Controlling Quantum Interference by Using a Driving Laser Field in the Four-level Ladder-vee Type Atomic System

The light-atom interaction in the four-level atomic system under a ladder-vee type configuration using the density matrix approach was investigated. The weak probe transmission signal is strongly driven by two intense lasers. Electromagnetically induced transparency (EIT) is suppressed, then switched completely to electromagnetically induced absorption (EIA) as increasing one of the driving intensity. The whole transforming process corresponding to three domains of driving Rabi frequency will be discussed. The weak field domain results in purely EIT reduction. The turning range brings about EIT suppression accompanied by EIA enhancement. The strong field regime causes EIA reduction and Autler-Townes splitting. Our analyses reveal the involvement of quantum interference in the course of EIT and EIA, which is distinguishable from the consequence of Autler-Townes splitting. Additionally, we found that there exists a critical point of coupling Rabi frequency for which the rate of transforming EIT to EIA is sensitive to the driving intensity. For the coupling Rabi frequency below this critical value, the initial EIA appears at resonance, it otherwise emerges on both sides of the resonance.