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arXiv · 2303.11834

Experimental Simulation of Symmetry-Protected Higher-Order Exceptional Points with Single Photons

Kunkun Wang·Lei Xiao·Haiqing Lin·Wei Yi·Emil J. Bergholtz·Peng Xue
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Abstract

Exceptional points (EPs) of non-Hermitian (NH) systems have recently attracted increasing attention due to their rich phenomenology and intriguing applications. Compared to the predominantly studied second-order EPs, higher-order EPs have been assumed to play a much less prominent role because they generically require the tuning of more parameters. Here we experimentally simulate two-dimensional topological NH band structures using single-photon interferometry, and observe topologically stable third-order EPs obtained by tuning only two real parameters in the presence of symmetry. In particular, we explore how different symmetries stabilize qualitatively different third-order EPs: the parity-time symmetry leads to a generic cube-root dispersion, while a generalized chiral symmetry implies a square-root dispersion coexisting with a flat band. Additionally, we simulate fourfold degeneracies, composed of the non-defective twofold degeneracies and second-order EPs. Our work reveals the abundant and conceptually richer higher-order EPs protected by symmetries and offers a versatile platform for further research on topological NH systems.

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Kunkun Wang, Lei Xiao, Haiqing Lin, Wei Yi, Emil J. Bergholtz, Peng Xue. 2023-03-21. Experimental Simulation of Symmetry-Protected Higher-Order Exceptional Points with Single Photons. https://doi.org/10.1126/sciadv.adi0732

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