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arXiv 2022年

作者： Lu, Zhanpeng Xu, Zhihao Zhang, Yunbo Institute of Theoretical Physics State Key Laboratory of Quantum Optics and Quantum Optics Devices Shanxi University Taiyuan030006 China Key Laboratory of Optical Field Manipulation of Zhejiang Province Physics Department of Zhejiang Sci-Tech University Hangzhou310018 China

We uncover the relationship of topology and disorder in a one-dimensional Su-Schrieffer-Heeger chain subjected to a slowly varying quasi-periodic modulation. By numerically calculating the disorder-averaged winding number and analytically studying the localization length of the zero modes, we obtain the topological phase diagram, which implies that the topological Anderson insulator (TAI) can be induced by a slowly varying quasiperiodic modulation. Moreover, unlike the localization properties in the TAI phase caused by random disorder, mobility edges can enter into the TAI region identified by the fractal dimension, the inverse participation ratio, and the spatial distributions of the wave functions, the boundaries of which coincide with our analytical results. © 2022, CC BY.

关键词： Fractal dimension

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Collisional dynamics of symmetric two-dimensional quantum droplets

arXiv

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arXiv 2024年

作者： Hu, Yanming Fei, Yifan Chen, Xiao-Long Zhang, Yunbo Institute of Theoretical Physics State Key Laboratory of Quantum Optics and Quantum Optics Devices Shanxi University Taiyuan030006 China Department of Physics Key Laboratory of Optical Field Manipulation of Zhejiang Province Zhejiang Sci-Tech University Hangzhou310018 China

The collisional dynamics of two symmetric droplets with equal intraspecies scattering lengths and particle number density for each component is studied by solving the corresponding extended Gross-Pitaevskii equation in two dimensions by including a logarithmic correction term in the usual contact interaction. We find the merging droplet after collision experiences a quadrupole oscillation in its shape and the oscillation period is found to be independent of the incidental momentum for small droplets. With increasing collision momentum the colliding droplets may separate into two, or even more, and finally into small pieces of droplets. For these dynamical phases, we manage to present boundaries determined by the remnant particle number in the central area and the damped oscillation of the quadrupole mode. A stability peak for the existence of droplets emerges at the critical particle number Nc 48 for the quasi-Gaussian and flat-top shapes of the droplets. © 2024, CC BY.

关键词： Drops

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Recognition of Schrödinger cat state based on CNN

arXiv

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arXiv 2024年

作者： Zhang, Tao Zhao, Chaoying School of Sciences Hangzhou Dianzi University Hangzhou310018 China State Key Laboratory of Quantum Optics and Quantum Optics Devices Institute of Opto-Electronics Shanxi University Taiyuan030006 China Zhejiang Key Laboratory of Quantum State Control and Optical Field Manipulation Hangzhou Dianzi University Hangzhou310018 China

We applied convolutional neural networks to the classification of cat states and coherent states. Initially, we generated datasets of Schrödinger cat states and coherent states from nonlinear processes and preprocessed these datasets. Subsequently, we constructed both LeNet and ResNet network architectures, adjusting parameters such as convolution kernels and strides to optimal values. We then trained both LeNet and ResNet on the training sets. The loss function values indicated that ResNet performs better in classifying cat states and coherent states. Finally, we evaluated the trained models on the test sets, achieving an accuracy of 97.5% for LeNet and 100% for ResNet. We evaluated cat states and coherent states with different α, demonstrating a certain degree of generalization capability. The results show that LeNet may mistakenly recognize coherent states as cat states without coherent features, while ResNet provides a feasible solution to the problem of mistakenly recognizing cat states and coherent states by traditional neural networks. Copyright © 2024, The Authors. All rights reserved.

关键词： Convolution

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Efficient evolution framework for chirality control in non-Hermitian systems with adiabaticity engineering

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Physical Review B 2024年第6期110卷 064308-064308页

作者： Dong Wang Wen-Xi Huang Bo Zhou Wenduo Yu Pei-Chao Cao Yu-Gui Peng Zheng-Yang Zhou Hongsheng Chen Xue-Feng Zhu Ying Li State Key Laboratory of Extreme Photonics and Instrumentation Key Laboratory of Advanced Micro/Nano Electronic Devices & Smart Systems of Zhejiang International Joint Innovation Center The Electromagnetics Academy at Jinhua Institute of Zhejiang University Shaoxing Institute of Zhejiang University School of Physics and Innovation Institute Key Laboratory of Optical Field Manipulation of Zhejiang Province Department of Physics

The eigenvalue of a non-Hermitian Hamiltonian often forms a self-intersecting Riemann surface, leading to a unique mode conversion phenomenon when the Hamiltonian evolves along certain loop paths around an exceptional point (EP). However, two fundamental problems exist with the conventional scheme of EP encircling: the speed of mode conversion is restricted by the adiabatic requirement, and the chirality cannot be freely controlled. Here, we introduce a method which dynamically engineers the adiabaticity in the evolution of non-Hermitian Hamiltonians that allows for both chiral and nonchiral mode conversion on the same path. Our method is based on quantifying and controlling the instantaneous adiabaticity, allowing for nonuniform evolution throughout the entire path. We apply our method into the microwave waveguide system and by optimizing the distributed adiabaticity along the evolution loop, we achieve the same quality of mode conversion as conventional quasiadiabatic evolution in only one-fourth of the time. Our approach provides an on-demand solution to address the speed and chirality challenges associated with EP encircling, which does not depend on specific model. It also facilitates the dynamic manipulation and regulation of nonadiabatic processes, thereby accelerating the operation and allowing for a selection among various mode conversion patterns.

