Entanglement and quantum discord in coherent Ising machines

We present analytical and numerical simulation results for squeezing, entanglement, and quantum discord in a dissipatively coupled coherent Ising machine (CIM). Both the analytical solutions and numerical simulation results, obtained with positive-P , truncated-Wigner and truncated-Husimi representations for the density operator, predict the presence of entanglement and quantum discord below and above the threshold of dissipatively coupled CIM. The entanglement criteria and the degree of quantum discord are evaluated as a function of the dissipative coupling strength relative to the background loss. The degrees of both the entanglement and quantum discord are maximum at the threshold. While the entanglement disappears as the linear loss exceeds the Ising coupling strength, the quantum discord remains even in a large linear loss case.