Number Fluctuations and Energy Dissipation in Sodium Spinor Condensates

We characterize fluctuations in atom number and spin populations in F=1
sodium spinor condensates. We find that the fluctuations enable a quantitative
measure of energy dissipation in the condensate. The time evolution of the
population fluctuations shows a maximum. We interpret this as evidence of a
dissipation-driven separatrix crossing in phase space. For a given initial
state, the critical time to the separatrix crossing is found to depend
exponentially on the magnetic field and linearly on condensate density. This
crossing is confirmed by tracking the energy of the spinor condensate as well
as by Faraday rotation spectroscopy. We also introduce a phenomenological model
that describes the observed dissipation with a single coefficient.