Logical and Physical Reversibility of Conservative Skyrmion Logic

Magnetic skyrmions are nanoscale whirls of magnetism that can be propagated with electrical currents. The repulsion between skyrmions inspires their use for reversible computing based on the elastic billiard ball collisions proposed for conservative logic in 1982. In this letter, we evaluate the logical and physical reversibility of this skyrmion logic paradigm, as well as the limitations that must be addressed before dissipation-free computation can be realized.

I. Introduction

The conventional nonreversible paradigm for general digital computing will eventually approach fundamental thermodynamic limits on its energy efficiency, which stem ultimately from the fact that this standard paradigm relies primarily on operations that systematically discard correlated logical information, and therefore increase entropy [Frank 2005, 2018, 2021]. For example, a typical digital logic architecture in complementary metal-oxide semiconductor (CMOS) destructively overwrites the output of each active logic gate with a new bit value on each clock cycle. It has been known ever since the field of the thermodynamics of computation was first elucidated by Landauer [1961] and Bennett [1973, 1982, 2003] that general digital computing technologies can only avoid the consequent limits on their energy efficiency if they are instead re-architected on the basis of logically reversible operations that are implemented (at the device and circuit level) in a nearly thermodynamically reversible way [Frank 2017].