arXiv subjects

Lu Zhou

Publications and source records attributed to Lu Zhou.

At least 73 records · Page 4Linked to original sources

arXiv2020

Self-trapped atomic matter wave in a ring cavity

We studied a system of atomic Bose-Einstein condensate coupled to a ring cavity within the mean-field theory. Due to the interaction between atoms and light field, the atoms can be self-trapped. This is verified with both variational and numerical methods. We examined the stability of these self-trapped states. For a weakly pumped cavity, they spread during the evolution; while at strong pumping, they can maintain the shape for a long time. We also studied the moving dynamics of these self-trapped waves, and found out that it can be strongly affected by the cavity decay rate. For a small cavity decay rate, the self-trapped waves undergo a damped oscillation. Increasing the cavity decay rate will lead to a deceleration of the self-trapped waves. We also compared the main results with the semiclassical theory in which atoms are treated as classical particles.

cond-mat.quant-gas↗

arXiv2020

Stückelberg interferometry using spin-orbit-coupled cold atoms in an optical lattice

Time evolution of spin-orbit-coupled cold atoms in an optical lattice is studied, with a two-band energy spectrum having two avoided crossings. A force is applied such that the atoms experience two consecutive Landau-Zener tunnelings while transversing the avoided crossings. Stückelberg interference arises from the phase accumulated during the adiabatic evolution between the two tunnelings. This phase is gauge field-dependent and thus provides new opportunities to measure the synthetic gauge field, which is verified via calculation of spin transition probabilities after a double passage process. Time-dependent and time-averaged spin probabilities are derived, in which resonances are found. We also demonstrate chiral Bloch oscillation and rich spin-momentum locking behavior in this system.

cond-mat.quant-gas↗

arXiv2020

Exploring the potentiality of standard sirens to probe cosmic opacity at high redshifts

In this work, using the Gaussian process, we explore the potentiality of future gravitational wave (GW) measurements to probe cosmic opacity at high redshifts through comparing its opacity-free luminosity distance (LD) with the opacity-dependent one from the combination of Type Ia supernovae (SNIa) and gamma-ray bursts (GRBs). The GW data, SNIa and GRB data are simulated from the measurements of the future Einstein Telescope, the actual Pantheon compilation and the latest observation of GRBs compiled by L. Amati {\it et al}, respectively. A nonparametric method is proposed to probe the spatial homogeneity of cosmic transparency at high redshift by comparing the LD reconstructed from the GW data with that reconstructed from the Pantheon and GRB data. In addition, the cosmic opacity is tested by using the parametrization for the optical depth, and the results show that the constraints on cosmic opacity are more stringent than the previous ones. It shows that the future GW measurements may be used as an important tool to probe the cosmic opacity in the high redshift region.

astro-ph.CO↗

arXiv2020

Unidirectional spin transport of a spin-orbit-coupled atomic matter wave using a moving Dirac $δ$-potential well

We study the transport of a spin-orbit-coupled atomic matter wave using a moving Dirac $δ$-potential well. In a spin-orbit-coupled system, bound states can be formed in both ground and excited energy levels with a Dirac $δ$ potential. Because Galilean invariance is broken in a spin-orbit-coupled system, moving of the potential will induce a velocity-dependent effective detuning. This induced detuning breaks the spin symmetry and makes the ground-state transporting channel be spin-$\uparrow$ ($\downarrow$) favored while makes the excited-state transporting channel be spin-$\downarrow$ ($\uparrow$) favored for a positive-direction (negative-direction) transporting. When the $δ$-potential well moves at a small velocity, both the ground-state and the excited-state channels contribute to the transportation, and thus both the spin components can be efficiently transported. However, when the moving velocity of the $δ$-potential well exceeds a critical value, the induced detuning is large enough to eliminate the excited bound state, and makes the ground bound state the only transporting channel, in which only the spin-$\uparrow$ ($\downarrow$) component can be efficiently transported in a positive (negative) direction. This work demonstrates a prototype of unidirectional spin transport.

cond-mat.quant-gas↗

arXiv2020

Bound states of spin-orbit coupled cold atoms in a Dirac delta-function potential

Dirac delta-function potential is widely studied in quantum mechanics because it usually can be exactly solved and at the same time is useful in modeling various physical systems. Here we study a system of delta-potential trapped spinorbit coupled cold atoms. The spin-orbit coupled atomic matter wave has two kinds of evanescent modes, one of which has pure imaginary wavevector and is an ordinary evanescent wave; while the other with a complex number wave vector is recognized as oscillating evanescent wave. We identified the eigenenergy spectra and the existence of bound states in this system. The bound states can be constructed analytically using the two kinds of evanescent modes and we found that they exhibit typical features of stripe phase, separated phase or zero-momentum phase. In addition to that, the properties of semi-bound states are also discussed, which is a localized wave packet on a plane wave background.

