High-Cooperativity Cavity QED with Magnons at Microwave Frequencies

Magnons are quantized quasiparticles that can in principle be used in quantum computation. To implement such computations in practice, magnons must be strongly coupled with photons, which transfer information between them. In this work, the authors demonstrate extremely strong couplings using a type of multipost microwave cavity that can focus a magnetic field into submillimeter-sized samples. This ultrastrong coupling of magnons and photons can be a building block in the architecture of high-fidelity hybrid quantum systems for the processors of the future.