Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

IEEE Transactions on Applied Superconductivity

Demonstration of Picosecond Time Resolution in Double-Oscillator Time-to-Digital Converter Using Single-Flux-Quantum Circuits

Yuma Tomitsuka, Yuki Yamanashi, Nobuyuki Zen, M. Ohkubo, Nobuyuki Yoshikawa

Published Mar 1, 2019• 6 citations
Publisher

Abstract

We have been developing a time-to-digital converter (TDC) using single-flux-quantum (SFQ) circuits in order to realize an imaging system based on a superconducting strip single-photon detector (SSPD). In this system, the absorption position of a single photon in a meander-shaped SSPD is determined by measuring the delay time of the detected signal propagating through an SSPD delay line. Increasing the time resolution of the TDC is the primary concern for improving the spatial resolution of the system. Here we focused on the double-oscillator SFQ TDC, where the difference of oscillation periods between two SFQ ring oscillators determines the time resolution. In the previous study, a time resolution of about 4 ps was demonstrated by using the Nb standard Josephson integrated circuit (IC) process with a critical current density of 2.5 kA/cm2. In this study, we improved the time resolution by adopting the Nb advanced Josephson IC process with a critical current density of 10 kA/cm2and by optimizing the circuit parameters of the coincidence detector. The histogram and the linearity of the delay measurements show that the time resolution is improved to up to 2 ps.

DOI
10.1109/tasc.2019.2902478

Related papers

Direct measurements of propagation delay of single-flux-quantum circuits by time-to-digital converters

Kazunori Nakamiya, Nobuyuki Yoshikawa, Akira Fujimaki +2 more

Direct measurements of propagation delay of single-flux-quantum (SFQ) circuits were performed using SFQ double-oscillator time-to-digital converters. The propagation delay of several SFQ logic gates in our cell library named CONNECT were measured in picosecond resolution. Small discrepancy in the propagation delay of picosecond level was observed between measurement and circuit simulation results. The discrepancy is well explained assuming the parasitic inductance around shunt resistors of Josephson junctions.

IEICE Electronics Express•Jan 1, 2008•5 citations

Design and Demonstration of a Single-Flux-Quantum Multi-Stop Time-to-Digital Converter for Time-of-Flight Mass Spectrometry

Kyosuke Sano, Yuki Yamanashi, Nobuyuki Yoshikawa

We have been developing a superconducting time-of-flight mass spectrometry (TOF-MS) system, which utilizes a superconductive strip ion detector (SSID) and a single-flux-quantum (SFQ) multi-stop time-to-digital converter (TDC). The SFQ multi-stop TDC can measure the time intervals between multiple input signals and directly convert them into binary data. In this study, we designed and implemented 24-bit SFQ multi-stop TDCs with a 3×24-bit FIFO buffer using the AIST Nb standard process (STP2), whose time resolution and dynamic range are 100ps and 1.6ms, respectively. The timing jitter of the TDC was investigated by comparing two types of TDCs: one uses an on-chip SFQ clock generator (CG) and the other uses a microwave oscillator at room temperature. We confirmed the correct operation of both TDCs and evaluated their timing jitter. The experimentally-obtained timing jitter is about 40ns and 700ps for the TDCs with and without the on-chip SFQ CG, respectively, for the measured time interval of 50µs, which linearly increases with increase of the measured time interval.

IEICE Transactions on Electronics•Jan 1, 2014•10 citations

Timing Jitter Characterization of the SFQ Coincidence Circuit by Optically Time-Controlled Signals From SSPDs

Shigehito Miki, Shigeyuki Miyajima, Masahiro Yabuno +7 more

We report on the timing jitter characterization of the superconducting single flux quantum (SFQ) coincidence circuit, which is an essential component of the superconducting coincidence photon counter. Two superconducting nanowire single photon detectors (SSPDs), each of which is irradiated with optically time-controlled photons, are connected to the SFQ coincidence circuit, and the timing jitter of the SFQ circuit is evaluated by changing the relative time delay between two input ports for the SFQ comparator unit. We successfully observe the transition curve of the probability of obtaining the signal from the SFQ coincidence circuit by sweeping photon arrival time to each SSPD and confirm that this curve shifts temporally upon changing the bias current to the Josephson transmission line (JTL) in the SFQ circuit. A systematic investigation reveals that the relation between time delay and the bias current to JTL can be estimated. The full width half maximum timing jitter of the SFQ circuit is 1.1 ps, which is sufficiently low so that it does not influence the entire timing jitter of the coincidence photon counter.

