# Harnessing Spectral Singularities in Non-Hermitian Cylindrical Structures

## TL;DR

This paper investigates spectral singularities in non-Hermitian cylindrical structures, revealing new ways to control scattering responses and enabling reconfigurable nanophotonic devices with potential applications in active optics.

## Contribution

It introduces the study of spectral singularities in cylindrical geometries and demonstrates their use in controlling scattering, absorption, and reconfigurability in nanophotonics.

## Key findings

- Demonstrates zero-forward-scattering and transverse scattering control.
- Shows gain-controlled reconfigurability of scattering patterns.
- Addresses stability issues in non-Hermitian cylindrical systems.

## Abstract

Non-Hermitian systems characterized by suitable spatial distributions of gain and loss can exhibit "spectral singularities" in the form of zero-width resonances associated to real-frequency poles in the scattering operator. Here, we study this intriguing phenomenon in connection with cylindrical geometries, and explore possible applications to controlling and tailoring in unconventional ways the scattering response of sub-wavelength and wavelength-sized objects. Among the possible implications and applications, we illustrate the additional degrees of freedom available in the scattering-absorption-extinction tradeoff, and address the engineering of zero-forward-scattering, transverse scattering, and gain-controlled reconfigurability of the scattering pattern, also paying attention to stability issues. Our results may open up new vistas in active and reconfigurable nanophotonics platforms.