title: Quantum Monte Carlo method for the Bose-Hubbard model with harmonic confining potential.
abstract: We study the Bose-Hubbard model with an external harmonic field, which is effective for modeling a cold atomic Bose gas trapped in an optical lattice. We modify the directed-loop algorithm to simulate large systems efficiently. As a demonstration we carry out the simulation of a system consisting of 1. 8 x 10{5} particles on a 64{3} lattice. These numbers are comparable to those in the pioneering experimental work by Greiner [Nature (London) 415, 39 (2002)]. Furthermore, we observe coherence between two superfluid spheres separated by a Mott insulator region in a "wedding-cake" structure.
authors.affiliation: Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwa-no-ha, Kashiwa, Chiba 277-8581, Japan.
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Kato
authors.forename: Naoki
authors.initials: N
authors.lastname: Kawashima