Phase ordering kinetics of the Bose gas.

We study the approach to equilibrium of a Bose gas to a superfluid state. We point out that dynamic scaling, characteristic of far from equilibrium phase-ordering systems, should hold. We stress the importance of a nondissipative Josephson precession term in driving the system to a new universality class. A model of coarsening in dimension {ital d}=2, involving a quench between two temperatures below the equilibrium superfluid transition temperature ({ital T}{sub {ital c}}), is exactly solved and demonstrates the relevance of the Josephson term. Numerical results on quenches from above {ital T}{sub {ital c}} in {ital d}=2,3 provide evidence for the scaling picture postulated. {copyright} {ital 1996 The American Physical Society.}