Generating and manipulating beating signals by a microwave field in four-level cold atoms

Abstract

We propose an efficient scheme for the dynamic generation and manipulation of beating signals in a sample of cold atoms driven into the four-level quasi-Λ configuration. This scheme relies on a procedure of light storage and retrieval controlled by a classical coupling field with a microwave field introduced only in the retrieval stage. One quantum probe field, incident upon this atomic sample, is transformed into a collective excitation of atomic spin coherence and then into two optical components characterized by different time-dependent phases. Consequently the retrieved quantum probe field exhibits a series of maxima and minima (beating signals) in intensity due to the alternative constructive and destructive interference. This interesting phenomenon, in fact, involves the coherent conversion between single-mode and two-mode dark-state polaritons and could be explored to measure the microwave intensity with high-precision beating signals.