In a recent experiment we have investigated the interaction of a propagating few-photon field interacting with an single two-plus-one level system. The system was realized by collectively coupling thousands of atoms to a Rydberg state in order to form a Rydberg superatom.
A. Paris-Mandoki, C. Braun, J. Kumlin, C. Tresp, I. Mirgorodskiy, F. Christaller, H. P. Büchler, and S. Hofferberth
Free-Space Quantum Electrodynamics with a Single Rydberg Superatom
Phys. Rev. X 7, 41010 (2017)
It is open access in PRX btw.