Bose-Einstein Condensates in the Large Gas Parameter Regime

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Bose-Einstein condensates of 10⁴ ⁸⁵Rb atoms in a cylindrical trap are studied using a recently proposed modified Gross-Pitaevskii equation. The existence of a Feshbach resonance allows for widely tuning the scattering length of the atoms, and values of the peak gas parameter, xpk, of the order of 10⁻² can be attained. We find large differences between the results of the modified Gross-Pitaevskii and of the standard Thomas-Fermi, and Gross-Pitaevskii equations in this region. The column densities at z=0 may differ by as much as 30% and the half maximum radius by 20%. The scattering lengths estimated by fitting the half maximum radius within different approaches can differ by 40%.