Coherent Ising machine (OPO network)
Realizes: Ising Hamiltonian ground state / combinatorial optimization (MAX-CUT, QUBO)
A network of degenerate optical parametric oscillator (DOPO) pulses circulating in a fiber ring cavity. Each pulse can oscillate in one of two phase states (0 or π), encoding a spin. Measurement-feedback electronics couple the pulses according to the Ising coupling matrix programmed by the user. As the pump power increases past threshold, the network undergoes bifurcation and settles into a low-energy spin configuration. NTT's 2021 system used 100,000 DOPO pulses in a 5-km fiber loop. Unlike classical or quantum annealers, the CIM operates at room temperature and exploits optical coherence rather than thermal or quantum fluctuations. Speed: microseconds per Ising problem instance. Capacity: up to 100,000 spins (NTT 2021); competitive with quantum annealers on dense graphs.
Examples
NTT — 100,000-spin coherent Ising machine (2021)
Announcement of the 100,000-DOPO coherent Ising machine demonstrating large-scale combinatorial optimization at room temperature
Large-scale coherent Ising machine based on optoelectronic parametric oscillator (Light: Sci. & Apps., 2022)
Detailed architecture and benchmarking of an optoelectronic CIM against D-Wave and classical solvers