Transient dynamics of bichromatically driven two-level atoms

We experimentally investigate the transient dynamics of two-level atoms under bichromatic optical excitation. Novel new dynamical behavior is observed that may be interpreted classically in terms of the vector model or in a modem vein as resonant monochromatic excitation of dressed atoms. We show the first observation of dressed-atom optical mutations. We also show that the system dynamics depend critically on the initial relative phase of the two excitation-field components and that controlled bichromatic excitation may lead to complete dressed-state polarization of initially ground-state atoms