Cavity mediated coherent coupling of magnetic moments

TL;DR

This paper demonstrates long-range strong coupling between spatially separated ferromagnetic spheres mediated by a microwave cavity, revealing cavity-mediated interactions and dark states in magnetostatic modes.

Contribution

It introduces a method to achieve and analyze cavity-mediated coherent coupling of magnetic moments in spatially separated ferromagnets.

Findings

Strong coupling of magnetostatic modes observed even when detuned from cavity modes.

Coupling strength exhibits a 1/Δ dependence on cavity detuning.

Dark states of magnetostatic modes are identified and explained.

Abstract

We demonstrate the long range strong coupling of magnetostatic modes in spatially separated ferromagnets mediated by a microwave frequency cavity. Two spheres of yttrium iron garnet are embedded in the cavity and their magnetostatic modes probed using a dispersive measurement technique. We find they are strongly coupled to each other even when detuned from the cavity modes. We investigate the dependence of the magnet-magnet coupling on the cavity detuning $\Delta$, and find a $1/\Delta$ dependence also characteristic of cavity-coupled superconducting qubits. Dark states of the coupled magnetostatic modes of the system are observed, and ascribed to mismatches between the symmetries of the modes and the drive field.