The emergence, coalescence and topological properties of multiple exceptional points and their experimental realization

TL;DR

This paper explores the emergence, interaction, and topological properties of multiple exceptional points in non-Hermitian systems, demonstrating their experimental realization using coupled acoustic cavities and revealing complex higher-order phenomena.

Contribution

It introduces the theoretical analysis and experimental demonstration of multiple exceptional points in a four-state non-Hermitian system, highlighting their interactions and topological features.

Findings

Multiple EPs can emerge and interact in a four-state system.

EPs can collide and merge, forming higher-order singularities.

Experimental realization confirms theoretical predictions of complex EP phenomena.

Abstract

Non-Hermitian systems distinguish themselves from Hermitian systems by exhibiting a phase transition point called an exceptional point (EP), which is the point at which two eigenstates coalesce under a system parameter variation. Many interesting EP phenomena such as level crossings/repulsions in nuclear/molecular and condensed matter physics, and unusual phenomena in optics such as loss-induced lasing and unidirectional transmission can be understood by considering a simple 2x2 non-Hermitian matrix. At a higher dimension, more complex EP physics not found in two-state systems arises. We consider the emergence and interaction of multiple EPs in a four-state system theoretically and realize the system experimentally using four coupled acoustic cavities with asymmetric losses. We find that multiple EPs can emerge and as the system parameters vary, these EPs can collide and merge, leading to higher order singularities and topological characteristics much richer than those seen in two-state systems.