Ultrastrong coupling regimes of light-matter interaction

TL;DR

This paper reviews recent theoretical and experimental advances in the ultrastrong and deep-strong light-matter coupling regimes, highlighting their potential for novel quantum phenomena and applications in quantum technologies.

Contribution

It provides a comprehensive overview of progress from the semiclassical to quantum models and summarizes key experimental platforms and future applications in the field.

Findings

Experimental demonstrations of USC and DSC regimes across various platforms

Theoretical developments from semiclassical to quantum Rabi models

Potential applications in quantum simulation and computation

Abstract

Recent experiments have demonstrated that light and matter can mix together to an extreme degree, and previously uncharted regimes of light-matter interactions are currently being explored in a variety of settings. The so-called ultrastrong coupling (USC) regime is established when the light-matter interaction energy is a comparable fraction of the bare frequencies of the uncoupled systems. Furthermore, when the interaction strengths become larger than the bare frequencies, the deep-strong coupling (DSC) regime emerges. This article reviews advances in the field of the USC and DSC regimes, in particular, for light modes confined in cavities interacting with two-level systems. An overview is first provided on the theoretical progress since the origins from the semiclassical Rabi model until recent developments of the quantum Rabi model. Next, several key experimental results from a variety of quantum platforms are described, including superconducting circuits, semiconductor quantum wells, and other hybrid quantum systems. Finally, anticipated applications are highlighted utilizing USC and DSC regimes, including novel quantum optical phenomena, quantum simulation, and quantum computation.