The ground state of Bose gases with repulsive interaction: A quantum Monte Carlo study

The capability of Feshbach resonances to experimentally tune the atomic interaction in trapped gases provides a rich opportunity to better understand the properties of strongly-correlated systems. We report results from many-body ground-state calculations of interacting Bose gases in 3D with repulsive interactions. We characterize the effect of many-body correlations as a function of atom-atom scattering length $a_s$. Calculations were done for both trapped atomic gases and bulk fluids at different densities. We use a recently developed Quantum Monte Carlo method\footnote{Phys. Rev. E 70, 056702 (2004)}, which gives a very good approximation to the true ground state. We put the bosons on a discrete mesh and model the interatomic interaction by an on-site, $\delta$-function potential parametrized by $a_s$. Results will be presented for the energetics, density profile, momentum distribution, condensate fraction, and correlation functions. We analyze the deviations of the standard Gross-Pitaevskii and Bogoliubov approaches from our results as the system becomes more strongly interacting, and discuss their implications.