Two-channel cross-phase modulation based on the reversible storage of light in a cold atomic system

We propose a five-level quasi-tripod type atomic system for realizing two-channel cross-phase modulation (XPM) based on the light-storage. Due to the existence of the double dark-state polaritons, both probe fields can be coherently mapped into and out of the cold atoms by switching off and on the coupling field adiabatically. The analytic results and the numerical simulations show that the application of an additional weak microwave field during the storage time can efficiently modify the atomic spin coherence, and a continuous and controllable phase shift can be imposed on the retrieved probe fields with negligible attenuation in the amplitude. The phase shift and the energy retrieving rate of the probe fields are neither influenced by the coupling field nor by the atomic optical density. Such a novel scheme can be easily extended to realize the XPM of multiple-probe fields and may find potential applications in multiple-channel classical and quantum information processing.