# Coupling of atomic quadrupole transitions with resonant surface plasmons

## TL;DR

This paper demonstrates the coupling of atomic quadrupole transitions with surface plasmons in a nanostructured metamaterial, revealing significant modifications in reflection spectra and highlighting the role of surface plasmon polaritons.

## Contribution

It presents the first experimental observation of quadrupole transition coupling with plasmonic excitations in a structured metallic metamaterial.

## Key findings

- Strong modification of reflection spectra due to coupling
- Doppler-free hyperfine structure resolved
- Surface plasmon polaritons influence quadrupole interaction

## Abstract

We report on the coupling of an electric quadrupole transition in atom with plasmonic excitation in a nanostructured metallic metamaterial. The quadrupole transition at 685 nm in the gas of Cesium atoms is optically pumped, while the induced ground state population depletion is probed with light tuned on the strong electric dipole transition at 852 nm. We use selective reflection to resolve the Doppler-free hyperfine structure of Cesium atoms. We observed a strong modification of the reflection spectra at the presence of metamaterial and discuss the role of the spatial variation of the surface plasmon polariton on the quadrupole coupling.