Observation of topological Phenomena in a Weyl Exceptional Ring with Single Photons

Abstract: Compared with Hermitian theory, non-Hermitian physics offers a fundamentally different mathematical framework, enabling the observation of topological phenomena that have no analogue in Hermitian systems. Among these, the exceptional point (EP) ring stands out as a quintessential topological feature unique to non-Hermitian systems. In this study, we employ single-photon interferometry to overcome the experimental challenge of precise phase control in quantum systems, thereby enabling a complete simulation of the non-Hermitian EP ring in three-dimensional parameter space without invoking any additional symmetry assumptions. By measuring the non-Hermitian dynamics in three-dimensional parameter space, we determine the system's eigenstates, which allows us to characterize the topological band structure of the system under different conditions. We describe the topological properties of the EP ring by extracting the Chern number and Berry phase for different parameter manifolds and observe the topological critical phenomena of the system. Our work paves the way for further exploration of topological non-Hermitian systems.