Causality in Condensates: Grey Solitons as Remnants of BEC Formation

TL;DR

This paper investigates how symmetry breaking during phase transitions in elongated Bose-Einstein condensates leads to the formation of long-lived grey solitons, which serve as remnants of the condensate formation process.

Contribution

It demonstrates that grey solitons form in elongated traps due to phase defect mechanisms, with their number increasing with the transition rate, highlighting a new aspect of BEC formation.

Findings

Grey solitons form in elongated BECs due to symmetry breaking.

Number of grey solitons increases with transition rate.

Formation mechanism differs from vortex defect formation in symmetric traps.

Abstract

Symmetry breaking during phase transitions can lead to the formation of topological defects (such as vortex lines in superfluids). However, the usually studied BEC's have the shape of a cigar, a geometry that impedes vortex formation, survival, and detection. I show that, in elongated traps, one can expect the formation of "grey solitons" (long-lived, non-topological "phase defects") as a result of the same mechanism. Their number will rise approximately in proportion to the transition rate. This steep rise is due to the increasing size of the region of the BEC cigar where the phase of the condensate wavefunction is chosen locally (rather than passed on from the already formed BEC).