Individual-particle addressing is a necessary capability in quantum information experiments.  We propose a simple method to spectrally resolve single-particles in a cold atomic system. The scheme uses a dressing field with a spatially-dependent coupling to the atoms. As a consequence,  the level spacing of each atom, in the dressed state picture,  become position dependent and individual atoms can be spectrally addressed.  We realized this scheme experimentally using a linear chain of trapped ions which were separated by ∼ 3 µm and dressed by a laser field that was resonant with the micro-motion sideband of a narrow optical transition. Here the spatially-varying coupling arose from the inhomogeneity of the ions’  micro-motion along the  chain.

N. Navon, S. Kotler, N. Akerman, Y. Glickman, I. Almog  and R. Ozeri,  arXiv:1210.7336 (2012).