Incorporating rank-free coupling and external field via an incoherent modulated spatial photonic Ising machine

TL;DR

This paper presents a scalable, amplitude-only spatial photonic Ising machine capable of encoding arbitrary high-rank couplings and external fields, operating at high speed and demonstrating complex problem solving.

Contribution

The authors introduce a rank-free, amplitude-only spatial photonic Ising machine that encodes arbitrary Hamiltonians using Hadamard products, enabling scalable and programmable optical simulation.

Findings

Successfully programmed 797-spin Ising models with external fields.

Solved a Max-Cut problem on a 424,108-vertex graph.

Observed phase transition in the Sherrington-Kirkpatrick model.

Abstract

Spatial photonic Ising machines offer a novel optical platform for optimization and spin-model simulation, but existing diffraction-based schemes rely on auxiliary spins or multiplexing to encode high-rank couplings and external fields, reducing either speed or spin count. We demonstrate an amplitude-only, rank-free spatial photonic Ising machine in which arbitrary Ising Hamiltonians are encoded as Hadamard products on aligned amplitude and binary spatial modulators and read out by a single-pixel intensity measurement. The machine directly programs fully connected 797-spin Ising models with external fields at nearly 9-bit precision and operates at a constant iteration rate of ~200 Hz. By removing zero-valued product terms, the same architecture scales to sparse problems and experimentally solves a Max-Cut instance on a 424,108-vertex Mobius ladder graph. We also observe the phase transition of the Sherrington-Kirkpatrick model, demonstrating programmable optical simulation beyond low-rank couplings. These results establish amplitude modulation as a scalable route to programmable photonic Ising machines.