Shell-shaped Bose-Einstein condensates realized with dual-species mixtures

Recently, there has been great interest in the properties of hollow Bose-Einstein condensates (BECs) which can be generated with radio-frequency (rf) dressing. As an alternative method, we consider the realization of hollow BECs by utilizing a dual-species mixture. A proper choice of the parameters allows us to create a ground state where one species is in the center and generates a repulsive effective potential for the second species, giving rise to a shell-shaped BEC.

In order to compare the main properties of our setup with the one based on rf-dressing, we solve both the Gross-Pitaevskii and the Bogoliubov-de Gennes equations. In particular, we investigate the free expansion dynamics and the spectrum of collective excitations. To highlight the potential of each realization, we additionally compare the deformation of the shell due to gravitational sag, being one of the main obstacles to create hollow BECs.