关键词： Photonics Non-Hermitian systems PT-symmetry

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Yu-Shiba-Rusinov states in s-wave kagome superconductors: Self-consistent Bogoliubov-de Gennes calculations

arXiv

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arXiv 2024年

作者： Ding, Shuaibo Bai, Yunfei Bulekov, A.A. Zhang, Wenhui Shanenko, A.A. Chen, Yajiang Zhejiang Key Laboratory of Quantum State Control and Optical Field Manipulation Department of Physics Zhejiang Sci-Tech University Hangzhou310018 China HSE University Moscow101000 Russia School of Electronic Engineering Nanjing Xiaozhuang University Nanjing China

Significant research has recently been conducted into the Yu-Shiba-Rusinov (YSR) states in kagome superconductors through theoretical modeling and experimental investigations. However, additional efforts are still needed to further understand the local superconductivity near magnetic impurities in the kagome lattice and clarify how relevant quantities depend on the interaction strength J between such impurities and electrons. In this study, we explore a self-consistent numerical solution of the Bogoliubov-de Gennes equations for an s-wave superconducting kagome model with a single classical magnetic impurity. Our study reveals that with increasing J, the local pair potential is systematically depressed in the vicinity of the impurity, similar to previous results obtained for the square and triangular lattices. Moreover, when further increasing J, the system undergoes a first-order phase transition with the appearance of stable and metastable states, reflecting the presence of the hysteresis loop in the pertinent quantities. As a consequence of this transition, the minimal energy of the stable YSR state is nonzero at any J, contrary to the expectations based on the assumption of a constant pair potential. A distinctive feature of the kagome lattice is that characteristics of the first-order transition are very sensitive to the position of the chemical potential within the kagome energy spectrum. Copyright © 2024, The Authors. All rights reserved.

关键词： Shear waves

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Doppler cooling of buffer-gas-cooled barium monofluoride molecules

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Physical Review A 2022年第3期105卷 033307-033307页

作者： Yuhe Zhang Zixuan Zeng Qian Liang Wenhao Bu Bo Yan Interdisciplinary Center of Quantum Information State Key Laboratory of Modern Optical Instrumentation and Zhejiang Province Key Laboratory of Quantum Technology and Device of Physics Department Zhejiang University Hangzhou 310027 China Beijing Automation Control Equipment Institute Beijing 100074 China

We demonstrate one-dimensional Doppler cooling of a beam of buffer-gas-cooled barium monofluoride (BaF) molecules. This represents a key step towards further cooling and trapping of BaF molecules. The dependencies of the cooling efficiency on the detuning of laser, the intensity of the laser, and the bias field are systematically studied. Furthermore, the numerical simulations with a Monte Carlo method agree quite well with our data.

关键词： Atom & ion cooling Cold and ultracold molecules

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Probing PT-Symmetry Breaking of Non-Hermitian Topological Photonic states via Strong Photon-Magnon Coupling

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Physical Review Letters 2024年第15期132卷 156901-156901页

作者： Jie Qian Jie Li Shi-Yao Zhu J. Q. You Yi-Pu Wang Zhejiang Key Laboratory of Micro-Nano Quantum Chips and Quantum Control School of Physics and State Key Laboratory for Extreme Photonics and Instrumentation Zhejiang University Hangzhou 310027 China College of Optical Science and Engineering Zhejiang University Hangzhou 310027 China Hefei National Laboratory Hefei 230088 China

Light-matter interaction is crucial to both understanding fundamental phenomena and developing versatile applications. Strong coupling, robustness, and controllability are the three most important aspects in realizing light-matter interactions. Topological and non-Hermitian photonics have provided frameworks for robustness and control flexibility, respectively. How to engineer the properties of the edge state such as photonic density of state by using non-Hermiticity while ensuring topological protection has not been fully studied. Here we construct a parity-time-symmetric dimerized photonic lattice and probe the spontaneous PT-symmetry breaking of the edge states by utilizing the strong coupling between the photonic mode and a spin ensemble. Our Letter presents an accurate and almost noninvasive approach for investigating non-Hermitian topological states, while also offering methodologies for the implementation and manipulation of topological light-matter interactions.

