Finite Temperature Excitations of an anisotropically trapped Bose gas : A diffusion Monte Carlo study

We calculate the exciation frequencies of m=0 mode and m=2 mode of Rb87 atoms confined in an anisotropic trap and interacting with repulsive forces by diffusion Monte Carlo method. The spectrum turns out to be strongly temperature dependent and we compare our results with other theories and experiments. This is the first Monte Carlo calculation for a trapped Bose Einstein condensed dilute gas which shows an excellent agreement with the JILA data for m=2 mode all the way up to T = 0.9Tc whereas most of the previous mean field type calculations had shown agreement with the experimental data only up to T = 0.6Tc.