Domain walls and bubble-droplets in immiscible binary Bose gases

TL;DR

This paper investigates the existence, stability, and dynamics of domain walls and bubble-droplet states in immiscible binary Bose gases, including BECs with cubic and quintic interactions and binary Tonks-Girardeau gases, using analytical and numerical methods.

Contribution

It introduces exact solutions for domain walls in symmetric BEC mixtures and explores stable asymmetric and composite bubble-droplet states in various binary Bose gas models.

Findings

Exact domain wall solutions for symmetric BEC mixtures.

Stable asymmetric domain walls in dissimilar interaction BECs.

Mobile bubble-droplet states combining dark and bright solitons.

Abstract

The existence and stability of domain walls (DWs) and bubble-droplet (BD) states in binary mixtures of quasi-one-dimensional ultracold Bose gases with inter- and intra-species repulsive interactions is considered. Previously, DWs were studied by means of coupled systems of Gross-Pitaevskii equations (GPEs) with cubic terms, which model immiscible binary Bose-Einstein condensates (BECs). We address immiscible BECs with two- and three-body repulsive interactions, as well as binary Tonks--Girardeau (TG) gases, using systems of GPEs with cubic and quintic nonlinearities for the binary BEC, and coupled nonlinear Schr\"{o}dinger equations with quintic terms for the TG gases. Exact DW\ solutions are found for the symmetric BEC mixture, with equal intra-species scattering lengths. Stable asymmetric DWs in the BEC mixtures with dissimilar interactions in the two components, as well as of symmetric and asymmetric DWs in the binary TG gas, are found by means of numerical and approximate analytical methods. In the BEC system, DWs can be easily put in motion by phase imprinting. Combining a DW and anti-DW on a ring, we construct BD states for both the BEC and TG models. These consist of a dark soliton in one component (the "bubble"), and a bright soliton (the "droplet") in the other. In the BEC system, these composite states are mobile too.