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 International Superconductive Electronics Conference (ISEC)

Design and Performance of Digital SQUID with Sub-Flux Quantum Resolution

Hiroaki Myoren, Kouhei Takatoku, Masato Naruse, Tohru Taino

Published Jul 1, 2015• 2 citations
Publisher

Abstract

Digital SQUIDs based on the single flux quantum (SFQ) logic have attractive characteristics, such as wide dynamic range and high slew rate. However, the resolution of digital SQUIDs is limited to SFQ. To realize sub-flux quantum resolution for these SQUIDs, we have adopted two types of feedback combinations: one with the SFQ input/output for a main loop and the other with a mutually coupled loop. The main loop receives direct Φ0feedback and sub-flux quantum feedback Φ0/n, where n is an integer, from the mutually coupled loop. We confirmed the correct operation of our device at a clock frequency of 1.25 GHz for a digital SQUID with a sub-Φ0flux feedback resolution of Φ0/8 from circuit simulation. The slew rate is found to be 1.56×108Φ0/s in this simulation (fc=1.25 GHz, n=8). The flux resolution for the digital SQUID shows improvement with increasing n and reached below 40 mΦ0with n=210; however the slew rate is decreased with increasing n and reached 1.22×106Φ0/swith fc=1.25 GHz and n=210.

DOI
10.1109/isec.2015.7383444

Related papers

High-Resolution Digital SQUID Magnetometer using Sub-Flux Quantum Feedback

Hiroaki Myoren, Kosuke Okabe, Ryo Matsunawa +3 more

Abstract Digital SQUIDs with the single flux quantum (SFQ) feedback have attracted much attention because of the feasibility of realizing a wide dynamic range and high slew rate for digital magnetometers. In order to realize higher resolution, we have studied a digital SQUID with sub-flux quantum feedback. Combining the sub-flux quantum feedback to a feedback loop and the direct SFQ feedback to a main loop triggered by carry SFQ pulses from an up/down counter. In this study, we discuss the method of multi-flux quantum generation and compact design of the SFQ up/down counter for high-speed operation of the digital SQUID magnetometer.

Journal of Physics Conference Series•Jun 1, 2020•0 citations

Design and Magnetic Field Noise of Magnetometer Using Digital SQUID With Subflux Quantum Feedback

Hiroaki Myoren, Kouhei Takatoku, Masato Naruse +1 more

Digital superconducting quantum interference devices (SQUIDs) based on single-flux quantum (SFQ) logic have attractive characteristics such as wide dynamic ranges and high slew rates. However, the resolution of a typical digital SQUID is limited by SFQ feedback. To realize lower magnetic field noise by magnetometers using digital SQUIDs, we have adopted two feedback combinations: one, utilizing the SFQ input/output for a main loop and the other, using a mutually coupled loop. The main loop receives direct Φ0feedback and subflux quantum feedback Φ0/n, where n is an integer from the mutually coupled loop. The flux resolution for the digital SQUID shows improvement with increasing n and reaches below 40 mΦ0at n = 210; however, the slew rate decreases with increasing n and reaches 1.22 × 106Φ0/s at fc= 1.25 GHz and n = 210. For a magnetometer using a digital SQUID with a pickup loop, we confirmed a magnetic field noise of less than 100 fT/√Hz with a signal bandwidth of 1 MHz for operation frequency fcof 20 GHz.

IEEE Transactions on Applied Superconductivity•May 20, 2016•7 citations

Performance of Digital SQUID with Sub-Flux Quantum Feedback Resolution Fabricated using 10 kA/cm2 Nb Process

Kohki Itagaki, Itta Oshima, Yuichi Hasegawa +4 more

Abstract Digital superconducting quantum interference device (SQUID with Single Flux Quantum (SFQ) feedback operates as a Δ-type oversampling A/D converter. Magnetic flux resolution at Nyquist frequency can be improved by taking sub SFQ feedback resolution and large oversampling ratio. Using high critical current density Nb process for fabricating SFQ circuits, we expected more higher operation speed for the digital SQUID and resulting to higher magnetic flux resolutions. We expected a performance of the digital SQUID magnetometer fabricated using 10 kA/cm2 Nb process based on CAD layout, with an up/down counter using T2FF cells and parallel SFQ feedback. For the clock frequency of 13 GHz and the Nyquist frequency of 1.587 MHz, the magnetic field noise was lower than 1.5 fT / Hz and the slew rate was exceeded 500 mT/s.

