DIRECT MEASUREMENT OF THE QUANTUM STATE OF RADIATION-FIELD FROM THE RESONANCE FLUORESCENCE-SPECTRUM

We show that, for a pure state, the quantum state of the radiation fie ld can be directly determined from the resonance fluorescence spectrum when the quantized field serves as the driving field for the two-leve l atoms. This happens when the vacuum Rabi frequency is much larger th an the atomic decay rate. The proposed method is insensitive to the de tector efficiency.