Higher-order exceptional point in a cavity magnonics system

TL;DR

This paper demonstrates the realization of higher-order exceptional points in a cavity magnonics system with pseudo-Hermiticity, showing how to achieve and detect these points through spectral measurements.

Contribution

It introduces a method to realize third-order exceptional points in a cavity magnonics system, extending the understanding of non-Hermitian physics beyond second-order exceptional points.

Findings

Existence of third-order exceptional point in the system

Eigenvalues can be all real or form complex conjugate pairs

Exceptional points can be observed via output spectrum measurements

Abstract

We propose to realize the pseudo-Hermiticity in a cavity magnonics system consisting of the Kittel modes in two small yttrium-iron-garnet spheres coupled to a microwave cavity mode. The effective gain of the cavity can be achieved using the coherent perfect absorption of the two input fields fed into the cavity. With certain constraints of the parameters, the Hamiltonian of the system has the pseudo-Hermiticity and its eigenvalues can be either all real or one real and other two constituting a complex-conjugate pair. By varying the coupling strengths between the two Kittel modes and the cavity mode, we find the existence of the third-order exceptional point in the parameter space, in addition to the usual second-order exceptional point existing in the system with parity-time symmetry. Also, we show that these exceptional points can be demonstrated by measuring the output spectrum of the cavity.