Quantum versus Classical Annealing of Ising Spin Glasses

TL;DR

This paper critically examines the potential quantum speedup in solving Ising spin glass problems, revealing that previous advantages seen in QMC simulations are artifacts of simulation methods rather than real quantum benefits.

Contribution

The study clarifies that continuous-time QMC simulations do not demonstrate quantum speedup, emphasizing the importance of simulation methods in evaluating quantum annealing performance.

Findings

QMC advantages are due to discretization and measurement artifacts.

Continuous-time QMC does not show quantum speedup.

No expected quantum speedup for 2D spin glasses.

Abstract

The strongest evidence for superiority of quantum annealing on spin glass problems has come from comparing simulated quantum annealing using quantum Monte Carlo (QMC) methods to simulated classical annealing [G. Santoro et al., Science 295, 2427(2002)]. Motivated by experiments on programmable quantum annealing devices we revisit the question of when quantum speedup may be expected for Ising spin glass problems. We find that even though a better scaling compared to simulated classical annealing can be achieved for QMC simulations, this advantage is due to time discretization and measurements which are not possible on a physical quantum annealing device. QMC 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 quantum speedup potential and are consistent with recent arguments that no quantum speedup should be expected for two-dimensional spin glass problems.