Two-Dimensional Quantum Droplets in a Mixture of Bose-Einstein Condensates

Abstract

Quantum droplets represent a striking manifestation of beyond-mean-field physics, with properties that depend sensitively on dimensionality. Although quantum droplets have been experimentally realized in one and three dimensions, their realization in two dimensions has remained elusive. Here, we observe the formation of a two-dimensional (2D) quantum droplet in a quasi-2D geometry by transferring the single-component Bose-Einstein condensates (BECs) into a spin mixture in the Lee-Huang-Yang (LHY) regime, where the LHY effect evidently deviates from its three-dimensional form. We find that, in our scheme, 2D quantum droplets are more stable and exhibit longer lifetimes than previously reported quantum droplets. By instead transferring the initial BECs into another single-spin state with a negative scattering length, we generate 2D Townes solitons. A comparison between the two types of self-bound states shows that, whereas 2D Townes solitons are stable only near a critical atom number determined by the scattering length, 2D quantum droplets remain well-defined and self-bound over a much broader parameter range. These realizations of quantum droplets and Townes solitons in two dimensions provide new insights into self-bound states and open new avenues for exploring nonlinear dynamics in quantum liquids.