Manifestation of the coupling phase in microwave cavity magnonics

TL;DR

This paper investigates how the phase factor in magnon-photon interactions affects the physics of microwave cavity magnonics, revealing its impact on applications like dark mode memories and cavity-mediated coupling, with implications for quantum information.

Contribution

It demonstrates the significance of the coupling phase in hybrid magnon-photon systems and its role in preserving or destroying quantum information applications.

Findings

Coupling phase can alter the physics of magnon/photon interactions.

Sign of coupling strength affects dark mode and cavity-mediated coupling.

Observable effects resemble a discrete Pancharatnam-Berry phase.

Abstract

The interaction between microwave photons and magnons is well understood and originates from the Zeeman coupling between spins and a magnetic field. Interestingly, the magnon/photon interaction is accompanied by a phase factor which can usually be neglected. However, under the rotating wave approximation, if two magnon modes simultaneously couple with two cavity resonances, this phase cannot be ignored as it changes the physics of the system. We consider two such systems, each differing by the sign of one of the magnon/photon coupling strengths. This simple difference, originating from the various coupling phases in the system, is shown to preserve, or destroy, two potential applications of hybrid photon/magnon systems, namely dark mode memories and cavity-mediated coupling. The observable consequences of the coupling phase in this system is akin to the manifestation of a discrete Pancharatnam-Berry phase, which may be useful for quantum information processing.