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Quantum Optics and Photon Counting

Electrical testing of SNSPD-SFQ two-photon coincidence correlator

Roman Sobolewski, I. Komissarov, Amir Jafari Salim, Jason Walter, Daniel T. Yohannes, Oleg A. Mukhanov, Andrei Talalaevskii, Elie K. Track, Timothy M. Rambo, Aaron Miller

Published Jun 6, 2025• 1 citation
Publisher
DOI
10.1117/12.3059863

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We present a two-signal single flux quantum (SFQ) detection scheme for the purpose of reading out two pixels of a superconducting nanowire single photon detector (SNSPD). The circuit is based on a coincidence buffer element which is able to output a signal when both of its input lines are triggered. The circuit model for the SNSPD element is simulated in SPICE and optimized to match the experimental SNSPD response data. The two-signal detection scheme is simulated using JSIM which allows for the simulation of Josephson junction elements in a circuit. We demonstrate a model of the two-signal circuit operating with two simulated SNSPD pixel inputs and investigate the response of the scheme when a phase shift is applied to one of the inputs. The scheme shows potential as a useful coincidence detector of single photons. We also present preliminary experimental results of nanobridge-based Josephson junctions to be used in the realization of the coincidence detector circuit. Evidence of the nanobridges exhibiting Josephson behavior (SQUID modulation) are presented.
We demonstrate the transfer of single photon triggered electrical pulses from a superconducting nanowire single photon detector (SNSPD) to a single flux quantum (SFQ) pulse. We describe design and test of a digital SFQ based SNSPD readout circuit and demonstrate its correct operation. Both circuits (SNSPD and SFQ) operate under the same cryogenic conditions and are directly connected by wire bonds. A future integration of the present multi-chip configuration seems feasible because both fabrication process and materials are very similar. In contrast to commonly used semiconductor amplifiers, SFQ circuits combine very low power dissipation (a few microwatts) with very high operation speed, thus enabling count-rates of several gigahertz. The SFQ interface circuit simplifies the SNSPD readout and enables large numbers of detectors for future compact multi-pixel systems with single photon counting resolution. The demonstrated circuit has great potential for scaling the present interface solution to 1,000 detectors by using a single SFQ chip.
A single-flux-quantum circuit is a promising device for a cryogenic signal processor for a superconducting nanostrip single photon detector （SNSPD） due to its high-speed operation, low power dissipation, and low timing jitter. The cryogenic signal processor based on the SFQ circuits can sense the output signals of multi-pixel SNSPDs with low timing jitter in a low temperature stage, which provides an advanced SNSPD system such as a high-count rate system, a two-photon coincidence system, a single-photon imaging system, and so forth. We have developed and demonstrated some SNSPD systems using an SFQ signal processor in a 0.1-W Gifford-McMahon （GM） cryocooler. In this review, we introduce a cryogenic signal processor based on SFQ circuits for advanced SNSPD systems.