When quantum relaxation benefits quantum annealing: a case study of ferromagnetic chains with alternating sectors

We study the behavior of a commercial quantum annealing processor on the problem of a ferromagnetic chain with alternating strength sectors. This is a problem for which, at constant run-time, the closed-system adiabatic quantum algorithm is known to exhibit exponentially decreasing success probability in the sector size. We find that the behavior of the quantum annealing processor departs significantly from the prediction of closed-system behavior, with the success probability rising for sufficiently large sector sizes. Rather than correlating with the size of quantum minimum gap, the success probability exhibits a strong correlation with the number of single-fermion states calculated at the minimum gap with an energy below the processor temperature. We demonstrate that this behavior is consistent with a quantum open-system description of the process, in which the excitation rate out of the ground states depends on the number of available excitations weighted by the ratio of the excitation energy to the temperature.