Strong coupling of magnons in a YIG sphere to photons in a planar superconducting resonator in the quantum limit

TL;DR

This paper demonstrates strong coupling between magnons in a YIG sphere and photons in a planar superconducting resonator, showing potential for integrated quantum magnonic and superconducting devices.

Contribution

It provides experimental evidence of strong magnon-photon coupling in a planar superconducting resonator with multiple magnon modes, advancing quantum magnonics integration.

Findings

Strong coupling observed with less than one excitation on average

Mode frequencies and coupling strengths match theoretical predictions

Oscillations at mode splitting frequency indicate coherent magnon-photon interactions

Abstract

We report measurements of a superconducting coplanar waveguide resonator (CPWR) coupled to a sphere of yttrium-iron garnet. The non-uniform CPWR field allows us to excite various magnon modes in the sphere. Mode frequencies and relative coupling strengths are consistent with theory. Strong coupling is observed to several modes even with, on average, less than one excitation present in the CPWR. The time response to square pulses shows oscillations at the mode splitting frequency. These results indicate the feasibility of combining magnonic and planar superconducting quantum devices.