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Superconductor Science and Technology

Cryogenic readout of superconducting nanowire single-photon detectors using high-sensitivity adiabatic quantum-flux-parametron circuits

Fumihiro China, Naoki Takeuchi, Shigehito Miki, Masahiro Yabuno, Shigeyuki Miyajima, Hirotaka Terai

Published Feb 18, 2021• 7 citations
Publisher

Abstract

Abstract We have been developing readout interfaces for superconducting nanowire single-photon detectors (SSPDs) using adiabatic quantum-flux-parametron (AQFP) logic. AQFP circuits operate with low power consumption, low bias currents, and high sensitivity, and thus are suitable as readout interfaces for large SSPD arrays. In this study, we develop a high-sensitivity AQFP interface, consisting of a current transformer, comparator, and rising-edge detector. We systematically investigated the current sensitivity of the AQFP interface by operating an NbTiN SSPD with the interface in a 0.1 W Gifford–McMahon cryocooler. We compared the outputs from the AQFP interface with the direct outputs from the SSPD, thereby demonstrating a sensitivity of 3.5 μ A, which is much smaller than that of the single-flux-quantum interfaces that we developed before.

DOI
10.1088/1361-6668/abe7ac

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Abstract We have been developing readout interfaces for superconducting nanowire single-photon detectors (SSPDs) using adiabatic quantum-flux-parametron (AQFP) logic. AQFP circuits operate with low power consumption, low bias currents, and high sensitivity, and thus are suitable as readout interfaces for large SSPD arrays. In this study, we develop a high-sensitivity AQFP interface, consisting of a current transformer, comparator, and rising-edge detector. We systematically investigated the current sensitivity of the AQFP interface by operating an NbTiN SSPD with the interface in a 0.1 W Gifford–McMahon cryocooler. We compared the outputs from the AQFP interface with the direct outputs from the SSPD, thereby demonstrating a sensitivity of 3.5 μ A, which is much smaller than that of the single-flux-quantum interfaces that we developed before.
We propose and demonstrate a low-power and low-current cryogenic readout interface for a superconducting nanowire single-photon detector (SSPD) using adiabatic quantum-flux-parametron (AQFP) logic. The AQFP readout interface samples and digitizes the current signal from an SSPD, generating binary output data in accordance with the detection behavior of the SSPD. We demonstrate the correct operation of an SSPD with the interface, where the AQFP readout interface and the SSPD are placed in separate 0.1-W Gifford–McMahon (GM) cryocoolers and are interconnected via coaxial cables. It was found that the temperature of the sample stage did not change even after the AQFP readout interface was turned on, which revealed that the AQFP readout interface uses sufficiently low power and current for a compact cryocooler.
Superconducting nanowire single-photon detectors (SSPDs or SNSPDs) have superior performance and are thus used for many applications, such as quantum information and laser communications. Lately, much effort has been spent on the development of multi-pixel SSPD arrays to achieve single-photon-level imaging. SSPD arrays require efficient readout schemes that reduce the number of coaxial cables for reading out the SSPD pixels. In a previous study, we proposed a readout interface using adiabatic quantum-flux-parametron (AQFP) logic, which digitizes the information of an SSPD at cryogenic temperature. In this study, we show the first demonstration of an SSPD that is read out by the AQFP readout interface placed in the same 0.1-W Gifford-McMahon cryocooler. The measurement results show that the AQFP readout interface reads out the SSPD with low error rates. Also, it is found that the temperature of the sample stage does not change even after the AQFP readout interface is turned on, which indicates that the power and current required for the AQFP readout interface are sufficiently low for the implementation using a compact cryocooler.
Adiabatic quantum-flux-parametron (AQFP) circuits can operate with extremely small energy dissipation (∼1 zJ per junction at 5 GHz) and high sensitivity (∼1 μA) owing to adiabatic switching. Thus, AQFP logic is suitable to use as readout interfaces for cryogenic detectors, such as superconducting nanowire single-photon detectors (SSPDs). In order to extend the application of AQFP logic to various detectors, it is crucial to achieve even better sensitivity because some detectors, such as WSi SSPDs and transition edge sensors (TESs), require sub-μA sensitivity. In the present study, we propose a high-sensitivity AQFP comparator with a current transformer (CT), which increases the equivalent input current and thereby improves the sensitivity. Numerical simulation shows that the proposed comparator achieves a sensitivity approximately six times better than that of a conventional AQFP comparator. Furthermore, we demonstrate a sensitivity of 46 nA at 4.2 K for a sampling frequency of 500 Hz in the experiment.
We propose a scalable readout interface for superconducting nanowire single-photon detector (SSPD) arrays, which we call the AQFP/RSFQ interface. This interface is composed of adiabatic quantum-flux-parametron (AQFP) and rapid single-flux-quantum (RSFQ) logic families. The AQFP part reads out the spatial information of an SSPD array via a single cable, and the RSFQ part reads out the temporal information via a single cable. The hybrid interface has high temporal resolution owing to low timing jitter in the operation of the RSFQ part. In addition, the hybrid interface achieves high circuit scalability because of low supply current in the operation of the AQFP part. Therefore, the hybrid interface is suitable for handling many-pixel SSPD arrays. We demonstrate a four-pixel SSPD array using the hybrid interface as proof of concept. The measurement results show that the hybrid interface can read out all of the pixels with a low error rate and low timing jitter.
We present the development of key technologies for realization of superconducting nanowire single photon detector array system, which enables high counting rates, and allow spatial and pseudo photon number resolution. Toward the realization of practical large-scale SSPD array system, primary issue is how to avoid heat flow into cryocooler system. One of the challenging tasks is the development of their readout electronics. In the conventional readout technique used for single pixel devices, the number of high-frequency coaxial cables increases proportionally with the number of arrays. This causes a significant increase in the heat load from room temperature, which makes the implementation of the SSPD arrays in a compact refrigerator difficult. To overcome this problem, we proposed applying readout electronics with superconducting single-flux-quantum (SFQ) logic circuitsWe show the implementation and successful operation of four pixels SSPD array connected to SFQ readout electronics with parallel bias scheme in a 0.1W GM cryocooler system.
Superconducting nanowire single-photon detectors (SSPDs) with a system detection efficiency (SDE) of over 80% are now commercially available and being used in compact Gifford-McMahon refrigerators. However, not only high SDE, but also total performance including a low dark count rate, high maximum count rate and/or low timing jitter are important for many applications. A multi-pixel SSPD combined with signal processing using a single-flux-quantum (SFQ) circuit is a very promising approach to improve the system performance of SSPDs. In this review, we introduce our recent activities on cryogenic signal processing using SFQ circuits to realize high-performance multi-pixel SSPDs.