Identifying the minor set cover of dense connected bipartite graphs via random matching edge sets

Abstract

Using quantum annealing to solve an optimization problem requires minor embedding a logic graph into a known hardware graph. In an effort to reduce the complexity of the minor embedding problem, we introduce the minor set cover (MSC) of a known graph $${\mathcal {G}}$$G: a subset of graph minors which contain any remaining minor of the graph as a subgraph. Any graph that can be embedded into $${\mathcal {G}}$$G will be embeddable into a member of the MSC. Focusing on embedding into the hardware graph of commercially available quantum annealers, we establish the MSC for a particular known virtual hardware, which is a complete bipartite graph. We show that the complete bipartite graph $$K_{N,N}$$KN,N has a MSC of N minors, from which $$K_{N+1}$$KN+1 is identified as the largest clique minor of $$K_{N,N}$$KN,N. The case of determining the largest clique minor of hardware with faults is briefly discussed but remains an open question.