CIMs manipulate coherent data amplitudes and** **support **quantum generalizations**.

The CIM data register comprises coherent amplitudes of a set of time-multiplexed degenerate optical parametric oscillator (DOPO) modes. As the pump amplitude is increased during a computational trajectory, the DOPOs ultimately undergo pitchfork bifurcations that discretize the state variables to yield an Ising-type (binary) solution configuration. Below threshold, however — during the early phase of the computation in which the coupled DOPO degrees-of-freedom are searching for optimal configurations — each DOPO is expected (on the basis of extensive prior quantum optics research) to exhibit vacuum squeezing. While the impacts of squeezed vacuum fluctuations in the DOPO amplitudes on optimization dynamics and the critical pitchfork bifurcation are not yet crisply understood, numerical simulation studies suggest that they may give rise to transient non-Gaussian (highly non-classical) DOPO states. Next-generation CIM prototypes that incorporate either scalable coherent coupling of DOPOs or specialized multi-pulse measurement protocols could generate sustainable entanglement among the DOPO modes. How precisely do coherence effects and/or non-Gaussian fluctuations impact the computational performance of current CIM prototypes, and can we engineer improved architectures to optimally exploit quantum phenomena in coupled-DOPO networks?

**See also:**

Y. Yamamoto *et al.*, “Coherent Ising machines — optical neural networks operating at the quantum limit,” npj Quantum Information **3**, 49 (2017).

R. Yanagimoto *et al.*, “Embedding entanglement generation within a measurement-feedback coherent Ising machine,” arXiv:1906.04902.

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