Realization of a resonant non-linear phase flip in cavity quantum   electrodynamics
  Optical nonlinearities sensitive to individual photons may be extremely useful as elements in quantum logic circuits for photonic qubits. A much cited example is the work of Turchette et al. [Phys. Rev. Lett. 75, 4710 (1995)], in which a phase shift of about 10 degrees was reported. To improve this result, we propose a single sided cavity geometry with minimal cavity losses. It should then be possible to achieve a nonlinear phase shift of 180 degrees. 
Holger F. Hofmann, Kunihiro Kojima, Shigeki Takeuchi, and Keiji Sasaki