Coupling phase enabled level transitions in pseudo-Hermitian magnon-polariton systems

TL;DR

This paper introduces a pseudo-Hermitian model for magnon-polariton systems that reveals phase-dependent energy spectrum transitions, including exceptional points, enabling advanced control of hybrid quantum states.

Contribution

It presents a novel pseudo-Hermitian framework linking phase transitions to mode coupling in magnon-polariton systems, advancing control strategies in spintronics.

Findings

Observation of exceptional points at symmetry breaking

Identification of level attraction and repulsion phenomena

Energy spectrum exhibits double Z-shape during phase transitions

Abstract

While cavity-magnon hybridization offers intriguing physics, its practical implementation is hindered by intrinsic damping in both cavity and magnon modes, leading to short coherence times and constrained applications. Recently, with the emergence of tunable external gain at the macroscopic scale, the research focus has shifted from purely lossy systems to gain-loss balanced non-Hermitian systems. Here, we propose a pseudo-Hermitian model with two magnon and two cavity modes coupled via phase-dependent interaction. We link the energy spectrum to phase transitions, observing exceptional points when pseudo-Hermitian symmetry breaks. We also observed level attraction and level repulsion. The former corresponds to four phase transitions and manifests as a double Z-shaped energy spectrum, the latter corresponds to two phase transitions, with the repulsive gap depending on the coupling phase. In the phase diagram defined by non-Hermiticity and coupling phase, we reveal a distinctive correspondence: pseudo-Hermitian symmetry breaking is intrinsically linked to coupling mode transitions, enabling new strategies for controlling hybrid quantum states in spintronic systems.