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IEEE Transactions on Applied Superconductivity

SFQ Parallel Encoders Promising for Video Imaging With Superconductor Stripline Detectors

Masamitsu Tanaka, Misaki Kozaka, Kyohei Kamiya, Kubra Usenmez, Eren Can Aydogan, Sasan Razmkhah, Ali Bozbey, Akira Fujimaki

Published Jul 31, 2020• 6 citations
Publisher

Abstract

We report demonstration of a readout circuit with high-throughput single flux quantum (SFQ) based encoders for a large-scale video imaging system with a conventional frame rate. The encoders are fully parallel and integrated on the same chip as linear arrays of serially connected superconductor stripline detectors (SSLDs), superconducting quantum interference device (SQUID) based comparators, and SFQ synchronizers. Mutual coupling of parallel SSLDs and SQUID-based comparators allows the use of only one dc bias line; it is possible to use thousands of SSLDs without increasing the bias current or number of bias ports. To achieve crosstalk-free readout, the serially connected SSLDs are separated by low-pass filters or large inductors. We experimentally demonstrated crosstalk-free readout including SFQ parallel encoders from 1-D or 2-D serially connected SSLD arrays.

DOI
10.1109/tasc.2020.3013385

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We report demonstration of a readout circuit with high-throughput single flux quantum (SFQ) based encoders for a large-scale video imaging system with a conventional frame rate. The encoders are fully parallel and integrated on the same chip as linear arrays of serially connected superconductor stripline detectors (SSLDs), superconducting quantum interference device (SQUID) based comparators, and SFQ synchronizers. Mutual coupling of parallel SSLDs and SQUID-based comparators allows the use of only one dc bias line; it is possible to use thousands of SSLDs without increasing the bias current or number of bias ports. To achieve crosstalk-free readout, the serially connected SSLDs are separated by low-pass filters or large inductors. We experimentally demonstrated crosstalk-free readout including SFQ parallel encoders from 1-D or 2-D serially connected SSLD arrays.
We report successful demonstration of individual readout of the response to an optical signal in serially-connected superconducting strip line detectors (SSLDs). Based on the numerical analysis, placement of low-pass filters between adjacent SSLDs and use of a current-source drive enable serially-connected SSLDs to work as independent multiple SSLDs. This leads to reduction of the number of cables from room temperature electronics. We irradiate a laser just on a certain SSLD (SSLD#1) with On/Off modulation. Synchronized voltage output is obtained at only corresponding SQUID. Then we move the position of a laser spot on the neighbor SSLD (SSLD#2). The voltage disappears at the SQUID connecting to SSLD#1, and the voltage is developed only at the SQUID connecting to SSLD#2. We have also given a demonstration of readout using the single-flux-quantum circuits connected to the SQUIDs. We confirmed from those experimental results that our driving method for multiple SSLDs is effective not only to enhance detecting area but also to obtain position sensitivity.
Toward the realization of a large-scale superconducting nanowire single-photon detector (SSPD) array system, we present the parallel bias operation of an SSPD array in which all elements are simultaneously biased in parallel by a single voltage source. We fabricated an SSPD array with uniform quality and implemented the device with/without single-flux-quantum (SFQ) readout circuit in a compact 0.1 W Gifford-McMahon cryocooler. By applying the time-resolved readout setup, we measured histograms of time-correlated single-photon counts to verify the parallel bias operation of the SSPD array with conventional and SFQ readout techniques. As a result, we confirmed crosstalk-free parallel bias operation of the four-element SSPD array by conventional and SFQ readouts.
We propose a single-flux-quantum (SFQ) based event-driven encoder for a large-pixel superconducting nanowire single-photon detector (SSPD) array with a row-column readout architecture. The designed SFQ encoder can acquire time-tagged address data with a high time resolution. To apply 32 × 32 pixel SSPD system with a row-column architecture, the SFQ encoder is equipped with two 32-channel input ports among which one is for positive pulses, whereas the other is for negative pulses. The number of Josephson junctions (JJs) in the designed circuit is 2780. The power dissipation and required total bias current are 0.21 mW and 170 mA, respectively, owing to the reductions in critical currents of the JJs and bias resistors. The circuit generates time-tagged address data by applying electrical pulses at room temperature not only in liquid helium but also in a 0.1-W Gifford-McMahon (GM) cryocooler.
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.
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We report the operation of superconducting single photon detectors (SSPDs) with integrated readout electronics based on a single-flux-quantum (SFQ) circuit. The SSPDs were connected to a SFQ readout circuit without bias tee in a cryocooler system, and detection efficiencies (DEs) were measured to verify their correct operation. The DE curves matched well with those measured by conventional readout electronics, and the maximum bias current for normal operation was increased. In addition, we confirmed that the SFQ circuit correctly merged the input signals from two SSPDs. SSPDs with a SFQ readout circuit demonstrated a favorable timing jitter of 50 ps.