Benchmarks and Recommendations for Quantum, Digital, and GPU Annealers in Combinatorial Optimization

Annealers leverage quadratic unconstrained binary optimization (QUBO) formulas to address combinatorial optimization problems (COPs) and have shown potential to outperform classical computers. This paper examines three prominent types of annealers: quantum, digital, and GPU annealers. Quantum annealers (QAs) are exemplified by the D-Wave Advantage, which relies on the quantum tunneling phenomenon to rapidly locate the minimum-energy system state corresponding to the optimal solution to a COP. Digital annealers (DAs) are typified by the Fujitsu Digital Annealing Unit (DAU), which is based on a quantum-inspired digital architecture to perform parallel and real-time optimization calculations to solve a COP. GPU annealers (GPUAs) are exemplified by the Compal Quantix solver, which harnesses graphics processing units (GPUs) to conduct the diverse adaptive bulk search for the optimal COP solution. This paper first provides an introductory overview of the QA, DA, and GPUA, and then proceeds to benchmark their performance on solving various well-known COPs such as the subset sum, maximum cut, vertex cover, 0/1 knapsack, graph coloring, Hamiltonian cycle, traveling salesperson, and job-shop scheduling problems. Their performance is also compared with that of state-of-the-art algorithms running on classical computers. Through comprehensive performance benchmarks in terms of the solution quality and the execution time, we identify the strengths and weaknesses of each annealer. In addition, we also provide recommendations to improve the performance of each annealer. Specifically, we recommend using the genetic algorithm, the improved particle swarm optimization algorithm, and the ant colony optimization algorithm in all annealers, using quantum pausing, quenching, and reverse annealing in the QA, using built-in separated penalty terms, one-way/two-way one-hot constraints, and linear inequality constraints in the DA, and implementing some parallel algorithms in the GPUA for performance improvement.