cond-mat.quant-gas↗

arXiv2019

Completion Reasoning Emulation for the Description Logic EL+

We present a new approach to integrating deep learning with knowledge-based systems that we believe shows promise. Our approach seeks to emulate reasoning structure, which can be inspected part-way through, rather than simply learning reasoner answers, which is typical in many of the black-box systems currently in use. We demonstrate that this idea is feasible by training a long short-term memory (LSTM) artificial neural network to learn EL+ reasoning patterns with two different data sets. We also show that this trained system is resistant to noise by corrupting a percentage of the test data and comparing the reasoner's and LSTM's predictions on corrupt data with correct answers.

cs.AI↗

arXiv2019

Probing the cosmic opacity from Future Gravitational Wave Standard Sirens

In this work, using the Gaussian Process, we explore the potentiality of future gravitational wave (GW) measurement to probe cosmic opacity through comparing its opacity-free luminosity distance (LD) with the opacity-dependent one from type Ia supernovae (SNIa). GW data points are simulated from the third generation Einstein Telescope, and SNIa data are taken from the Joint Light Analysis (JLA) or Pantheon compilation. The advantages of using Gaussian Process are that one may match SNIa data with GW data at the same redshift and use all available data to probe cosmic opacity. We obtain that the error bar of the constraint on cosmic opacity can be reduced to $σ_ε\sim 0.011$ and $0.006$ at $1σ$ confidence level (CL) for JLA and Pantheon respectively in a cosmological-independent way. Thus, the future GW measurements can give competitive results on the cosmic opacity test. Furthermore, we propose a method to probe the spatial homogeneity of the cosmic transparency through comparing the reconstructed LD from the mock GW with the reconstructed one from SNIa data in a flat $Λ$CDM with the Gaussian Process. The result shows that a transparent universe is favored at $1σ$ CL, although the best-fit value of cosmic opacity is redshift-dependent.

gr-qc↗

arXiv2019

Nonlinear Floquet dynamics of spinor condensates in an optical cavity: Cavity-amplified parametric resonance

We investigate Floquet dynamics of a cavity-spinor Bose-Einstein condensate coupling system via periodic modulation of the cavity pump laser. Parametric resonances are predicted and we show that due to cavity feedback-induced nonlinearity the spin oscillation can be amplified to all orders of resonance, thus facilitating its detection. Real-time observation on Floquet dynamics via cavity output is also discussed.

cond-mat.quant-gas↗

arXiv2019

Testing Cosmic Distance-Duality Relation from Future Gravitational Wave Standard Sirens

A validation of the cosmic distance-duality relation (CDDR) is crucial because any observational departure from it could be a signal of new physics. In this work, we explore the potentialities of luminosity distance data from the gravitational wave (GW) standard sirens of future Einstein Telescope (ET) to test the CDDR. The angular diameter distance data are used from the galaxy clusters samples and the baryon acoustic oscillation (BAO) measurements. The basic advantage of GW measurements substituting for the observations from the type Ia supernovae (SNIa) is that the luminosity distance from it is insensitive to the non-conservation of the number of photons. By simulating 550 and 1000 data points of future GW measurements in the low redshift range $0<z<1$, we show that the measurements of future GW events will be a powerful tool to test the CDDR.

gr-qc↗

arXiv2019

Bloch oscillations of spin-orbit-coupled cold atoms in an optical lattice and spin current generation

We study the Bloch oscillation dynamics of a spin-orbit-coupled cold atomic gas trapped inside a one-dimensioanl optical lattice. The eigenspectra of the system is identified as two interpenetrating Wannier-Stark ladder. Based on that, we carefully analyzed the Bloch oscillation dynamics and found out that intraladder coupling between neighboring rungs of Wannier-Stark ladder give rise to ordinary Bloch oscillation while interladder coupling lead to small amplitude high frequency oscillation superimposed on it. Specifically spin-orbit interaction breaks Galilean invariance, which can be reflected by out-of-phase oscillation of the two spin components in the accelerated frame. The possibility of generating spin current in this system are also explored.

cond-mat.quant-gas↗

arXiv2018

Relativistic Measurement Backaction in the Quantum Dirac Oscillator

An elegant method to circumvent quantum measurement backaction is the use of quantum mechanics free subsystems (QMFS), with one approach involving the use of two oscillators with effective masses of opposite signs. Since negative energies, and hence masses, are a characteristic of relativistic systems a natural question is to what extent QMFS can be realized in this context. Using the example of a one-dimensional Dirac oscillator we investigate conditions under which this can be achieved, and identify Zitterbewegung or virtual pair creation as the physical mechanism that fundamentally limits the feasibility of the scheme. We propose a tabletop implementation of a Dirac oscillator system based on a spin-orbit coupled ultracold atomic sample that allows for a direct observation of the corresponding analog of virtual pair creation on quantum measurement backaction.

