A Novel Oscillator Ising Machine Coupling Scheme for High-Quality Optimization

Oscillator Ising Machines (OIMs) are networks of coupled nonlinear oscillators that solve the NP-hard Ising problem heuristically. Conventionally, the oscillators in an OIM are coupled using resistors. However, the phase-domain properties of such couplers are unsatisfactory; resistively-coupled OIMs do not realize the optimization performance predicted by simulations of idealized OIMs. This has been a major hurdle impeding the development of high quality analog OIMs on integrated circuits. In this paper, we present a novel coupling scheme, the sampling coupler, that addresses this issue theoretically and practically. Essentially, a sampling coupler injects a current that depends on the phase difference between interacting oscillators. We prove analytically that using sampling couplers leads to idealized OIMs, abstracting away the waveforms and innate phase sensitivities of the oscillators. We evaluate sampling-coupler OIMs (using simulation) on a practically-important digital wireless communication problem and show that the performance is near-optimal. Sampling couplers therefore open up a way to implement practically feasible, high-performance analog OIMs using virtually any oscillator.