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 Select Resonant Quantum Search with Monitor Qubits Frank Wilczek, Hong-Ye Hu, Biao Wu Chin. Phys. Lett.    2020, 37 (5): 050304 .   DOI: 10.1088/0256-307X/37/5/050304 Abstract   HTML   PDF (582KB) We present an algorithm for the generalized search problem (searching $k$ marked items among $N$ items) based on a continuous Hamiltonian and exploiting resonance. This resonant algorithm has the same time complexity $O(\sqrt{N/k})$ as the Grover algorithm. A natural extension of the algorithm, incorporating auxiliary "monitor" qubits, can determine $k$ precisely, if it is unknown. The time complexity of our counting algorithm is $O(\sqrt{N})$, similar to the best quantum approximate counting algorithm, or better, given appropriate physical resources.
 Select Soliton Molecules and Some Hybrid Solutions for the Nonlinear Schrödinger Equation Bao Wang, Zhao Zhang, Biao Li Chin. Phys. Lett.    2020, 37 (3): 030501 .   DOI: 10.1088/0256-307X/37/3/030501 Abstract   HTML   PDF (719KB) Based on velocity resonance and Darboux transformation, soliton molecules and hybrid solutions consisting of soliton molecules and smooth positons are derived. Two new interesting results are obtained: the first is that the relationship between soliton molecules and smooth positons is clearly pointed out, and the second is that we find two different interactions between smooth positons called strong interaction and weak interaction, respectively. The strong interaction will only disappear when $t \to \infty$. This strong interaction can also excite some periodic phenomena.
 Select A Two-Dimensional Architecture for Fast Large-Scale Trapped-Ion Quantum Computing Y.-K. Wu  and L.-M. Duan Chin. Phys. Lett.    2020, 37 (7): 070302 .   DOI: 10.1088/0256-307X/37/7/070302 Abstract   HTML   PDF (1064KB) Building blocks of quantum computers have been demonstrated in small to intermediate-scale systems. As one of the leading platforms, the trapped ion system has attracted wide attention. A significant challenge in this system is to combine fast high-fidelity gates with scalability and convenience in ion trap fabrication. Here we propose an architecture for large-scale quantum computing with a two-dimensional array of atomic ions trapped at such large distance which is convenient for ion-trap fabrication but usually believed to be unsuitable for quantum computing as the conventional gates would be too slow. Using gate operations far outside of the Lamb–Dicke region, we show that fast and robust entangling gates can be realized in any large ion arrays. The gate operations are intrinsically parallel and robust to thermal noise, which, together with their high speed and scalability of the proposed architecture, makes this approach an attractive one for large-scale quantum computing.
 Select Imaginary Time Crystal of Thermal Quantum Matter Zi Cai, Yizhen Huang, W. Vincent Liu Chin. Phys. Lett.    2020, 37 (5): 050503 .   DOI: 10.1088/0256-307X/37/5/050503 Abstract   HTML   PDF (2767KB) Temperature is a fundamental thermodynamic variable for matter. Physical observables are often found to either increase or decrease with it, or show a non-monotonic dependence with peaks signaling underlying phase transitions or anomalies. Statistical field theory has established connection between temperature and time: a quantum ensemble with inverse temperature $\beta$ is formally equivalent to a dynamic system evolving along an imaginary time from 0 to $i\beta$ in the space one dimension higher. Here we report that a gas of hard-core bosons interacting with a thermal bath manifests an unexpected temperature-periodic oscillation of its macroscopic observables, arising from the microscopic origin of space-time locked translational symmetry breaking and crystalline ordering. Such a temperature crystal, supported by quantum Monte Carlo simulation, generalizes the concept of purely spatial density-wave order to the imaginary time axis for Euclidean action.
