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We apply linear-response analysis to the Gross-Pitaevskii equation to obtain the excitation frequencies of a Bose-Einstein condensate in a vortex state, and apply it to a system of rubidium atoms confined in a time-averaged orbiting potential trap. The excitation frequencies of a vortex differ significantly from those of the ground state, and may therefore be used to obtain a spectroscopic signature of the presence of a vortex state.
Dodd et al. (Tue,) studied this question.