Two-photon processes in faint biphoton fields
  The goal of this research is to determine and study a physical system that will enable a fast and intrinsically two-photon detector, which would be of interest for quantum information and metrology applications. We consider two types of two-photon processes that can be observed using a very faint, but quantum-correlated biphoton field. These are optical up-conversion and an external photoelectric effect. We estimate the correlation enhancement factor for the biphoton light compared to coherent light, report and discuss the preliminary experimental results. 
Dmitry V. Strekalov, Matt Stowe, Maria V. Chekhova and Jonathan P.   Dowling