Title:

"Strong photon-photon interactions using Rydberg atoms"

Abstract

We realize effective interactions between propagating photons by coupling light to highly-excited atoms (Rydberg atoms) in a gas. We use ultracold atomic ensembles, warm atomic vapors in micro-cells and around tapered optical fibers, and (in the near future) ordered arrays of single trapped atoms. In the regime of strong photon-photon interaction, we observe two-photon (conditional) phase shifts exceeding pi, photonic bound states, genuine three-photon interaction, and the formation of optical quantum vortices.