Optimizing the magnon-phonon cooperativity in planar geometries

TL;DR

This paper demonstrates how to optimize magnon-phonon coupling in planar magnetic geometries by adjusting magnetic field orientation and matching frequencies, achieving a maximum cooperativity of about 6 in garnets.

Contribution

It introduces a method to tune magnon-phonon cooperativity in planar geometries through magnetic field orientation and frequency matching, enhancing coupling strength.

Findings

Coupling strength doubles in out-of-plane magnetized geometry.

Maximum cooperativity of about 6 achieved in garnets.

Optimal overlap occurs when Kittel frequency matches acoustic resonance.

Abstract

Optimizing the cooperativity between two distinct particles is an important feature of quantum information processing. Of particular interest is the coupling between spin and phonon, which allows for integrated long range communication between gates operating at GHz frequency. Using local light scattering, we show that, in magnetic planar geometries, this attribute can be tuned by adjusting the orientation and strength of an external magnetic field. The coupling strength is enhanced by about a factor of 2 for the out-of-plane magnetized geometry where the Kittel mode is coupled to circularly polarized phonons, compared to the in-plane one where it couples to linearly polarized phonons. We also show that the overlap between magnon and phonon is maximized by matching the Kittel frequency with an acoustic resonance that satisfies the half-wave plate condition across the magnetic film thickness. Taking the frequency dependence of the damping into account, a maximum cooperativity of about 6 is reached in garnets for the normal configuration near 5.5 GHz.