Localized modes in quasi-2D Bose-Einstein condensates with spin-orbit and Rabi couplings

TL;DR

This paper derives and analyzes a system of 2D nonpolynomial Schrödinger equations for a spin-orbit and Rabi coupled Bose-Einstein condensate, revealing conditions for stable localized solitons in a quasi-2D setting.

Contribution

It introduces a new 2D NPSE model for spin-orbit and Rabi coupled BECs and demonstrates stability regions for solitons without external trapping.

Findings

Derived 2D NPSE system for coupled BECs with SO and Rabi couplings.

Found parameter regions where 2D solitons are stable due to SO and Rabi effects.

Provided approximate and numerical localized solutions for the system.

Abstract

We consider a two-component pancake-shaped, i.e., effectively two-dimensional (2D), Bose-Einstein condensate (BEC) coupled by the spin-orbit (SO) and Rabi terms. The SO coupling adopted here is of the mixed Rashba-Dresselhaus type. For this configuration, we derive a system of two 2D nonpolynomial Schr\"odinger equations (NPSEs), for both attractive and repulsive interatomic interactions. In the low- and high-density limits, the system amounts to previously known models, namely, the usual 2D Gross-Pitaevskii equation, or the Schr\"odinger equation with the nonlinearity of power 7/3. We present simple approximate localized solutions, obtained by treating the SO and Rabi terms as perturbations. Localized solutions of the full NPSE system are obtained in a numerical form. Remarkably, in the case of the attractive nonlinearity acting in free space (i.e., without any 2D trapping potential), we find parameter regions where the SO and Rabi couplings make 2D fundamental solitons dynamically stable.