Ultra strong coupling is studied in a modulation-doped parabolic potential well coupled to an inductance-capacitance resonant circuit. In this system, in accordance to Kohn's theorem, strong reduction of the energy level separation caused by the electron-electron interaction compensates the depolarization shift. As a result, a very large ratio of 27% of the Rabi frequency to the center resonance frequency as well as a polariton gap of width 2? ? 670GHz are observed, suggesting parabolic quantum wells as the system of choice in order to explore the ultra-strong coupling regime.
@article{arxiv.1111.7266,
title = {Ultra strong coupling regime and plasmon-polaritons in parabolic semiconductor quantum wells},
author = {Markus Geiser and Fabrizio Castellano and Giacomo Scalari and Mattias Beck and Laurent Nevou and Jérôme Faist},
journal= {arXiv preprint arXiv:1111.7266},
year = {2012}
}