Abstract

Trapped bosonic gases have been shown to exhibit enhanced first-order coherence in various interferometric measurements when cooled below the critical temperature of Bose-Einstein condensation. However, first-order coherence does not reveal many-atom features for which higher-order atomic correlations must be explored. Here the second-order coherence is studied in the context of classicality of atom-atom correlations. To lowest order with respect to the inverse atom number an inequality for the condensate mode is derived that should hold for purely classical atom-atom correlations. A possible violation of this classical inequality is shown to be hardly possible, so that below the critical temperature the atomic gas should be considered as classical. © 2007 IOP Publishing Ltd.