As the counterpart of $\mathcal{P}\mathcal{T}$ symmetry, for anti-$\mathcal{P}\mathcal{T}$-symmetry abundant phenomena and potential applications have been predicted or demonstrated theoretically. However, experimental realization of the coupling required in anti-$\mathcal{P}\mathcal{T}$ symmetry is difficult. By our coupling two yttrium iron garnet spheres commonly to a microwave cavity, the large cavity dissipation rate makes the magnon-magnon coupling dissipative and purely imaginary. Thereby, the hybrid magnon-cavity system obeys a two-dimensional anti-$\mathcal{P}\mathcal{T}$ Hamiltonian. In terms of the magnon-readout method, the method adopted here, we demonstrate the validity of our method in constructing an anti-$\mathcal{P}\mathcal{T}$ system and present the counterintuitive level-attraction process. Our work provides a platform to explore the anti-$\mathcal{P}\mathcal{T}$-symmetry properties and paves the way to study dynamical evolution and topological properties around exceptional points in multimagnon-cavity systems.

• Received 1 July 2019
• Revised 29 October 2019

DOI:https://doi.org/10.1103/PhysRevApplied.13.014053