Quantum coherence dynamics of a three-level atom in a two-mode field

The correlated dynamics of a three-level atom resonantly coupled to an electromagnetic cavity field is calculated (Lambda, V, and L models). A diagrammatic representation of quantum dynamics is proposed for these models. As an example, Lambda-atom dynamics is examined to demonstrate how the use of conventional von Neumann's reduction leads to internal decoherence (disentanglement-induced decoherence) and to the absence of atomic coherence under multiphoton excitation. The predicted absence of atomic coherence is inconsistent with characteristics of an experimentally observed atom-photon entangled state. It is shown that the correlated reduction of a composite quantum system proposed in [18] qualitatively predicts the occurrence and evolution of atomic coherence under multiphoton excitation if a seed coherence is introduced into any subsystem (the atom or a cavity mode).