Reconfigurable Superconducting Logic for On-Chip Photon Coincidence Detection

Scaling photonic quantum-information platforms requires arrays of superconducting nanowire single-photon detectors (SNSPDs) for feedforward control, in which optical operations are conditioned on preceding Bell-state measurements that typically rely on photon coincidence detections. On-chip superconducting cryotron electronics, performing logic directly on detector outputs and subsequently driving optical modulators, could substantially reduce latency and room-temperature interconnect complexity for feedforward schemes. To date, no cryotron logic gates specifically designed to process SNSPD outputs for quantum applications have been demonstrated. We demonstrate a bias-programmable logic gate based on three nanocryotrons (nTrons), fabricated using the same thin-film technology as SNSPDs. The circuit implements selectable AND (coincidence), XOR (odd-parity), and OR functions on two externally generated electrical pulses at 4.2 K, with bit-error rates below $10^{-3}$, bias margins up to $\pm24\%$, and operation extending to 25 MHz over narrower bias windows. Moreover, it performs coincidence and odd-parity detection on two co-fabricated SNSPDs' outputs with bit-error rates below $3.2 \times 10^{-2}$. As a proof-of-concept, we show that nTrons can drive capacitive loads up to 1.15 V, potentially enabling compatibility with electro-optic modulators in feedforward schemes.