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    Modes decomposition in particle-in-cell software CEMPIC
    Aiping Fang(方爱平)†, Shanshan Liang(梁闪闪), Yongdong Li(李永东), Hongguang Wang(王洪广), and Yue Wang(王玥)
    Chin. Phys. B, 2020, 29 (10): 100205.   DOI: 10.1088/1674-1056/abaed6
    Abstract220)   HTML    PDF (624KB)(4765)      

    The numerical method of modes analysis and decomposition of the output signal in 3D electromagnetic particle-in-cell simulation is presented. By the method, multiple modes can be resolved at one time using a set of diagnostic data, the amplitudes and the phases of the specified modes can all be given separately. Based on the method, the output signals of one X-band tri-bend mode converter used for one high power microwave device, with ionization process in the device due to the strong normal electric field, are analyzed and decomposed.

    Fractal sorting vector-based least significant bit chaotic permutation for image encryption
    Yong-Jin Xian(咸永锦), Xing-Yuan Wang(王兴元), Ying-Qian Zhang(张盈谦), Xiao-Yu Wang(王晓雨), and Xiao-Hui Du(杜晓慧)
    Chin. Phys. B, 2021, 30 (6): 060508.   DOI: 10.1088/1674-1056/abda35
    Abstract1344)   HTML30)    PDF (10704KB)(1897)      
    The image's least significant bit (LSB) covers lots of the details that have been commonly used in image encryption analysis. The newly proposed fractal sorting vector (FSV) and FSV-based LSB chaotic permutation (FSV-LSBCP) is a novel chaotic image encryption cryptosystem introduced in this article. The FSV-LSBCP effectively strengthens the security of the cryptographic scheme concerning the properties of the FSV. Key analysis, statistical analysis, resistance differential attack analysis, and resistance to cropping attacks and noise attacks are the focus of the suggested image encryption cryptosystem. The security experiment shows that the cryptosystem is adequate to achieve the desired degree of security.
    Calculations of atomic polarizability for beryllium using MCDHF method
    Hui Dong(董辉), Jun Jiang(蒋军), Zhongwen Wu(武中文), Chenzhong Dong(董晨钟), and Gediminas Gaigalas
    Chin. Phys. B, 2021, 30 (4): 043103.   DOI: 10.1088/1674-1056/abd92d
    Abstract309)   HTML0)    PDF (745KB)(1575)      
    Based on the fully relativistic multiconfiguration Dirac-Hartree-Fock (MCDHF) method and the corresponding program package GRASP2018, a new program for calculating the polarizabilities is developed. As the first application, the static electric-dipole polarizabilities of the ground state 2s2 1S0 and excited state 2s2p 3P0 of beryllium are calculated. By means of these polarizabilities, the blackbody radiation (BBR) shift of the 2s2p $^3P_0 \to \rm 2s^2$ 1S0 clock transition is determined. The present results agree very well with other available theoretical results.
    Radiation force and torque on a two-dimensional circular cross-section of a non-viscous eccentric layered compressible cylinder in acoustical standing waves
    F G Mitri
    Chin. Phys. B, 2021, 30 (2): 024302.   DOI: 10.1088/1674-1056/abbbd9
    Abstract183)   HTML1)    PDF (10104KB)(1090)      
    The purpose of this study is to develop an analytical formalism and derive series expansions for the time-averaged force and torque exerted on a compound coated compressible liquid-like cylinder, insonified by acoustic standing waves having an arbitrary angle of incidence in the polar (transverse) plane. The host medium of wave propagation and the eccentric liquid-like cylinder are non-viscous. Numerical computations illustrate the theoretical analysis with particular emphases on the eccentricity of the cylinder, the angle of incidence and the dimensionless size parameters of the inner and coating cylindrical fluid materials. The method to derive the acoustical scattering, and radiation force and torque components conjointly uses modal matching with the addition theorem, which adequately account for the multiple wave interaction effects between the layer and core fluid materials. The results demonstrate that longitudinal and lateral radiation force components arise. Moreover, an axial radiation torque component is quantified and computed for the non-absorptive compound cylinder, arising from geometrical asymmetry considerations as the eccentricity increases. The computational results reveal the emergence of neutral, positive, and negative radiation force and torque depending on the size parameter of the cylinder, the eccentricity, and the angle of incidence of the insonifying field. Moreover, based on the law of energy conservation applied to scattering, numerical verification is accomplished by computing the extinction/scattering energy efficiency. The results may find some related applications in fluid dynamics, particle trapping, mixing and manipulation using acoustical standing waves.
