Quantum interference in a Λ system using a low frequency driving field

We investigate the quantum interference effects in a cyclic three-level system with a microwave field driving transition between two low levels. By solving the relative density matrix equations of motion, we obtain the absorption profile of the probe field and identify the conditions under which gain may develop. We demonstrate numerically that the absorption line shape depends on the ratio of the intensities of coupling and driving microwave field. When the intensity of coupling field. is much weaker than that of driving field, there is a multi-EITs in the probe absorption spectrum. However, if the intensity of both fields is strong; amplification without inversion occurs in different regime of probe frequency. In addition, we predict that larger amplification is obtained when the coupling field is detuned from exact resonance.