Increasing ising machine capacity with multi-chip architectures

Abstract

Nature has inspired a lot of problem solving techniques over the decades. More recently, researchers have increasingly turned to harnessing nature to solve problems directly. Ising machines are a good example and there are numerous research prototypes as well as many design concepts. They can map a family of NP-complete problems and derive competitive solutions at speeds much greater than conventional algorithms and in some cases, at a fraction of the energy cost of a von Neumann computer. However, physical Ising machines are often fixed in its problem solving capacity. Without any support, a bigger problem cannot be solved at all. With a simple divide-and-conquer strategy, it turns out, the advantage of using an Ising machine quickly diminishes. It is therefore desirable for Ising machines to have a scalable architecture where multiple instances can collaborate to solve a bigger problem. We then discuss scalable architecture design issues which lead to a multiprocessor Ising machine architecture. Experimental analyses show that our proposed architectures allow an Ising machine to scale in capacity and maintain its significant performance advantage (about 2200x speedup over a state-of-the-art computational substrate). In the case of communication bandwidth-limited systems, our proposed optimizations in supporting batch mode operation can cut down communication demand by about 4--5x without a significant impact on solution quality.