Reexamining classical and quantum models for the D-Wave One processor

TL;DR

This paper critically reexamines the evidence for quantum annealing in the D-Wave One processor, showing that classical models do not fully explain the experimental data, highlighting the need for more comprehensive models.

Contribution

It introduces new measures considering ground state degeneracy and excited states, revealing discrepancies between the D-Wave device data and classical or quantum models.

Findings

Classical rotor model and SQA do not fully match D-Wave data with new measures.

SQA and rotor model closely correlate with each other.

Differences in ground state sets depend on device calibration and simulation parameters.

Abstract

We revisit the evidence for quantum annealing in the D-Wave One device (DW1) based on the study of random Ising instances. Using the probability distributions of finding the ground states of such instances, previous work found agreement with both simulated quantum annealing (SQA) and a classical rotor model. Thus the DW1 ground state success probabilities are consistent with both models, and a different measure is needed to distinguish the data and the models. Here we consider measures that account for ground state degeneracy and the distributions of excited states, and present evidence that for these new measures neither SQA nor the classical rotor model correlate perfectly with the DW1 experiments. We thus provide evidence that SQA and the classical rotor model, both of which are classically efficient algorithms, do not satisfactorily explain all the DW1 data. A complete model for the DW1 remains an open problem. Using the same criteria we find that, on the other hand, SQA and the classical rotor model correlate closely with each other. To explain this we show that the rotor model can be derived as the semiclassical limit of the spin-coherent states path integral. We also find differences in which set of ground states is found by each method, though this feature is sensitive to calibration errors of the DW1 device and to simulation parameters.