Phase-dependent electromagnetically induced transparency in a four-level atom system

Abstract

We present a method to control the electromagnetically induced transparency (EIT) in a four-level system with a coupling field, a weak probe field and two microwave driven fields. By sloving the density matrix equations, the numerious result is obtained. It is shown that the EIT resonance can be split into doublets and the spectral position of EIT window is determined by the relative phase between two microwave fields for fixed intensity of the microwave field. Therefore, the microwave field can be used to open more than one EIT window and by controlling their phase difference we can perform EIT frequency tuning. The structure in the spectrum can be explained using the dressed-state formalism.