arXiv subjects

Xiaobing Luo

Publications and source records attributed to Xiaobing Luo.

At least 37 records · Page 2Linked to original sources

arXiv2022

Phase control of localization in the nonlinear two-mode system from harmonic mixing driving: Perturbative analysis and symmetry consideration

In this paper, we present a rigorous analysis of symmetry and underlying physics of the nonlinear two-mode system driven by a harmonic mixing field, by means of multiple scale asymptotic analysis method. The effective description in the framework of the second-order perturbative theory provides an accurate picture for understanding the Floquet eigenspectrum and dynamical features of the nonlinear two-mode system, showing full agreement with the prediction of symmetry considerations. We find that two types of symmetries play significant role in the dynamical features of this model, the mechanism behind which can be interpreted in terms of the effective description. The results are of relevance for the phase control of the atomic localization in Bose-Einstein condensates or switch of the optical signals in nonlinear mediums.

quant-ph↗

arXiv2022

The $\mathbf{Z}_{2}$ topological invariants in 2D and 3D topological superconductors without time reversal symmetry

In theory of topological classification, the 2D topological superconductors without time reversal symmetry are characterized by Chern numbers. However, in reality, we find the Chern numbers can not reveal the whole properties of the boundary states of the topological superconductors. We figure out some particle-hole symmetry related $\mathbf{Z}_{2}$ invariants, which provide more additional information of the topological superconductors than the Chern numbers provide. With the $\mathbf{Z}_{2}$ invariant, we define weak and strong topological superconductors in 2D systems. Moreover, we explain the causes of mismatch between the Chern numbers and the numbers of boundary states in topological superconductors, and claim that the robust Majorana zero modes are characterized by the $\mathbf{Z}_{2}$ invariant rather than the Chern numbers. We also extend the $\mathbf{Z}_{2}$ invariants to 3D non-time-reversal symmetry superconductor systems including gapful and gapless situations.

cond-mat.supr-con↗

arXiv2021

Coherent control of spin tunneling in a spin-orbit coupled bosonic triple well

We study the coherent control of spin tunneling for a spin-orbit (SO) coupled boson held in a driven triple well. Under high-frequency approximation, we analytically obtain the quasienergies of the SO-coupled bosonic triple-well system and fine energy band structure is displayed. By adjusting the driving parameters, we reveal that the directed selective spin-flipping or spin-conserving tunneling of a SO-coupled boson occurs along different pathways and in different directions. The analytical results are numerically confirmed and perfect agreements are found. Further, a scheme of quantum spin switch with or without spin-flipping is presented. These results may be useful for quantum information processing and the design of spintronic devices.

physics.atom-ph↗

arXiv2021

Controlling directed atomic motion and second-order tunneling of a spin-orbit-coupled atom in optical lattices

We theoretically explore the tunneling dynamics for the tight-binding (TB) model of a single spin-orbit-coupled atom trapped in an optical lattice subjected to lattice shaking and to time-periodic Zeeman field. By means of analytical and numerical methods, we demonstrate that the spin-orbit (SO) coupling adds some new results to the tunneling dynamics in both multiphoton resonance and far-off-resonance parameter regimes. When the driving frequency is resonant with the static Zeeman field (multi-photon resonances), we obtain an unexpected new dynamical localization (DL) phenomenon where the single SO-coupled atom is restricted to making perfect two-site Rabi oscillation accompanied by spin flipping.By using the unconventional DL phenomenon, we are able to generate a ratchetlike effect which enables directed atomic motion towards different directions and accompanies periodic spin-flipping under the action of SO coupling. For the far-off-resonance case, we show that by suppressing the usual inter-site tunneling alone, it is possible to realize a type of spin-conserving second-order tunneling between next-nearest-neighboring sites, which is not accessible in the conventional lattice system without SO coupling. We also show that simultaneous controls of the usual inter-site tunneling and the SO-coupling-related second-order-tunneling are necessary for quasienergies flatness (collapse) and completely frozen dynamics to exist. These results may be relevant to potential applications such as spin-based quantum information processing and design of novel spintronics devices.