    High-resolution bone microstructure imaging based on ultrasonic frequency-domain full-waveform inversion
    Yifang Li(李义方), Qinzhen Shi(石勤振), Ying Li(李颖), Xiaojun Song(宋小军), Chengcheng Liu(刘成成), Dean Ta(他得安), and Weiqi Wang(王威琪)
    Chin. Phys. B, 2021, 30 (1): 014302.   DOI: 10.1088/1674-1056/abc7aa
    Abstract572)   HTML5)    PDF (9210KB)(833)      
    The main challenge in bone ultrasound imaging is the large acoustic impedance contrast and sound velocity differences between the bone and surrounding soft tissue. It is difficult for conventional pulse-echo modalities to give accurate ultrasound images for irregular bone boundaries and microstructures using uniform sound velocity assumption rather than getting a prior knowledge of sound speed. To overcome these limitations, this paper proposed a frequency-domain full-waveform inversion (FDFWI) algorithm for bone quantitative imaging utilizing ultrasonic computed tomography (USCT). The forward model was calculated in the frequency domain by solving the full-wave equation. The inverse problem was solved iteratively from low to high discrete frequency components via minimizing a cost function between the modeled and measured data. A quasi-Newton method called the limited-memory Broyden-Fletcher-Goldfarb-Shanno algorithm (L-BFGS) was utilized in the optimization process. Then, bone images were obtained based on the estimation of the velocity and density. The performance of the proposed method was verified by numerical examples, from tubular bone phantom to single distal fibula model, and finally with a distal tibia-fibula pair model. Compared with the high-resolution peripheral quantitative computed tomography (HR-pQCT), the proposed FDFWI can also clearly and accurately presented the wavelength scaled pores and trabeculae in bone images. The results proved that the FDFWI is capable of reconstructing high-resolution ultrasound bone images with sub-millimeter resolution. The parametric bone images may have the potential for the diagnosis of bone disease.
    Acoustic radiation force and torque on a lossless eccentric layered fluid cylinder
    F G Mitri
    Chin. Phys. B, 2020, 29 (11): 114302.   DOI: 10.1088/1674-1056/aba27a
    Abstract331)   HTML    PDF (3021KB)(742)      

    Exact analytical equations and computations for the longitudinal and transverse acoustic radiation force and axial torque components for a lossless eccentric liquid cylinder submerged in a nonviscous fluid and insonified by plane waves progressive waves (of arbitrary incidence in the polar plane) are established and computed numerically. The modal matching method and the translational addition theorem in cylindrical coordinates are used to derive exact mathematical expressions applicable to any inner and outer cylinder sizes without any approximations, and taking into account the interaction effects between the waves propagating in the layer and those scattered from the cylindrical core. The results show that longitudinal and transverse radiation force components arise, in addition to the emergence of an axial radiation torque component acting on the non-absorptive compound cylinder due to geometrical asymmetry as the eccentricity increases. The computations demonstrate that the axial torque component, which arises due to a geometrical asymmetry, can be positive (causing counter-clockwise rotation in the polar plane), negative (clockwise rotation) or neutral (rotation cancellation) depending on the size parameter of the cylinder and the amount of eccentricity. Furthermore, verification and validation of the results have been accomplished from the standpoint of energy conservation law applied to scattering, and based on the reciprocity theorem.

