Maximum count rate of large area superconducting single photon detectors

An analysis of different strategies for increasing the maximum count rate of superconducting single photon detectors using parallel nanowires is performed with particular emphasis on the expected behaviour when the detector area is increased. We find that for a serial connection of blocks of parallel nanowires, the maximum count rate decreases with the square root of the detector area, whereas it decreases proportional to the detector area for current meandered detectors. Using this design we estimate that a signal pulse falltime of 7.8 ns for a 84 × 84 µm2 parallel detector based on current material parameters should be obtainable. We argue that the slow decrease of count rate with detector area might permit detectors based on parallel nanowires to fully exploit the available cooling power.