 Select Classical-Noise-Free Sensing Based on Quantum Correlation Measurement Ping Wang , Chong Chen , and Ren-Bao Liu Chin. Phys. Lett.    2021, 38 (1): 010301 .   DOI: 10.1088/0256-307X/38/1/010301 Abstract   HTML   PDF (791KB) Quantum sensing, using quantum properties of sensors, can enhance resolution, precision, and sensitivity of imaging, spectroscopy, and detection. An intriguing question is: Can the quantum nature (quantumness) of sensors and targets be exploited to enable schemes that are not possible for classical probes or classical targets? Here we show that measurement of the quantum correlations of a quantum target indeed allows for sensing schemes that have no classical counterparts. As a concrete example, in the case that the second-order classical correlation of a quantum target could be totally concealed by non-stationary classical noise, the higher-order quantum correlations can single out a quantum target from the classical noise background, regardless of the spectrum, statistics, or intensity of the noise. Hence a classical-noise-free sensing scheme is proposed. This finding suggests that the quantumness of sensors and targets is still to be explored to realize the full potential of quantum sensing. New opportunities include sensitivity beyond classical approaches, non-classical correlations as a new approach to quantum many-body physics, loophole-free tests of the quantum foundation, et cetera.
 Select Butterfly-Like Anisotropic Magnetoresistance and Angle-Dependent Berry Phase in a Type-II Weyl Semimetal WP$_{2}$ Kaixuan Zhang, Yongping Du, Pengdong Wang, Laiming Wei, Lin Li, Qiang Zhang, Wei Qin, Zhiyong Lin, Bin Cheng, Yifan Wang, Han Xu, Xiaodong Fan, Zhe Sun, Xiangang Wan, and Changgan Zeng Chin. Phys. Lett.    2020, 37 (9): 090301 .   DOI: 10.1088/0256-307X/37/9/090301 Abstract   HTML   PDF (2807KB) The Weyl semimetal has emerged as a new topologically nontrivial phase of matter, hosting low-energy excitations of massless Weyl fermions. Here, we present a comprehensive study of a type-II Weyl semimetal WP$_{2}$. Transport studies show a butterfly-like magnetoresistance at low temperature, reflecting the anisotropy of the electron Fermi surfaces. This four-lobed feature gradually evolves into a two-lobed variant with an increase in temperature, mainly due to the reduced relative contribution of electron Fermi surfaces compared to hole Fermi surfaces for magnetoresistance. Moreover, an angle-dependent Berry phase is also discovered, based on quantum oscillations, which is ascribed to the effective manipulation of extremal Fermi orbits by the magnetic field to feel nearby topological singularities in the momentum space. The revealed topological character and anisotropic Fermi surfaces of the WP$_{2}$ substantially enrich the physical properties of Weyl semimetals, and show great promises in terms of potential topological electronic and Fermitronic device applications.
 Select Pressure Generation above 35 GPa in a Walker-Type Large-Volume Press Yu-Chen Shang, Fang-Ren Shen, Xu-Yuan Hou, Lu-Yao Chen, Kuo Hu, Xin Li, Ran Liu, Qiang Tao, Pin-Wen Zhu, Zhao-Dong Liu, Ming-Guang Yao, Qiang Zhou, Tian Cui, and Bing-Bing Liu Chin. Phys. Lett.    2020, 37 (8): 080701 .   DOI: 10.1088/0256-307X/37/8/080701 Abstract   HTML   PDF (3565KB) Pressure generation to a higher pressure range in a large-volume press (LVP) denotes our ability to explore more functional materials and deeper Earth's interior. Pressure generated by normal tungsten carbide (WC) anvils in a commercial way is mostly limited to 25 GPa in LVPs due to the limitation of their hardness and design of cell assemblies. We adopt three newly developed WC anvils for ultrahigh pressure generation in a Walker-type LVP with a maximum press load of 1000 ton. The hardest ZK01F WC anvils exhibit the highest efficiency of pressure generation than ZK10F and ZK20F WC anvils, which is related to their performances of plastic deformations. Pressure up to 35 GPa at room temperature is achieved at a relatively low press load of 4.5 MN by adopting the hardest ZK01F WC anvils with three tapering surfaces in conjunction with an optimized cell assembly, while pressure above 35 GPa at 1700 K is achieved at a higher press load of 7.5 MN. Temperature above 2000 K can be generated by our cell assemblies at pressure below 30 GPa. We adopt such high-pressure and high-temperature techniques to fabricate several high-quality and well-sintered polycrystalline minerals for practical use. The present development of high-pressure techniques expands the pressure and temperature ranges in Walker-type LVPs and has wide applications in physics, materials, chemistry, and Earth science.