    Quantization of the band at the surface of charge density wave material 2H-TaSe2
    Man Li(李满), Nan Xu(徐楠), Jianfeng Zhang(张建丰), Rui Lou(娄睿), Ming Shi(史明), Lijun Li(黎丽君), Hechang Lei(雷和畅), Cedomir Petrovic, Zhonghao Liu(刘中灏), Kai Liu(刘凯), Yaobo Huang(黄耀波), and Shancai Wang(王善才)
    Chin. Phys. B, 2021, 30 (4): 047305.   DOI: 10.1088/1674-1056/abe9a8
    Abstract728)   HTML0)    PDF (1794KB)(734)      
    By using angle-resolved photoemission spectroscopy (ARPES) combined with the first-principles electronic structure calculations, we report the quantized states at the surface of a single crystal 2H-TaSe2. We have observed sub-bands of quantized states at the three-dimensional Brillouin zone center due to a highly dispersive band with light effective mass along kz direction. The quantized sub-bands shift upward towards EF while the bulk band at $\varGamma$ shifts downward with the decrease of temperature across charge density wave (CDW) formation. The band shifts could be intimately related to the CDW. While neither the two-dimensional Fermi-surface nesting nor purely strong electron-phonon coupling can explain the mechanism of CDW in 2H-TaSe2, our experiment may ignite the interest in understanding the CDW mechanism in this family.
    Evolution of domain structure in Fe3GeTe2
    Siqi Yin(尹思琪), Le Zhao(赵乐), Cheng Song(宋成), Yuan Huang(黄元), Youdi Gu(顾有地), Ruyi Chen(陈如意), Wenxuan Zhu(朱文轩), Yiming Sun(孙一鸣), Wanjun Jiang(江万军), Xiaozhong Zhang(章晓中), and Feng Pan(潘峰)
    Chin. Phys. B, 2021, 30 (2): 027505.   DOI: 10.1088/1674-1056/abd693
    Abstract715)   HTML7)    PDF (1057KB)(724)      
    Two-dimensional (2D) magnets provide an ideal platform to explore new physical phenomena in fundamental magnetism and to realize the miniaturization of magnetic devices. The study on its domain structure evolution with thickness is of great significance for better understanding the 2D magnetism. Here, we investigate the magnetization reversal and domain structure evolution in 2D ferromagnet Fe3GeTe2 (FGT) with a thickness range of 11.2-112 nm. Three types of domain structures and their corresponding hysteresis loops can be obtained. The magnetic domain varies from a circular domain via a dendritic domain to a labyrinthian domain with increasing FGT thickness, which is accompanied by a transition from squared to slanted hysteresis loops with reduced coercive fields. These features can be ascribed to the total energy changes from exchange interaction-dominated to dipolar interaction-dominated with increasing FGT thickness. Our finding not only enriches the fundamental magnetism, but also paves a way towards spintronics based on 2D magnet.
    A concise review of Rydberg atom based quantum computation and quantum simulation
    Xiaoling Wu(吴晓凌), Xinhui Liang(梁昕晖), Yaoqi Tian(田曜齐), Fan Yang(杨帆), Cheng Chen(陈丞), Yong-Chun Liu(刘永椿), Meng Khoon Tey(郑盟锟), and Li You(尤力)
    Chin. Phys. B, 2021, 30 (2): 020305.   DOI: 10.1088/1674-1056/abd76f
    Abstract1059)   HTML30)    PDF (3178KB)(706)      
    Quantum information processing based on Rydberg atoms emerged as a promising direction two decades ago. Recent experimental and theoretical progresses have shined exciting light on this avenue. In this concise review, we will briefly introduce the basics of Rydberg atoms and their recent applications in associated areas of neutral atom quantum computation and simulation. We shall also include related discussions on quantum optics with Rydberg atomic ensembles, which are increasingly used to explore quantum computation and quantum simulation with photons.
