Quantum versus classical annealing of Ising spin glasses

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Science  12 Mar 2015:
DOI: 10.1126/science.aaa4170

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Quantum annealers use quantum fluctuations to escape local minima and find low energy configurations of a physical system. Strong evidence for superiority of quantum annealing has come from comparing quantum annealing implemented through quantum Monte Carlo (QMC) simulations to classical annealing. Motivated by recent experiments we revisit the question of when quantum speedup may be expected. Even though, for two-dimensional Ising spin glasses, a better scaling is seen for quantum annealing, this advantage is due to time discretization artifacts and measurements which are not possible on a physical quantum annealer. Simulations in the physically relevant continuous time limit, on the other hand, do not show superiority. Our results imply that care has to be taken when using QMC simulations to assess potential for quantum speedup.

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