Self-bound quantum droplets in atomic mixtures

TL;DR

This paper reports the experimental realization of self-bound quantum droplets in ultracold atomic mixtures, demonstrating their formation in free space and characterizing their properties, paving the way for future quantum studies.

Contribution

First experimental observation of self-bound quantum droplets in free space using an attractive bosonic mixture, confirming theoretical predictions.

Findings

Droplets form due to balance of attractive and repulsive forces.

Self-bound droplets observed in free space with optical levitation.

Conditions for formation and equilibrium properties characterized.

Abstract

Self-bound quantum droplets are a newly discovered phase in the context of ultracold atoms. In this work we report their experimental realization following the original proposal by Petrov [Phys. Rev. Lett. 115, 155302 (2015)], using an attractive bosonic mixture. In this system spherical droplets form due to the balance of competing attractive and repulsive forces, provided by the mean-field energy close to the collapse threshold and the first-order correction due to quantum fluctuations. Thanks to an optical levitating potential with negligible residual confinement we observe self-bound droplets in free space and we characterize the conditions for their formation as well as their equilibrium properties. This work sets the stage for future studies on quantum droplets, from the measurement of their peculiar excitation spectrum, to the exploration of their superfluid nature.