Photonic spin Hall effect in $\mathcal{PT}$-symmetric non-Hermitian cavity magnomechanics

TL;DR

This paper explores the photonic spin Hall effect in a non-Hermitian cavity magnomechanics system with PT-symmetry, demonstrating tunable control of the effect via exceptional points and effective magnon-photon coupling.

Contribution

It introduces a PT-symmetric non-Hermitian cavity magnomechanics model and analyzes the control of the photonic spin Hall effect through exceptional points and system parameters.

Findings

Emergence of third-order exceptional point (EP_3) under tunable coupling.

Enhanced or suppressed photonic spin Hall effect via magnon-photon coupling.

Intracavity length influences the transverse shift of the PSHE.

Abstract

Non-Hermitian cavity magnomechanics (CMM), which incorporates the magnon-photon and magnon-phonon interactions simultaneously, enables rich physical phenomena, including exceptional-point-enhanced sensing, and offers pathways toward topological transitions and nonreciprocal quantum transformation. These interactions exert a pivotal influence on the optical response of a weak probe field and pave the way for novel applications in quantum technologies. In this work, we consider a yttrium-iron-garnet (YIG) sphere coupled to a microwave cavity. The magnon mode of the YIG sphere is directly excited through microwave field coupling, whereas the cavity mode is probed via a weak-field interrogation scheme. The direct interaction of a traveling field with the magnon mode induces gain in the system, thereby establishing non-Hermitian dynamics. The parity-time (PT)-symmetric behavior of a hybrid non-Hermitian CMM is designed and investigated. Eigenvalue spectrum analysis demonstrates that a third-order exceptional point (EP_3) emerges under tunable effective magnon-photon coupling when the traveling field is oriented at an angle of \pi/2 relative to the cavity's x-axis. The photonic spin Hall effect (PSHE) in a reflected probe field is subsequently examined in such a system. Under balanced gain and loss conditions and in the presence of effective magnon-phonon coupling, tunable effective magnon-photon coupling enables coherent control of the PSHE across the broken PT-symmetric phase, at the EP_3, and in the PT-symmetric phase. Investigation reveals that the PSHE can be significantly enhanced or suppressed via effective magnon-photon coupling. The influence of intracavity length on the PSHE is further explored, providing an additional parameter for fine-tuning the transverse shift. These findings establish a direct correspondence between the PSHE and the underlying non-Hermitian eigenvalue spectrum.