Phases of a 2D Bose Gas in an Optical Lattice

TL;DR

This paper investigates the phase transition of a 2D Bose gas in an optical lattice, demonstrating the superfluid to Mott insulator transition in a trapped system and confirming theoretical predictions with experimental data.

Contribution

It provides experimental validation of the quantum Monte Carlo universal state diagram for trapped 2D Bose gases, highlighting the effects of harmonic confinement.

Findings

Observation of superfluid to Mott insulator transition

Agreement with quantum Monte Carlo predictions

Effect of harmonic trap on phase transition

Abstract

Ultra-cold atoms in optical lattices realize simple, fundamental models in condensed matter physics. Our 87Rb Bose-Einstein condensate is confined in a harmonic trapping potential to which we add an optical lattice potential. Here we realize the 2D Bose-Hubbard Hamiltonian and focus on the effects of the harmonic trap, not present in bulk condensed matter systems. By measuring condensate fraction we identify the transition from superfluid to Mott insulator as a function of atom density and lattice depth. Our results are in excellent agreement with the quantum Monte Carlo universal state diagram, suitable for trapped systems, introduced by Rigol et al. (Phys. Rev. A 79, 053605 (2009)).