# $\mathcal{PT}$-symmetric wave guide system with evidence of a third-order exceptional point

## TL;DR

This paper reports the experimental realization of a $PT$-symmetric wave guide system exhibiting a third-order exceptional point (EP3), highlighting the challenges of detecting EP3 due to high parameter sensitivity and exploring nearby branch points.

## Contribution

It extends previous idealized models to realistic wave guide systems and investigates the sensitivity and nearby spectral branch points of EP3.

## Key findings

- Successful experimental setup of a $PT$-symmetric wave guide with EP3.
- High parameter sensitivity complicates EP3 detection.
- Identification of cubic and square root branch points near EP3.

## Abstract

An experimental setup of three coupled $\mathcal{PT}$-symmetric wave guides showing the characteristics of a third-order exceptional point (EP3) has been investigated in an idealized model of three delta-functions wave guides in W.~D. Heiss and G.~Wunner, J. Phys. A 49, 495303 (2016). Here we extend these investigations to realistic, extended wave guide systems. We place major focus on the strong parameter sensitivity rendering the discovery of an EP3 a challenging task. We also investigate the vicinity of the EP3 for further branch points of either cubic or square root type behavior.