Physics of hollow Bose-Einstein condensates

TL;DR

This paper investigates the collective excitations of hollow Bose-Einstein condensates, revealing distinctive spectral signatures of the transition from filled to hollow states, with implications for experimental realization in microgravity conditions.

Contribution

It provides a theoretical analysis of the topological transition in spherical condensates and identifies universal spectral features associated with hollowing.

Findings

Breathing mode frequencies decrease during hollowing transition.

Emergence of a new inner surface alters collective mode spectra.

Universal spectral signatures characterize the topological change.

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.