Suppression of inhomogeneous broadening in rf spectroscopy of optically   trapped atoms
  We present a novel method for reducing the inhomogeneous frequency broadening in the hyperfine splitting of the ground state of optically trapped atoms. This reduction is achieved by the addition of a weak light field, spatially mode-matched with the trapping field and whose frequency is tuned in-between the two hyperfine levels. We experimentally demonstrate the new scheme with Rb 85 atoms, and report a 50-fold narrowing of the rf spectrum. 
Ariel Kaplan, Mikkel Fredslund Andersen, and Nir Davidson