    Transport property of inhomogeneous strained graphene
    Bing-Lan Wu(吴冰兰), Qiang Wei(魏强), Zhi-Qiang Zhang(张智强), and Hua Jiang(江华)
    Chin. Phys. B, 2021, 30 (3): 030504.   DOI: 10.1088/1674-1056/abe3e3
    Abstract665)   HTML8)    PDF (1974KB)(669)      
    In analogy to real magnetic field, the pseudo-magnetic field (PMF) induced by inhomogeneous strain can also form the Landau levels and edge states. In this paper, the transport properties of graphene under inhomogeneous strain are studied. We find that the Landau levels have non-zero group velocity, and construct one-dimensional conducting channels. In addition, the edge states and the Landau level states in PMF are both fragile under disorder. We also confirm that the backscattering of these states could be suppressed by applying a real magnetic filed (MF). Therefore, the transmission coefficient for each conducting channel can be manipulated by adjusting the MF strength, which indicates the application of switching devices.
    Search for topological defect of axionlike model with cesium atomic comagnetometer
    Yucheng Yang(杨雨成), Teng Wu(吴腾), Jianwei Zhang(张建玮), and Hong Guo(郭弘)
    Chin. Phys. B, 2021, 30 (5): 050704.   DOI: 10.1088/1674-1056/abf132
    Abstract626)   HTML1)    PDF (916KB)(623)      
    Many terrestrial experiments have been designed to detect domain walls composed of axions or axionlike particles (ALPs), which are promising candidates of dark matter. When the domain wall crosses over the Earth, the pseudoscalar field of ALPs could couple to the atomic spins. Such exotic spin-dependent couplings can be searched for by monitoring the transient-in-time change of the atomic spin precession frequency in the presence of a magnetic field. We propose here a single-species cesium atomic comagnetometer, which measures the spin precession frequencies of atoms in different ground-state hyperfine levels, to eliminate the common-mode magnetic-field variations and search for the exotic non-magnetic couplings solely between protons and ALPs. With the single-species atomic comagnetometer, we experimentally rule out the possibility that the decay constant of the linear pseudoscalar couplings of ALPs to protons is $f_{\rm p}\lesssim 3.71\times 10^{7}~\rm{GeV}$. The advanced system has the potential to constrain the constant to be $f_{\rm p}\lesssim 10.7\times 10^{9}~\rm{GeV}$, promising to improve astrophysical constraint level by at least one order of magnitude. Our system could provide a sensitive detection method for the global network of optical magnetometers to search for exotic physics.
    Numerical analysis of motional mode coupling of sympathetically cooled two-ion crystals
    Li-Jun Du(杜丽军), Yan-Song Meng(蒙艳松), Yu-Ling He(贺玉玲), and Jun Xie(谢军)
    Chin. Phys. B, 2021, 30 (7): 073702.   DOI: 10.1088/1674-1056/abfc3e
    Abstract211)   HTML0)    PDF (1029KB)(622)      
    A two-ion pair in a linear Paul trap is extensively used in the research of the simplest quantum-logic system; however, there are few quantitative and comprehensive studies on the motional mode coupling of two-ion systems yet. This study proposes a method to investigate the motional mode coupling of sympathetically cooled two-ion crystals by quantifying three-dimensional (3D) secular spectra of trapped ions using molecular dynamics simulations. The 3D resonance peaks of the 40Ca+-27Al+ pair obtained by using this method were in good agreement with the 3D in- and out-of-phase modes predicted by the mode coupling theory for two ions in equilibrium and the frequency matching errors were lower than 2%. The obtained and predicted amplitudes of these modes were also qualitatively similar. It was observed that the strength of the sympathetic interaction of the 40Ca+-27Al+ pair was primarily determined by its axial in-phase coupling. In addition, the frequencies and amplitudes of the ion pair's resonance modes (in all dimensions) were sensitive to the relative masses of the ion pair, and a decrease in the mass mismatch enhanced the sympathetic cooling rates. The sympathetic interactions of the 40Ca+-27Al+ pair were slightly weaker than those of the 24Mg+-27Al+ pair, but significantly stronger than those of 9Be+-27Al+. However, the Doppler cooling limit temperature of 40Ca+ is comparable to that of 9Be+ but lower than approximately half of that of 24Mg+. Furthermore, laser cooling systems for 40Ca+ are more reliable than those for 24Mg+ and 9Be+. Therefore, 40Ca+ is probably the best laser-cooled ion for sympathetic cooling and quantum-logic operations of 27Al+ and has particularly more notable comprehensive advantages in the development of high reliability, compact, and transportable 27Al+ optical clocks. This methodology may be extended to multi-ion systems, and it will greatly aid efforts to control the dynamic behaviors of sympathetic cooling as well as the development of low-heating-rate quantum logic clocks.
