# Topological Properties of a Coupled Spin-Photon System Induced by Damping

## TL;DR

This paper experimentally investigates the topological properties of a damped, strongly coupled spin-photon system, revealing non-Hermitian phenomena, exceptional points, and dynamic mode switching, advancing understanding of topological effects in quantum systems.

## Contribution

It demonstrates the topological nature of damping-induced phenomena in spin-photon systems and highlights the significance of exceptional points in defining coupling regimes.

## Key findings

- Observation of resonance crossing above cooperativity one
- Identification of exceptional points where eigenvectors coalesce
- Dynamic mode switching when encircling the EP

## Abstract

We experimentally examine the topological nature of a strongly coupled spin-photon system induced by damping. The presence of both spin and photonic losses results in a non-Hermitian system with a variety of exotic phenomena dictated by the topological structure of the eigenvalue spectra and the presence of an exceptional point (EP), where the coupled spin-photon eigenvectors coalesce. By controlling both the spin resonance frequency and the spin-photon coupling strength we observe a resonance crossing for cooperativities above one, suggesting that the boundary between weak and strong coupling should be based on the EP location rather than the cooperativity. Furthermore we observe dynamic mode switching when encircling the EP and identify the potential to engineer the topological structure of coupled spin-photon systems with additional modes. Our work therefore further highlights the role of damping within the strong coupling regime, and demonstrates the potential and great flexibility of spin-photon systems for studies of non-Hermitian physics.