Manipulating Synchronous Optical Signals with a Double $Λ$ Atomic Ensemble

We analyze a double $Λ$ atomic configuration interacting with two signal beams and two control beams. Because of the quantum interference between the two $Λ$ channels, the four fields are phase-matched in electromagnetically induced transparency. Our numerical simulation shows that this system is able to manipulate synchronous optical signals, such as generation of optical twin signals, data correction, signal transfer and amplification in the atomic storage.