    Widely tunable single-photon source with high spectral-purity from telecom wavelength to mid-infrared wavelength based on MgO:PPLN
    Chang-Wei Sun(孙昌伟), Yu Sun(孙宇), Jia-Chen Duan(端家晨), Guang-Tai Xue(薛广太), Yi-Chen Liu(刘奕辰), Liang-Liang Lu(陆亮亮), Qun-Yong Zhang(张群永), Yan-Xiao Gong(龚彦晓), Ping Xu(徐平), and Shi-Ning Zhu(祝世宁)
    Chin. Phys. B, 2021, 30 (10): 100312.   DOI: 10.1088/1674-1056/ac20cb
    Abstract658)   HTML2)    PDF (1543KB)(609)      
    By utilizing the extended phase-matching (EPM) method, we investigate the generation of single photons with high spectral-purity in a magnesium-doped periodically-poled lithium niobate (MgO:PPLN) crystal via the spontaneous parametric down-conversion (SPDC) process. By adjusting the temperature and pump wavelength, the wavelength of the single photons can be tuned from telecom to mid-infrared (MIR) wavelengths, for which the spectral-purity can be above 0.95 with high transmission filters. In experiments, we engineer a MgO:PPLN with poling period of 20.35 μ which emits the EPM photon pair centered at 1496.6 nm and 1644.0 nm and carry out the joint spectral intensity (JSI) and Glauber's second-order self-correlation measurements to characterize the spectral purity. The results are in good agreement with the numerical simulations. Our work may provide a valuable approach for the generation of spectrally pure single photons at a wide range of wavelengths which is competent for various photonic quantum technologies.
    Topology and ferroelectricity in group-V monolayers
    Mutee Ur Rehman, Chenqiang Hua(华陈强), Yunhao Lu(陆赟豪)
    Chin. Phys. B, 2020, 29 (5): 057304.   DOI: 10.1088/1674-1056/ab81ff
    Abstract549)   HTML    PDF (5383KB)(598)      
    The group-V monolayers (MLs) have been studied intensively after the experimental fabrication of two-dimensional (2D) graphene and black phosphorus. The observation of novel quantum phenomena, such as quantum spin Hall effect and ferroelectricity in group-V elemental layers, has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics in the 2D limit. In this review, we comprehensively review recent research progress in engineering of topology and ferroelectricity, and several effective methods to control the quantum phase transition are discussed. We then introduce the coupling between topological orders and ferroelectric orders. The research directions and outlooks are discussed at the end of the perspective. It is expected that the comprehensive overview of topology and ferroelectricity in 2D group-V materials can provide guidelines for researchers in the area and inspire further explorations of interplay between multiple quantum phenomena in low-dimensional systems.
    In-memory computing to break the memory wall
    Xiaohe Huang(黄晓合), Chunsen Liu(刘春森), Yu-Gang Jiang(姜育刚), Peng Zhou(周鹏)
    Chin. Phys. B, 2020, 29 (7): 078504.   DOI: 10.1088/1674-1056/ab90e7
    Abstract757)   HTML    PDF (3505KB)(576)      
    Facing the computing demands of Internet of things (IoT) and artificial intelligence (AI), the cost induced by moving the data between the central processing unit (CPU) and memory is the key problem and a chip featured with flexible structural unit, ultra-low power consumption, and huge parallelism will be needed. In-memory computing, a non-von Neumann architecture fusing memory units and computing units, can eliminate the data transfer time and energy consumption while performing massive parallel computations. Prototype in-memory computing schemes modified from different memory technologies have shown orders of magnitude improvement in computing efficiency, making it be regarded as the ultimate computing paradigm. Here we review the state-of-the-art memory device technologies potential for in-memory computing, summarize their versatile applications in neural network, stochastic generation, and hybrid precision digital computing, with promising solutions for unprecedented computing tasks, and also discuss the challenges of stability and integration for general in-memory computing.
