Non-linear optics using cold Rydberg atoms
  The implementation of electromagnetically induced transparency (EIT) in a cold Rydberg gas provides an attractive route towards strong photon--photon interactions and fully deterministic all-optical quantum information processing. In this brief review we discuss the underlying principles of how large single photon non-linearities are achieved in this system and describe experimental progress to date. 
J. D. Pritchard, K. J. Weatherill and C. S. Adams
quant-ph physics.atom-ph