Bright Integrated Photon-Pair Source for Practical Passive Decoy-State   Quantum Key Distribution
  We report on a bright, nondegenerate type-I parametric down-conversion source, which is well suited for passive decoy-state quantum key distribution. We show the photon-number-resolved analysis over a broad range of pump powers and we prove heralded higher-order $n$-photon states up to $n=4$. The inferred photon click statistics exhibit excellent agreements to the theoretical predictions. From our measurement results we conclude that our source meets the requirements to avert photon-number-splitting attacks. 
Stephan Krapick, Michael Stefszky, Michal Jachura, Benjamin Brecht,   Malte Avenhaus, Christine Silberhorn
quant-ph