Microwave-optical spectroscopy of Rydberg excitons in the ultrastrong driving regime

TL;DR

This paper investigates the behavior of Rydberg excitons in Cu$_2$O under ultrastrong microwave driving, revealing new phenomena and providing a comprehensive theoretical model that aligns closely with experimental results.

Contribution

It introduces a Floquet theory-based model for Rydberg excitons under ultrastrong microwave fields, extending understanding beyond the rotating wave approximation.

Findings

Observation of sidebands in optical absorption spectra.

Near-quantitative agreement between theory and experiment.

Emergence of an absorption continuum without ionization.

Abstract

We study the ultrastrong driving of Rydberg excitons in Cu$_2$O by a microwave field. The effect of the field is studied using optical absorption spectroscopy, and through the observation of sidebands on the transmitted laser light. A model based on Floquet theory is constructed to study the system beyond the rotating wave approximation. We obtain near quantitative agreement between theory and experiment across a 16-fold range of microwave field strengths spanning from the perturbative to the ultrastrong driving regime. Compared to Rydberg atoms, the large non-radiative widths of Rydberg excitons leads to new behaviour such as the emergence of an absorption continuum without ionization.