Multi-Qubit Correction for Quantum Annealers

TL;DR

This paper introduces multi-qubit correction (MQC), a new postprocessing technique for quantum annealers that improves solution quality by reducing excited states to lower energy states, enhancing the accuracy and reproducibility of quantum annealing results.

Contribution

MQC is a novel postprocessing method that leverages virtual tunnels to systematically lower energy states in quantum annealer outputs, outperforming existing techniques.

Findings

MQC finds samples with significantly lower energy values.

MQC improves reproducibility of quantum annealing results.

MQC outperforms spin-reversal and classical postprocessing methods.

Abstract

We present \emph{multi-qubit correction} (MQC) as a novel postprocessing method for quantum annealers that views the evolution in an open-system as a Gibbs sampler and reduces a set of excited states to a new synthetic state with lower energy value. After sampling from the ground state of a given (Ising) Hamiltonian, MQC compares pairs of excited states to recognize virtual tunnels--i.e., a group of qubits that changing their states simultaneously can result in a new state with lower energy value--and successively converges to the ground state. Experimental results using D-Wave 2000Q quantum annealers demonstrate that MQC finds samples with notably lower energy values and improves the reproducibility of results when compared to recent hardware/software advances in the realm of quantum annealing, such as spin-reversal transforms, classical postprocessing techniques, and increased inter-sample delay between successive measurements.