Control of the coupling strength and linewidth of a cavity magnon-polariton

The full coherent control of hybridized systems such as strongly coupled cavity-magnon states is a crucial step to enable future information processing technologies. Thus, it is particularly interesting to engineer deliberate control mechanisms such as the full control of the coupling strength which can act as a measure for coherent information exchange. In this work, we employ cavity resonator spectroscopy to demonstrate the complete control of the coupling strength of hybridized cavity-magnon states. For this, we use two driving microwave inputs which can be tuned at will. For these inputs, both the relative phase φ and relative amplitude ratio δ0 can be independently controlled. We demonstrate that for specific quadratures between both tones we can increase the coupling strength, close the anticrossing gap, and enter a regime of level merging. At the transition, the absolute cavity signal is modified by 30 dB and we observe an additional linewidth decrease of 13% at resonance level merging. This kind of control over the coupling, and hence linewidth, opens an avenue to enable or suppress an exchange of information and bridges the gap between quantum information and spintronics applications.