Optical switching mediated by quantum interference of Raman transitions.

We report an experimental study of quantum interference between two-photon Raman transitions and demonstration of the phase control of light attenuation/transmission in cold Rb atoms. By varying the phase and frequency of a weak control laser, either constructive interference or destructive interference between the two-photon Raman transitions in a three-level Lambda system can be manipulated. The interference enables absorptive switching of one field by another field at low light levels.