Giant nonlinearity and entanglement of single photons in photonic   bandgap structures
  Giantly enhanced cross-phase modulation with suppressed spectral broadening is predicted between optically-induced dark-state polaritons whose propagation is strongly affected by photonic bandgaps of spatially periodic media with multilevel dopants. This mechanism is shown to be capable of fully entangling two single-photon pulses with high fidelity. 
I. Friedler, G. Kurizki and D. Petrosyan