Spin nematic order in antiferromagnetic spinor condensates

TL;DR

This paper provides experimental evidence for spin-nematic order in a spin-1 Bose-Einstein condensate, revealing a new magnetic phase characterized by a second rank tensor, and introduces a method to detect complex magnetic orders through spin noise analysis.

Contribution

The study demonstrates direct experimental detection of spin-nematic order in a spinor condensate and introduces a novel spin noise measurement technique to reveal hidden magnetic phases.

Findings

Evidence of spin-nematic ordering in sodium spin-1 BEC

Spin noise after rotation reveals hidden order

Method applicable to high spin systems

Abstract

Large spin systems can exhibit unconventional types of magnetic ordering different from the ferromagnetic or N\'eel-like antiferromagnetic order commonly found in spin 1/2 systems. Spin-nematic phases, for instance, do not break time-reversal invariance and their magnetic order parameter is characterized by a second rank tensor with the symmetry of an ellipsoid. Here we show direct experimental evidence for spin-nematic ordering in a spin-1 Bose-Einstein condensate of sodium atoms with antiferromagnetic interactions. In a mean field description this order is enforced by locking the relative phase between spin components. We reveal this mechanism by studying the spin noise after a spin rotation, which is shown to contain information hidden when looking only at averages. The method should be applicable to high spin systems in order to reveal complex magnetic phases.