    Structural and electrical transport properties of Cu-doped Fe1 -xCuxSe single crystals
    He Li(李贺), Ming-Wei Ma(马明伟), Shao-Bo Liu(刘少博), Fang Zhou(周放), and Xiao-Li Dong(董晓莉)
    Chin. Phys. B, 2020, 29 (12): 127404.   DOI: 10.1088/1674-1056/abc3af
    Abstract613)   HTML    PDF (859KB)(575)      
    We report the structural and electrical transport properties of Fe1 -xCuxSe (x = 0, 0.02, 0.05, 0.10) single crystals grown by a chemical vapor transport method. Substituting Cu for Fe suppresses both the nematicity and superconductivity of FeSe single crystal, and provokes a metal-insulator transition. Our Hall measurements show that the Cu substitution also changes an electron dominance at low temperature of un-doped FeSe to a hole dominance of Cu-doped Fe1 -xCuxSe at x = 0.02 and 0.1, and reduces the sign-change temperature (TR) of the Hall coefficient (R H).
    Perpendicular magnetization switching by large spin—orbit torques from sputtered Bi2Te3
    Zhenyi Zheng(郑臻益), Yue Zhang(张悦), Daoqian Zhu(朱道乾), Kun Zhang(张昆), Xueqiang Feng(冯学强), Yu He(何宇), Lei Chen(陈磊), Zhizhong Zhang(张志仲), Dijun Liu(刘迪军), Youguang Zhang(张有光), Pedram Khalili Amiri, Weisheng Zhao(赵巍胜)
    Chin. Phys. B, 2020, 29 (7): 078505.   DOI: 10.1088/1674-1056/ab9439
    Abstract739)   HTML    PDF (1025KB)(531)      
    Spin-orbit torque (SOT) effect is considered as an efficient way to switch the magnetization and can inspire various high-performance spintronic devices. Recently, topological insulators (TIs) have gained extensive attention, as they are demonstrated to maintain a large effective spin Hall angle (θSHeff), even at room temperature. However, molecular beam epitaxy (MBE), as a precise deposition method, is required to guarantee favorable surface states of TIs, which hinders the prospect of TIs towards industrial application. In this paper, we demonstrate that Bi2Te3 films grown by magnetron sputtering can provide a notable SOT effect in the heterostructure with perpendicular magnetic anisotropy CoTb ferrimagnetic alloy. By harmonic Hall measurement, a high SOT efficiency (8.7±0.9 Oe/(109 A/m2)) and a large θSHeff (3.3±0.3) are obtained at room temperature. Besides, we also observe an ultra-low critical switching current density (9.7×109 A/m2). Moreover, the low-power characteristic of the sputtered Bi2Te3 film is investigated by drawing a comparison with different sputtered SOT sources. Our work may provide an alternative to leverage chalcogenides as a realistic and efficient SOT source in future spintronic devices.