cond-mat.quant-gas↗

arXiv2020

Controlling stable tunneling in a non-Hermitian spin-orbit coupled bosonic junction

In this paper, we study how to apply a periodic driving field to control stable spin tunneling in a non-Hermitian spin-orbit coupled bosonic double-well system. By means of a high-frequency approximation, we obtain the analytical Floquet solutions and their associated quasienergies and thus construct the general non-Floquet solutions of the dissipative spin-orbit coupled bosonic system. Based on detailed analysis of the Floquet quasienergy spectrum, the profound effect of system parameters and the periodic driving field on the stability of spin-dependent tunneling is investigated analytically and numerically for both balanced and unbalanced gain-loss between two wells. Under balanced gain and loss, we find that the stable spin-flipping tunneling is preferentially suppressed with the increase of gain-loss strength. When the ratio of Zeeman field strength to periodic driving frequency $Ω/ω$ is even, there is a possibility that \emph{continuous} stable parameter regions will exist. When $Ω/ω$ is odd, nevertheless, only \emph{discrete} stable parameter regions are found. Under unbalanced gain and loss, whether $Ω/ω$ is even or odd, we can get parametric equilibrium conditions for the existence of stable spin tunneling. The results could be useful for the experiments of controlling stable spin transportation in a non-Hermitian spin-orbit coupled system.

quant-ph↗

arXiv2020

Coherent control of dissipative dynamics in a periodically driven lattice array

We find a different mechanism for suppression of decay in an open one-dimensional lattice system, which originates from a dark Floquet state, a sink state to which the system is asymptotically driven, whose overall probability is determined only by the parameters of the periodic driving field. The zero-quasienergy of dark Floquet state has been shown to be not a real zero, but a vanishingly small negative imaginary number which will cause undesirable physical effect in long-time evolution of quantum states, which is extremely different from the conservative counterpart. Another important finding is that the value of the system's effective decay, determined by the size of the non-zero imaginary part of the dark-Floquet-state-related quasienergy, depends not on how many localized lossy sites there are but on which one of the lossy sites is nearest to the driven site. Thus, for specially designed local dissipation, by controlling the driving parameters, it is possible for us to drive the system to a dark Floquet state with a much lower level of overall probability loss as compared to the undriven case and with good stability over enough longer evolution time. These results are applicable to the multisite lattice system with an odd number of sites and may be significant for long-time control of decay in a vast family of multistate physical systems with localized dissipation.

quant-ph↗

arXiv2018

Dynamics of spin-orbit-coupled cold atomic gases in a Floquet lattice with an impurity

In this study, we have studied the quantum tunneling of a single spin-orbit-coupled atom held in a periodically modulated optical lattice with an impurity. At the pseudocollapse points of quasienergy bands, where the dynamical localization takes place globally, two types of local second-order tunneling processes appear beyond expectation between the two nearest-neighbor sites of the impurity with the spin unchanged and with impurity site population negligible all the time, when the impurity potential is far off-resonant with the driving field. Though tunneling behaviors of the two types seem to be the same, they are believed to involve two distinct mechanisms: one is related to spin-independent process, while the other is to spin-dependent tunneling process. The two types of second-order processes can be identified by means of resonant tunneling with or without spin-flipping by tuning the impurity potential to be in resonance with the driving field. In the Floquet picture, the second-order processes are manifested as subtle and fine avoided crossings of quasienergy spectrums near the pseudocollapse region. These results are confirmed analytically on the basis of effective three-site model and multiple-time-scale asymptotic perturbative method, and may be exploited for engineering the spin-dependent quantum transport in realistic experiments.

quant-ph↗

arXiv2017

Analytical results for a parity-time symmetric two-level system under synchronous combined modulations

We propose a simple method of combined synchronous modulations to generate the analytically exact solutions for a parity-time symmetric two-level system. Such exact solutions are expressible in terms of simple elementary functions and helpful for illuminating some generalizations of appealing concepts originating in the Hermitian system. Some intriguing physical phenomena, such as stabilization of a non-Hermitian system by periodic driving, non-Hermitian analogs of coherent destruction of tunneling (CDT) and complete population inversion (CPI), are demonstrated analytically and confirmed numerically. In addition, by using these exact solutions we derive a pulse area theorem for such non-Hermitian CPI in the parity-time symmetric two-level system. Our results may provide an additional possibility for pulse manipulation and coherent control of the parity-time symmetric two-level system.

