QUANTUM INTERFERENCE EFFECTS IN THE AUTLER-TOWNES SPONTANEOUS SPECTRUM

The quantum interference effects in the Autler-Townes spectrum associa ted with the spontaneous emission between two levels in an atomic syst em are studied. It is shown that when the upper level is coupled by a coherent field to a third level, then the interference between two pro cesses of decay from two dressed upper levels to the same lower level results in a dark line in the spectrum. The presence of the dark line is independent of the Rabi frequency of the coherent field. By increas ing the detuning of the coherent field with the atomic transition, one of the two peaks in the Autler-Townes doublet becomes narrower while its height remains constant. On the other hand, when the lower level i s coupled by a coherent field to another level, there is no interferen ce, and consequently no dark line is present. In this case, by increas ing the detuning, the height of one of the two peaks is decreased whil e its width remains constant.