  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. Here 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.
