Condensed ground states of frustrated BoseHubbard models
Abstract
We study theoretically the ground states of twodimensional BoseHubbard models which are frustrated by gauge fields. Motivated by recent proposals for the implementation of optically induced gauge potentials, we focus on the situation in which the imposed gauge fields give rise to a pattern of staggered fluxes of magnitude α and alternating in sign along one of the principal axes. For α=1/2 this model is equivalent to the case of uniform flux per plaquette n_{ϕ}=1/2, which, in the hardcore limit, realizes the “fully frustrated” spin1/2 XY model. We show that the meanfield ground states of this frustrated BoseHubbard model typically break translational symmetry. Given the presence of both a nonzero superfluid fraction and translational symmetry breaking, these phases are supersolid. We introduce a general numerical technique to detect broken symmetry condensates in exact diagonalization studies. Using this technique we show that, for all cases studied, the ground state of the BoseHubbard model with staggered flux α is condensed, and we obtain quantitative determinations of the condensate fraction. We discuss the experimental consequences of our results. In particular, we explain the meaning of gauge invariance in ultracoldatom systems subject to optically induced gauge potentials and show how the ability to imprint phase patterns prior to expansion can allow very useful additional information to be extracted from expansion images.
 Publication:

Physical Review A
 Pub Date:
 December 2010
 DOI:
 10.1103/PhysRevA.82.063625
 arXiv:
 arXiv:1009.4420
 Bibcode:
 2010PhRvA..82f3625M
 Keywords:

 03.75.Lm;
 67.85.Hj;
 Tunneling Josephson effect BoseEinstein condensates in periodic potentials solitons vortices and topological excitations;
 BoseEinstein condensates in optical potentials;
 Condensed Matter  Quantum Gases
 EPrint:
 14 pages, 10 figures