Coupled non-Hermitian skin effect with exceptional points.

Non-Hermitian systems exhibit two unique hallmarks: exceptional points (EPs) and non-Hermitian skin effect (NHSE). The EP arises from the interplay of multiple energy levels, marked by degeneracy in eigenvalue spectra, while the NHSE is associated with the localization feature of eigenfunctions. Due to their different origins and consequences, the interplay between the two hallmarks has drawn considerable interest. Here, we propose the concept of coupled NHSE, i.e., two non-Hermitian systems with independent NHSE are coupled together. We find that by introducing non-Hermitian losses with special symmetry, multiple pairs of EPs can appear, greatly compressing the eigenvalue spectrum and accelerating the breakdown of the coupled NHSE. In contrast, the attenuation of coupled NHSE is significantly alleviated in systems without EPs. In this sense, the EP can act as a degree of freedom to tune the NHSE and govern the non-Hermitian dynamics. The proposed concept is experimentally realized in photonic lattices with artificial gauge fields, which will bridge these two significant concepts and open avenues for non-Hermitian applications simultaneously associated with them.