Condensation dynamics in a quantum-quenched Bose gas.

By quenching the strength of interactions in a partially condensed Bose gas, we create a "supersaturated" vapor which has more thermal atoms than it can contain in equilibrium. Subsequently, the number of condensed atoms (N(0)) grows even though the temperature (T) rises and the total atom number decays. We show that the nonequilibrium evolution of the system is isoenergetic and, for small initial N(0), observe a clear separation between T and N(0) dynamics, thus explicitly demonstrating the theoretically expected "two-step" picture of condensate growth. For increasing initial N(0) values, we observe a crossover to classical relaxation dynamics. The size of the observed quench-induced effects can be explained using a simple equation of state for an interacting harmonically trapped atomic gas.