The role of tunable nonlinear dark resonances on vacuum Rabi splitting and optical bistability in an atom-cavity system.

The phenomenon of "dark resonances" is a well-known concept in quantum optics and laser spectroscopy. As a general rule, interactions involving in such a "dark state" lead to multiple quantum superposition states that interact coherently and are undesirable. In this paper, two types nonlinear interaction in an atomic cavity, namely the nested and cascaded interactions, are theoretically analyzed how the dark resonances form the dark state peak to modulate the vacuum Rabi splitting (VRS) and optical bistability (OB) behavior. In both the zero- and high order modes, there are four VRS peaks generated in the nested interaction and three in the cascade interaction. Dark resonance can modulate not only the peak number of VRS, but also the OB thresholds. It is found that dark state can determine the asymmetric OB distribution of nested type and symmetric OB distribution of cascade type. Besides that, the distinctive OB thresholds in two kinds of interaction also be studied. The observations not only conceptually extend the conventional "dark resonances" phenomenon, but also opens the door for a variety of new applications in tunable all-optical switch and quantum communication.