关键词： Density of states Edge states Hybrid quantum systems Light-matter interaction Magnons PT-symmetric quantum mechanics Photonics Spintronics Split-ring resonators Symmetry protected topological states Topological effects in photonic systems Topological materials Topological phase transition

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Spin-Nematic Vortex states in Cold Atoms

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Physical Review Letters 2020年第19期125卷 195303-195303页

作者： Li Chen Yunbo Zhang Han Pu Institute of Theoretical Physics and State Key Laboratory of Quantum Optics and Quantum Optics Devices Shanxi University Taiyuan 030006 China Institute for Advanced Study Tsinghua University Beijing 100084 China Key Laboratory of Optical Field Manipulation of Zhejiang Province and Physics Department of Zhejiang Sci-Tech University Hangzhou 310018 China Department of Physics and Astronomy and Rice Center for Quantum Materials Rice University Houston Texas 77005 USA

The (pseudo)spin degrees of freedom greatly enriches the physics of cold atoms. This is particularly so for systems with high spins (i.e., spin quantum number larger than 1/2). For example, one can construct not only the rank-1 spin vector, but also the rank-2 spin tensor in high spin systems. Here we propose a simple scheme to couple the spin tensor and the center-of-mass orbital angular momentum in a spin-1 cold atom system and show that this leads to a new quantum phase of the matter: the spin-nematic vortex state that features vorticity in an SU(2) spin-nematic tensor subspace. Under proper conditions, such states are characterized by quantized topological numbers. Our work opens up new avenues of research in topological quantum matter with high spins.

关键词： Cold atoms & matter waves Magnetic order Magnetic texture Nematic order Spin-orbit coupling Spinor Bose-Einstein condensates Synthetic gauge fields

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Spin squeezing in a spin-orbit-coupled Bose-Einstein condensate

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Physical Review A 2020年第2期102卷 023317-023317页

作者： Li Chen Yunbo Zhang Han Pu Institute for Advanced Study Tsinghua University Beijing 100084 China Institute of Theoretical Physics and State Key Laboratory of Quantum Optics and Quantum Optics Devices Shanxi University Taiyuan 030006 China Key Laboratory of Optical Field Manipulation of Zhejiang Province and Physics Department of Zhejiang Sci-Tech University Hangzhou 310018 China Department of Physics and Astronomy and Rice Center for Quantum Materials Rice University Houston Texas 77005 USA

We study the spin squeezing in a spin-1/2 Bose-Einstein condensates (BEC) with Raman-induced spin-orbit coupling (SOC). Under the condition of two-photon resonance and weak Raman coupling strength, the system possesses two degenerate ground states, using which we construct an effective two-mode model. The Hamiltonian of the two-mode model takes the form of the one-axis-twisting Hamiltonian, which is known to generate spin squeezing. More importantly, we show that the SOC provides a convenient control knob to adjust the spin nonlinearity responsible for spin squeezing. Specifically, the spin nonlinearity strength can be tuned to be comparable to the two-body density-density interaction, and hence is much larger than the intrinsic spin-dependent interaction strength in conventional two-component BEC systems such as Rb87 and Na23 in the absence of the SOC. We confirm the spin squeezing by carrying out a fully beyond-mean-field numerical calculation using the truncated Wigner method. Additionally, the experimental implementation is also discussed.

关键词： Spin-orbit coupling Spinor Bose-Einstein condensates Squeezing of quantum noise

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Coherent-cluster-state generation in networks of degenerate optical parametric oscillators

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Physical Review A 2023年第2期108卷 023704-023704页

作者： Zheng-Yang Zhou Clemens Gneiting J. Q. You Franco Nori Key Laboratory of Optical Field Manipulation of Zhejiang Province Department of Physics ZSTU Hangzhou 310018 China Theoretical Quantum Physics Laboratory Cluster for Pioneering Research RIKEN Wakoshi Saitama 351-0198 Japan Beijing Computational Science Research Center Beijing 100094 China Center for Quantum Computing RIKEN Wakoshi Saitama 351-0198 Japan Interdisciplinary Center of Quantum Information State Key Laboratory of Modern Optical Instrumentation Zhejiang Province Key Laboratory of Quantum Technology and Device School of Physics Zhejiang University Hangzhou 310027 China Physics Department University of Michigan Ann Arbor Michigan 48109-1040 USA

Cluster states are versatile quantum resources and an essential building block for measurement-based quantum computing. The possibility to generate cluster states in specific systems may thus serve as an indicator regarding if and to what extent these systems can be harnessed for quantum technologies and quantum information processing in particular. Here, we apply this analysis to networks of degenerate optical parametric oscillators (DOPOs), also called coherent Ising machines (CIMs). CIMs are distinguished by their highly flexible coupling capabilities, which makes it possible to use them, e.g., to emulate large spin systems. As CIMs typically operate with coherent states (and superpositions thereof), it is natural to consider cluster states formed by superpositions of coherent states, i.e., coherent cluster states. As we show, such coherent cluster states can, under ideal conditions, be generated in DOPO networks with the help of beam splitters and classical pumps. Our subsequent numerical analysis provides the minimum requirements for the generation of coherent cluster states under realistic conditions. Moreover, we discuss how nonequilibrium pumps can improve the generation of coherent cluster states. In order to assess the quality of the cluster-state generation, we map the generated states to an effective spin space using modular variables, which allows us to apply entanglement criteria tailored for spin-based cluster states.

关键词： Open quantum systems quantum optics Fiber lasers

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