A photon number resolving detector system includes a photon source positioned at an input end, first and second photon detectors positioned at a detection end, and a plurality of optical couplers positioned between the input and detection ends. The plurality of optical couplers include an initial optical coupler optically coupled to the photon source, a final optical coupler optically coupled to the first and second photon detectors, and intermediate optical couplers positioned between the initial optical coupler and the final optical coupler. A first input link is optically coupled to the photon source and the initial optical coupler and a plurality of dual path spans are optically coupled to adjacent optical couplers. The plurality of dual path spans each include an undelayed path having an undelayed fiber link and a delayed path having a quantum memory positioned between and optically coupled to input and output sub-links.