Fluorescence spectrum quantum interference

Another area of interest in quantum interference effects, which has been studied extensively, is the response of a V-type three-level atom to a coherent laser field directly coupled to the decaying transitions. This was studied by Cardimona et al. [36], who found that the system can be driven into a trapping state in which quantum interference prevents any fluorescence from the excited levels, regardless of the intensity of the driving laser. Similar predictions have been reported by Zhou and Swain [5], who have shown that ultrasharp spectral lines can be predicted in the fluorescence spectrum when the dipole moments of the atomic transitions are nearly parallel and the fluorescence can be completely quenched when the dipole moments are exactly parallel. 

It is important to note, that this line narrowing effects only occur if the phase of the decaying signal is preserved. This is always the case when the detection is based on interference effects, such as level crossing, quantum beats or interferometric detection, if the shutter is placed behind the interference device. For these examples the cosine Fourier transform can be measured separately. If, however, the detection only measures the power spectrum of the fluorescence, without phase information, the signal is represented by... 

---