Regulation of multiple exceptional points in a plasmonic quadrumer

Abstract

Exceptional points (EPs), which signify the singularity of eigenvalues and eigenstates in non-Hermitian systems, have garnered considerable attention in two-state systems, revealing a wealth of intriguing phenomena. However, the potential of EPs in multi-state systems, particularly their interaction and coalescence, has been underexplored, especially in the context of electromagnetic fields where far-field coupling can revolutionize spatial wave control. Here, we theoretically and computationally explore the coalescence of multiple EPs within a designer surface plasmonic quadrumer system. The coupled mode model shows that the multiple EPs can emerge and collide as the system parameters vary, leading to higher-order singularities. Numerically calculated results showcase that multiple EPs with different orders have special far-field responses. This pioneering strategy heralds a new era of wavefront engineering in non-Hermitian photonic structures, presenting a transformative class of radiative systems that transcend the conventional frequency spectrum from microwave to optical realms.