Dressed state "engineering" with double-dark states: experimental observation of hyper-Raman transitions

Summary form only given. Dark states are coherent superpositions of metastable states in multilevel systems that can be generated by a pair of electromagnetic fields (e.g. by probe and pump fields), but are not coupled by the fields. As a rule, any perturbations of such a state are undesirable, since they result in reduction of coherence. However, it has been recently predicted that coherent perturbation of the dark state does not necessarily lead to simple destruction of coherence. In the case when a third meta-stable state coupled by a weak radio frequency (RF) field additional sharp resonances on the spectrum displaying electromagnetically induced transparency (EIT, dashed line) have been predicted. This phenomenon is a generalization of the well-known EIT concept to higher-order hyper-Raman transitions.