quant-ph↗

arXiv2017

Mixed-gap vector solitons in PT-symmetric lattices with saturable nonlinearity

We have investigated mixed-gap vector solitons involving incoherently coupled fundamental and dipole components in a parity-time (PT) symmetric lattice with saturable nonlinearity. For the focusing case, vector solitons emerge from the semi-infinite and the first finite gaps, while for the defocusing case, vector solitons emerge from the first finite and the second finite gaps. For both cases, we find that stronger saturable nonlinearity is relative to sharper increase/decrease of soliton power with propagation constant and to narrower existence domain of vector solitons. This finding is helpful for realizing high-power solitons with limited range of propagation constant. Additionally, our numerical calculations show that increasing the weight of dipole component results in destabilization of vector solitons, while stronger saturable nonlinearity to certain extent suppresses the instability of vector solitons.

physics.optics↗

arXiv2016

Directed tunneling of a prescribed number of dipolar bosons in shaken triple-well potentials

We propose a scheme for precise control of tunneling dynamics of dipolar bosons in shaken triple-well potentials. In the high-frequency regimes and under the resonance conditions, we have analytically and numerically demonstrated that we can transport a priori prescribed number of dipolar bosons along different pathways and different directions by adjusting the driving parameters. These results extend the previous many-body selective coherent destruction of tunneling (CDT) schemes for nondipolar bosons in double-well potentials[Phys. Rev. Lett. 103, 133002 (2009); Phys. Rev. A 86, 044102 (2012)], thus offering an efficient way to design the long-range coherent quantum transportation.

quant-ph↗

arXiv2016

Exact control of parity-time symmetry in periodically modulated nonlinear optical couplers

We propose a mechanism for realization of exact control of parity-time (PT) symmetry by using a periodically modulated nonlinear optical coupler with balanced gain and loss. It is shown that for certain appropriately chosen values of the modulation parameters, we can construct a family of exact analytical solutions for the two-mode equations describing the dynamics of such nonlinear couplers. These exact solutions give explicit examples that allow us to precisely manipulate the system from nonlinearity-induced symmetry breaking to PT symmetry, thus providing an analytical approach to the all-optical signal control in nonlinear PT-symmetric structures.

physics.optics↗

arXiv2016

Switching management by adiabatic passage in two periodically modulated nonlinear waveguides

We theoretically investigate light propagation in two periodically modulated nonlinear waveguides with certain propagation constant detuning between two guides. By slowly varying the amplitude of modulation, we can steer the light to the desired output waveguide when equal amounts of lights are launched into each waveguide. We also reveal that the light propagation dynamics depends sensitively on the detuning between two guides. Our findings can be explained qualitatively by means of adiabatic navigation of the extended nonlinear Floquet states.

physics.optics↗

arXiv2016

Analog of photon-assisted tunneling originated from dark Floquet state in periodically modulated waveguide arrays

We theoretically report an analog of photon-assisted tunneling (PAT) in a periodically driven lattice array without a static biased potential by studying a three-channel waveguide system. This analog of PAT can be achieved by only periodically modulating the top waveguide and adjusting the distance between the bottom and its adjacent waveguide. It is numerically shown that the PAT resonances also exist in the five-channel waveguide system and probably exist in the waveguide arrays with other odd numbers of waveguides, but they will become weak as the number of waveguides increases. With origin different from traditional PAT, this type of PAT found in our work is closely linked to the existence of the zero-energy (dark) Floquet states. It is readily observable under currently accessible experimental conditions and may be useful for controlling light propagation in waveguide arrays.

