Signatures of single-site addressability in resonance fluorescence spectra

Pioneering methods in recent optical-lattice experiments allow focusing laser beams down to a spot size that is comparable to the lattice constant. Inspired by this achievement, we examine the resonance fluorescence spectra of two-level atoms positioned in adjacent lattice sites and compare the case where the laser hits only one atom (single-site addressing) with cases where several atoms are illuminated. In contrast to the case where the laser hits several atoms, the spectrum for single-site addressing is no longer symmetric around the laser frequency. The shape of the spectrum of fluorescent light, therefore, can serve as a test for single-site addressing. The effects we find can be attributed to a dipole-dipole interaction between the atoms due to the mutual exchange of photons.