Graph theory approach to exceptional points in wave scattering

Abstract

In this paper, we use graph theory to solve wave scattering problems in the discrete dipole approx- imation. As a key result of this work, in the presence of active scatterers, we present a systematic method to find arbitrary large–order zero eigenvalue exceptional points (EPs). This is achieved by solving a set of non–linear equations that we interpret, in a graph theory picture, as vanishing sums of scattering events. We then show how the total field of the system responds to parameter perturbations at the EP. Finally, we investigate the sensitivity of the power output to imaginary perturbation in the design frequency. This perturbation can be employed to trade sensitivity for a different dissipation balance of the system. The purpose of the results of this paper is manifold. On the one hand, we aim to shed light on the link between graph theory and wave scattering. On the other hand, the results of this paper find application in all those settings where zero eigenvalue EPs play a unique role like in coherent perfect absorption (CPA) structures.