FPGA-based Single Photon Counting and Timing from an Array of Superconducting Nanowire Single Photon Detectors

Counting single photons and measuring their arrival time is of crucial importance for imaging, computing or communication applications that use single photons or few photons to outperform classical techniques. Single photons or pair of photons can for instance be used to enhance the resolution of optical imaging techniques [1], or to transmit information with ultimate security using quantum cryptography [2]. In order to maintain this performance gain in such applications, the exact number of photons and their arrival time must be measured and monitored. In this contribution, we present a method to measure the number of photons and their arrival time by using 16 Superconducting Nanowire Single Photon Detectors (SNSPDs) [3] optically coupled to a weak laser via a fiber multiplexer. Since a single SNSPD is not sensitive to the number of incoming photons, the optical signal multiplexing is necessary to measure photon correlations among the channels and thus reconstruct the statistics of the optical pulse. The readout and counting of the photon arrivals is performed with a fast multi-channel Asynchronous-Correlated-Digital-Counter (ACDC) [4] whereas the arrival time is measured by an high resolution multi-channel Time-to-Digital Converter (TDC) with resolution of 10 ps, full-scale-range of 640 ns and global precision guaranteed below 22 ps r.m.s. referred to each single channel [5, 6]. Both of the ACDC and the TDC are implemented in the Programmable Logic (PL) of a Xilinx Zynq®-7 XC7Z020 Xilinx System-of-Chip (SoC) device hosted in a customized acquisition board interfaced outside by means of a USB 3.0 communication gate.