Symmetry Breaking and Enhanced Condensate Fraction in a Matter-Wave Bright Soliton

TL;DR

This paper demonstrates through exact diagonalization that in a quasi-one-dimensional attractive Bose-Einstein condensate, the formation of a bright soliton involves symmetry breaking and results in a transition from a fragmented to a single condensate, with enhanced coherence.

Contribution

It provides a detailed many-body analysis showing how symmetry breaking leads to a condensed state with a higher eigenvalue of the single-particle density matrix.

Findings

Formation of a bright soliton is associated with a Goldstone mode.

The maximum eigenvalue of the single-particle density matrix increases significantly.

Symmetry breaking converts a fragmented condensate into a single condensate.

Abstract

An exact diagonalization study reveals that a matter-wave bright soliton and the Goldstone mode are simultaneously created in a quasi-one-dimensional attractive Bose-Einstein condensate by superpositions of quasi-degenerate low-lying many-body states. Upon formation of the soliton the maximum eigenvalue of the single-particle density matrix increases dramatically, indicating that a fragmented condensate converts into a single condensate as a consequence of the breaking of translation symmetry.