Physics / mechanism
Ising machines map combinatorial optimization problems onto the ground-state search of an Ising Hamiltonian (H = −Σ J_ij σ_i σ_j − Σ h_i σ_i). Physical implementations include coupled parametric oscillators (OPO-based coherent Ising machines, CIM), CMOS oscillator networks, memristor crossbars, and quantum annealing (D-Wave). Stochastic versions inject controlled noise to escape local minima — probabilistic bits (p-bits) built from stochastic MTJ devices operating at room temperature. Current SoA: Fujitsu Digital Annealer handles ~100k fully-connected spins in CMOS; NTT/Stanford CIM demonstrated 2,000 spins at optical clock rates; D-Wave Advantage runs ~5,000 qubits but restricted topology. Target problem classes: QUBO, MaxCut, portfolio optimisation, drug docking, logistics.
Competitive landscape
| Approach | Substrate | Spins / Scale | Maturity |
|---|---|---|---|
| CMOS Ising / Digital Annealer | Standard CMOS | 10k–100k | Commercial (Fujitsu, Toshiba) |
| Coherent Ising Machine (OPO) | Photonics + FPGA | 2k–10k | Lab / early product |
| Quantum Annealing (D-Wave) | Superconducting | ~5k qubits | Commercial, niche |
| p-bit / MTJ stochastic | Spintronics | <1k (scaling) | Research |
Companies using
Connected ideas
Sources
Frontier (open questions)
- To be added.