Reducing multi-photon rates in pulsed down-conversion by temporal   multiplexing
  We present a simple technique to reduce the emission rate of higher-order photon events from pulsed spontaneous parametric down-conversion. The technique uses extra-cavity control over a mode locked ultrafast laser to simultaneously increase repetition rate and reduce the energy of each pulse from the pump beam. We apply our scheme to a photonic quantum gate, showing improvements in the non-classical interference visibility for 2-photon and 4-photon experiments, and in the quantum-gate fidelity and entangled state production in the 2-photon case. 
Matthew A. Broome, Marcelo P. Almeida, Alessandro Fedrizzi, Andrew G.   White
quant-ph physics.optics