Thermal destabilization of self-bound ultradilute quantum droplets

TL;DR

This paper theoretically studies how thermal fluctuations destabilize self-bound ultradilute quantum droplets in Bose-Bose mixtures, showing that temperature can destroy the droplets above a certain threshold, which depends on interaction energies.

Contribution

It provides a detailed theoretical analysis of thermal effects on quantum droplets, revealing the destabilization mechanism and threshold temperatures in different dimensions.

Findings

Thermal fluctuations destabilize quantum droplets above a threshold temperature.

Threshold temperature is related to intra-species interaction energy in 3D.

Droplet density decreases with increasing temperature and vanishes at the threshold.

Abstract

We theoretically investigate the temperature effect in a Bose-Bose mixture with attractive inter-species interactions, in the regime where a self-bound ultradilute quantum droplet forms due to the subtle balance between the attractive mean-field force and the repulsive force provided by Lee-Huang-Yang quantum fluctuations. We find that in contrast to quantum fluctuations, thermal fluctuations destabilize the droplet state and completely destroy it above a threshold temperature. We show that the threshold temperature is determined by the intra-species interaction energy. For a three-dimensional Bose-Bose mixture, the threshold temperature is less than one-tenth of the Bose-Einstein condensation temperature under the typical experimental conditions. With increasing temperature, the droplet's equilibrium density gradually decreases and can be reduced by several tens of percent upon reaching the threshold temperature. We also consider a one-dimensional quantum droplet and find a similar destabilization effect due to thermal fluctuations. The threshold temperature in one dimension is roughly set by the binding energy of the inter-species dimer. The pronounced thermal instability of a self-bound quantum droplet predicted in our work could be examined in future experiments, by measuring the temperature dependence of its central density and observing its sudden disappearance at the threshold temperature.