quant-ph↗

arXiv2016

Spin-sensitive atom mirror via spin-orbit interaction

Based on the spin-orbit coupling recently implemented in a neutral cold-atom gas, we propose a scheme to realize spin-dependent scattering of cold atoms. In particular we consider a matter wave packet of cold-atom gas impinging upon a step potential created by the optical light field, inside of which the atoms are subject to spin-orbit interaction. We show that the proposed system can act as a spin polarizer or spin-selective atom mirror for the incident atomic beam. The principle and the operating parameter regime of the system are carefully discussed.

cond-mat.quant-gas↗

arXiv2015

Goos-Hänchen shifts in spin-orbit-coupled cold atoms

We consider a matter wave packet of cold atom gas impinging upon a step potential created by the optical light field. In the presence of spin-orbit (SO) coupling, the atomic eigenstates contain two types of evanescent states, one of which is the ordinary evanescent state with pure imaginary wave vector while the other possesses complex wave vector and is recognized as oscillating evanescent state. We show that the presence and interplay of these two types of evanescent states can give rise to two different mechanisms for total internal reflection (TIR), and thus lead to unusual Goos-Hänchen (GH) effect. As a result, not only large positive but also large negative GH shift can be observed in the reflected atomic beam. The dependence of the GH shift on the incident angle, energy and height of the step potential is studied numerically.

cond-mat.quant-gas↗

arXiv2014

Cavity-Assisted Dynamical Spin-Orbit Coupling in Cold Atoms

We consider ultracold atoms subjected to a cavity-assisted two-photon Raman transition. The Raman coupling gives rise to effective spin-orbit interaction which couples atom's center-of-mass motion to its pseudospin degrees of freedom. Meanwhile, the cavity photon is dynamically affected by the atom. This feedback between atom and photon leads to a dramatic modification of the atomic dispersion relation, and further leads to dynamical instability of the system. We propose to detect the change of cavity photon number as a direct way to demonstrate dynamical instability.

cond-mat.quant-gas↗

arXiv2013

Anisotropic deformation of Rydberg blockade sphere in few-atom systems

Rydberg blockade sphere persists an intriguing picture by which a number of collective many-body effects caused by the strong Rydberg-Rydberg interactions can be clearly understood and profoundly investigated. In the present work, we develop a new definition for the effective two-atom blockade radius and show that the original spherically shaped blockade surface would be deformed when the real number of atoms increases from two to three. This deformation of blockade sphere reveals spatially anisotropic and shrunken properties which strongly depend on the interatomic distance. In addition, we also study the optimal conditions for the Rydberg antiblockade effect and make predictions for improving the antiblockade efficiency in few-atom systems.

physics.atom-ph↗

arXiv2013

Quantum phases of strongly interacting Rydberg atoms in triangular lattices

We present a theoretical study on the system of laser-driven strongly interacting Rydberg atoms trapped in a two-dimensional triangular lattice, in which the dipole-dipole interactions between Rydberg states result in exotic quantum phases. By using the mean-field theory, we investigate the steady state solutions and analyze their dynamical stabilities. We find that in the strong-interaction limit, the dynamics of the system is chaotic and exhibits random oscillations under appropriate laser detunings. Lyapunov exponent criterion is introduced to confirm the existence of this chaotic behavior. In addition, we present a full quantum calculation based on a six-atom model, and find that the system exhibits some bi-antiferromagnetic properties in every triangular cell when the one-photon detuning is exactly resonant or blue-shifted.

cond-mat.quant-gas↗

arXiv2013

Anderson Localization of cold atomic gases with effective spin-orbit interaction in a quasiperiodic optical lattice

We theoretically investigate the localization properties of a spin-orbit coupled spin-1/2 particle moving in a one-dimensional quasiperiodic potential, which can be experimentally implemented using cold atoms trapped in a quasiperiodic optical lattice potential and external laser fields. We present the phase diagram in the parameter space of the disorder strength and those related to the spin-orbit coupling. The phase diagram is verified via multifractal analysis of the atomic wavefunctions and the numerical simulation of diffusion dynamics. We found that spin-orbit coupling can lead to the spectra mixing (coexistence of extended and localized states) and the appearance of mobility edges.

cond-mat.quant-gas↗

arXiv2012

Phase Diagram of Rydberg atoms in a nonequilibrium optical lattice

We study the quantum nonequilibrium dynamics of ultracold three-level atoms trapped in an optical lattice, which are excited to their Rydberg states via a two-photon excitation with nonnegligible spontaneous emission. Rich quantum phases including uniform phase, antiferromagnetic phase and oscillatory phase are identified. We map out the phase diagram and find these phases can be controlled by adjusting the ratio of intensity of the pump light to the control light, and that of two-photon detuning to the Rydberg interaction strength. When the two-photon detuning is blue-shifted and the latter ratio is less than 1, bistability exists among the phases. Actually, this ratio controls the Rydberg-blockade and antiblockade effect, thus the phase transition in this system can be considered as a possible approach to study both effects.

cond-mat.quant-gas↗