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Nat Commun. 2017 Nov 8;8(1):1368. doi: 10.1038/s41467-017-01634-w.

Observation of the exceptional point in cavity magnon-polaritons.

Author information

1
Quantum Physics and Quantum Information Division, Beijing Computational Science Research Center, Beijing, 100193, China.
2
Department of Engineering, University of Cambridge, Cambridge, CB3 0FA, UK.
3
Institute of Microelectronics, Tsinghua National Laboratory of Information Science and Technology, Tsinghua University, Beijing, 100084, China. litf@tsinghua.edu.cn.
4
Quantum Physics and Quantum Information Division, Beijing Computational Science Research Center, Beijing, 100193, China. jqyou@csrc.ac.cn.

Abstract

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.

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