Quantum Mechanical Stabilization of a Collapsing Bose-Bose Mixture

TL;DR

This paper demonstrates that quantum fluctuations can stabilize a collapsing Bose-Bose mixture into a dilute droplet state, revealing beyond mean-field effects and unique excitation properties.

Contribution

It provides the first direct evidence of quantum fluctuation stabilization of Bose-Bose mixtures into liquid-like droplets beyond mean-field theory.

Findings

Mixture forms a stable droplet due to quantum fluctuations.

Excitation spectrum lies above particle emission threshold.

Droplet evaporates to zero temperature naturally.

Abstract

According to the mean-field theory a condensed Bose-Bose mixture collapses when the interspecies attraction becomes stronger than the geometrical average of the intraspecies repulsions, $g_{12}^2>g_{11} g_{22}$. We show that instead of collapsing such a mixture gets into a dilute liquid-like droplet state stabilized by quantum fluctuations thus providing a direct manifestation of beyond mean-field effects. We study various properties of the droplet and find, in particular, that in a wide range of parameters its excitation spectrum lies entirely above the particle emission threshold. The droplet thus automatically evaporates itself to zero temperature, the property potentially interesting by itself and from the viewpoint of sympathetic cooling of other systems.