查看更多>>摘要：Motivated by recent experimental progress on the quasi-one-dimensional quantum magnet NiNb2O6,we study the spin dynamics of an S=1 ferromagnetic Heisenberg chain with single-ion anisotropy by using a semiclassical molecular dynamics approach.This system undergoes a quantum phase transition from a ferromagnetic to a paramagnetic state under a transverse magnetic field,and the magnetic response reflecting this transition is well described by our semiclassical method.We show that at low temperature the transverse component of the dynamical structure factor depicts clearly the magnon dispersion,and the longitudinal component exhibits two continua associated with single-and two-magnon excitations,respectively.These spin excitation spectra show interesting temperature dependence as effects of magnon interactions.Our findings shed light on the experimental detection of spin excitations in a large class of quasi-one-dimensional magnets.
查看更多>>摘要：We investigate the evolution of magnetic properties as well as the content and distribution of Mn for Mn(Sb1-xBix)2Te4 single crystals grown by large-temperature-gradient chemical vapor transport method.It is found that the ferromagnetic MnSb2Te4 changes to antiferromagnetism with Bi doping when x ≥ 0.25.Further analysis implies that the occupations of Mn ions at Sb/Bi site Mnsb/Bi and Mn site MnMn have a strong influence on the magnetic ground states of these systems.With the decrease of MnMn and increase of MnSb/Bi,the system will favor the ferromagnetic ground state.In addition,the rapid decrease of TC/N with increasing Bi content when x ≤ 0.25 and the insensitivity of TN to x when x ≥ 0.25 suggest that the main magnetic interaction may change from the Ruderman-Kittel-Kasuya-Yosida type at low Bi doping region to the van-Vleck type in high Bi doped samples.
查看更多>>摘要：Topological Dirac semimetals are a parent state from which other exotic topological phases of matter,such as Weyl semimetals and topological insulators,can emerge.In this study,we investigate a Dirac semimetal possessing sixfold rotational symmetry and hosting higher-order topological hinge Fermi arc states,which is irradiated by circularly polarized light.Our findings reveal that circularly polarized light splits each Dirac node into a pair of Weyl nodes due to the breaking of time-reversal symmetry,resulting in the realization of the Weyl semimetal phase.This Weyl semimetal phase exhibits rich boundary states,including two-dimensional surface Fermi arc states and hinge Fermi arc states confined to six hinges.Furthermore,by adjusting the incident direction of the circularly polarized light,we can control the degree of tilt of the resulting Weyl cones,enabling the realization of different types of Weyl semimetals.
查看更多>>摘要：Under investigation in this paper is a complex modified Korteweg-de Vries(KdV)equation,which describes the prop-agation of short pulses in optical fibers.Bilinear forms and multi-soliton solutions are obtained through the Hirota method and symbolic computation.Breather-like and bound-state solitons are constructed in which the signs of the imaginary parts of the complex wave numbers and the initial separations of the two parallel solitons are important factors for the interaction patterns.The periodic structures and position-induced phase shift of some solutions are introduced.
查看更多>>摘要：A dynamical model is constructed to depict the spatial-temporal evolution of malware in mobile wireless sensor networks(MWSNs).Based on such a model,we design a hybrid control scheme combining parameter perturbation and state feedback to effectively manipulate the spatiotemporal dynamics of malware propagation.The hybrid control can not only suppress the Turing instability caused by diffusion factor but can also adjust the occurrence of Hopf bifurcation induced by time delay.Numerical simulation results show that the hybrid control strategy can efficiently manipulate the transmission dynamics to achieve our expected desired properties,thus reducing the harm of malware propagation to MWSNs.
查看更多>>摘要：This paper focuses on the stochastic analysis of a viscoelastic bistable energy harvesting system under colored noise and harmonic excitation,and adopts the time-delayed feedback control to improve its harvesting efficiency.Firstly,to obtain the dimensionless governing equation of the system,the original bistable system is approximated as a system without viscoelastic term by using the stochastic averaging method of energy envelope,and then is further decoupled to derive an equivalent system.The credibility of the proposed method is validated by contrasting the consistency between the numerical and the analytical results of the equivalent system under different noise conditions.The influence of system parameters on average output power is analyzed,and the control effect of the time-delayed feedback control on system performance is compared.The output performance of the system is improved with the occurrence of stochastic resonance(SR).Therefore,the signal-to-noise ratio expression for measuring SR is derived,and the dependence of its SR behavior on different parameters is explored.
查看更多>>摘要：We construct a one-dimensional quasiperiodic quantum walk to investigate the localization-delocalization transition.The inverse participation ratio and Lyapunov exponent are employed as two indexes to determine the mobility edge,a critical energy to distinguish the energy regions of extended and localized states.The analytical solution of mobility edge is obtained by the Lyapunov exponents in global theory,and the consistency of the two indexes is confirmed.We further study the dynamic characteristics of the quantum walk and show that the probabilities are localized to some specific lattice sites with time evolution.This phenomenon is explained by the effective potential of the Hamiltonian which corresponds to the phase in the coin operator of the quantum walk.
查看更多>>摘要：The conditions for the emergence of the non-Hermitian skin effect,as a unique physical response of non-Hermitian systems,have now become one of the hot research topics.In this paper,we study the novel physical responses of non-Hermitian systems with anomalous time-reversal symmetry,in both one dimension and two dimensions.Specifically,we focus on whether the systems will exhibit a non-Hermitian skin effect.We employ the theory of generalized Brillouin zone and also numerical methods to show that the anomalous time-reversal symmetry can prevent the skin effect in one-dimensional non-Hermitian systems,but is unable to exert the same effectiveness in two-dimensional cases.
查看更多>>摘要：Quantum discord,one of the famous quantum correlations,has been recently generalized to multipartite systems by Radhakrishnan et al.Here we give analytical solutions of the quantum discord for a family of N-qubit quantum states.For the bipartite system,we derive a zero quantum discord which will remain unchanged under the phase damping channel.For multiparitite systems,it is found that the quantum discord can be classified into three categories and the quantum discord for odd-partite systems can exhibit freezing under the phase damping channel,while the freezing does not exist in the even-partite systems.
查看更多>>摘要：Quantum multi-parameter estimation has recently attracted increased attention due to its wide applications,with a primary goal of designing high-precision measurement schemes for unknown parameters.While existing research has predominantly concentrated on time-independent Hamiltonians,little has been known about quantum multi-parameter es-timation for time-dependent Hamiltonians due to the complexity of quantum dynamics.This work bridges the gap by investigating the precision limit of multi-parameter quantum estimation for a qubit in an oscillating magnetic field model with multiple unknown frequencies.As the well-known quantum Cramér-Rao bound is generally unattainable due to the potential incompatibility between the optimal measurements for different parameters,we use the most informative bound instead which is always attainable and equivalent to the Holevo bound in the asymptotic limit.Moreover,we apply addi-tional Hamiltonian to the system to engineer the dynamics of the qubit.By utilizing the quasi-Newton method,we explore the optimal schemes to attain the highest precision for the unknown frequencies of the magnetic field,including the simulta-neous optimization of initial state preparation,the control Hamiltonian and the final measurement.The results indicate that the optimization can yield much higher precisions for the field frequencies than those without the optimizations.Finally,we study the robustness of the optimal control scheme with respect to the fluctuation of the interested frequencies,and the optimized scheme exhibits superior robustness to the scenario without any optimization.
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