Boosting fluxons for ballistic-logic power using an Aharonov-Casher ring

Abstract

Superconducting logic is fast and energy-efficient relative to CMOS, but also fundamental studies are needed to scale up circuits for greater utility. Recently, ballistic shift registers for single-flux quanta (SFQ) bits were shown in simulation to allow high-efficiency superconducting gates. However, these gates are unpowered such that the bits slow after each gate operation and only a short sequence of gates is possible without added power. Here we show that a circuit based on an Aharonov-Casher ring can power these shift registers by boosting the bit velocity to a constant value, despite their unusual bit states constituted by two polarities of SFQ. As a step in its operation, each bit state is forced into a different ring arm and then accelerated. The circuit dynamics depend on various circuit parameters and choices of how to merge the bit-state paths. One design from each merge design choice is proposed to enable scaling up to an array of gates by adding serial biasing in a relatively simple way. We find adequate performance for ballistic logic in terms of boosted velocity, energy efficiency, and parameter margins. We also discuss the circuit's classical barriers; in a different regime this relates to the Aharonov-Casher effect.