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

Cryogenic Signal Processing based on Single-Flux-Quantum Circuit for Advanced Superconducting Nanostrip Single-Photon Detector Systems

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

Published Mar 19, 2024• 0 citations
Publisher

Abstract

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.

DOI
10.2221/jcsj.59.88

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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.
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.
We developed a monolithic integration process for a superconducting nanostrip single-photon detector (SNSPD) and a cryogenic signal processor based on a single-flux-quantum (SFQ) circuit. Sixteen-pixel SNSPDs consisting of a 10-nm-thick and 100-nm-wide NbTiN nanowire were fabricated on a 3-in. Si wafer with an SFQ merger fabricated by the National Institute of Advanced Industrial Science and Technology Nb 2.5 kA/cm2 standard process 2. Subsequently, we illuminated the photons on the 16-pixel SNSPD array through an optical fiber and obtained a similar bias-current dependence of the detection efficiency with a single-pixel SNSPD without the SFQ merger. This indicates that the SFQ merger works correctly, and that the power dissipation of the SFQ circuit, which is estimated to be 200 μW, does not deteriorate the photon detection of SNSPD fabricated on the same chip with a size of 5 × 5 mm2. Furthermore, we measured timing jitter using a pulsed laser as the photon source. Owing to the careful tuning of the wiring length between each pixel of the 16-pixel SNSPD and each input port of the SFQ merger, the obtained timing jitter was 41.4 ps, which is approximately equal to or less than that of the single-pixel SNSPD.
We demonstrated a coincidence circuit based on single flux quantum (SFQ) circuits with high-time accuracy for a two-photon interferometer using superconducting nanostrip photon detectors (SNSPDs). The coincidence circuit was designed to have 3 different time windows of 30 ps, 100 ps, and 200 ps, which can be selectable on demand. Furthermore, each time window can be fine-tuned by changing the applied bias currents. The circuit was fabricated by the AIST high-speed standard process based on Nb/AlOx/Nb junctions with critical current density of 10 kA/cm2. We experimentally evaluated the time window of the coincidence circuit at temperatures below 2.4 K in a 0.1-W Gifford-McMahon (GM) cryocooler.
The superconducting nanowire single-photon detector (SNSPD) is a leading technology for quantum information science applications using photons, and is finding increasing uses in photon-starved classical imaging applications. Critical detector characteristics, such as timing resolution (jitter), reset time, and maximum count rate, are heavily influenced by the readout electronics that sense and amplify the photon detection signal. We describe a readout circuit for SNSPDs using commercial off-the-shelf amplifiers operating at cryogenic temperatures. Our design demonstrates a 35 ps timing resolution and a maximum count rate of over 2 × 107 counts per second, while maintaining <3 mW power consumption per channel, making it suitable for a multichannel readout.
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.
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.