Spatial Photonic Ising Machine with Time/Space Division Multiplexing

The spatial photonic Ising machine (SPIM) is an unconventional computing architecture based on parallel propagation/processing with spatial light modulation. SPIM enables the handling of an Ising model using light as a pseudospin. This chapter presents SPIMs with multiplexing to enhance their functionality. Handling a fully connected Ising model with a rank-2 or higher spin-interaction matrix becomes possible with multiplexing, drastically improving its applicability in practical applications. We constructed and examined systems based on time- and space-division multiplexing to handle Ising models with ranks of no less than one while maintaining high scalability owing to the features of spatial light modulation. Experimental results with knapsack problems demonstrate that these methods can compute the Hamiltonian consisting of objective and constraint terms, which require multiplexing, and can determine the ground-state spin configuration. In particular, in space-division multiplexing SPIM, the characteristics of the solution search vary based on the physical parameters of the optical system. A numerical study also suggested the effectiveness of the dynamic parameter settings in improving the Ising machine performance. These results demonstrate the high capability of SPIMs with multiplexing.