title: Phase diagram for a Bose-Einstein condensate moving in an optical lattice.
abstract: The stability of superfluid currents in a system of ultracold bosons was studied using a moving optical lattice. Superfluid currents in a very weak lattice become unstable when their momentum exceeds 0.5 recoil momentum. Superfluidity vanishes already for zero momentum as the lattice deep reaches the Mott insulator (MI) phase transition. We study the phase diagram for the disappearance of superfluidity as a function of momentum and lattice depth between these two limits. Our phase boundary extrapolates to the critical lattice depth for the superfluid-to-MI transition with 2% precision. When a one-dimensional gas was loaded into a moving optical lattice a sudden broadening of the transition between stable and unstable phases was observed.
authors.affiliation: MIT-Harvard Center for Ultracold Atoms, Research Laboratory of Electronics, and Department of Physics, MIT, Cambridge, Massachusetts 02139, USA.
authors.forename: Jongchul
authors.initials: J
authors.lastname: Mun
authors.forename: Patrick
authors.initials: P
authors.lastname: Medley
authors.forename: Gretchen K
authors.initials: GK
authors.lastname: Campbell
authors.forename: Luis G
authors.initials: LG
authors.lastname: Marcassa
authors.forename: David E
authors.initials: DE
authors.lastname: Pritchard
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Ketterle