Realization of exceptional points along a synthetic orbital angular momentum dimension
Mu Yang, Haoqing Zhang, Yu‐Wei Liao, Zhenghao Liu, Zheng-Wei Zhou, Xingxiang Zhou, Jin‐Shi Xu, Yong‐Jian Han, Chuan‐Feng Li, Guang‐Can Guo
Abstract
Exceptional points (EPs), at which more than one eigenvalue and eigenvector coalesce, are unique spectral features of non-Hermiticity (NH) systems. They exist widely in open systems with complex energy spectra. We experimentally demonstrate the appearance of paired EPs in a periodical-driven degenerate optical cavity along the synthetic orbital angular momentum dimension with a tunable parameter. The complex-energy band structures and the key features of EPs, i.e., their bulk Fermi arcs, parity-time symmetry breaking transition, energy swapping, and half-integer band windings, are directly observed by detecting the wavefront angle-resolved transmission spectrum. Our results demonstrate the flexibility of using the photonic synthetic dimensions to implement NH systems beyond their geometric dimension and EP-based sensing.