 Select Superfluid-Mott-Insulator Transition in an Optical Lattice with Adjustable Ensemble-Averaged Filling Factors Shifeng Yang, Tianwei Zhou, Chen Li, Kaixiang Yang, Yueyang Zhai, Xuguang Yue, Xuzong Chen Chin. Phys. Lett.    2020, 37 (4): 040301 .   DOI: 10.1088/0256-307X/37/4/040301 Abstract   HTML   PDF (1409KB) We study the quantum phase transition from a superfluid to a Mott insulator of ultracold atoms in a three-dimensional optical lattice with adjustable filling factors. Based on the density-adjustable Bose–Einstein condensate we prepared, the excitation spectrum in the superfluid and the Mott insulator regime is measured with different ensemble-averaged filling factors. We show that for the superfluid phase, the center of the excitation spectrum is positively correlated with the ensemble-averaged filling factor, indicating a higher sound speed of the system. For the Mott insulator phase, the discrete feature of the excitation spectrum becomes less pronounced as the ensemble-averaged filling factor increases, implying that it is harder for the system to enter the Mott insulator regime with higher filling factors. The ability to manipulate the filling factor affords further potential in performing quantum simulation with cold atoms trapped in optical lattices.
 Select Lax Pairs of Integrable Systems in Bidifferential Graded Algebras Danda Zhang, Da-Jun Zhang, Sen-Yue Lou Chin. Phys. Lett.    2020, 37 (4): 040201 .   DOI: 10.1088/0256-307X/37/4/040201 Abstract   HTML   PDF (416KB) Lax pairs regarded as foundations of the inverse scattering methods play an important role in integrable systems. In the framework of bidifferential graded algebras, we propose a straightforward approach to constructing the Lax pairs of integrable systems in functional environment. Some continuous equations and discrete equations are presented.
 Select Negative Thermal Transport in Conduction and Advection Liujun Xu and Jiping Huang Chin. Phys. Lett.    2020, 37 (8): 080502 .   DOI: 10.1088/0256-307X/37/8/080502 Abstract   HTML   PDF (1064KB) Negative refractive index has drawn a great deal of attention due to its unique properties and practical applications in wave systems. To promote the related physics in thermotics, here we manage to coin a complex thermal conductivity whose imaginary part corresponds to the real part of complex refractive index. Therefore, the thermal counterpart of negative refractive index is just negative imaginary thermal conductivity, which is featured by the opposite directions of energy flow and wave vector in thermal conduction and advection, thus called negative thermal transport herein. To avoid violating causality, we design an open system with energy exchange and explore three different cases to reveal negative thermal transport. We further provide experimental suggestions with a solid ring structure. All finite-element simulations agree with theoretical analyses, indicating that negative thermal transport is physically feasible. These results have potential applications such as designing the inverse Doppler effect in thermal conduction and advection.
 Select Quantized Superfluid Vortex Filaments Induced by the Axial Flow Effect Hao Li, Chong Liu, Zhan-Ying Yang, Wen-Li Yang Chin. Phys. Lett.    2020, 37 (3): 030302 .   DOI: 10.1088/0256-307X/37/3/030302 Abstract   HTML   PDF (1130KB) We report the quantized superfluid vortex filaments induced by the axial flow effect, which exhibit intriguing loop structures on helical vortexes. Such new vortex filaments correspond to a series of soliton excitations including the multipeak soliton, W-shaped soliton, and anti-dark soliton, which have no analogue when the axial flow effect is absent. In particular, we show that the vortex filaments induced by the multipeak soliton and W-shaped soliton arise from the dual action of bending and twisting of the vortex, while the vortex filament induced by the anti-dark soliton is caused only by the bending action, which is consistent with the case of the standard bright soliton. These results will deepen our understanding of breather-induced vortex filaments and will be helpful for controllable ring-like excitations on vortices.
