Branching high-order exceptional points in non-hermitian optical systems

Abstract: Exceptional points are complex-valued spectral singularities that lead to a host of intriguing features such as loss-induced transparency - a counterintuitive process in which an increase in the system's overall loss can lead to enhanced transmission. In general, the associated enhancements scale with the order of the exceptional points. Consequently, it is of great interest to devise new strategies to implement realistic devices capable of exhibiting high-order exceptional points. Here, we show that high-order N-photon exceptional points can be generated by exciting non-hermitian waveguide arrangements with coherent light states. Using photon-number resolving detectors it then becomes possible to observe N-photon enhanced loss-induced transparency in the quantum realm. Further, we analytically show that the number-resolved dynamics occurring in the same nonconservative waveguide arrays will exhibit eigenspectral ramifications having several exceptional points associated to different sets of eigenmodes and dissipation rates.