IEEE Transactions on Applied Superconductivity•Apr 15, 2019•2 citations

Design of integrated SSPD-SFQ two-photon coincidence correlator

I. Komissarov, Amir Jafari Salim, Oleg A. Mukhanov +3 more

We present a single-flux-quantum (SFQ) based digital correlator to trace independent signals from two superconducting single-photon detectors (SSPDs) triggering its inputs. In our design two SSPDs are magnetically coupled to inputs of a readout system where direct current (DC)-to-SFQ converters are used to convert transient SSPD output pulses, triggered by detection of single-photon events, to SFQ pulses. The coincidence verification of SFQ pulses, generated by the two DC-to-SFQ converters, is performed with a modified SFQ coincidence buffer. The coincidence buffer is designed to generate an SFQ output pulse only when its both inputs are triggered simultaneously, or within a preset margin time. The output of the coincidence buffer is connected via, this time, an SFQ-to-DC converter, to a pulse counter operated at room temperature. We performed extensive simulations of both the SSPD equivalent circuit and correlator redout elements for the proposed coincidence scheme, using a WRSpice and PSCAN2 simulation platforms that are specifically designated to model Josephson junctions and widely used to simulate operation of the SFQ circuitry. In particular, we investigated our coincidence correlator scheme for measurements of the second-order correlation function, used to demonstrate the antibunching effect in the single-photon detection of non-classical light.

Quantum Optics and Photon Counting•Jun 6, 2023•2 citations

Single-Flux-Quantum Based Coincidence Circuits Using Nb/AlOx/Nb Josephson Junctions with Critical Current Density of 10 kA/cm2

Shigeyuki Miyajima, Hirotaka Terai, Shigehito Miki

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.

IEICE Transactions on Electronics•Nov 27, 2024•0 citations

Reduction of the supply current of single-flux-quantum time-to-digital converters by current recycling techniques

Kyosuke Sano, Tomoki Shimoda, Yutaka Abe +4 more

We have been developing superconducting time-of-flight mass spectrometry systems that utilize superconducting strip particle detectors and single-flux-quantum (SFQ) time-to-digital converters (TDCs). We previously demonstrated a 24-bit SFQ TDC with a 3 × 24-bit first-in first-out (FIFO) buffer using the AIST Nb standard process (STP2) with a time resolution of 100 ps. In this study, we improved the SFQ TDC by using a current recycling technique. The technique enables us to increase the FIFO buffer capacity without increasing the total supply current, and the result is an improvement of ion count rates. We designed and demonstrated the SFQ TDC with a 12 × 24-bit FIFO buffer, whose total supply current was reduced by 71% with the current recycling technique.

