Quantum crystals in a trapped Rydberg-dressed Bose-Einstein condensate

Based on a mean-field approach, spontaneously crystalline ground states, called quantum crystals, of a trapped Rydberg-dressed Bose-Einstein condensate are numerically investigated. In a quasi-two-dimensional geometry, a hexagonal lattice of condensate droplets manifests when dressed coupling is above a critical value. The onset of the crystallized state is characterized by a drastic drop of the nonclassical rotational inertia fraction (NCRIF). Nevertheless, the NCRIF remains a large value for a large span of dressed coupling, which indicates that the long-range phase coherence of a superfluid is preserved in the crystallized state. By relaxing the confinement against the two-dimensional geometry and by introducing an anisotropic interaction, an AB stacking bilayer lattice and a nearly square lattice, respectively, are also available in the system. A quasi-one-dimensional lattice is also shown.