Quantum Bubbles in Microgravity

TL;DR

This paper investigates the properties of Bose-Einstein condensates in bubble traps under microgravity, analyzing critical temperature, density distribution, expansion dynamics, and superfluidity through simulations, providing benchmarks for future experiments.

Contribution

It offers the first detailed theoretical analysis of bubble-shaped Bose-Einstein condensates, including critical temperature reduction and superfluidity in thin shells, using Gross-Pitaevskii and quantum Monte Carlo methods.

Findings

Critical temperature is significantly reduced compared to harmonic traps.

The condensate exhibits self-interference filling the bubble hole during expansion.

Superfluidity persists in thin shell geometries as shown by quantum Monte Carlo simulations.

Abstract

The recent developments of microgravity experiments with ultracold atoms have produced a relevant boost in the study of shell-shaped ellipsoidal Bose-Einstein condensates. For realistic bubble-trap parameters, here we calculate the critical temperature of Bose-Einstein condensation, which, if compared to the one of the bare harmonic trap with the same frequencies, shows a strong reduction. We simulate the zero-temperature density distribution with the Gross-Pitaevskii equation, and we study the free expansion of the hollow condensate. While part of the atoms expands in the outward direction, the condensate self-interferes inside the bubble trap, filling the hole in experimentally observable times. For a mesoscopic number of particles in a strongly interacting regime, for which more refined approaches are needed, we employ quantum Monte Carlo simulations, proving that the nontrivial topology of a thin shell allows superfluidity. Our work constitutes a reliable benchmark for the forthcoming scientific investigations with bubble traps.