Suppression of inhomogeneous broadening in rf spectroscopy of optically trapped atoms

A method for reducing the inhomogeneous broadening in the spectroscopic measurement of the hyperfine splitting of the ground state of optically trapped atoms is demonstrated. This reduction is achieved by the addition of a very weak light field (the "compensating beam"), whose frequency is tuned between the two hyperfine levels. The total shift is obtained by adding the shifts from the trap and the compensating beam, and a complete cancellation of the inhomogeneous broadening will occur for an intensity ratio of ∼ (ΔHF/2δ)². With the suppression of inhomogeneous broadening, the atomic coherence time is next limited by the much smaller spontaneous scattering time. Finally, the introduction of the compensating beam provides with an experimental method to control the decoherence rate of the atomic ensemble, and thus to study the interesting interplay between dynamics and coherence in systems with a rich phase-space, for example in atom-optics billiards.