Resonance fluorescence of a two-level atom excited by a superposition of coherent states, and the instability of the average atomic dipole moment

We find the evolution of average atomic variables in the resonance fluorescence of a two-level atom excited by a superposition of coherent states shifted in phase by pi. A new effect is predicted, the quantum instability of the average atomic dipole moment, with a strong correlation between atom and field being the reason. We propose different ways of verifying the effect in experiments involving high-e optical and microwave cavities. (C) 1997 American Institute of Physics.