Generating target graph couplings for the quantum approximate optimization algorithm from native quantum hardware couplings

We present methods for constructing any target coupling graph using limited global controls in an Ising-like quantum spin system. Our approach is motivated by implementing the quantum approximate optimization algorithm (QAOA) on trapped-ion quantum hardware to find approximate solutions to MaxCut. We present a mathematical description of the problem and provide approximately optimal algorithmic constructions that generate arbitrary unweighted coupling graphs with n nodes in O(n) global entangling operations and weighted graphs with m edges in O(m) operations. These upper bounds are not tight in general, and we formulate a mixed-integer program to solve the graph coupling problem to optimality. We perform numeric experiments on small graphs with n 8 and show that optimal sequences, which use fewer operations, can be found using mixed-integer programs. Noisy simulations of MaxCut QAOA show that our implementation is less susceptible to noise than the standard gate-based compilation.

Automated summary

In this study, methods for constructing any target coupling graph using limited global controls in an Ising-like quantum spin system are presented. The results of numerical experiments and noise simulations demonstrate the superiority of this approach.