Persistent currents in spinor condensates.

We create and study persistent currents in a toroidal two-component Bose gas, consisting of 87Rb atoms in two different spin states. For a large spin-population imbalance we observe supercurrents persisting for over two minutes. However, we find that the supercurrent is unstable for spin polarization below a well-defined critical value.

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.

Can a Bose gas be saturated?

We scrutinize the concept of saturation of the thermal component in a partially condensed trapped Bose gas. Using a 39K gas with tunable interactions, we demonstrate strong deviation from Einstein's textbook concept of a saturated vapor. However, the saturation picture can be recovered by extrapolation to the strictly noninteracting limit.