Source-linked AI summary
Quantum versus Classical Annealing of Ising Spin Glasses
Bettina Heim, Troels F. Rønnow, Sergei V. Isakov, Matthias Troyer
TL;DR
The paper revisits whether quantum annealing can outperform classical annealing for Ising spin glasses, addressing conflicting evidence from simulated quantum annealing. It compares discrete- and continuous-time QMC simulations and finds that the apparent advantage disappears under physically relevant continuous-time measurement conditions.
Problem
The paper asks when quantum speedup should be expected for Ising spin glasses, because prior simulated-annealing comparisons suggested an advantage while hardware studies had not found clear speedup.
Method
The paper compares simulated classical annealing with path-integral simulated quantum annealing, varying time-slice discretization, temperature, computational effort, and measurement procedure.
Results
The apparent SQA advantage comes from large imaginary-time steps and selecting the lowest-energy time slice; with continuous time and average-energy measurement, the advantage vanishes.
Takeaways & Limitations
QMC-based assessments of quantum speedup must use the continuous-time limit and experimentally accessible measurements when estimating physical quantum-annealer performance.
Takeaways & Limitations
SQA reliably reflects physical QA only when thermalization, at least within a local minimum, is fast compared with the annealing time.
Abstract
from arXiv · showhide
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.