    Gate-controlled magnetic transitions in Fe3GeTe2 with lithium ion conducting glass substrate
    Guangyi Chen(陈光毅), Yu Zhang(张玉), Shaomian Qi(齐少勉), and Jian-Hao Chen(陈剑豪)
    Chin. Phys. B, 2021, 30 (9): 097504.   DOI: 10.1088/1674-1056/ac1338
    Abstract512)   HTML1)    PDF (806KB)(508)      
    Since the discovery of magnetism in two dimensions, effective manipulation of magnetism in van der Waals magnets has always been a crucial goal. Ionic gating is a promising method for such manipulation, yet devices gated with conventional ionic liquid may have some restrictions in applications due to the liquid nature of the gate dielectric. Lithium-ion conducting glass-ceramics (LICGC), a solid Li+ electrolyte, could be used as a substrate while simultaneously acts as a promising substitute for ionic liquid. Here we demonstrate that the ferromagnetism of Fe3GeTe2 (FGT) could be modulated via LICGC. By applying a voltage between FGT and the back side of LICGC substrate, Li+ doping occurs and causes the decrease of the coercive field (Hc) and ferromagnetic transition temperature (Tc) in FGT nanoflakes. A modulation efficiency for Hc of up to ~ 24.6% under Vg = 3.5 V at T =100 K is achieved. Our results provide another method to construct electrically-controlled magnetoelectronics, with potential applications in future information technology.
    Measuring Loschmidt echo via Floquet engineering in superconducting circuits
    Shou-Kuan Zhao(赵寿宽), Zi-Yong Ge(葛自勇), Zhong-Cheng Xiang(相忠诚), Guang-Ming Xue(薛光明), Hai-Sheng Yan(严海生), Zi-Ting Wang(王子婷), Zhan Wang(王战), Hui-Kai Xu(徐晖凯), Fei-Fan Su(宿非凡), Zhao-Hua Yang(杨钊华), He Zhang(张贺), Yu-Ran Zhang(张煜然), Xue-Yi Guo(郭学仪), Kai Xu(许凯), Ye Tian(田野), Hai-Feng Yu(于海峰), Dong-Ning Zheng(郑东宁), Heng Fan(范桁), and Shi-Ping Zhao(赵士平)
    Chin. Phys. B, 2022, 31 (3): 030307.   DOI: 10.1088/1674-1056/ac40f8
    Abstract543)   HTML1)    PDF (1107KB)(501)      
    The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearest-neighbor (NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.
    Density functional theory investigation on lattice dynamics, elastic properties and origin of vanished magnetism in Heusler compounds CoMnVZ (Z= Al, Ga)
    Guijiang Li(李贵江), Enke Liu(刘恩克), Guodong Liu(刘国栋), Wenhong Wang(王文洪), and Guangheng Wu(吴光恒)
    Chin. Phys. B, 2021, 30 (8): 083103.   DOI: 10.1088/1674-1056/ac0a6a
    Abstract578)   HTML5)    PDF (1511KB)(485)      
    The lattice dynamics, elastic properties and the origin of vanished magnetism in equiatomic quaternary Heusler compounds CoMnVZ (Z=Al, Ga) are investigated by first principle calculations in this work. Due to the similar constituent atoms in CoMnVAl and CoMnVGa compounds, they are both stable in LiMgPdSn-type structure with comparable lattice size, phonon dispersions and electronic structures. Comparatively, we find that CoMnVAl is more structurally stable than CoMnVGa. Meanwhile, the increased covalent bonding component in CoMnVAl enhances its mechanical strength and Vickers hardness, which leads to better comprehensive mechanical properties than those of CoMnVGa. Practically and importantly, structural and chemical compatibilities at the interface make non-magnetic semiconductor CoMnVAl and magnetic topological semimetals Co2MnAl/Ga more suitable to be grown in heterostructures. Owing to atomic preferential occupation in CoMnVAl/Ga, the localized atoms Mn occupy C (0.5, 0.5, 0.5) Wyckoff site rather than B (0.25, 0.25, 0.25) and D (0.75, 0.75, 0.75) Wyckoff sites in LiMgPdSn-type structure, which results in symmetric band filling and consequently drives them to be non-magnetic. Correspondingly, by tuning localized atoms Mn to occupy B (0.25, 0.25, 0.25) or/and D (0.75, 0.75, 0.75) Wyckoff sites in off-stoichiometric Co-Mn-V-Al/Ga compounds and keeping the total valence electrons as 24, newly compensated ferrimagnetic compounds are theoretically achieved. We hope that our work will provide more choices for spintronic applications.
ISSN 1674-1056   CN 11-5639/O4

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