We report the experimental observation of collective multi-mode vacuum Rabi splitting in free space. In contrast to optical cavities, the atoms couple to a continuum of modes, and the optical thickness of the cloud provides a measure of this coupling. The splitting, also referred as normal mode splitting, is monitored through the Rabi oscillations in the scattered intensity, and the results are fully explained by a linear-dispersion theory.
Cite
@article{arxiv.1909.06454,
title = {Collective Multi-mode Vacuum Rabi Splitting},
author = {W. Guerin and T. S. do Espirito Santo and P. Weiss and A. Cipris and J. Schachenmayer and R. Kaiser and R. Bachelard},
journal= {arXiv preprint arXiv:1909.06454},
year = {2019}
}