  In a recent preprint (arXiv:1305.4904) entitled "Classical signature of
quantum annealing" Smolin and Smith point out that a bimodal distribution
presented in (arXiv:1304.4595) for the success probability in the D-Wave device
does not in itself provide sufficient evidence for quantum annealing, by
presenting a classical model that also exhibits bimodality. Here we analyze
their model and in addition present a similar model derived from the
semi-classical limit of quantum spin dynamics, which also exhibits a bimodal
distribution. We find that in both cases the correlations between the success
probabilities of these classical models and the D-Wave device are weak compared
to the correlations between a simulated quantum annealer and the D-Wave device.
Indeed, the evidence for quantum annealing presented in arXiv:1304.4595 is not
limited to the bimodality, but relies in addition on the success probability
correlations between the D-Wave device and the simulated quantum annealer. The
Smolin-Smith model and our semi-classical spin model both fail this correlation
test.
