Photon-number-resolution with sub-30-ps timing using multi-element   superconducting nanowire single photon detectors
  A photon-number-resolving detector based on a four-element superconducting nanowire single photon detector is demonstrated to have sub-30-ps resolution in measuring the arrival time of individual photons. This detector can be used to characterize the photon statistics of non-pulsed light sources and to mitigate dead-time effects in high-speed photon counting applications. Furthermore, a 25% system detection efficiency at 1550 nm was demonstrated, making the detector useful for both low-flux source characterization and high-speed photon-counting and quantum communication applications. The design, fabrication and testing of this detector are described, and a comparison between the measured and theoretical performance is presented. 
Eric A. Dauler, Andrew J. Kerman, Bryan S. Robinson, Joel K. W. Yang,   Boris Voronov, Gregory Gol'tsman, Scott A. Hamilton,...