Multi-normal-mode splitting of a cavity in the presence of atoms -- towards the superstrong coupling regime

TL;DR

This paper reports the experimental observation of multi-normal-mode splitting in a cavity with Doppler-broadened atoms, reaching a superstrong coupling regime where multiple cavity modes interact strongly due to high atomic density.

Contribution

It demonstrates the realization of superstrong atom-cavity coupling with multi-normal-mode splitting, expanding understanding of light-matter interactions in high-density atomic systems.

Findings

Multi-normal-mode splitting peaks observed experimentally.

Superstrong coupling condition achieved with high atomic density.

Linear dispersion explains the multi-mode splitting phenomena.

Abstract

Multi-normal-mode splitting peaks are experimentally observed in a system with Doppler-broadened two-level atoms inside a relatively long optical cavity. In this system, the atoms-cavity interaction can reach the ``superstrong coupling" condition with atoms-cavity coupling strength $g\sqrt{N}$ to be near or larger than the cavity free-spectral range $\Delta_{FSR}$. In such case, normal-mode splitting can occur in many cavity longitudinal modes to generate the multi-normal-mode splitting peaks, which can be well explained by the linear dispersion enhancement due to the largely increased atomic density in the cavity. Many new interesting phenomena might come out of this superstrong atoms-cavity coupling regime.