Optical Fock-state synthesizer
  We suggest a tunable optical device to synthesize Fock states and their superpositions starting from a coherent source. The scheme involves an avalanche triggering photodetector and a ring cavity coupled to a traveling wave through a cross-Kerr medium. Low quantum efficiency at the photodetector improves the synthesizing quality at the expense of reducing the synthesizing rate. 
G. M. D'Ariano, L. Maccone, M. G. A. Paris, and M. F. Sacchi