 Select Dynamical Algebras in the 1+1 Dirac Oscillator and the Jaynes–Cummings Model Wen-Ya Song, Fu-Lin Zhang Chin. Phys. Lett.    2020, 37 (5): 050301 .   DOI: 10.1088/0256-307X/37/5/050301 Abstract   HTML   PDF (445KB) We study the algebraic structure of the one-dimensional Dirac oscillator by extending the concept of spin symmetry to a noncommutative case. An $SO(4)$ algebra is found connecting the eigenstates of the Dirac oscillator, in which the two elements of Cartan subalgebra are conserved quantities. Similar results are obtained in the Jaynes–Cummings model.
 Select Energy Variance in Decoherence Zi-Gang Yuan, Xin-Yu Zhang, He Zhao, Yan-Chao Li Chin. Phys. Lett.    2020, 37 (3): 030301 .   DOI: 10.1088/0256-307X/37/3/030301 Abstract   HTML   PDF (512KB) We study the effect of the initial-state energy variance to the short-time behavior of the Loschmidt echo (LE) in a purely dephasing model. We find that the short-time LE behaves as a Gaussian function with the width determined by the initial-state energy variance of the interaction Hamiltonian, while it is a quartic decaying function with the width determined by the initial-state energy variance of the commutator between the interaction Hamiltonian and the environmental Hamiltonian when the initial state is an eigenstate of the interaction Hamiltonian. Furthermore, the Gaussian envelope in the temporal evolution of LE in strong coupling regime is determined by the inband variance. We will also verify the above conclusion in the XY spin model (as environment).
 Select Search for 2D Ferromagnets: Molecular Beam Epitaxy is a Critical Tool Matthias Batzill Chin. Phys. Lett.    2020, 37 (8): 080101 .   DOI: 10.1088/0256-307X/37/8/080101 Abstract   HTML   PDF (277KB)
 Select Quantum Secure Multiparty Computation with Symmetric Boolean Functions Hao Cao, Wenping Ma, Ge Liu, Liangdong Lü, Zheng-Yuan Xue Chin. Phys. Lett.    2020, 37 (5): 050303 .   DOI: 10.1088/0256-307X/37/5/050303 Abstract   HTML   PDF (612KB) We propose a class of $n$-variable Boolean functions which can be used to implement quantum secure multiparty computation. We also give an implementation of a special quantum secure multiparty computation protocol. An advantage of our protocol is that only 1 qubit is needed to compute the $n$-tuple pairwise AND function, which is more efficient comparing with previous protocols. We demonstrate our protocol on the IBM quantum cloud platform, with a probability of correct output as high as 94.63%. Therefore, our protocol presents a promising generalization in realization of various secure multipartite quantum tasks.
 Select Breather Interaction Properties Induced by Self-Steepening and Space-Time Correction Yu-Han Wu, Chong Liu, Zhan-Ying Yang, Wen-Li Yang Chin. Phys. Lett.    2020, 37 (4): 040501 .   DOI: 10.1088/0256-307X/37/4/040501 Abstract   HTML   PDF (794KB) We study the properties of breather interactions in nonlinear Kerr media with self-steepening and space-time correction and with either self-focusing or self-defocusing nonlinearity, and present a new family of exact breather solutions via the Darboux transformation with a special-designed quadratic spectral parameter. In contrast to the previous results of the nonlinear Schrödinger equation (NLSE) hierarchy, we show that the relative phase of colliding breathers has a significant effect on the collision manifestation. In particular, only the out-of-phase interactions can generate small amplitude waves at the collision center, which are analogous to the NLSE super-regular breathers. Our results will deepen our understanding of the properties of breather interactions and they will offer the possibility of experimental observations of super-regular breather dynamics in systems with self-steepening and space-time correction.
