Quantum droplets of dipolar molecules

Quantum droplets are self-bound clusters of interacting particles that arise from a delicate interplay between attractive and repulsive forces. To date, experimentally observed droplets in ultracold atomic systems have been weakly interacting and dilute. Recent advances in double microwave shielding have enabled the creation of a molecular Bose–Einstein condensate with broadly tunable dipolar interactions [1, 2]. We report on the observation of self-bound droplets and droplet arrays in an ultracold gas of strongly dipolar sodium–cesium molecules [3]. The observed droplet densities are up to 100 times higher than those of the weakly dipolar molecular BEC. The ratio of the interparticle spacing to the dipolar length places the system in the strongly interacting regime, pointing to the possible emergence of a quantum-liquid or crystalline state.