title: Internal state conversion in ultracold gases.
abstract: We consider an ultracold gas of (noncondensed) bosons or fermions with two internal states, and we study the effect of a gradient of the transition frequency between these states. When a pi/2 rf pulse is applied to the sample, exchange effects during collisions transfer the atoms into internal states which depend on the direction of their velocity. This results, after a short time, in a spatial separation between the two states. A kinetic equation is solved analytically and numerically; the results agree well with the recent observations of Lewandowski et al.
authors.affiliation: LKB, Laboratoire de Physique de l'ENS, 24 rue Lhomond, 75005 Paris, France. fuchs@lkb.ens.fr
authors.forename: J N
authors.initials: JN
authors.lastname: Fuchs
authors.forename: D M
authors.initials: DM
authors.lastname: Gangardt
authors.forename: F
authors.initials: F
authors.lastname: Laloë