CONDITIONAL RESONANCE-FLUORESCENCE SPECTRA OF SINGLE ATOMS

The temporal behavior of a single quantum system may contain informati on, for instance, about macroscopic dark periods in electron shelving, which is washed out or even lost in ensemble averages. The same is tr ue in principle for spectral information. For example, for an atom wit h light and dark periods one might try to spectrally analyze the light emitted in alight period of given length or, more generally, the ligh t emitted into one solid angle while monitoring the temporal emission in another solid angle. Considering different emission behaviors one m ay get different spectra, i.e., spectra that are dependent on the cond itions imposed. In this paper, such questions, in particular the notio n of spectrum in a light period, are studied. To this end we generaliz e the recent quantum jump approach to include resonance-fluorescence s pectra of single atoms. We explicitly show that the theory developed i n this paper easily generalizes, e.g., to absorption spectra. We apply the theory to a V system that has one metastable level and that may e xhibit intermittent fluorescence when driven by two lasers. We show th at the spectrum of resonance fluorescence of the complete ensemble dif fers substantially from that observed in a light period. A physical ex planation of this behavior is presented.