We predict a dynamical classical superfluid–insulator transition in a Bose–Einstein condensate (BEC) trapped in combined optical and axially symmetrical harmonic potentials initiated by the periodic modulation of the radial trapping potential. The transition is marked by a loss of phase coherence in the BEC and a subsequent destruction of the interference pattern upon free expansion. For a weak modulation of the radial potential the phase coherence is maintained. For a stronger modulation and a longer holding time in the modulated trap, the phase coherence is destroyed thus signalling a classical superfluid–insulator transition. The results are illustrated by a complete numerical solution of the axially symmetrical mean-field Gross–Pitaevskii equation for a repulsive BEC. Suggestions for future experimentation are made.
It is shown that by experimentally controlling a weak optical lattice potential to equilibrate the interatomic interactions, we can construct a set of exact solutions of the Gross-Pitaevskii equations (GPE) for a two-component Bose-Einstein condensate (BEC). The exact solutions describe some balance superfluid phases with different flow-density amplitudes that supply several different and useful sources of the atom lasers. In the definition of dynamical superfluid-insulator transition (DSIT), (see Smerzi A. et al. , Phys. Rev. Lett. 89 (2002) 170402), the DSITs from the balance superfluid phases to the balance insulator phases are studied. The DSITs can be detected experimentally by observing the deformation of the periodic structure and the losses of the interference pattern and stability.
We have studied the effects of a disordered optical potential on the transport and phase coherence of a Bose-Einstein condensate (BEC) of
7Li atoms. At moderate disorder strengths
(VD), we observe inhibited transport and damping of dipole excitations, while in time-of-flight images, random but reproducible interference patterns are observed. In situ images reveal that the appearance of interference is correlated with density modulation, without complete fragmentation. At higher
VD, the interference contrast diminishes as the BEC fragments into multiple pieces with little phase coherence.