Journal of Physics Conference Series•Jul 1, 2020•0 citations

Digital SQUIDs: New definitions and results

Vasili K. Semenov

Recently we found that several simple SFQ circuits (normally used as ADC comparators) dramatically outperform conventional SQUIDs in time resolution and slew rate. For example, it is possible to reach a resolution of about a few percent of flux quantum by using a single-shot measurement that takes only a few picoseconds. All these SFQ circuits produce during each clock period only one bit of information that indicates whether the applied flux is larger or smaller the threshold. As a result it is natural to call them digital (or logic) SQUIDs. The new sensors can be used to detect a direction of the electrical current induced in a superconductor loop by the external field and digitally compensated by another SFQ devices. This composite device contains two kinds of digital components and also could be called a Digital SQUID. It has a limited practical value with a hundreds MHz clock rate. Fortunately, the clock frequency could be increased to tens of GHz. But in this case the third digital device (a decimation filter) should be added to filter out off-band noise and reduce the output clock frequency. The last device is rather similar to an ADC and also could be called a Digital SQUID. It is easy to show that the last Digital SQUID has a practically unlimited slew rate and dynamic range without suffering significant loss of energy sensitivity of the conventional two-junction SQUID.

IEEE Transactions on Applied Superconductivity•Jun 1, 2003•29 citations

Results on a fast digital DROS

M. Podt, A.J. Mieog, B. G.A. Rolink +2 more

A digital double relaxation oscillation (DROS) superconducting quantum interference device (SQUID) has the potential for a very large dynamic range and a slew rate that is orders of magnitude larger than that of conventional SQUID systems. This is, for example, advantageous when using the SQUID in an unshielded environment. An important characteristic of the digital DROS is that the feedback flux is quantized since this flux is supplied by a superconducting up-down counter. Together with the clock frequency, the quantization unit of the feedback flux determines the maximum slew rate. In an optimized design, the quantization unit is adapted to the broadband flux noise of the DROS, so that the slew rate is maximized without compromising the sensitivity. Simulations on our optimized digital DROS showed proper operation for slew rates up to 5×10 6 Φ 0 s -1 . The relaxation oscillations generated at a frequency of 100 MHz deliver an on-chip clock signal, so that no external clock is required. Slew rates up to 10 8 Φ 0 s -1 can be achieved by increasing the relaxation oscillation frequency to a few GHz. This means that sub-µm 2 Josephson junctions with high critical current densities are required. The first experiments using low- T c ramp-type Josephson junctions are presented in this paper.

Superconductor Science and Technology•Nov 21, 2001•7 citations

Design of Digital DROS With SFQ Up/Down Counter for Wide Dynamic Operation Range

Hiroaki Myoren, Kimimoto Yun, Kosuke Terui +1 more

We designed a digital double relaxation oscillation SQUID (DROS) with an SFQ up/down counter. The DROS is connected to a feedback SQUID loop and a signal magnetic flux is input to the feedback SQUID loop. The DROS generates two kinds of voltage pulses corresponding to the total magnetic flux in the feedback SQUID loop. Two kind of voltage pulses are converted to SFQ and anti-SFQ pulses and input to the feedback SQUID loop to keep the magnetic flux in the SQUID loop constant. The number of the generated SFQ pulses is counted using the SFQ up/down counter. Thus, the count corresponds to the input magnetic flux. Because the SFQ up/down counter is operated in the pulse driven mode, the digital DROS needs only dc bias current for operation. We designed and fabricated a digital DROS with a relaxation oscillation frequency of 3 GHz and an 8-bit SFQ up/down counter. Numerical simulation suggested the designed digital DROS has a dynamic range exceeding ±100 Φ0and magnetic flux slew rate of 3 × 109Φ0/s.

