Direct probing of strong magnon-photon coupling in a planar geometry

TL;DR

This paper demonstrates direct probing of strong magnon-photon coupling in a planar device using Brillouin light scattering, highlighting its advantages over microwave spectroscopy and advancing integration prospects for quantum technologies.

Contribution

It introduces a planar geometry for direct probing of magnon-photon coupling with Brillouin light scattering, showing enhanced capabilities for hybrid quantum system integration.

Findings

Cooperativity of 4.5 for 200 nm-thick YIG films.

Cooperativity of 137.4 for 2.46 μm-thick YIG films.

Brillouin light scattering effectively probes magnonic character of polaritons.

Abstract

We demonstrate direct probing of strong magnon-photon coupling using Brillouin light scattering spectroscopy in a planar geometry. The magnonic hybrid system comprises a split-ring resonator loaded with epitaxial yttrium iron garnet thin films of 200 nm and 2.46 $\mu$m thickness. The Brillouin light scattering measurements are combined with microwave spectroscopy measurements where both biasing magnetic field and microwave excitation frequency are varied. The cooperativity for the 200 nm-thick YIG films is 4.5, and larger cooperativity of 137.4 is found for the 2.46 $\mu$m-thick YIG film. We show that Brillouin light scattering is advantageous for probing the magnonic character of magnon-photon polaritons, while microwave absorption is more sensitive to the photonic character of the hybrid excitation. A miniaturized, planar device design is imperative for the potential integration of magnonic hybrid systems in future coherent information technologies, and our results are a first stepping stone in this regard. Furthermore, successfully detecting the magnonic hybrid excitation by Brillouin light scattering is an essential step for the up-conversion of quantum signals from the optical to the microwave regime in hybrid quantum systems.