Unraveling Quantum Annealers using Classical Hardness

TL;DR

This paper investigates the quantum nature of D-Wave quantum annealers by analyzing their performance on problems with varying classical hardness, revealing classical effects that may obscure their quantum capabilities.

Contribution

It introduces a general method inspired by spin-glass theory to assess quantum annealers and applies it to experimentally study the D-Wave chip's response to classical hardness.

Findings

D-Wave's performance scales unfavorably compared to classical algorithms.

Classical effects may mask the quantum behavior of the annealer.

The method helps distinguish quantum from classical contributions in optimization.

Abstract

Recent advances in quantum technology have led to the development and manufacturing of experimental programmable quantum annealing optimizers that contain hundreds of quantum bits. These optimizers, named `D-Wave' chips, promise to solve practical optimization problems potentially faster than conventional `classical' computers. Attempts to quantify the quantum nature of these chips have been met with both excitement and skepticism but have also brought up numerous fundamental questions pertaining to the distinguishability of quantum annealers from their classical thermal counterparts. Here, we propose a general method aimed at answering these, and apply it to experimentally study the D-Wave chip. Inspired by spin-glass theory, we generate optimization problems with a wide spectrum of `classical hardness', which we also define. By investigating the chip's response to classical hardness, we surprisingly find that the chip's performance scales unfavorably as compared to several analogous classical algorithms. We detect, quantify and discuss purely classical effects that possibly mask the quantum behavior of the chip.