# Collective strong coupling of cold atoms to an all-fiber ring cavity

## TL;DR

This paper demonstrates a novel all-fiber ring cavity system with cold atoms, showing collective strong coupling via vacuum Rabi splitting and a method for cavity frequency stabilization using nanofiber thermal properties.

## Contribution

It introduces a new all-fiber ring cavity setup with cold atoms and models the collective atom-light interactions in this configuration.

## Key findings

- Observation of vacuum Rabi splitting indicating strong coupling.
- Control and stabilization of cavity resonance using nanofiber thermal effects.
- Experimental validation of collective enhancement in atom-light interactions.

## Abstract

We experimentally demonstrate a ring geometry all-fiber cavity system for cavity quantum electrodynamics with an ensemble of cold atoms. The fiber cavity contains a nanofiber section which mediates atom-light interactions through an evanescent field. We observe well-resolved, vacuum Rabi splitting of the cavity transmission spectrum in the weak driving limit due to a collective enhancement of the coupling rate by the ensemble of atoms within the evanescent field, and we present a simple theoretical model to describe this. In addition, we demonstrate a method to control and stabilize the resonant frequency of the cavity by utilizing the thermal properties of the nanofiber.