arXiv subjects

Wu-Ming Liu

Publications and source records attributed to Wu-Ming Liu.

At least 163 records · Page 9Linked to original sources

arXiv2012

Superradiant Solid in Cavity QED Coupled to a Lattice of Rydberg Gas

We study an optical cavity coupled to a lattice of Rydberg atoms, which can be represented by a generalized Dicke model. We show that the competition between the atomic interaction and atom-light coupling induces a rich phase diagram. A novel "superradiant solid" (SRS) phase is found, where both the superradiance and crystalline orders coexist. Different from the normal second order superradiance (SR) transition, here both the Solid-1/2 and SRS to SR phase transitions are first order. These results are confirmed by the large scale quantum Monte Carlo simulations.

cond-mat.quant-gas↗

arXiv2012

Bose-Einstein Condensates in a Cavity-mediated Triple-well

We investigate the energy structures and the dynamics of a Bose-Einstein condensates (BEC) in a triple-well potential coupled a high finesse optical cavity within a mean field approach. Due to the intrinsic atom-cavity field nonlinearity, several interesting phenomena arise which are the focuses of this work. For the energy structure, the bistability appears in the energy levels due to this atoms-cavity field nonlinearity, and the same phenomena can be found in the intra-cavity photons number. With an increase of the pump-cavity detunings, the higher and lower energy levels show a loop structure due to this cavity-mediated effects. In the dynamical process, an extensive numerical simulation of localization of the BECs for atoms initially trapped in one-, two-, and three-wells are performed for the symmetric and asymmetric cases in detail. It is shown that the the transition from oscillation to the localization can be modified by the cavity-mediated potential, which will enlarge the regions of oscillation. With the increasing of the atomic interaction, the oscillation is blocked and the localization emerges. The condensates atoms can be trapped either in one-, two-, or in three wells eventually where they are initially uploaded for certain parameters. In particular, we find that the transition from the oscillation to the localization is accompanied with some irregular regime where tunneling dynamics is dominated by chaos for this cavity-mediated system.

cond-mat.quant-gas↗

arXiv2012

Quantum Spin Hall Insulators with Interactions and Lattice Anisotropy

We investigate the interplay between spin-orbit coupling and electron-electron interactions on the honeycomb lattice combining the cellular dynamical mean-field theory and its real space extension with analytical approaches. We provide a thorough analysis of the phase diagram and temperature effects at weak spin-orbit coupling. We systematically discuss the stability of the quantum spin Hall phase toward interactions and lattice anisotropy resulting in the plaquette-honeycomb model. We also show the evolution of the helical edge states characteristic of quantum spin Hall insulators as a function of Hubbard interaction and anisotropy. At very weak spin-orbit coupling and intermediate electron-electron interactions, we substantiate the existence of a quantum spin liquid phase.

cond-mat.str-el↗

arXiv2012

Quantum-correlating power of local quantum channels

Quantum correlation can be created by local operations from a classically correlated state. We define quantum-correlating power (QCP) of a local quantum channel as the maximum amount of quantum correlation that can be created by the channel. The quantum correlation that we discuss in this article is defined on the left part of the bipartite state. We prove that for any local channel, the optimal input state, which corresponds to the maximum quantum correlation in the output state, must be a classical-classical state. Further, the single-qubit channels with maximum QCP can be found in the class of rank-1 channels which take their optimal input states to rank-2 quantum-classical states. The analytic expression for QCP of single-qubit amplitude damping channel is obtained. Super-activation property of QCP, i.e., two zero-QCP channels can consist a positive-QCP channel, is discussed for single-qubit phase damping channels.

quant-ph↗

arXiv2012

Necessary and sufficient conditions for local creation of quantum correlation

Quantum correlation can be created by a local operation from some initially classical states. We prove that the necessary and sufficient condition for a local trace-preserving channel to create quantum correlation is that it is not a commutativity-preserving channel. This condition is valid for arbitrary finite dimension systems. We also derive the explicit form of commutativity-preserving channels. For a qubit, a commutativity-preserving channel is either a completely decohering channel or a mixing channel. For a three-dimensional system (qutrit), a commutativity-preserving channel is either a completely decohering channel or an isotropic channel.

quant-ph↗

arXiv2012

Thermalization from a general canonical principle

We investigate the time evolution of a generic and finite isolated quantum many-body system starting from a pure quantum state. We find the kinematical general canonical principle proposed by Popescu-Short-Winter for statistical mechanics can be built in a more solid ground by studying the thermalization, i.e. comparing the density matrices themselves rather than the measures of distances. In particular, this allows us to explicitly identify that, from any instantaneous pure state after thermalization, the state of subsystem is like from a microcanonical ensemble or a generalized Gibbs ensemble, but neither a canonical nor a thermal ones due to finite-size effect. Our results are expected to bring the task of characterizing the state after thermalization to completion. In addition, thermalization of coupled systems with different temperatures corresponding to mixed initial states is studied.

