Nonequilibrium dynamics of fluctuations in an ultracold atomic mixture

We investigate an ultracold mixture of Bose gases interacting via spin-changing collisions by studying the dynamics of spin fluctuations. The experimental implementation employs 23Na and 7Li atoms, which are prepared out of equilibrium across a wide range of initial conditions. We identify three regimes in the dynamics of the system for different initial states: a long-lived metastable regime, an instability range with strong growth of fluctuations, and a regime approaching thermal equilibrium. Theoretical modeling of the data allows us to reconstruct effective potentials which characterize the different dynamical regimes of the system.