Condensation Dynamics in a Quantum-Quenched Bose Gas

By quenching the strength of interactions in a partially condensed Bose gas, we create a super-saturated 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.