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Applied Physics Letters

Superconducting single photon detectors integrated with single flux quantum readout circuits in a cryocooler

Shigehito Miki, Hirotaka Terai, Taro Yamashita, Kazumasa Makise, Mikio Fujiwara, Masahide Sasaki, Zhen Wang

Published Sep 12, 2011• 55 citations
Publisher

Abstract

We report the operation of superconducting single photon detectors (SSPDs) with integrated readout electronics based on a single-flux-quantum (SFQ) circuit. The SSPDs were connected to a SFQ readout circuit without bias tee in a cryocooler system, and detection efficiencies (DEs) were measured to verify their correct operation. The DE curves matched well with those measured by conventional readout electronics, and the maximum bias current for normal operation was increased. In addition, we confirmed that the SFQ circuit correctly merged the input signals from two SSPDs. SSPDs with a SFQ readout circuit demonstrated a favorable timing jitter of 50 ps.

DOI
10.1063/1.3640503

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We report the operation of superconducting single photon detectors (SSPDs) with integrated readout electronics based on a single-flux-quantum (SFQ) circuit. The SSPDs were connected to a SFQ readout circuit without bias tee in a cryocooler system, and detection efficiencies (DEs) were measured to verify their correct operation. The DE curves matched well with those measured by conventional readout electronics, and the maximum bias current for normal operation was increased. In addition, we confirmed that the SFQ circuit correctly merged the input signals from two SSPDs. SSPDs with a SFQ readout circuit demonstrated a favorable timing jitter of 50 ps.
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.
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.
Superconducting single-photon detectors (SSPDs) based on NbN nanowires possess properties such as high counting rate, low dark count rate and small timing jitter, which are promising characteristics for a quantum key distribution system. An SSPD array has recently attracted attention, because it can provide a higher counting rate, and spatial and photon-number resolutions. We propose readout electronics using single-flux-quantum (SFQ) circuits to process a large number of output signals from an SSPD array. We designed and tested an interface circuit between an SSPD and SFQ circuit, and successfully observed SFQ pulse generation for an input pulse with a current amplitude of 17.4 ~ 36.4 muA , which is comparable with an output current amplitude of the SSPD. The interface circuit was also operational for an input pulse duration of 1.6 ns, which is shorter than the typical recovery time of the SSPD.
We demonstrate the successful operation of a multielement superconducting nanowire single-photon detector (SSPD) array integrated with a single-flux-quantum (SFQ) readout circuit in a compact 0.1 W Gifford-McMahon cryocooler. A time-resolved readout technique, where output signals from each element enter the SFQ readout circuit with finite time intervals, revealed crosstalk-free operation of the four-element SSPD array connected with the SFQ readout circuit. The timing jitter and the system detection efficiency were measured to be 50 ps and 11.4%, respectively, which were comparable to the performance of practical single-pixel SSPD systems.
We demonstrate the successful operation of a multi-element superconducting nanowire single-photon detector (SSPD) array integrated with a single-flux-quantum (SFQ) readout circuit in a compact 0.1 W Gifford-McMahon cryocooler. A time-resolved readout technique, where output signals from each element enter the SFQ readout circuit with finite time intervals, revealed crosstalk-free operation of the four-element SSPD array connected with the SFQ readout circuit. The timing jitter and the system detection efficiency were measured to be 50 ps and 11.4%, respectively, which were comparable to the performance of practical single-pixel SSPD systems.
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.