quant-ph↗

arXiv2012

Kondo Metal and Ferrimagnetic Insulator on the Triangular Kagomé Lattice

We obtain the rich phase diagrams in the Hubbard model on the triangular Kagomé lattice as a function of interaction, temperature and asymmetry, by combining the cellular dynamical mean-field theory with the continuous time quantum Monte Carlo method. The phase diagrams show the asymmetry separates the critical points in Mott transition of two sublattices on the triangular Kagomé lattice and produces two novel phases called plaquette insulator with an obvious gap and a gapless Kondo metal. When the Coulomb interaction is stronger than the critical value Uc, a short range paramagnetic insulating phase, which is a candidate for the short rang resonating valence-bond spin liquid, emerges before the ferrimagnetic order is formed independent of asymmetry. Furthermore, we discuss how to measure these phases in future experiments.

cond-mat.str-el↗

arXiv2012

Dynamics of Geometric Discord and Measurement-Induced Nonlocality at Finite Temperature

By using geometric measure of discord (\texttt{GMOD})[Phys. Rev. Lett, 105, 109502 (2010)] and measurement-induced nonlocality (\texttt{MIN})[Phys. Rev. Lett, 106, 120401 (2011)], we investigate quantum correlation of a pair of two-level systems, each of which is interacting with a reservoir at finite temperature $T$. We show that, for a broad class of states of the system, \texttt{GMOD} and \texttt{MIN} can endure sudden death, and there is no asymptotic decay for \texttt{MIN} while asymptotic decay exists for \texttt{GMOD}. We also give the dynamics of \texttt{GMOD} and \texttt{MIN} with respect to the temperature and illustrate their different characteristics.

quant-ph↗

arXiv2011

Bound-state QED solutions of the photons off-shell propagating behavior in atoms

We use the S-matrix formalism of bound-state QED to study the photon-atom scattering. We find that the internal lines in Feynman diagrams which describing the propagation of off-shell bound electrons provide the off-shell amplitudes of photons' propagation in atoms phenomenally. Our work set up the connection between the property of Feynman propagators in bound-state QED and the superluminal but casual propagating behavior of light in atomic media. We also studied the relation between the bound-state QED and the widely used light-atom interacting model in quantum optics, and give the experimental condition where only the bound-state QED is valid.

physics.atom-ph↗

arXiv2011

Tuning the Tricritical Point with Spin-orbit Coupling in Polarized Fermionic Condensates

We investigate a two-component atomic Fermi gas with population imbalance in the presence of Rashba-type spin-orbit coupling (SOC). As a competition between SOC and population imbalance, the finite-temperature phase diagram reveals a large varieties of new features, including the expanding of the superfluid state regime and the shrinking of both the phase separation and the normal regimes. For sufficiently strong SOC, the phase separation region disappears, giving way to the superfluid state. We find that the tricritical point moves toward regime of low temperature, high magnetic field, and high polarization as the SOC increases.

cond-mat.quant-gas↗

arXiv2011

Conditions on local operations to create quantum correlation

We prove the condition for local trace-preserving channels to create quantum correlation from initially classical states. For two-qubit states, the necessary and sufficient condition for a channel that cannot create quantum correlation in any initially classical state is that it is either a completely decohering channel or a mixing channel. For states in higher dimensions, we show that even a mixing channel can create quantum correlation from a classically correlated state. Our results reveal that mixedness is important for creation of quantum correlation in high-dimension quantum systems.

quant-ph↗

arXiv2011

Solution and testing of the Abraham-Minkowski controversy in light-atom interacting system

We present the origin of the Abraham-Minkowski controversy of light-matter wave interacting system, which is a special case of the centaury-old Abraham-Minkowski controversy. We solve the controversy of laser-atom interacting case and find that for systems with perfect atomic spatial coherence, the systems prefer to show Minkowski momentum and canonical momentum for the atoms and light, respectively; while for the systems where the atoms are spatially incoherent, the momenta of light and atoms would choose the Abraham and kinetic forms. The provement of our solution can be realized with current techniques, using three-dimensional optical lattices and electromagnetically-induced absorption (EIA) to distinguish the kinetic and canonical recoil momentum of ultra-cold atoms.

