Ground states of a Bose-Einstein Condensate in a one-dimensional laser-assisted optical lattice

TL;DR

This paper investigates the ground-state phases of a Bose-Einstein Condensate in a 1D laser-assisted optical lattice, revealing complex phase diagrams with stripe, plane wave, and zero-momentum phases influenced by spin-orbit coupling and interactions.

Contribution

It introduces an effective model for BEC in a multilayer optical lattice with spin-orbit coupling, analyzing the resulting phase diagrams and many-body ground states.

Findings

Identification of three distinct ground-state phases.

Existence of a quantum tricritical point in the phase diagram.

Many-body states can have finite momentum even when single-particle states do not.

Abstract

We study the ground-state behavior of a Bose-Einstein Condensate (BEC) in a Raman-laser-assisted one-dimensional (1D) optical lattice potential forming a multilayer system. We find that, such system can be described by an effective model with spin-orbit coupling (SOC) of pseudospin $(N-1)/2$, where $N$ is the number of layers. Due to the intricate interplay between atomic interactions, SOC and laser-assisted tunnelings, the ground-state phase diagrams generally consist of three phases -- a stripe, a plane wave and a normal phase with zero-momentum, touching at a quantum tricritical point. More important, even though the single-particle states only minimize at zero-momentum for odd $N$, the many-body ground states may still develop finite momenta. The underlying mechanisms are elucidated. Our results provide an alternative way to realize an effective spin-orbit coupling of Bose gas with the Raman-laser-assisted optical lattice, and would also be beneficial to the studies on SOC effects in spinor Bose systems with large spin.