Lee-Huang-Yang effects in the ultracold mixture of $^{23}$Na and $^{87}$Rb with attractive interspecies interactions

TL;DR

This paper investigates the Lee-Huang-Yang quantum correction effects in an ultracold Na-Rb mixture with attractive interactions, revealing their role in quantum droplet formation and anomalous expansion behaviors.

Contribution

It provides the first experimental observation of LHY effects in a Na-Rb mixture with tunable attraction, including phase diagram mapping and expansion dynamics analysis.

Findings

Observation of self-bound quantum droplets due to LHY effects

Identification of a liquid-to-gas phase transition point

Anomalous expansion with increased release energy for stronger attractions

Abstract

The beyond-mean-field Lee-Huang-Yang (LHY) correction is ubiquitous in dilute ultracold quantum gases. However, its effects are often elusive due to the typically much larger influence of the mean-field energy. In this work, we study an ultracold mixture of $^{23}$Na and $^{87}$Rb with tunable attractive interspecies interactions. The LHY effects manifest in the formation of self-bound quantum liquid droplets and the expansion dynamics of the gas-phase sample. A liquid-to-gas phase diagram is obtained by measuring the critical atom numbers below which the self-bound behavior disappears. In stark contrast to trapped gas-phase condensates, the gas-phase mixture formed following the liquid-to-gas phase transition shows an anomalous expansion featuring a larger release energy for increasing mean-field attractions.