Nonlinear absorption in interacting Rydberg electromagnetically-induced-transparency spectra on two-photon resonance

TL;DR

This paper experimentally studies the nonlinear transmission spectra of Rydberg EIT media on two-photon resonance, revealing limitations of existing models and emphasizing the need for more comprehensive theories to understand photon interactions.

Contribution

It provides the first detailed two-dimensional spectral analysis of Rydberg EIT on two-photon resonance, highlighting the inadequacies of mean-field and rate-equation models.

Findings

Spectral features differ significantly at two-photon resonance.

Mean-field and rate-equation models fail to fully describe the nonlinear response.

A third-order nonlinear susceptibility captures pair-wise interaction effects.

Abstract

We experimentally investigate the nonlinear transmission spectrum of coherent light fields propagating through a Rydberg EIT medium with strong atomic interactions. In contrast to previous investigations, which have largely focused on resonant control fields, we explore here the full two-dimensional spectral response of the Rydberg gas. Our measurements confirm previously observed spectral features for a vanishing control-field detuning, but also reveal significant differences on two-photon resonance. In particular, we find qualitative deficiencies of mean-field models and rate-equation simulations as well as a third-order nonlinear susceptibility that accounts for pair-wise interaction effects at low probe-field intensities in describing the nonlinear probe-field response under EIT conditions. Our results suggest that a more complete understanding of Rydberg-EIT and emerging photon interactions requires to go beyond existing simplified models as well as few-photon theories.