A Practical Cross-Platform, Multi-Algorithm Study of Quantum Optimisation for Configurational Analysis of Materials

Abstract: Quantum computers show potential for achieving computational advantage over classical computers, with many candidate applications in the domains of chemistry and materials science. We consider the well-studied problem of configurational analysis of materials and, more specifically, finding the lowest energy configuration of defective graphene structures. This problem acts as a test-case which allows us to study various algorithms that are applicable to Quadratic Unconstrained Binary Optimisation (QUBO) problems, which are generally classically intractable exactly. To solve this problem, we implement two methods, the Variational Quantum Eigensolver (VQE) and Quantum Annealing (QA), on commercially-available gate-based and quantum annealing devices that are accessible via Quantum-Computing-as-a-Service (QCaaS) models. To analyse the performance of these algorithms, we use a toolbox of relevant metrics and compare performance against three classical algorithms. We employ quantum methods to solve fully-connected QUBOs of up to $72$ variables, and find that algorithm performance beyond this is restricted by device connectivity, noise and classical computation time overheads. The applicability of our approach goes beyond the selected configurational analysis test-case, and we anticipate that our approach will be of use for optimisation problems in general.