New AC-Powered SFQ Digital Circuits

TL;DR

This paper introduces and demonstrates new AC-powered SFQ digital circuits, including an on-chip AC/DC converter and a large-scale 8192-bit shift register, highlighting their potential for benchmarking and imaging applications.

Contribution

It presents the first successful demonstration of AC-powered SFQ circuits and explores their synergy with DC biasing schemes, expanding the design space for superconductor digital electronics.

Findings

Demonstrated an 8192-bit shift register with over 32,800 Josephson junctions

Developed an on-chip AC/DC converter for SFQ circuits

Proposed niche applications like benchmarking and magnetic imaging

Abstract

Recent progress of Reciprocal Quantum Logic (RQL) has renewed interest in AC powering of superconductor digital circuits, which had been abandoned since the famous IBM project of 1970s. In this work we propose and demonstrate new AC-biased Single Flux Quantum (SFQ) circuits, and search for synergy of AC and currently dominating DC biasing schemes. As the first step, we suggest an on-chip AC/DC converter capable of feeding a few DC-biased gates surrounded by their AC-biased counterparts. As the second step, we introduce and present the first successful demonstration of a new AC-powered circuit - an 8192-bit shift register with over 32,800 Josephson junctions (JJs) and JJ density of about 6x$10^5$ JJ per $cm^2$. We suggest a few niche applications for this type of AC-biased circuits, not requiring high clock rates. E.g., these, scalable to millions of JJs per chip, circuits can serve as a convenient benchmark for new SFQ fabrication technology nodes, allowing the operating margins of individual cells to be extracted and, thus, 'visualize' individual fabrication defects and flux trapping events. The circuit can also be developed into a mega-pixel imaging array for a magnetic field microscope.