Journal Article

Observation of the exceptional point in cavity magnon-polaritons

Luo, Xiao-Qing, Wang, Yi-Pu, Li, Tie-Fu, Zhang, Dengke, You, J. Q.

2017

Overview

Magnon–polaritons are hybrid light–matter quasiparticles originating from the strong coupling between magnons and photons. They have emerged as a potential candidate for implementing quantum transducers and memories. Owing to the dampings of both photons and magnons, the polaritons have limited lifetimes. However, stationary magnon–polariton states can be reached by a dynamical balance between pumping and losses, so the intrinsically nonequilibrium system may be described by a non-Hermitian Hamiltonian. Here we design a tunable cavity quantum electrodynamics system with a small ferromagnetic sphere in a microwave cavity and engineer the dissipations of photons and magnons to create cavity magnon–polaritons which have non-Hermitian spectral degeneracies. By tuning the magnon–photon coupling strength, we observe the polaritonic coherent perfect absorption and demonstrate the phase transition at the exceptional point. Our experiment offers a novel macroscopic quantum platform to explore the non-Hermitian physics of the cavity magnon–polaritons. Strong coupling between magnons and photons allows coupling of magnongs to qubits, suggesting that magnon-polaritons could find applications in quantum information. Here, Zhang et al. observe an exceptional point and spontaneous symmetry breaking in a cavity magnon-polariton system.

• Publisher: Nature Publishing Group UK,Nature Publishing Group,Nature Portfolio
• Subject: 639/624/400/2797 / 639/766/119/2793 / Coupling / Ferromagnetism / Humanities and Social Sciences / Magnons / multidisciplinary / Phase transitions / Photons / Polaritons / Quantum electrodynamics / Quantum theory / Science / Science (multidisciplinary) / Transducers