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Applied Physics Letters

Superconducting race arbiter with subpicosecond timing discrimination

G. S. Lee, Rich Ruby, H.L. Ko, Andrew T. Barfknecht

Published Nov 25, 1991• 9 citations
Publisher

Abstract

A novel race arbiter for ultrahigh resolution time discrimination is proposed and has been designed, fabricated, and tested in an all-niobium Josephson junction technology. The arbiter is based on a pair of quantum flux parametrons, which are single flux quantum switching devices, and is hence called a BiQFP for Bi-quantum Flux Parametron. High-speed experiments have demonstrated a rms single-shot time jitter of ±200–300 fs.

DOI
10.1063/1.105843

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A novel race arbiter for ultrahigh resolution time discrimination is proposed and has been designed, fabricated, and tested in an all-niobium Josephson junction technology. The arbiter is based on a pair of quantum flux parametrons, which are single flux quantum switching devices, and is hence called a BiQFP for Bi-quantum Flux Parametron. High-speed experiments have demonstrated a rms single-shot time jitter of ±200–300 fs.
A root-mean-square (RMS) time jitter of 380 fs has been demonstrated in a single quantum flux parametron (QFP) race arbiter circuit with approximately 60-ps-risetime signal inputs. Because of the simple relationship between the QFP current comparator and the race arbiter, it is possible to make direct comparison of the time jitter and current noise results. The measured current noise in a QFP current comparator implies that, for a signal risetime of 10 ps, a time jitter of approximately 200 fs is expected for this race arbiter circuit. Circuit modeling suggests that an optimized design can achieve approximately 100-fs time jitter.>
As we rapidly advance through the information age, the power consumed by computers, data centers, and networks grows exponentially. This has inspired a race to develop alternative low-power computational technologies. A new adiabatic configuration of a decades-old superconducting digital logic device has darted into the lead called quantum flux parametrons (QFP). QFP operate with dissipation so low that they seemingly violate the laws of thermodynamics. In just a short span of time, they have gone from simple single NOT gates to complex processors containing thousands of gates. They are fabricated from elemental niobium superconductors cooled to just a few degrees above absolute zero. However, their efficiency is so great that for large high-performance computers with several gates, the energy savings are immense. For smaller computational platforms QFPs from high-temperature superconductors (high-Tc) are highly desirable. In this work, we take the first steps towards this goal with the demonstration of a high-T C QFP shift register. Our device is fabricated using focused helium ion beam lithography where the material is modified with an ion beam at the nanoscale to directly pattern these circuits into a high-T C thin film. We validate the correct logical operation at 25 K, over 6 times higher than niobium devices with an estimated bit energy of 0.1 attoJoule at 10 GHz.
The Quantum Flux Parametron (QFP) is a new cryogenic switching device based on the parametron principle and Josephson technology. Due to the magnetic flux quantization in superconducting devices, the switching mechanism of the QFP is quite different from that of semiconductors. This presentation describes the device characteristics. QFPs have been fabricated using the Nb/Pb-alloy Josephson junction process, and their basic operation is evaluated. Over 20dB current gain is attained. One-half frequency-divider operation up to 1.8GHz has been successfully observed.
A quantum flux parametron (QFP), a single quantum flux superconductive device that has a potential of up to 100-GHz switching with nW-order power dissipation, is considered. The potential of the QFP and key technologies when QFPs are applied to a Josephson supercomputer are described. Switching speed, stability, and power dissipation of a QFP are discussed. QFP gates, circuits, and systems are next described. Then, ultra-fast clock distribution using a standing wave is explained. High-speed operation at more than 10 GHz and 10/sup 14/ error-free operations per QFP have been demonstrated. Finally described is a high-density packaging scheme by three-dimensional integration, which is very important for ultra-high speed circuits because the propagation delay becomes dominant in such circuits.>
The adiabatic quantum flux parametron (AQFP) is an energy-efficient, high-speed superconducting logic device. To observe the tiny output currents from the AQFP in experiments, high-speed voltage drivers are indispensable. In the present study, we develop a compact voltage driver for AQFP logic based on a Josephson latching driver (JLD), which has been used as a high-speed driver for rapid single-flux-quantum (RSFQ) logic. In the JLD-based voltage driver, the signal currents of AQFP gates are converted into gap-voltage-level signals via an AQFP/RSFQ interface and a four-junction logic gate. Furthermore, this voltage driver includes only 15 Josephson junctions, which is much fewer than in the case for the previously designed driver based on dc superconducting quantum interference devices (60 junctions). In measurement, we successfully operate the JLD-based voltage driver up to 4 GHz. We also evaluate the bit error rate (BER) of the driver and find that the BER is 7.92×10-10 and 2.67×10-3 at 1GHz and 4GHz, respectively.
The Quantum Flux Parametron (QFP) is a new cryogenic switching device based on the parametron principle and Josephson technology. Due to the magnetic flux quantization in superconducting devices, the switching mechanism of the QFP is quite different from that of semiconductors. This presentation describes the device characteristics. QFPs have been fabricated using the Nb/Pb-alloy Josephson junction process, and their basic operation is evaluated. Over 20dB current gain is attained. One-half frequency-divider operation up to 1.8GHz has been successfully observed.