Superfluid BKT transition of 2D bubble-trapped condensates

A relevant role in the superfluid transition of ultracold bosonic atoms is played by the complex interplay between the system topology and the external trapping potential. We discuss here the qualitative and quantitative aspects of the superfluid BKT transition of two-dimensional bubble-trapped superfluids. Due to technical limitations in ground-based experiments, these curved quantum systems are currently produced in the Cold Atom Lab (CAL), a microgravity facility for studying Bose-Einstein condensates on board of the International Space Station. In our work, relying on a new derivation of the equation of state of these topologically-nontrivial systems, we analyze the nonuniversal character of BKT physics, and we discuss how the vanishing of the superfluid density affects the hydrodynamic modes. Our theoretical predictions are of immediate experimental interest, being tailored on the typical parameters and regimes of CAL experiments.