An Adiabatic Superconductor Comparator With 46 nA Sensitivity

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.

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

“…We confirmed a wide plateau region for each I x , while the width of the plateau region slightly depends on the amplitude of I x . The I x dependence of plateau regions might be due to the speed dependence of the AQFP comparators' sensitivity [31]. As the amplitude of I x increases, the circuit state of the AQFP comparator changes more quickly, resulting in a deterioration in sensitivity.…”

“…Thus, the output logic of an AQFP comparator is stochastically determined by thermal noise when |I in | is less than approximately ∆I [33]. To improve the input current sensitivity, a current transformer comprising L 1 , L 2 , and k is added to the input port of the AQFP comparator [31]. Accordingly, the current signal from an SSPD (I sspd ) is increased by n times, i.e.…”

“…In this paper, we investigate the sensitivity of an AQFP interface to show the minimum output current from an SSPD that the AQFP interface can digitize. We utilize a high-sensitivity AQFP interface with a current transformer [31], with which an AQFP comparator showed a potential sensitivity of 46 nA for a DC input current and low operating frequency of 500 Hz. We conduct experiments by implementing this interface and an SSPD in the same 0.1 W Gifford-McMahon (GM) cryocooler for a high operating frequency of 100 MHz.…”

Adiabatic Quantum-Flux-Parametron: A Tutorial Review

“…4. We have demonstrated a highsensitivity AQFP comparator with a sensitivity of 46 nA [93]. High-sensitivity circuits enable the analog-todigital conversion of tiny signal currents from cryogenic detectors, such as superconducting nanowire singlephoton detectors (SSPDs or SNSPDs) [94,95], inside a cryocooler.…”