Full quantum Monte Carlo treatment of BEC in traps from the dilute to dense regimes
Abstract
We investigate the properties of hard core Bosons in harmonic traps from the extreme dilute regime to liquid helium densities. BoseEinstein condensation is formulated using the onebody Density Matrix (OBDM) which is valid at all densities. The OBDM is calculated using diffusion Monte Carlo and is diagonalized to obtain the ``natural" single particle orbitals and their occupation, including the condensate fraction. At low Boson density, na^3 < 10^{5}, where n = N/V and a is the hard core diameter, the condensate is localized at the center of the trap. With increasing na^3, the condensate is depleted in the dense central region but the local condensate fraction remains large in the dilute region at the edges of the trap. Comparisons with the GrossPitaevskii (GP) theory of the condensate show that up to na^3 ≤ 10^{4} GP theory describes the whole system within 1%. At na^3 ≈ 10^{3} corrections are 3% to the GP energy but 30% to the Bogoliubov prediction of the condensate depletion. Mean field theory fails to describe the condensate at na^3 ≥ 10^{2} as local correlations play a significant role. For na^3 ≥ 0.1, these systems have more in common with a liquid ^4He droplet than a trapped Boson gas(J.L. DuBois, H.R. Glyde. Phys. Rev. A 68, 033602 (2003)).
 Publication:

APS March Meeting Abstracts
 Pub Date:
 March 2004
 Bibcode:
 2004APS..MARL15002D