PT -symmetric magnon laser in cavity optomagnonics

Abstract

Nonlinear magnonics based on the coupling of magnons and optical photons has become a crucial topic in the quantum magnonic field. Here, we demonstrate the magnon laser, the analog of the optical laser in magnonics, in a parity-time ($\mathcal{PT}$) symmetric cavity optomagnonical system involving active and passive optical whispering gallery modes and the magnon mode. We show that the stimulated emitted magnon number can be coherently amplified above a threshold driving power in the $\mathcal{PT}$-symmetric regime where the splitting of optical supermodes is resonant with the magnon frequency, indicating the occurrence of the magnon laser. And this magnon laser action can work with low threshold when the system approaches the optical gain-loss balance and when increasing the optomagnonic coupling. Furthermore, the frequency of the magnon laser can be continuously tuned by adjusting the applied magnetic field strength, which is a distinct feature compared to the photon or phonon amplification by stimulated emission. The study of the $\mathcal{PT}$-symmetric magnon laser may promote the intersection and merging of various disciplines like non-Hermitian physics and quantum magnonics, and provide the theoretical basis and reference for the research and development of new frequency-tunable laser devices.