Droplet under confinement: Competition and coexistence with soliton bound state

TL;DR

This paper investigates how confinement affects the stability and phase transitions between quantum droplets and soliton bound states in ultracold Bose-Bose mixtures, revealing a rich phase diagram with coexistence and reentrant phenomena.

Contribution

It provides the first detailed analysis of confinement-induced boundary effects on droplet and soliton stability, mapping out phase diagrams in ultracold Bose mixtures.

Findings

Confinement can destabilize quantum droplets, favoring soliton formation.

Reentrant soliton ground states occur with increasing atom number.

Droplet and soliton states can coexist as local energy minima.

Abstract

We study the stability of quantum droplet and its associated phase transitions in ultracold Bose-Bose mixtures uniformly confined in quasi-two-dimension. We show that the confinement-induced boundary effect can be significant when increasing the atom number or reducing the confinement length, which destabilizes the quantum droplet towards the formation of a soliton bound state. In particular, as increasing the atom number we find the reentrance of soliton ground state, while the droplet is stabilized only within a finite number window that sensitively depends on the confinement length. Near the droplet-soliton transitions, they can coexist with each other as two local minima in the energy landscape. Take the two-species $^{39}$K bosons for instance, we have mapped out the phase diagram for droplet-soliton transition and coexistence in terms of atom number and confinement length. The revealed intriguing competition between quantum droplet and soliton under confinement can be readily probed in current cold atoms experiments.