Parallel Quantum Annealing

TL;DR

This paper introduces parallel quantum annealing, a method that solves multiple problems simultaneously on a quantum annealer, significantly reducing time-to-solution for NP-hard problems like Maximum Clique.

Contribution

The paper proposes a novel parallel quantum annealing technique that efficiently utilizes available qubits to solve multiple problems concurrently, improving speed without major quality loss.

Findings

Dramatic speed-ups in Time-to-Solution for Maximum Clique problems.

Parallel annealing reduces TTS for single problems.

Method maintains acceptable solution quality despite parallelization.

Abstract

Quantum annealers of D-Wave Systems, Inc., offer an efficient way to compute high quality solutions of NP-hard problems. This is done by mapping a problem onto the physical qubits of the quantum chip, from which a solution is obtained after quantum annealing. However, since the connectivity of the physical qubits on the chip is limited, a minor embedding of the problem structure onto the chip is required. In this process, and especially for smaller problems, many qubits will stay unused. We propose a novel method, called parallel quantum annealing, to make better use of available qubits, wherein either the same or several independent problems are solved in the same annealing cycle of a quantum annealer, assuming enough physical qubits are available to embed more than one problem. Although the individual solution quality may be slightly decreased when solving several problems in parallel (as opposed to solving each problem separately), we demonstrate that our method may give dramatic speed-ups in terms of Time-to-Solution (TTS) for solving instances of the Maximum Clique problem when compared to solving each problem sequentially on the quantum annealer. Additionally, we show that solving a single Maximum Clique problem using parallel quantum annealing reduces the TTS significantly.