Reversible loss of superfluidity of a Bose–Einstein condensate in a 1D optical lattice

We apply a one-dimensional (1D) optical lattice, formed by two laser beams with a wavelength of 852 nm, to a 3D (87)Rb Bose-Einstein condensate (BEC) in a shallow magnetic trap. We use Kapitza-Dirac scattering to determine the depth of the optical lattice. A qualitative change in behavior of the BEC is observed at a lattice depth of 30E(rec), where the quantum gas undergoes a reversible transition from a superfluid state to a state that lacks well-to-well phase coherence. Our observations are consistent with a 1D Mott insulator transition, but could also be explained by mean-field effects.