Quantum Phase Transitions and Continuous Observation of Spinor Dynamics in an Antiferromagnetic Condensate

Condensates of spin-1 sodium display rich spin dynamics due to the
antiferromagnetic nature of the interactions in this system. We use Faraday
rotation spectroscopy to make a continuous and minimally destructive
measurement of the dynamics over multiple spin oscillations on a single
evolving condensate. This method provides a sharp signature to locate a
magnetically tuned separatrix in phase space which depends on the net
magnetization. We also observe a phase transition from a two- to a
three-component condensate at a low but finite temperature using a
Stern-Gerlach imaging technique. This transition should be preserved as a
zero-temperature quantum phase transition.