance on a linear segmented surface-electrode ion trap platform for the first time. This method is proven to be effective from near the motional ground state to a few mean phonon numbers. Our theoretical analysis and experimental verification demonstrate that the scheme can accurately and efficiently measure the temperature in ion crystals. △ Less

Submitted 21 July, 2024; originally announced July 2024.

Field Test of Quantum Key Distribution with High Key Creation Efficiency

Authors: Yung-Cheng Kao, Sheng-Hsuan Huang, Chin-Hsuan Chang, Chih-Hsiang Wu, Shih-Hsien Chu, Jian Jiang, An-Chi Zhang, Sheng-Yao Huang, Jhih-Heng Yan, Kai-Ming Feng, Chih-Sung Chuu

Abstract: Quantumkey distribution (QKD) promises unconditional security for communication. However, the random choices of the measurement basis in QKD usually result in low key creation efficiency. This drawback is overcome in the differential-phase-shift QKD, provided that each photon can be prepared in a large number of time bins with a proper waveform. In this work we develop a miniature 1550-nm single-p… ▽ More Quantumkey distribution (QKD) promises unconditional security for communication. However, the random choices of the measurement basis in QKD usually result in low key creation efficiency. This drawback is overcome in the differential-phase-shift QKD, provided that each photon can be prepared in a large number of time bins with a proper waveform. In this work we develop a miniature 1550-nm single-photon source to generate narrowband single photon in 50 time bins with a nearly optimal waveform for achieving unity key creation efficiency. By utilizing these single photons in the field test, we demonstrate the differential-phase-shift QKD with a key creation efficiency of 97%. Our work shows that the practical QKD can benefit from the narrowband single photons with controllable waveforms. △ Less

Submitted 11 June, 2024; originally announced June 2024.

Comments: 9pages, 4figures

Journal ref: Opt. Express 31, 30239-30247 (2023)

Phonon Number Measurement Using Optimal Composite Pulses

Authors: Xie-Qian Li, Chun-Wang Wu, Ping-Xing Chen

Abstract: Measuring the phonon number of the laser-cooled ions is an indispensable step in evaluating whether an ion is in ground state. At present, commonly used methods in the experiments are red-to-blue sideband ratios and adiabatic evolution red-sideband methods. We theoretically propose a method using composite pulses which does not need a fit of state evolution and can directly measure the population… ▽ More Measuring the phonon number of the laser-cooled ions is an indispensable step in evaluating whether an ion is in ground state. At present, commonly used methods in the experiments are red-to-blue sideband ratios and adiabatic evolution red-sideband methods. We theoretically propose a method using composite pulses which does not need a fit of state evolution and can directly measure the population of the selected Fock state. It can measure higher Fock state population more directly comparing with the adiabatic evolution red-sideband method. We use quantum optimal control method to improve the fidelity of unitary operation of the composite pulses. With quantum optimal control technology, we can discuss the situation where the laser strength is strong, and many approximations will not be necessary, where the gate fidelity can be further improved. Then we give a method to modify the measurement result for a higher accuracy which has a good performance, and we give an example to illustrate its application on high Fock state measurement. △ Less

Submitted 25 November, 2024; v1 submitted 27 May, 2024; originally announced May 2024.

Sharing Quantum Steering via Standard Projective Measurements

Authors: Shufen Dong, Zinuo Cai, Chunfeng Wu, Changliang Ren

Abstract: We propose a scheme for the sharing of quantum steering among three observers, Alice, Bob, and Charlie using standard projective measurements. We show that in the unilateral sequential scenario, Alice can steer Bob's and Charlie's states and conversely, Bob and Charlie can steer Alice's state. Unlike the quantum steering sharing achieved through weak measurements, we use the standard projective me… ▽ More We propose a scheme for the sharing of quantum steering among three observers, Alice, Bob, and Charlie using standard projective measurements. We show that in the unilateral sequential scenario, Alice can steer Bob's and Charlie's states and conversely, Bob and Charlie can steer Alice's state. Unlike the quantum steering sharing achieved through weak measurements, we use the standard projective measurements to enable quantum steering sharing. Quantum steering is demonstrated by the violations of the linear steering inequality among different observer combinations. We find that Alice can simultaneously steer both Bob's and Charlie's states, and Bob and Charlie can simultaneously steer Alice's state, regardless of whether they are in maximally entangled states or partially entangled states. The maximum double violation of the linear steering inequalities obtained from partially entangled states can be greater in some cases than that obtained from maximally entangled states when randomly combining the case of two projective measurements and the case of two identity measurements. Additionally, we verify hybrid quantum correlation sharing through the double violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality and the linear steering inequality. Our results provide a new perspective for the study of quantum steering and may lead to applications in quantum random access code, randomness certification, and self-testing process. △ Less

Submitted 14 May, 2024; originally announced May 2024.

Protecting quantum gates from arbitrary single- and two-qubit errors

Authors: Chunfeng Wu, Gangcheng Wang, Xun-Li Feng

Abstract: We explore the protection of quantum gates from arbitrary single- and two-qubit noises with properly designed dynamical decoupling pulses. The proposed dynamical decoupling method is a concatenation of a sequence of pulses formed by $σ_x$, $σ_xσ_x$ with another sequence constructed by $σ_z$, $σ_zσ_z$. The concatenation of the two sequences results in desired pulses to fight agianst any single- and… ▽ More We explore the protection of quantum gates from arbitrary single- and two-qubit noises with properly designed dynamical decoupling pulses. The proposed dynamical decoupling method is a concatenation of a sequence of pulses formed by $σ_x$, $σ_xσ_x$ with another sequence constructed by $σ_z$, $σ_zσ_z$. The concatenation of the two sequences results in desired pulses to fight agianst any single- and two-qubit errors. The success of our method relies on the ability to adjust system parameters or interaction terms, which can be achieved in different physical systems, including trapped ions and superconducting qubits. We finally explore the performance of our method numerically with the above-mentioned errors that are changing at any moment and show the preferred protection offered by the method. Therefore, our method is a timely step forward in preserving quantum gates at the level of physical qubits. △ Less

Submitted 7 May, 2024; originally announced May 2024.

Comments: 5 pages