IEEE Transactions on Applied Superconductivity•Dec 30, 2016•20 citations
We have been developing a time-to-digital converter (TDC) using single-flux-quantum (SFQ) circuits in order to realize an imaging system based on a superconducting strip single-photon detector (SSPD). In this system, the absorption position of a single photon in a meander-shaped SSPD is determined by measuring the delay time of the detected signal propagating through an SSPD delay line. Increasing the time resolution of the TDC is the primary concern for improving the spatial resolution of the system. Here we focused on the double-oscillator SFQ TDC, where the difference of oscillation periods between two SFQ ring oscillators determines the time resolution. In the previous study, a time resolution of about 4 ps was demonstrated by using the Nb standard Josephson integrated circuit (IC) process with a critical current density of 2.5 kA/cm2. In this study, we improved the time resolution by adopting the Nb advanced Josephson IC process with a critical current density of 10 kA/cm2and by optimizing the circuit parameters of the coincidence detector. The histogram and the linearity of the delay measurements show that the time resolution is improved to up to 2 ps.
Direct measurements of propagation delay of single-flux-quantum (SFQ) circuits were performed using SFQ double-oscillator time-to-digital converters. The propagation delay of several SFQ logic gates in our cell library named CONNECT were measured in picosecond resolution. Small discrepancy in the propagation delay of picosecond level was observed between measurement and circuit simulation results. The discrepancy is well explained assuming the parasitic inductance around shunt resistors of Josephson junctions.
We have been developing a superconducting time-of-flight mass spectrometry (TOF-MS) system, which utilizes a superconductive strip ion detector (SSID) and a single-flux-quantum (SFQ) multi-stop time-to-digital converter (TDC). The SFQ multi-stop TDC can measure the time intervals between multiple input signals and directly convert them into binary data. In this study, we designed and implemented 24-bit SFQ multi-stop TDCs with a 3×24-bit FIFO buffer using the AIST Nb standard process (STP2), whose time resolution and dynamic range are 100ps and 1.6ms, respectively. The timing jitter of the TDC was investigated by comparing two types of TDCs: one uses an on-chip SFQ clock generator (CG) and the other uses a microwave oscillator at room temperature. We confirmed the correct operation of both TDCs and evaluated their timing jitter. The experimentally-obtained timing jitter is about 40ns and 700ps for the TDCs with and without the on-chip SFQ CG, respectively, for the measured time interval of 50µs, which linearly increases with increase of the measured time interval.
We report on the timing jitter characterization of the superconducting single flux quantum (SFQ) coincidence circuit, which is an essential component of the superconducting coincidence photon counter. Two superconducting nanowire single photon detectors (SSPDs), each of which is irradiated with optically time-controlled photons, are connected to the SFQ coincidence circuit, and the timing jitter of the SFQ circuit is evaluated by changing the relative time delay between two input ports for the SFQ comparator unit. We successfully observe the transition curve of the probability of obtaining the signal from the SFQ coincidence circuit by sweeping photon arrival time to each SSPD and confirm that this curve shifts temporally upon changing the bias current to the Josephson transmission line (JTL) in the SFQ circuit. A systematic investigation reveals that the relation between time delay and the bias current to JTL can be estimated. The full width half maximum timing jitter of the SFQ circuit is 1.1 ps, which is sufficiently low so that it does not influence the entire timing jitter of the coincidence photon counter.
We present a single-flux-quantum (SFQ) based digital correlator to trace independent signals from two superconducting single-photon detectors (SSPDs) triggering its inputs. In our design two SSPDs are magnetically coupled to inputs of a readout system where direct current (DC)-to-SFQ converters are used to convert transient SSPD output pulses, triggered by detection of single-photon events, to SFQ pulses. The coincidence verification of SFQ pulses, generated by the two DC-to-SFQ converters, is performed with a modified SFQ coincidence buffer. The coincidence buffer is designed to generate an SFQ output pulse only when its both inputs are triggered simultaneously, or within a preset margin time. The output of the coincidence buffer is connected via, this time, an SFQ-to-DC converter, to a pulse counter operated at room temperature. We performed extensive simulations of both the SSPD equivalent circuit and correlator redout elements for the proposed coincidence scheme, using a WRSpice and PSCAN2 simulation platforms that are specifically designated to model Josephson junctions and widely used to simulate operation of the SFQ circuitry. In particular, we investigated our coincidence correlator scheme for measurements of the second-order correlation function, used to demonstrate the antibunching effect in the single-photon detection of non-classical light.
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.
We have been developing superconducting time-of-flight mass spectrometry systems that utilize superconducting strip particle detectors and single-flux-quantum (SFQ) time-to-digital converters (TDCs). We previously demonstrated a 24-bit SFQ TDC with a 3 × 24-bit first-in first-out (FIFO) buffer using the AIST Nb standard process (STP2) with a time resolution of 100 ps. In this study, we improved the SFQ TDC by using a current recycling technique. The technique enables us to increase the FIFO buffer capacity without increasing the total supply current, and the result is an improvement of ion count rates. We designed and demonstrated the SFQ TDC with a 12 × 24-bit FIFO buffer, whose total supply current was reduced by 71% with the current recycling technique.