Cooperative effects in the two atom resonance fluorescence spectrum

Abstract

We consider the resonance fluorescence spectrum of two similar interacting atoms in the limit of high photon densities. The excitation spectrum of the symmetric modes contains two sidebands in addition to the usual three peaks which are analogous to those of the isolated atom. These two new sidebands are due entirely to the cooperative behaviour of the two atoms and vanish when the atoms are far apart. The energy shifts and spectral widths for these two sidebands are two and five times larger than those for the isolated atom respectively. The probability of occurrence of these sidebands depends on the parameters VAB/Ω and γ20/Ω2, where VAB is the dipole-dipole interaction energy, γ0 is the spontaneous emission probability and Ω is the Rabi frequency. The asymmetric broadening of both sidebands depends on the parameter γ0/Ω. The possibility to measure the dipole-dipole energy through the observation of these sidebands is discussed.