Coherent transition between adjacent Zeeman sublevels in an alkali-metal atom without populating other sublevels

We report on a spectroscopic method to coherently drive a selective transition between two levels in a ladder system of equally spaced energy levels. A typical example of such a ladder system is a set of Zeeman sublevels in the same hyperfine level of a ground-state alkali-metal atom. The scheme is based on a stimulated Raman transition with a Zeeman sublevel belonging to the other hyperfine level as an intermediate state. We identify quantization conditions on a single-photon detuning and Rabi frequencies for either a π/2 or a π transition between adjacent Zeeman sublevels without populating the intermediate state. We experimentally demonstrate the scheme using lithium atoms in an optical trap. Application of the scheme includes manipulating a pair of Zeeman sublevels as a quantum bit or probing Zeeman coherence established by coherent population trapping.