physics.atom-ph↗

arXiv2011

Quantum correlations in spin models

Bell nonlocality, entanglement and nonclassical correlations are different aspects of quantum correlations for a given state. There are many methods to measure nonclassical correlations. In this paper, nonclassical correlations in two-qubit spin models are measured by use of measurement-induced disturbance (MID) [Phys. Rev. A, 77, 022301 (2008)] and geometric measure of quantum discord (GQD) [Phys. Rev. Lett. 105, 190502 (2010)]. Their dependencies on external magnetic field, spin-spin coupling, and Dzyaloshinski-Moriya (DM) interaction are presented in detail. We also compare Bell nonlocality, entanglement measured by concurrence, MID and GQD and illustrate their different characteristics.

quant-ph↗

arXiv2011

Thermal-assisted Anisotropy and Thermal-driven Instability in the Superfluidity state of Two-Species Polar Fermi Gas

We study the superfluid state of two-species heteronuclear Fermi gases with isotropic contact and anisotropic long-range dipolar interactions. By explicitly taking account of Fock exchange contribution, we derive self-consistent equations describing the pairing states in the system. Exploiting the symmetry of the system, we developed an efficient way of solving the self-consistent equations by exploiting the symmetries. We find that the temperature tends to increase the anisotropy of the pairing state, which is rather counterintuitive. We study the anisotropic properties of the system by examining the angular dependence of the number density distribution, the excitation spectrum and the pair correlation function. The competing effects of the contact interaction and the dipolar interaction upon the anisotropy are revealed. We derive and compute the superfluid mass density $ρ_{ij}$ for the system. Astonishingly, we find that $ρ_{zz}$ becomes negative above some certain temperature $T^*$($T<T_c$), signaling some instability of the system. This suggests that the elusive FFLO state may be observed in experiments, due to an anisotropic state with a spontaneously generated superflow.

cond-mat.quant-gas↗

arXiv2011

Diffractions of Bose-Einstein Condensate in Quantized Light Fields

We investigate the atomic diffractions of a Bose-Einstein condensate in quantized light fields. Situations in which the light fields are in number states or coherent states are studied theoretically. Analytical derivation and numerical calculation are carried out to simulate the dynamics of the atomic motion. In condition that atoms are scattered by light in the number states with imbalanced photon number distribution, the atomic transitions between different momentum modes would sensitively depend on the transition order and the photon number distribution. The number-state-nature of the light fields modifies the period of atomic momentum oscillations and makes forward and backward atomic transitions unequal. For light fields in coherent states, no matter the intensities of the light fields are balanced or not, the atomic diffractions are symmetric and independent on the transition order.

cond-mat.quant-gas↗

arXiv2011

Localized tendency for the superfluid and Mott insulator state in the array of dissipative cavities

The features of superfluid-Mott insulator phase transition in the array of dissipative cavities is analyzed. Employing a kind of quasi-boson and a mean-filed approach, we show analytically how dissipation and decoherence influence the critical behaviors and the time evolution of the system. We find that there is a localized tendency, which could lead to the break of superfluidity for a superfluid state and suppress the appearance of the long-range order form a Mott state. Eventually, a collection of mixture states localized on each site will arise.

quant-ph↗

arXiv2010

Spontaneous Parity--Time Symmetry Breaking and Stability of Solitons in Bose-Einstein Condensates

We report explicitly a novel family of exact PT-symmetric solitons and further study their spontaneous PT symmetry breaking, stabilities and collisions in Bose-Einstein condensates trapped in a PT-symmetric harmonic trap and a Hermite-Gaussian gain/loss potential. We observe the significant effects of mean-field interaction by modifying the threshold point of spontaneous PT symmetry breaking in Bose-Einstein condensates. Our scenario provides a promising approach to study PT-related universal behaviors in non-Hermitian quantum system based on the manipulation of gain/loss potential in Bose-Einstein condensates.

cond-mat.quant-gas↗

arXiv2010

An Artificial Frustrated System: Cold Atoms in 2D Triangular Optical Lattice

We investigate the strongly correlated effect of cold atoms in triangular optical lattice by dynamical cluster approximation combining with the continuous time quantum Monte Carlo method proposed recently. It is found the double occupancy is suppressed as the atomic interaction increases. By calculating the density of states, we show how the system evolves from Fermi liquid with an obvious quasi-particle peak into Mott insulator with an opened gap for increasing interaction. The transition between Fermi liquid and pseudogap shows a reentrant behavior due to the Kondo effect. At low temperature, a Kondo peak appears before the splitting of the Fermi-liquid-like peak. The Fermi surface evolves from a circular ring with high amplitude into a °at elliptical ring with low amplitude for the increasing interaction. We give an experimental protocol to observe these phenomena by varying the lattice depth and the atomic interaction via Feshbach resonance in future experiments.

cond-mat.quant-gas↗