Source: Nanowerk December 15,2017
A team of researchers in the US (Duke University, Ohio State University, industry) used the superconducting nanowire single-photon detector (SNSPD) method to show multi-photon detection indicating number resolution up to four photons. They paid special attention to the specific shape of the initial spike in the electrical signal to correctly count at least four photons traveling together in a packet. Photon-number-resolution is very useful for a lot of quantum information/communication and quantum optics experiment; it could greatly increase the speed of quantum encryption techniques… read more.  Open Access TECHNICAL ARTICLE
The image depicts three photons passing through a superconducting nanowire, causing the nanowire to heat up and disrupting the super-current. (Image: Duke University)