Spontaneous symmetry breaking in a quenched ferromagnetic spinor Bose condensate

TL;DR

This paper reports the experimental observation of spontaneous symmetry breaking and topological defect formation in a quenched ferromagnetic spinor Bose-Einstein condensate, revealing new insights into quantum phase transitions and superfluid magnetism.

Contribution

It demonstrates the first phase-sensitive in-situ detection of vortices and spin textures in a gaseous superfluid during a quantum phase transition.

Findings

Observation of spontaneous symmetry breaking in a spinor BEC

Detection of polar-core spin-vortices with non-zero spin current

Formation of ferromagnetic domains and spin textures

Abstract

A central goal in condensed matter and modern atomic physics is the exploration of many-body quantum phases and the universal characteristics of quantum phase transitions in so far as they differ from those established for thermal phase transitions. Compared with condensed-matter systems, atomic gases are more precisely constructed and also provide the unique opportunity to explore quantum dynamics far from equilibrium. Here we identify a second-order quantum phase transition in a gaseous spinor Bose-Einstein condensate, a quantum fluid in which superfluidity and magnetism, both associated with symmetry breaking, are simultaneously realized. $^{87}$Rb spinor condensates were rapidly quenched across this transition to a ferromagnetic state and probed using in-situ magnetization imaging to observe spontaneous symmetry breaking through the formation of spin textures, ferromagnetic domains and domain walls. The observation of topological defects produced by this symmetry breaking, identified as polar-core spin-vortices containing non-zero spin current but no net mass current, represents the first phase-sensitive in-situ detection of vortices in a gaseous superfluid.