A Whole Surface of Exceptional Points

Abstract

Exceptional points (EPs) are singularities of energy levels in generalized eigenvalue systems. In this Letter, we demonstrate the surface of EPs on a magnon polariton platform composed of coupled magnons and microwave photons. Our experiments show that EPs form a three-dimensional exceptional surface (ES) when the system is tuned in a four-dimensional synthetic space. We demonstrate that there exists an exceptional saddle point (ESP) in the ES which originates from the unique couplings between magnons and microwave photons. Such an ESP exhibits unique anisotropic behaviors in both the real and imaginary parts of the eigenfrequencies. To the best of our knowledge, this is the first experimental observation of ES, opening up new opportunities for high-dimensional control of non-Hermitian systems.

Coherent and Dissipative Cavity Magnonics

“…9,143 Other control parameters have also been used to manipulate cavity-magnonic EPs, 8,21,22 and higher order exceptional points, occurring when many eigenstates coalesce, further enhance the sensitivity. 24,144 Furthermore, the creation of exceptional surfaces in cavity magnonics 24 could be further exploited for enhanced sensitivity with increased flexibility, as has been done in photonic systems. 145,146 In addition to EPs, cavity-magnonic systems may also contain BICs, and in fact, both may exist in the same device.…”