IEEE Transactions on Applied Superconductivity•Jan 28, 2011•15 citations
Digital SQUIDs based on the single flux quantum (SFQ) logic have attractive characteristics, such as wide dynamic range and high slew rate. However, the resolution of digital SQUIDs is limited to SFQ. To realize sub-flux quantum resolution for these SQUIDs, we have adopted two types of feedback combinations: one with the SFQ input/output for a main loop and the other with a mutually coupled loop. The main loop receives direct Φ0feedback and sub-flux quantum feedback Φ0/n, where n is an integer, from the mutually coupled loop. We confirmed the correct operation of our device at a clock frequency of 1.25 GHz for a digital SQUID with a sub-Φ0flux feedback resolution of Φ0/8 from circuit simulation. The slew rate is found to be 1.56×108Φ0/s in this simulation (fc=1.25 GHz, n=8). The flux resolution for the digital SQUID shows improvement with increasing n and reached below 40 mΦ0with n=210; however the slew rate is decreased with increasing n and reached 1.22×106Φ0/swith fc=1.25 GHz and n=210.
Abstract Digital SQUIDs with the single flux quantum (SFQ) feedback have attracted much attention because of the feasibility of realizing a wide dynamic range and high slew rate for digital magnetometers. In order to realize higher resolution, we have studied a digital SQUID with sub-flux quantum feedback. Combining the sub-flux quantum feedback to a feedback loop and the direct SFQ feedback to a main loop triggered by carry SFQ pulses from an up/down counter. In this study, we discuss the method of multi-flux quantum generation and compact design of the SFQ up/down counter for high-speed operation of the digital SQUID magnetometer.
Digital superconducting quantum interference devices (SQUIDs) based on single-flux quantum (SFQ) logic have attractive characteristics such as wide dynamic ranges and high slew rates. However, the resolution of a typical digital SQUID is limited by SFQ feedback. To realize lower magnetic field noise by magnetometers using digital SQUIDs, we have adopted two feedback combinations: one, utilizing the SFQ input/output for a main loop and the other, using a mutually coupled loop. The main loop receives direct Φ0feedback and subflux quantum feedback Φ0/n, where n is an integer from the mutually coupled loop. The flux resolution for the digital SQUID shows improvement with increasing n and reaches below 40 mΦ0at n = 210; however, the slew rate decreases with increasing n and reaches 1.22 × 106Φ0/s at fc= 1.25 GHz and n = 210. For a magnetometer using a digital SQUID with a pickup loop, we confirmed a magnetic field noise of less than 100 fT/√Hz with a signal bandwidth of 1 MHz for operation frequency fcof 20 GHz.
Abstract Digital superconducting quantum interference device (SQUID with Single Flux Quantum (SFQ) feedback operates as a Δ-type oversampling A/D converter. Magnetic flux resolution at Nyquist frequency can be improved by taking sub SFQ feedback resolution and large oversampling ratio. Using high critical current density Nb process for fabricating SFQ circuits, we expected more higher operation speed for the digital SQUID and resulting to higher magnetic flux resolutions. We expected a performance of the digital SQUID magnetometer fabricated using 10 kA/cm2 Nb process based on CAD layout, with an up/down counter using T2FF cells and parallel SFQ feedback. For the clock frequency of 13 GHz and the Nyquist frequency of 1.587 MHz, the magnetic field noise was lower than 1.5 fT / Hz and the slew rate was exceeded 500 mT/s.
Recently we found that several simple SFQ circuits (normally used as ADC comparators) dramatically outperform conventional SQUIDs in time resolution and slew rate. For example, it is possible to reach a resolution of about a few percent of flux quantum by using a single-shot measurement that takes only a few picoseconds. All these SFQ circuits produce during each clock period only one bit of information that indicates whether the applied flux is larger or smaller the threshold. As a result it is natural to call them digital (or logic) SQUIDs. The new sensors can be used to detect a direction of the electrical current induced in a superconductor loop by the external field and digitally compensated by another SFQ devices. This composite device contains two kinds of digital components and also could be called a Digital SQUID. It has a limited practical value with a hundreds MHz clock rate. Fortunately, the clock frequency could be increased to tens of GHz. But in this case the third digital device (a decimation filter) should be added to filter out off-band noise and reduce the output clock frequency. The last device is rather similar to an ADC and also could be called a Digital SQUID. It is easy to show that the last Digital SQUID has a practically unlimited slew rate and dynamic range without suffering significant loss of energy sensitivity of the conventional two-junction SQUID.
A digital double relaxation oscillation (DROS) superconducting quantum interference device (SQUID) has the potential for a very large dynamic range and a slew rate that is orders of magnitude larger than that of conventional SQUID systems. This is, for example, advantageous when using the SQUID in an unshielded environment. An important characteristic of the digital DROS is that the feedback flux is quantized since this flux is supplied by a superconducting up-down counter. Together with the clock frequency, the quantization unit of the feedback flux determines the maximum slew rate. In an optimized design, the quantization unit is adapted to the broadband flux noise of the DROS, so that the slew rate is maximized without compromising the sensitivity. Simulations on our optimized digital DROS showed proper operation for slew rates up to 5×10 6 Φ 0 s -1 . The relaxation oscillations generated at a frequency of 100 MHz deliver an on-chip clock signal, so that no external clock is required. Slew rates up to 10 8 Φ 0 s -1 can be achieved by increasing the relaxation oscillation frequency to a few GHz. This means that sub-µm 2 Josephson junctions with high critical current densities are required. The first experiments using low- T c ramp-type Josephson junctions are presented in this paper.
We designed a digital double relaxation oscillation SQUID (DROS) with an SFQ up/down counter. The DROS is connected to a feedback SQUID loop and a signal magnetic flux is input to the feedback SQUID loop. The DROS generates two kinds of voltage pulses corresponding to the total magnetic flux in the feedback SQUID loop. Two kind of voltage pulses are converted to SFQ and anti-SFQ pulses and input to the feedback SQUID loop to keep the magnetic flux in the SQUID loop constant. The number of the generated SFQ pulses is counted using the SFQ up/down counter. Thus, the count corresponds to the input magnetic flux. Because the SFQ up/down counter is operated in the pulse driven mode, the digital DROS needs only dc bias current for operation. We designed and fabricated a digital DROS with a relaxation oscillation frequency of 3 GHz and an 8-bit SFQ up/down counter. Numerical simulation suggested the designed digital DROS has a dynamic range exceeding ±100 Φ0and magnetic flux slew rate of 3 × 109Φ0/s.