Dan-Wei Zhang

Relativistic quantum effects of Dirac particles simulated by ultracold atoms

Quantum simulation is a powerful tool to study a variety of problems in physics, ranging from high-energy physics to condensed-matter physics. In this article, we review the recent theoretical and experimental progress in quantum simulation of Dirac equation with tunable parameters by using ultracold neutral atoms trapped in optical lattices or subject to light-induced synthetic gauge fields. The effective theories for the quasiparticles become relativistic under certain conditions in these systems, making them ideal platforms for studying the exotic relativistic effects. We focus on the realization of one, two, and three dimensional Dirac equations as well as the detection of some relativistic effects, including particularly the well-known Zitterbewegung effect and Klein tunneling. The realization of quantum anomalous Hall effects is also briefly discussed.

Josephson dynamics of a spin-orbit-coupled Bose-Einstein condensate in a double-well potential

We investigate the quantum dynamics of an experimentally realized spin-orbit coupled Bose-Einstein condensate in a double well potential. The spin-orbit coupling can significantly enhance the atomic inter-well tunneling. We find the coexistence of internal and external Josephson effects in the system, which are moreover inherently coupled in a complicated form even in the absence of interatomic interactions. Moreover, we show that the spin-dependent tunneling between two wells can induce a net atomic spin current referred as spin Josephson effects. Such novel spin Josephson effects can be observable for realistically experimental conditions.

Simulating and exploring Weyl semimetal physics with cold atoms in a two-dimensional optical lattice

Synergetic Innovation Center of Quantum Information and Quantum Physics,University of Science and Technology of China, Hefei 230026, China(Dated: April 30, 2015)We propose a scheme to simulate and explore Weyl semimetal physics with ultracold fermionicatoms in a two-dimensional square optical lattice subjected to experimentally realizable spin-orbitcoupling and an artificial dimension from an external parameter space, which may increase experi-mental feasibility compared with the cases in three-dimensional optical lattices. It is shown that thissystem with a tight-binding model is able to describe essentially three-dimensional Weyl semimetalswith tunable Weyl points. The relevant topological properties are also addressed by means of theChern number and the gapless edge states. Furthermore, we illustrate that the mimicked Weylpoints can be experimentally detected by measuring the atomic transfer fractions in a Bloch-Zeneroscillation, and the characteristic topological invariant can be measured with the particle pumpingapproach.

Macroscopic Klein tunneling in spin-orbit-coupled Bose-Einstein condensates

We propose an experimental scheme to detect macroscopic Klein tunneling with spin-orbit coupled Bose-Einstein condensates (BECs). We show that a nonlinear Dirac equation with tunable parameters can be realized with such BECs. %in a simple configuration to generate the artificial spin-orbit coupling. Through numerical calculations, we demonstrate that macroscopic Klein tunneling can be clearly detected under realistic conditions. Macroscopic quantum coherence in such relativistic tunneling is clarified and a BEC with a negative energy is shown to be able to transmit transparently through a wide Gaussian potential barrier.

Quantum Simulation of Exotic PT-invariant Topological Nodal Loop Bands with Ultracold Atoms in an Optical Lattice

Since the well-known

Superfluid and magnetic states of an ultracold Bose gas with synthetic three-dimensional spin-orbit coupling in an optical lattice

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Exploring topological double-Weyl semimetals with cold atoms in optical lattices

symmetry has its fundamental significance and implication in physics, where

Emergent pseudospin-1 Maxwell fermions with a threefold degeneracy in optical lattices

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Topological insulator and particle pumping in a one-dimensional shaken optical lattice

denotes a joint operation of space inversion

Particle-number fractionalization of a one-dimensional atomic Fermi gas with synthetic spin-orbit coupling

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