Manipulating synchronous optical signals with a double-Λ atomic ensemble

We study the interaction of two time-dependent signal beams and two stationary control beams with a double-Λ atomic configuration. Because of the quantum coherence between the two lower atomic levels existing in electromagnetically induced transparency (EIT), the two signal beams are shape matched, and affected by the two control beams. Our numerical simulations show that this system can be used to manipulate synchronous optical signals, such as generation of twin optical signals, data correction, signal transfer and amplification.