 Select Dark Soliton of Polariton Condensates under Nonresonant $\mathcal{P}\mathcal{T}$-Symmetric Pumping Chun-Yu Jia, Zhao-Xin Liang Chin. Phys. Lett.    2020, 37 (4): 040502 .   DOI: 10.1088/0256-307X/37/4/040502 Abstract   HTML   PDF (3089KB) A quantum system in complex potentials obeying parity-time ($\mathcal{P}\mathcal{T}$) symmetry could exhibit all real spectra, starting out in non-Hermitian quantum mechanics. The key physics behind a $\mathcal{P}\mathcal{T}$-symmetric system consists of the balanced gain and loss of the complex potential. We plan to include the nonequilibrium nature (i.e., the intrinsic kinds of gain and loss of a system) to a $\mathcal{P}\mathcal{T}$-symmetric many-body quantum system, with an emphasis on the combined effects of non-Hermitian due to nonequilibrium nature and $\mathcal{P}\mathcal{T}$ symmetry in determining the properties of a system. To this end, we investigate the static and dynamical properties of a dark soliton of a polariton Bose–Einstein condensate under the $\mathcal{P}\mathcal{T}$-symmetric non-resonant pumping by solving the driven-dissipative Gross–Pitaevskii equation both analytically and numerically. We derive the equation of motion for the center of mass of the dark soliton's center analytically with the help of the Hamiltonian approach. The resulting equation captures how the combination of the open-dissipative character and $\mathcal{P}\mathcal{T}$-symmetry affects the properties of the dark soliton; i.e., the soliton relaxes by blending with the background at a finite time. Further numerical solutions are in excellent agreement with the analytical results.
 Select A Direct Derivation of the Dark Soliton Excitation Energy Li-Chen Zhao, Yan-Hong Qin, Wen-Long Wang, Zhan-Ying Yang Chin. Phys. Lett.    2020, 37 (5): 050502 .   DOI: 10.1088/0256-307X/37/5/050502 Abstract   HTML   PDF (409KB) Dark solitons are common topological excitations in a wide array of nonlinear waves. The dark soliton excitation energy is crucial for exploring dark soliton dynamics and is necessarily calculated in a renormalized form due to its existence on a finite background. Despite its tremendous importance and success, the renormalized energy form was at first only suggested with no detailed derivation, and was then "derived" in the grand canonical ensemble. We revisit this fundamental problem and provide an alternative and intuitive derivation of the energy form from the fundamental field energy by utilizing a limiting procedure that conserves number of particles. Our derivation yields the same result, thus putting the dark soliton energy form on a solid basis.
 Select Self-Assembly of Dimer Motors under Confined Conditions An Zhou, Li-Yan Qiao, Gui-Na Wei, Zhou-Ting Jiang, Ye-Hua Zhao Chin. Phys. Lett.    2020, 37 (5): 050501 .   DOI: 10.1088/0256-307X/37/5/050501 Abstract   HTML   PDF (843KB) Chemically synthetic nanomotors can consume fuel in the environment and utilize the self-generated concentration gradient to self-propel themselves in the system. We study the collective dynamics of an ensemble of sphere dimers built from linked catalytic and noncatalytic monomers. Because of the confinement from the fuel field and the interactions among motors, the ensemble of dimer motors can self-organize into various nanostructures, such as a radial pattern in the spherical fuel field and a staggered radial pattern in a cylindrical fuel field. The influence of the dimer volume fraction on the self-assembly is also investigated and the formed nanostructures are analyzed in detail. The results presented here may give insight into the application of the self-assembly of active materials.
 Select Quantum Deletion of Copies of Two Non-orthogonal Quantum States via Weak Measurement Wei-Min Shang, Jie Zhou, Hui-Xian Meng, Jing-Ling Chen Chin. Phys. Lett.    2020, 37 (5): 050302 .   DOI: 10.1088/0256-307X/37/5/050302 Abstract   HTML   PDF (538KB) We propose a scenario to increase the probability of probabilistic quantum deletion and to enhance the fidelity of approximate quantum deletion for two non-orthogonal states via weak measurement. More interestingly, by pretreating the given non-orthogonal states, the probability of probabilistic quantum deletion and fidelity of approximate quantum deletion can reach 1. Since outcomes of the weak measurement that we required are probabilistic, we perform the subsequent deleting process only when the outcome of weak measurement is "yes". Remarkably, we find that our scenario has better performance in quantum information process; for example, it costs less quantum resources and time.
