The quantum coherence as a phase property of the wave function

The quantum coherence as a phase property of the most fundamental quantum mechanical entity, the wave function, is explained for the first time. Phase-sensitive nonadiabatic dressed states, arising from the interaction of a quantum system and a coherent external electromagnetic field, are used in these considerations. Two types of phase correlations in the multilevel phase-sensitive nonadiabatic dressed states are found: a rapidly changing phase correlation between the real and the virtual components and a stationary phase correlation between different virtual components of these states.