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Modified Superconducting Single-Flux Quantum Two-Photon Coincidence Correlator for Single-Photon Measurements

I. Komissarov, Amir Jafari Salim, Oleg A. Mukhanov, Timothy M. Rambo, Aaron Miller, Roman Sobolewski

Published Jan 1, 2024• 0 citations
Publisher

Abstract

A design and performance of a single-flux-quantum–based digital correlator is presented to trace independent signals from two superconducting single-photon detectors, triggering its inputs.
DOI
10.1364/cleo_at.2024.jw2a.89

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We present a single-flux-quantum (SFQ) based digital correlator to trace independent signals from two superconducting single-photon detectors (SSPDs) triggering its inputs. In our design two SSPDs are magnetically coupled to inputs of a readout system where direct current (DC)-to-SFQ converters are used to convert transient SSPD output pulses, triggered by detection of single-photon events, to SFQ pulses. The coincidence verification of SFQ pulses, generated by the two DC-to-SFQ converters, is performed with a modified SFQ coincidence buffer. The coincidence buffer is designed to generate an SFQ output pulse only when its both inputs are triggered simultaneously, or within a preset margin time. The output of the coincidence buffer is connected via, this time, an SFQ-to-DC converter, to a pulse counter operated at room temperature. We performed extensive simulations of both the SSPD equivalent circuit and correlator redout elements for the proposed coincidence scheme, using a WRSpice and PSCAN2 simulation platforms that are specifically designated to model Josephson junctions and widely used to simulate operation of the SFQ circuitry. In particular, we investigated our coincidence correlator scheme for measurements of the second-order correlation function, used to demonstrate the antibunching effect in the single-photon detection of non-classical light.
A readout circuit using superconducting single-flux-quantum (SFQ) circuits has been developed to realize an independently addressable array of superconducting single-photon detectors (SSPDs). We tested the SFQ readout circuits by connecting with SSPDs. The error rates of readout circuits were below 10−5 for input signal amplitude of greater than 18.2 μA. Detection efficiencies (DEs) for single-photon incidents were measured both with and without the connection of a readout circuit. The observed DEs traced almost the same curves regardless of the connection of the readout circuit, except that the SSPD is likely to latch by connecting the readout circuit.
We demonstrate the operation of a coincidence photon detector with a short timing jitter consisting of two superconducting nanowire single photon detectors (SSPDs) and a single flux quantum (SFQ) circuit. By utilizing the timing discrimination capability of the SFQ coincidence circuit, the full width at half maximum timing jitter of the entire coincidence photon detector was evaluated as 32.3 ps, which is 36 ps less than that of the standard commercial time correlated single photon counting module, and the timing jitter of the SSPD was estimated as ∼15 ps. Owing to the short timing jitter characteristics, our coincidence photon detector could correctly capture the effect of pulse-width broadening by insertion of an optical bandpass filter. We have also demonstrated that our coincidence photon detection clearly shows Hong-Ou-Mandel interference with a weak coherent pulse. These results are a crucial step to realizing high timing resolution coincidence measurements, ushering in a technology for timing measurement based multi-photon quantum interference.
We developed a single-flux-quantum (SFQ) readout technology for superconducting single-photon detectors (SSPDs) to achieve low-jitter signal readout. By optimizing circuit parameters of the SFQ readout circuit, the input current sensitivity was improved below 10 μA, which is smaller than a typical critical current of SSPD. The experiment using a pulse-pattern generator as an input pulse source revealed that the measured jitter of the SFQ readout circuit is well below the system jitter of our measurement setup for the input current level above 15 μA. The measured jitter of the SSPD connected to the SFQ readout circuit was 37 ps full width at half maximum (FWHM) for an SSPD bias current of around 18 μA, which is a significant improvement on 67 ps FWHM jitter observed in conventional readout without an SFQ readout circuit.
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In this work, we present a novel device that is a combination of a superconducting nanowire single-photon detector and a superconducting multilevel memory. We show that these devices can be used to count the number of detections through single-photon to single-flux conversion. Electrical characterization of the memory properties demonstrates single-flux quantum (SFQ) separated states. Optical measurements using attenuated laser pulses with different mean photon number, pulse energies and repetition rates are shown to differentiate single-photon detection from other possible phenomena, such as multiphoton detection and thermal activation. Finally, different geometries and material stacks to improve device performance, as well as arraying methods, are discussed.