Interacting trapped bosons yield fragmented condensate states in low dimensions

TL;DR

This paper explores how low-dimensional trapped Bose gases with repulsive interactions develop fragmented condensate states due to interactions, even before reaching the thermodynamic limit, highlighting the role of confinement and interactions.

Contribution

It provides a variational analysis showing the emergence of fragmented condensates in low-dimensional Bose gases under weak confinement, a phenomenon not previously characterized.

Findings

Fragmentation occurs into two or three parts in quasi-1D and quasi-2D systems.

Fragmented states appear before the thermodynamic limit, driven by interactions.

Phase fluctuations lead to nonmacroscopic fragments in low dimensions.

Abstract

We investigate the level population statistics and degree of coherence encoded in the single-particle density matrix of harmonically trapped low-dimensional [quasi-one-dimensional (quasi-1D) or quasi-two-dimensional (quasi-2D)] Bose gases with repulsive contact interactions. Using a variational analysis, we derive fragmentation of the condensate in the weakly confining directions into two (quasi-1D) respectively three (quasi-2D) mutually incoherent macroscopic pieces, upon increasing a dimensionless interaction measure beyond a critical value. Fragmented condensate many-body states in low-dimensional systems therefore occur well before the thermodynamic limit of infinite extension is reached, in which phase fluctuations of the matter wave field create an infinite number of nonmacroscopic fragments.