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 Ω is comparable to the bare transition frequency ω . 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 ωΩ=0.89 are reached and the system appears highly scalable far into the microwave range.
@article{arxiv.1611.09151,
title = {THz ultrastrong light-matter coupling},
author = {Giacomo Scalari and Curdin Maissen and Sara Cibella and Roberto Leoni and Christian Reichl and Werner Wegscheider and Mattias Beck and Jérôme Faist},
journal= {arXiv preprint arXiv:1611.09151},
year = {2016}
}