Competing interlayer charge order and quantum monopole reorganization in bilayer Kagome spin ice via quantum annealing

TL;DR

This study uses quantum annealing to explore interlayer charge order and monopole reorganization in bilayer Kagome spin ice, revealing a sharp phase transition and providing concrete engineering targets.

Contribution

First implementation of bilayer Kagome spin ice on a quantum annealer with independent control of monopole density and interlayer charge order.

Findings

Identified a sharp ferroelectric-to-antiferroelectric transition at a specific interlayer coupling.

Corrected charge structure factor estimations for more accurate order measurement.

Provided a quantum renormalisation ratio to guide hardware design for circuit-QED implementations.

Abstract

Frustrated magnets host emergent magnetic monopoles whose confinement and ordering are governed by two experimental handles that existing platforms cannot vary independently. We realize a bilayer Kagome spin ice across $1{,}536$ logical spins on a D-Wave Advantage2 quantum annealer, providing orthogonal control of monopole density through a quantum drive $\Gamma_{\mathrm{eff}}$ and of interlayer charge order through an independent coupling $\Jz$. Interlayer exchange drives a sharp ferroelectric-to-antiferroelectric Ice-II transition at $(J_{\perp}/J_1)^{*}\approx0.042$, stable across five decades of annealing time and forbidden in any single-layer system. Restricting the charge structure factor to ice-rule plaquettes corrects a systematic order-of-magnitude underestimation in conventional all-plaquette estimators. The quantum renormalisation ratio $\rho_{\max}=0.2771$ converts the hardware gap into a concrete engineering target $\Gamma_c\gtrsim0.6\,\Jone$ for transmon circuit-QED implementations. Three falsifiable predictions for existing Ni$_{81}$Fe$_{19}$ nanowire bilayer architectures follow, all testable without new fabrication.