 Select Machine Learning for Many-Body Localization Transition Wen-Jia Rao Chin. Phys. Lett.    2020, 37 (8): 080501 .   DOI: 10.1088/0256-307X/37/8/080501 Abstract   HTML   PDF (770KB) We employ the methods of machine learning to study the many-body localization (MBL) transition in a 1D random spin system. By using the raw energy spectrum without pre-processing as training data, it is shown that the MBL transition point is correctly predicted by the machine. The structure of the neural network reveals the nature of this dynamical phase transition that involves all energy levels, while the bandwidth of the spectrum and nearest level spacing are the two dominant patterns and the latter stands out to classify phases. We further use a comparative unsupervised learning method, i.e., principal component analysis, to confirm these results.
 Select Enhancing Phase Sensitivity in Mach–Zehnder Interferometers for Arbitrary Input States Hongbin Liang, Jiancheng Pei, and Xiaoguang Wang Chin. Phys. Lett.    2020, 37 (7): 070301 .   DOI: 10.1088/0256-307X/37/7/070301 Abstract   HTML   PDF (545KB) To enhance the phase sensitivity of Mach–Zehnder interferometers, we use a tunable phase shift before the light beams are injected into the interferometer. The analytical result of the optimal phase shift is obtained, which only depends on the initial input states. For a non-zero optimal phase shift, the phase sensitivity of the interferometers in the output ports is always enhanced. We can achieve this enhancement for most states, including entangled and mixed states. The optimal phase shift is exhibited in three examples. Compared to previous methods, this scheme provides a general way to improve phase sensitivity and could find wide applications in optical phase estimations.
 Select Making Axion Dynamical in Non-Centrosymmetric Magnetic Topological Insulators Chaoxing Liu Chin. Phys. Lett.    2021, 38 (1): 010101 .   DOI: 10.1088/0256-307X/38/1/010101 Abstract   HTML   PDF (276KB)
 Select Solution to the Fokker–Planck Equation with Piecewise-Constant Drift Bin Cheng, Ya-Ming Chen, Xiao-Gang Deng Chin. Phys. Lett.    2020, 37 (6): 060201 .   DOI: 10.1088/0256-307X/37/6/060201 Abstract   HTML   PDF (494KB) We study the solution to the Fokker–Planck equation with piecewise-constant drift, taking the case with two jumps in the drift as an example. The solution in Laplace space can be expressed in closed analytic form, and its inverse can be obtained conveniently using some numerical inversion methods. The results obtained by numerical inversion can be regarded as exact solutions, enabling us to demonstrate the validity of some numerical methods for solving the Fokker–Planck equation. In particular, we use the solved problem as a benchmark example for demonstrating the fifth-order convergence rate of the finite difference scheme proposed previously [Chen Y and Deng X Phys. Rev. E 100 (2019) 053303].
