Physics of hollow Bose-Einstein condensates

¹ Department of Physics, University of Illinois at Urbana-Champaign - Urbana, IL 61801-3080, USA
² Department of Physics, The University of Texas at Dallas - Richardson, TX 75080-3021, USA
³ Department of Physics, Smith College - Northampton, MA 01063, USA
⁴ Department of Physics, University of Massachusetts - Amherst, MA 01003-9300, USA

^(a) kuei.sun@utdallas.edu
^(b) clannert@smith.edu
^(c) smivish@illinois.edu

Received: 19 August 2017
Accepted: 19 December 2017

Abstract

Bose-Einstein condensate shells, while occurring in ultracold systems of coexisting phases and potentially within neutron stars, have yet to be realized in isolation on Earth due to the experimental challenge of overcoming gravitational sag. Motivated by the expected realization of hollow condensates by the space-based Cold Atomic Laboratory in microgravity conditions, we study a spherical condensate undergoing a topological change from a filled sphere to a hollow shell. We argue that the collective modes of the system show marked and robust signatures of this hollowing transition accompanied by the appearance of a new boundary. In particular, we demonstrate that the frequency spectrum of the breathing modes shows a pronounced depression as it evolves from the filled-sphere limit to the hollowing transition. Furthermore, when the center of the system becomes hollow surface modes show a global restructuring of their spectrum due to the availability of a new, inner, surface for supporting density distortions. We pinpoint universal features of this topological transition as well as analyse the spectral evolution of collective modes in the experimentally relevant case of a bubble-trap.