Optimizing the cooperativity between magnetic and acoustic planar waves

The ability to adjust the cooperativity between distinct waveforms is an important feature of quantum information devices. The coupling between spin and phonon is of particular interest, which allows for long-range communication at GHz frequency [1,2]. Using local light scattering, we demonstrate that one can maximize this attribute in thin films by adjusting the orientation and strength of an external magnetic field. Their overlap can be enhanced by about a factor of 2 by coupling the Kittel mode to circularly polarized acoustic waves (out-of-plane geometry) instead of linearly polarized ones (in-plane geometry). Additionally their overlap is maximized by matching the Kittel frequency with the half-wave plate condition for the acoustic wave. Considering the frequency-dependent damping of the magnetic and acoustic systems, we find an optimum working frequency for the two quasi-particle interconversion.