quant-ph↗

arXiv2016

Coherent destruction of tunneling in a lattice array with controllable boundary

We have investigated how the dynamics of a quantum particle initially localized in the left boundary site under periodic driving can be manipulated via control of the right boundary site of a lattice array. Because of the adjustable coupling between the right boundary site and its nearest-neighbor, we can realize either coherent destruction of tunneling to coherent tunneling (CDT-CT) transition or coherent tunneling to coherent destruction of tunneling (CT-CDT) transition, by driving or moving the right boundary site while keeping the left boundary site driven by a periodically oscillating field with a fixed driving parameter. In particular, the transition direction shows odd-even sensitivity to the number of lattice sites. We have also revealed that our proposed CDT-CT transition is robust against the second order coupling (SOC) between next-nearest-neighbor sites in odd-$N$-site systems, whereas localization can be significantly enhanced by SOC in even-$N$-site systems. More interestingly, it is found destruction and revival of CDT observable in non-high-frequency regimes. Our results can be readily verified within the capacity of current experiments.

quant-ph↗

arXiv2013

Pseudo Parity-Time Symmetry in Optical Systems

We introduce a novel concept of the {\em pseudo} parity-time ($\mathcal{PT}$) symmetry in periodically modulated optical systems with balanced gain and loss. We demonstrate that whether the original system is $\mathcal{PT}$-symmetric or not, we can manipulate the property of the $\mathcal{PT}$ symmetry by applying a periodic modulation in such a way that the effective system derived by the high-frequency Floquet method is $\mathcal{PT}$ symmetric. If the original system is non-$\mathcal{PT}$ symmetric, the $\mathcal{PT}$ symmetry in the effective system will lead to quasi-stationary propagation that can be associated with the \emph{pseudo $\mathcal{PT}$ symmetry}. Our results provide a promising approach for manipulating the $\mathcal{PT}$ symmetry of realistic systems.

physics.optics↗

arXiv2013

Coherent Destruction of Tunneling and Dark Floquet State

We study a system of three coherently coupled states, where one state is shifted periodically against the other two. We discover such a system possesses a dark Floquet state at zero quasienergy and always with negligible population at the intermediate state. This dark Floquet state manifests itself dynamically in terms of the suppression of inter-state tunneling, a phenomenon known as coherent destruction of tunneling. We suggest to call it dark coherent destruction of tunneling (DCDT). At high frequency limit for the periodic driving, this Floquet state reduces to the well-known dark state widely used for STIRAP. Our results can be generalized to systems with more states and can be verified with easily implemented experiments within current technologies.

quant-ph↗

arXiv2012

Formation and structure of vortex lattices in a rotating double-well Bose-Einstein condensate

We investigate the dynamics of vortex formation and the structure of vortex lattices in a Bose-Einstein condensate confined within a rotating double-well (DW) potential. The dynamical process is a formation process of "ghost" vortices, "hidden" vortices and "visible" vortices. The critical rotation frequency for the creation of visible vortex is indicated by a sudden jump in the angular momentum evolution and an inflexion in the energy evolution. Different visible vortex structures can be formed by ruling the rotation frequency. In particular, structural change of visible vortex patterns can be achieved by regulating the anisotropy parameter of the DW potential. This feature allows to flexibly control the distribution of angular momentum in macroscopic quantum systems and study the interplay among rotation, interparticle interaction and external potential in superfluids.

cond-mat.quant-gas↗

arXiv2011

Coherent destruction of tunneling in a lattice array under selective in-phase modulations

We explore the coherent destruction of tunneling (CDT) in a lattice array under selective in-phase harmonic modulations, in which some selected lattice sites are driven by in-phase harmonic oscillating fields and other lattice sites are undriven. Due to the occurrence of CDT, if the driving amplitude $A$ and the driving frequency $ω$ are tuned to satisfy the zeroth-order Bessel function $J_0(A/ω)=0$, the driven lattice sites are approximately decoupled with the undriven lattice sites. The CDT even takes place in lattice systems with high-order couplings between non-nearest lattice sites. By using the CDT, we propose a scheme for realizing directed transport of a single particle. It is possible to observe the CDT in the engineered optical waveguide array, which provides a new opportunity for controlling light propagation and designing switch-like couplers.

quant-ph↗