Phase coherence and control of stored photonic information

We report the demonstration of phase coherence and control for the recently developed “light-storage” technique. Specifically, we employ a dynamic form of electromagnetically induced transparency to bring the group velocity of a light pulse to zero, thereby mapping the photonic information into an ensemble spin coherence in warm Rb vapor. We then apply a pulsed magnetic field to vary the phase of the atomic spin excitations and map the altered information back into light. We detect the resultant phase shift in an optical interferometric measurement, thus confirming that the storage process preserves phase coherence.