title: Phases of a two-dimensional bose gas in an optical lattice.
abstract: Ultracold atoms in optical lattices realize simple condensed matter models. We create an ensemble of ≈60 harmonically trapped 2D Bose-Hubbard systems from a 87Rb Bose-Einstein condensate in an optical lattice and use a magnetic resonance imaging approach to select a few 2D systems for study, thereby eliminating ensemble averaging. Our identification of the transition from superfluid to Mott insulator, as a function of both atom density and lattice depth, is in excellent agreement with a universal state diagram [M. Rigol, Phys. Rev. A 79 053605 (2009)] suitable for our trapped system. In agreement with theory, our data suggest a failure of the local density approximation in the transition region.
authors.affiliation: Joint Quantum Institute, National Institute of Standards and Technology, and University of Maryland, Gaithersburg, Maryland, 20899, USA.
authors.forename: K
authors.initials: K
authors.lastname: Jiménez-García
authors.forename: R L
authors.initials: RL
authors.lastname: Compton
authors.forename: Y-J
authors.initials: YJ
authors.lastname: Lin
authors.forename: W D
authors.initials: WD
authors.lastname: Phillips
authors.forename: J V
authors.initials: JV
authors.lastname: Porto
authors.forename: I B
authors.initials: IB
authors.lastname: Spielman