Enhanced many-body effects in the excitation spectrum of a weakly-interacting rotating Bose-Einstein condensate

TL;DR

This paper investigates how rotation-induced vortices in a 2D Bose-Einstein condensate lead to significant many-body effects in the excitation spectrum, surpassing mean-field predictions even with large particle numbers.

Contribution

It demonstrates that rotation enhances many-body effects in the excitation spectrum of a BEC, especially with increased vorticity, beyond mean-field theory, for large atom numbers.

Findings

Many-body effects grow with vorticity.

Deviations from mean-field persist at large N.

Rotation amplifies many-body effects even in weakly interacting BECs.

Abstract

The excitation spectrum of a highly-condensed two-dimensional trapped Bose-Einstein condensate (BEC) is investigated within the rotating frame of reference. The rotation is used to transfer high-lying excited states to the low-energy spectrum of the BEC. We employ many-body linear-response theory and show that, once the rotation leads to a quantized vortex in the ground state, already the low-energy part of the excitation spectrum shows substantial many-body effects beyond the realm of mean-field theory. We demonstrate numerically that the many-body effects grow with the vorticity of the ground state, meaning that the rotation enhances them even for very weak repulsion. Furthermore, we explore the impact of the number of bosons $N$ in the condensate on a low-lying single-particle excitation, which is describable within mean-field theory. Our analysis shows deviations between the many-body and mean-field results which clearly persist when $N$ is increased up to the experimentally relevant regime, typically ranging from several thousand up to a million bosons in size. Implications are briefly discussed.