 Select Meter-Level Optical Delay Line on a Low-Loss Lithium Niobate Nanophotonics Chip Shining Zhu Chin. Phys. Lett.    2020, 37 (8): 080102 .   DOI: 10.1088/0256-307X/37/8/080102 Abstract   HTML   PDF (284KB)
 Select Strong Anisotropy of 3D Diffusion in Living Cells Xiaosong Chen Chin. Phys. Lett.    2020, 37 (8): 080103 .   DOI: 10.1088/0256-307X/37/8/080103 Abstract   HTML   PDF (269KB)
 Select Direct Strong Measurement of a High-Dimensional Quantum State Chen-Rui Zhang, Meng-Jun Hu, Guo-Yong Xiang, Yong-Sheng Zhang, Chuan-Feng Li, and Guang-Can Guo Chin. Phys. Lett.    2020, 37 (8): 080301 .   DOI: 10.1088/0256-307X/37/8/080301 Abstract   HTML   PDF (3985KB) It is of great importance to determine an unknown quantum state for fundamental studies of quantum mechanics, yet it is still difficult to characterize systems of large dimensions in practice. Although the scan-free direct measurement approach based on a weak measurement scheme was proposed to measure a high-dimensional photonic state, how weak the interaction should be to give a correct estimation remains unclear. Here we propose and experimentally demonstrate a technique that measures a high-dimensional quantum state with the combination of scan-free measurement and direct strong measurement. The procedure involves sequential strong measurement, in which case no approximation is made similarly to the conventional direct weak measurement. We use this method to measure a transverse state of a photon with effective dimensionality of $65000$ without the time-consumed scanning process. Furthermore, the high fidelity of the result and the simplicity of the experimental apparatus show that our approach can be readily used to measure the complex field of a beam in diverse applications such as wavefront sensing and quantitative phase imaging.
 Select Dynamics of the Entanglement Spectrum of the Haldane Model under a Sudden Quench Lin-Han Mo, Qiu-Lan Zhang, Xin Wan Chin. Phys. Lett.    2020, 37 (6): 060301 .   DOI: 10.1088/0256-307X/37/6/060301 Abstract   HTML   PDF (4108KB) One of the appealing features of topological systems is the presence of robust edge modes. Under a sudden quantum quench, the edge modes survive for a characteristic time that scales with the system size, during which the nontrivial topology continues to manifest in entanglement properties, even though the post-quench Hamiltonian belongs to a trivial phase. We exemplify this in the quench dynamics of a two-dimensional Haldane model with the help of one-particle entanglement spectrum and the probability density of its mid-states. We find that, beyond our knowledge in one-dimensional models, the momentum dependence of the transverse velocity plays a crucial role in the out-of-equilibrium evolution of the entanglement properties.
 Select The Analytic Eigenvalue Structure of the 1+1 Dirac Oscillator Bo-Xing Cao  and Fu-Lin Zhang Chin. Phys. Lett.    2020, 37 (9): 090303 .   DOI: 10.1088/0256-307X/37/9/090303 Abstract   HTML   PDF (689KB) We study the analytic structure for the eigenvalues of the one-dimensional Dirac oscillator, by analytically continuing its frequency on the complex plane. A twofold Riemann surface is found, connecting the two states of a pair of particle and antiparticle. One can, at least in principle, accomplish the transition from a positive energy state to its antiparticle state by moving the frequency continuously on the complex plane, without changing the Hamiltonian after transition. This result provides a visual explanation for the absence of a negative energy state with the quantum number $n=0$.
 Select Chiral State Conversion in a Levitated Micromechanical Oscillator with ${\boldsymbol In~Situ}$ Control of Parameter Loops Peiran Yin, Xiaohui Luo, Liang Zhang, Shaochun Lin, Tian Tian, Rui Li, Zizhe Wang, Changkui Duan, Pu Huang, and Jiangfeng Du Chin. Phys. Lett.    2020, 37 (10): 100301 .   DOI: 10.1088/0256-307X/37/10/100301 Abstract   HTML   PDF (4741KB) Physical systems with gain and loss can be described by a non-Hermitian Hamiltonian, which is degenerated at the exceptional points (EPs). Many new and unexpected features have been explored in the non-Hermitian systems with a great deal of recent interest. One of the most fascinating features is that chiral state conversion appears when one EP is encircled dynamically. Here, we propose an easy-controllable levitated microparticle system that carries a pair of EPs and realize slow evolution of the Hamiltonian along loops in the parameter plane. Utilizing the controllable rotation angle, gain and loss coefficients, we can control the structure, size and location of the loops in situ. We demonstrate that, under the joint action of topological structure of energy surfaces and nonadiabatic transitions, the chiral behavior emerges both along a loop encircling an EP and even along a straight path away from the EP. This work broadens the range of parameter space for the chiral state conversion, and proposes a useful platform to explore the interesting properties of exceptional points physics.
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