Duplication-Aware Retiming and Cell Interface Redesign for Superconductor Circuit Minimization

2026-10-01

AI Summary

This study addresses the gate duplication and Josephson junction redundancy issues induced by dual-rail encoding in superconducting circuits. To overcome these challenges, we propose a replication-aware retiming methodology that co-optimizes register allocation and signal polarity. By restructuring single-flux-quantum (SFQ) cell interfaces and designing novel amplifier cells, the approach integrates a tailored retiming algorithm to achieve circuit-level comprehensive optimization. Experimental results demonstrate that the proposed technique significantly reduces both circuit area and critical path delay. Specifically, the number of Josephson junctions is decreased by 63%–71% in single-cycle circuits and by 41%–66% in multi-cycle circuits. These improvements establish a new Pareto frontier for superconducting circuit design, offering a highly efficient synthesis framework for next-generation quantum-classical hybrid computing architectures.

Abstract

Superconductor electronics have increasingly shifted away from RSFQ and its variants toward logic families that eliminate explicit gate-level clocking. While this transition enables simpler circuits and more efficient architectures, it also introduces an implicit reliance on dual-rail codes, resulting in inherent gate duplication. This work presents a duplication-aware retiming methodology for Josephson junction (JJ) count minimization, co-optimizing register placement and polarity assignment. The approach applies beyond SFQ to any monotonic circuit. We further identify cell interfaces---specifically, interconnect drivers, receivers, and fanout (FO) elements---as dominant contributors to JJ count in each cell. A new amplifier design is introduced to reduce these costs, integrated within existing SFQ cells, experimentally verified, and characterized to form a new SFQ cell library. Our results demonstrate a 63-71% JJ count reduction in single-cycle implementations and 41-66% reduction in multi-cycle implementations compared to the prior state-of-the-art. The latter establishes a new Pareto frontier, achieving both shorter critical paths and lower JJ counts than the best-to-date single-cycle implementations.

Problem

• Superconductor circuits
• Josephson junction minimization
• Dual-rail codes
• Gate duplication
• Cell interface

Innovation

• Duplication-Aware Retiming
• Josephson Junction Minimization
• Superconductor Circuits
• Cell Interface Redesign
• SFQ Cell Library