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arXiv:2010.13584 · IEEE Transactions on Applied Superconductivity

An Adiabatic Superconductor Comparator With 46 nA Sensitivity

Naoki Takeuchi, Taiki Yamae, Hideo Suzuki, Nobuyuki Yoshikawa

Published Feb 24, 2021• 8 citations
arXivHTMLPDF

Abstract

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.

DOI
10.1109/tasc.2021.3061947

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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.
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.
Abstract We report on the design and implementation of adiabatic quantum flux parametron (AQFP) buffer gates utilizing cross-type Nb/AlO x /Nb Josephson junctions with I C of 20 μ A, designed to operate at mK temperatures. We, therefore, discuss design considerations, circuit simulation and optimization and their technological implementation. The preliminary results of the test circuit at 4.2 K are demonstrated focusing on the performance. Particularly, we emphasize on the current sensitivity of the circuit based on the output switching probability. The measurement results, show a narrow grayzone width of 0.48 μ A for low-speed operation, demonstrating a higher current sensitivity. Additionally, the designed AQFP circuit exhibits a wide operating margins, further endorsing their potential for high sensitivity based superconducting sensors and scalable interface circuits for quantum electronics.
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.
Adiabatic quantum-flux-parametron (AQFP) circuits are very low-power due to zero static power consumption and adiabatic switching operations. However, compared to other superconducting circuits, such as rapid single-flux-quantum logic, the operation frequency is relatively low and the latency is relatively large. In this work, we propose multi-excitation AQFP (ME-AQFP) circuits for high-speed and low-latency operations. In ME-AQFP, the intrinsic periodicity of the potential energy of a Josephson device with respect to applied magnetic fluxes is utilized to multiply operation frequencies and reduce latency. In a numerical simulation, we demonstrated an ME-AQFP AND gate, which operates at 10 GHz or 20 GHz with 5-GHz excitation currents. We also evaluated the energy efficiency of ME-AQFP circuits. In an experiment, we successfully demonstrated an ME-AQFP XOR gate and an ME-AQFP full adder.