SFQ Amplified Circuit for Photon-Number-Resolving SNSPD Array

Superconducting nanowire single-photon detectors (SNSPDs) with series-parallel meander-type configuration are demonstrated to have photon-number- resolving (PNR) capabilities. Based on this unique feature, SNSPDs are expected to be used in the evaluation of single photon sources. However, increasing the number of SNSPDs causes an increase in the heat flow and further degradation in the timing jitter. To resolve this problem, the use of single flux quantum (SFQ) logic circuits is proposed. In this study, we present the read-out circuit for the SNSPD array, based on the SFQ logic. Our design of the read- out circuit makes it feasible to simultaneously process six SNSPD signals at 500 MHz and amplify the output voltage as an input to other circuits without the need for any amplifiers. We confirm using simulations that our designed read-out circuit has these capabilities. Furthermore, it is shown that the output voltage increases by 4.8 mV, proportional to the number of SNSPD signals and the output voltage is between 4.8 and 27.8 mV.