Quantum Phase Transition in an Antiferromagnetic Spinor Bose-Einstein Condensate

TL;DR

This paper experimentally investigates the quantum phase transition in an antiferromagnetic sodium Bose-Einstein condensate, focusing on the dynamical evolution and domain formation as the system crosses the transition point.

Contribution

It demonstrates the real-time dynamics and domain coarsening in a spinor BEC during a quantum phase transition induced by microwave control.

Findings

Observed the transition from polar to antiferromagnetic phase at q=0

Measured the population dynamics of hyperfine states near the transition

Documented domain coarsening and instability growth for q<0

Abstract

We have experimentally observed the dynamics of an antiferromagnetic sodium Bose-Einstein condensate (BEC) quenched through a quantum phase transition. Using an off-resonant microwave field coupling the F = 1 and F = 2 atomic hyperfine levels, we rapidly switched the quadratic energy shift q from positive to negative values. At q = 0 the system undergoes a transition from a polar to antiferromagnetic phase. We measured the dynamical evolution of the population in the F = 1, m_F = 0 state in the vicinity of this transition point and observed a mixed state of all 3 hyperfine components for q < 0. We also observed the coarsening dynamics of the instability for q<0, as it nucleated small domains that grew to the axial size of the cloud.