# Nonlinear photon-atom coupling with 4Pi microscopy

## TL;DR

This paper demonstrates the adaptation of 4Pi microscopy, a super-resolution imaging technique, to enhance nonlinear photon-atom interactions, achieving significant extinction and nonlinear effects at the single-photon level.

## Contribution

It introduces a novel application of 4Pi microscopy for efficient single-atom photon coupling, surpassing diffraction limits in quantum optics experiments.

## Key findings

- 36.6% extinction of incident light
- Modified photon statistics indicating nonlinear interaction
- Enhanced coupling efficiency beyond traditional focusing methods

## Abstract

Implementing nonlinear interactions between single photons and single atoms is at the forefront of optical physics. Motivated by the prospects of deterministic all-optical quantum logic, many efforts are currently underway to find suitable experimental techniques. Focusing the incident photons onto the atom with a lens yielded promising results, but is limited by diffraction to moderate interaction strengths. However, techniques to exceed the diffraction limit are known from high-resolution imaging. In this work, we adapt a super-resolution imaging technique, 4Pi microscopy, to efficiently couple light to a single atom. We observe 36.6(3)% extinction of the incident field, and a modified photon statistics of the transmitted field -- indicating nonlinear interaction at the single-photon level.