Level attraction in a quasiclosed cavity: Antiresonance in magnonic devices

We provide a comprehensive analytical description of the effective coupling associated with an antiresonance within a hybrid system comprising a quasiclosed photonic cavity and a ferrimagnetic material. While so-called level attraction between a resonant system inside an open cavity is well understood, the physical underpinnings of this phenomenon within quasiclosed cavities have remained elusive. Leveraging input-output theory, we successfully differentiate between the repulsive and attractive aspects of this coupling. Our proposed model demonstrates that by understanding the phase jump at the resonances and the studied antiresonance, we can predict the nature of the effective coupling of the antiresonance for a given position of the ferrimagnet in the cavity.