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TEION KOGAKU (Journal of Cryogenics and Superconductivity Society of Japan)

Superconducting Single-Flux-Quantum Logic Circuit

Hirotaka Terai, Taro YAMASHITA, Shigehito Miki, Kazumasa Makise, Zhen WANG

Published Jan 1, 2013• 0 citations
Publisher

Abstract

The superconducting single-flux-quantum (SFQ) circuit is the ultimate energy-efficient digital circuit technology. The SFQ circuits are very promising for applications not only to huge systems such as supercomputers and/or high-end routers but also to the signal processing circuit operating with superconducting detectors. We introduce the recent progress in the SFQ circuit technology focusing on the application combined with superconducting single-photon detectors (SSPDs). The four-pixel SSPD array was successfully operated with the SFQ signal processing circuit in the 0.1 W Gifford McMahon refrigerator.

DOI
10.2221/jcsj.48.77

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The superconducting single-flux-quantum (SFQ) circuit is the ultimate energy-efficient digital circuit technology. The SFQ circuits are very promising for applications not only to huge systems such as supercomputers and/or high-end routers but also to the signal processing circuit operating with superconducting detectors. We introduce the recent progress in the SFQ circuit technology focusing on the application combined with superconducting single-photon detectors (SSPDs). The four-pixel SSPD array was successfully operated with the SFQ signal processing circuit in the 0.1 W Gifford McMahon refrigerator.
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.
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.
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.
Single flux quantum (SFQ) logic circuits, in which a single flux quantum is used for an information carrier, have a possibility to open a new digital system operated with over 100 GHz clock frequencies at extremely low power dissipations. Recently, much progress in basic technologies for designing SFQ circuits and operating circuits with high speeds has been done. By taking advancements in these designing tools, circuits including more than several thousands junctions easily operated with the clock frequency of more than several tens GHz. Applications of SFQ circuits such as high performance computers, high end router and high end servers are being developed in the world taking advantages of the high through-put nature and the low power dissipation of the SFQ logic.
Single-flux quantum logic (SFQ) circuits, in which a flux quantum is used as an information carrier, have the possibility for opening the door to a new digital system operated at over 100-GHz clock frequency at extremely low power dissipation. The SFQ logic system is a so-called pulse logic, which is completely different from the level logic for semiconductors like CMOS, so circuit design technologies for SFQ logic circuits have to be newly developed. Recently, much progress in basic technologies for designing SFQ circuits and operating circuits at high speeds has been made. With advances in these design tools, large-scale circuits including more than several thousand junctions can be easily operated with the clock frequency of more than several tens of gigahertz. High-end routers and high-end computers are possible applications of SFQ logic circuits because of their high throughput nature and the low power dissipation of SFQ logic. In this paper, recent advances of SFQ circuit design technologies and recent developments of switches for high-end routers and microprocessors for high-end computers that are considered possible applications for SFQ logic will be described.
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.