Experimental demonstration of an anisotropic exceptional point

TL;DR

This paper reports the first experimental demonstration of an anisotropic exceptional point in an acoustic system, where the singular behavior varies with approach direction, arising from the coalescence of two identical-chirality square-root EPs.

Contribution

It introduces the concept and experimental realization of an anisotropic EP, expanding understanding of non-Hermitian degeneracies beyond isotropic cases.

Findings

Anisotropic EP exhibits direction-dependent singular behavior.

Experimental validation in an acoustic system.

Coalescence of two square-root EPs with same chirality causes anisotropy.

Abstract

Exceptional points (EPs) associated with a square-root singularity have been found in many non-Hermitian systems. In most of the studies, the EPs found are isotropic meaning that the same singular behavior is obtained independent of the direction from which they are approached in the parameter space. In this work, we demonstrate both theoretically and experimentally the existence of an anisotropic EP in an acoustic system that shows different singular behaviors when the anisotropic EP is approached from different directions in the parameter space. Such an anisotropic EP arises from the coalescence of two square-root EPs having the same chirality.