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 (MF) energy. In this work, we study an ultracold mixture of $^{23}\mathrm{Na}$ and $^{87}\mathrm{Rb}$ 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 MF attractions.
Highlights
Bose-Einstein condensate (BEC) of dilute atomic gases is a very natural platform for testing the rich physics of interacting Bose gases
While the behavior of BECs is typically dictated by the mean-field (MF) interaction, effects caused by the beyond-MF Lee-Huang-Yang (LHY) correction ELHY [1] are of great interest due to their deep connections with many-body correlation and quantum fluctuations
The situation can be very different in a double BEC with repulsive intraspecies interactions and a tunable attractive interspecies interaction
Summary
350.451 G (left) and the droplet phase at 349.849 G (right). (c) Cloud sizes obtained from (b) reveal the very different behaviors of the two phases. After about 10 ms, the sample sizes start to increase while the atom numbers stay nearly constant This is consistent with a phase transition from droplet to gas when the atom numbers are reduced to below the critical values [see Fig. 1(a)]. Erel depends on δg, N1, and N2 and the density overlap between the two species In this range of δg, the densities of the double BEC are still rather high even in the gas phase, and significant three-body losses are observed during the TOF. This is similar to previous observations on the expansion dynamics of the erbium dipolar system [17] This behavior can be qualitatively understood from the competition between ELHY, Ekin, and EMF for the droplet near the phase-transition point.
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