Interplay of vacuum-mediated inter- and intraatomic couplings in a pair of atoms

The resonance fluorescence emitted by a system of two dipole-dipole interacting nearby four-level atoms in J=1/2 - J=1/2 configuration is studied. This setup is the simplest realistic model system which provides a complete description of the (interatomic) dipole-dipole interaction for arbitrary orientation of the interatomic distance vector, and at the same time allows for intraatomic spontaneously generated coherences. We discuss different methods to analyze the contribution of the various vacuum-induced coupling constants to the total resonance fluorescence spectrum. These allow us to find a dressed state interpretation of the contribution of the different interatomic dipole-dipole couplings to the total spectrum. We further study the role of the spontaneously generated coherences, and identify two different contributions to the single-particle vacuum-induced couplings. We show that they have a noticeable impact on the total resonance fluorescence spectrum down to small interatomic distances, even though the dipole-dipole couplings constants then are much larger in magnitude than the the single-particle coupling constants. Interestingly, we find that the interatomic couplings can induce an effect of the intraatomic spontaneously generated coherences on the observed spectra which is not present in single-atom systems.