Superfluid and dissipative dynamics of a Bose-Einstein condensate in a periodic optical potential

We create Bose-Einstein condensates of Rb-87 in a static magnetic trap with a superimposed blue-detuned 1D optical lattice. By displacing the magnetic trap center we are able to control the condensate evolution. We observe a change in the frequency of the center-of-mass oscillation in the harmonic t rapping potential, in analogy with an increase in effective mass. For fluid velocities greater than a local speed of sound, we observe the onset of di ssipative processes up to full removal of the superfluid component. A paral lel simulation study visualizes the dynamics of the Bose-Einstein condensat e and accounts for the main features of the observed behavior.