Boris Nowak, Thomas Gasenzer
The dynamical process of Bose-Einstein (BE) condensation of a dilute ultracold gas is found to occur in two distinctly different forms. If the particle flux into the low-energy modes is sufficiently strong, the Bose gas behaves predominantly like an incompressible fluid. It exhibits chaotic (Vinen) superfluid turbulence which marks the presence of a \emph{non-thermal fixed point} of the evolution. The approach of this state can be identified by the build-up of a characteristic power-law single-particle spectrum $n(k)\sim k^{-5}$. Alternatively, for a weak flux in energy space, during the condensation process phase defects reminiscent of superfluid turbulence appear but a separation of the incompressible and compressible components, as well as the $k^{-5}$ scaling of the low-energy modes are absent.
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http://arxiv.org/abs/1206.3181
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