Quantum beats in photon correlations of spontaneous emission from two nonidentical atoms

The appearance of quantum beats in a two-time second-order correlation function is discussed for the case of spontaneous emission from two nonidentical atoms. The atoms are separated by distances comparable with the resonance wavelength and have different transition frequencies and natural line widths. It is shown that quantum beats appear for nonidentical and identical atoms. In the latter case the dipole–dipole interaction between the atoms is a necessary condition for the appearance of quantum beats. Two mechanisms lead to quantum beats in the case of nonidentical atoms and such beats may appear even for independent atoms. The effect is similar to that of interference between independent beams.