Adiabatically changing the phase-space density of a trapped Bose gas
  We show that the degeneracy parameter of a trapped Bose gas can be changed adiabatically in a reversible way, both in the Boltzmann regime and in the degenerate Bose regime. We have performed measurements on spin-polarized atomic hydrogen in the Boltzmann regime demonstrating reversible changes of the degeneracy parameter (phase-space density) by more than a factor of two. This result is in perfect agreement with theory. By extending our theoretical analysis to the quantum degenerate regime we predict that, starting close enough to the Bose-Einstein phase transition, one can cross the transition by an adiabatic change of the trap shape. 
P.W.H. Pinkse, A. Mosk, M. Weidem\"uller, M.W. Reynolds, T.W. Hijmans,   and J.T.M. Walraven (University of Amsterdam)