  We compared the noise correlation and the success probability of coherent
Ising machines (CIMs) with optical delay-line, measurement feedback, and
mean-field couplings. We theoretically studied three metrics for the noise
correlations in these CIMs: quantum entanglement, quantum discord, and
normalized correlation of canonical coordinates. The success probability was
obtained through numerical simulations of truncated stochastic differential
equations based on the Wigner distribution function. The results indicate that
the success probability is more directly related to the normalized correlation
function rather than entanglement or quantum discord.
