Magnon-photon strong interaction with magnetic nanowires

Nanoscopic spin excitations in confined geometries open a wide range of opportunities both for fundamental investigations and for applications.An archetypal spin excitation is embodied in the magnetic vortex.In order to minimize the total magnetostatic energy in a mesoscopic disc, the magnetization curls clockwise or counter-clockwise, defining the vortex circulation. At the core, exchange interaction forces the magnetization to point up or down defining the vortex polarity. Magnetic vortices have been extensively investigated and exploited due to their stable non-uniform magnetization.

We present our first steps towards the coherent coupling between magnetic vortex excitations and resonant photons living in a superconducting cavity. Using a coplanar superconducting transmission line, we perform broad-band ferromagnetic resonance of thin-film mesoscopic magnets. This allows identifying the low-energy Kittel spin-wave excitation (with infinite wavelength). By patterning gap capacitors, we transform this transmission line into a cavity where resonant photons strong couple to the Kittel mode, as evidenced by the observation of an anti-crossing in the transmission spectra. We also develop the theory for coupling between magnetic textures (vortices and skyrmions) and microwave photons.