Elimination of inhomogeneous broadening for a ground-state hyperfine transition in an optical trap

We propose a way to eliminate the inhomogeneous broadening for a ground-state hyperfine transition of an alkali metal atom in an optical trap by using a properly polarized trapping field. The ac Stark shift contribution from the vector polarizability has opposite sign for a pair of ground hyperfine levels. It can be used to eliminate the inhomogeneous broadening from the difference in the scalar polarizbilities due to the hyperfine splitting. The size of the vector term is determined by the polarization state of the trapping field, and by controlling the polarization tightly one can achieve a very narrow linewidth. We estimate required tolerance in the polarization control to achieve 1-Hz linewidth for a specific case of a cesium atom. This proposal has significant implications for an electric dipole moment measurement using cesium atoms and quantum information processing using an optical lattice.