Bose-Einstein condensates in the large-gas-parameter regime - art. no. 063610

Bose-Einstein condensates of 10(4) Rb-85 atoms in a cylindrical trap are st udied using a recently proposed approach based on a local-density approxima tion. Since the existence of a Feshbach resonance allows for widely tuning the scattering length of the atoms, values of the peak gas parameter x(pk) of the order of 10(-2) May be attained and the standard analysis based on G ross-Pitaevskii and/or Thomas-Fermi equations may result in being questiona ble. Energy functionals derived from the correlated basis functions theory and the low-density expansion for a homogeneous hard-spheres gas are used t o estimate corrections to the Gross-Pitaevskii equation. The two functional s give similar results, both showing large differences with respect to the Thomas-Fermi and Gross-Pitaevskii ones, The column densities at z=0 may dif fer by as much as similar to 30% and the half Maximum radius by similar to 20%. The scattering lengths estimated by fitting the half maximum radius ma y differ by similar to 40% from those given by a Thomas-Fermi-based analysi s of the experimental data.