Atomic micromotion and geometric forces in a triaxial magnetic trap

Nonadiabatic motion of Bose-Einstein condensates of rubidium atoms arising from the dynamical nature of a time-orbiting-potential (TOP) trap was obser ved experimentally. The orbital micromotion of the condensate in velocity s pace at the frequency of the rotating bias field of the TOP was detected by a time-of-flight method. A dependence of the equilibrium position of the a toms on the sense of rotation of the bias field was observed. We have compa red our experimental findings with numerical simulations. The nonadiabatic following of the atomic spin in the trap rotating magnetic field produces g eometric forces acting on the trapped atoms.