THz ultrastrong light-matter coupling

TL;DR

This paper reviews experiments on ultrastrong light-matter coupling, highlighting a new platform with 2DEG and split-ring resonators achieving record-high coupling ratios in the microwave range.

Contribution

It introduces a novel system where 2DEG transitions are strongly coupled to subwavelength resonators, reaching unprecedented coupling ratios.

Findings

Record-high normalized coupling ratio of 0.89 achieved.

System scalable into the microwave range.

Demonstrates manipulation of cavity quantum electrodynamic ground state.

Abstract

Cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems displaying the capability to manipulate the cavity quantum electrodynamic ground state with controllable physical properties. Here we review a series of experiments aimed at probing the ultrastrong light-matter coupling regime, where the vacuum Rabi splitting $\Omega$ is comparable to the bare transition frequency $\omega$ . We present a new platform where the inter-Landau level transition of a two-dimensional electron gas (2DEG) is strongly coupled to the fundamental mode of deeply subwavelength split-ring resonators operating in the mm-wave range. Record-high values of the normalized light-matter coupling ratio $\frac{\Omega}{\omega}= 0.89$ are reached and the system appears highly scalable far into the microwave range.