Identifying quantum coherence in quantum annealers

TL;DR

This paper proposes a method using many-body coherent oscillations to detect quantum coherence in large-scale quantum annealers, demonstrating its effectiveness through theoretical analysis and experiments on D-Wave devices.

Contribution

It introduces many-body coherent oscillations as a novel diagnostic tool for identifying quantum coherence in analog quantum simulators and applies it to D-Wave quantum annealers.

Findings

Defect densities follow Kibble-Zurek scaling in quenches.

Expected oscillatory signatures are absent in current annealing protocols.

Modifications to annealing schedules can enhance oscillation visibility.

Abstract

Demonstrating genuine many-body quantum coherence in large-scale quantum processors remains a central challenge for near-term quantum technologies. Recent experiments on D-Wave quantum annealers have investigated quenches of Ising chains and observed defect densities that show Kibble-Zurek scaling, consistent with coherent quantum dynamics. However, identical scaling can arise from classical or thermal processes. Here we propose the use of many-body coherent oscillations (MBCO) as a diagnostic for the identification of system-wide coherence in analog quantum simulators. Solving the time-dependent Schrodinger equation, we show that quenches of a staggered one-dimensional Ising chain across a quantum critical point produce oscillatory signatures in defect observables. We implement this model on the D-Wave Advantage quantum annealer. Using fast-anneal protocols, we find that, although defect densities follow Kibble-Zurek scaling, the expected oscillatory behavior is absent. We demonstrate that static disorder associated with individual qubits is not likely responsible for the absence of MBCO. Modest modifications to annealing schedules can dramatically enhance oscillation visibility. This work gives a general roadmap for the search for quantum coherence in noisy, large-scale quantum platforms.