Ultrastrong coupling of the cyclotron transition of a two-dimensional electron gas to a THz metamaterial

Artificial cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems, due to the possibility of manipulating the cavity quantum electrodynamic ground state with controllable physical properties. We report here experiments showing ultrastrong light-matter coupling in a terahertz metamaterial where the cyclotron transition of a high mobility two-dimensional electron gas is coupled to the photonic modes of an array of electronic split-ring resonators. We observe a normalized coupling ratio $\frac{\Omega}{\omega_c}=0.58$ between the vacuum Rabi frequency $\Omega$ and the cyclotron frequency $\omega_c$. Our system appears to be scalable in frequency and could be brought to the microwave spectral range with the potential of strongly controlling the magnetotransport properties of a high-mobility 2DEG

Asymmetry in polariton dispersion as function of light and matter frequencies in the ultrastrong coupling regime

In the ultrastrong light–matter coupling regime, non-perturbative effects are observed even for large detuning of the light and matter frequencies. In this regime, the rotating wave approximation breaks down and the contributions of counter-rotating and diamagnetic terms lead to significant spectral modifications. Using split ring resonators coupled to the cyclotron transition in a two dimensional electron gas, we show that the diamagnetic terms lead to an asymmetry between the light and matter branches. Our system allows tuning both, the cavity and the matter frequency over more than two octaves. We find, that the assumption of constant coupling rate Ω as function of detuning is not generally valid for the large frequency range relevant to ultrastrong coupling phenomena.ISSN:1367-263

Supplement 1: Electrically tunable graphene anti-dot array terahertz plasmonic crystals exhibiting multi-band resonances

Originally published in Optica on 20 February 2015 (optica-2-2-135

Gate and magnetic field tunable ultrastrong coupling between a magnetoplasmon and the optical mode of an LC cavity

The coupling between the optical mode of an LC cavity and a magnetoplasmon is studied by terahertz transmission spectroscopy. The magnetoplasmons are created by etching a high-mobility two-dimensional electron gas into stripes. As a result, we identify three different regimes, depending on the plasmon frequency relative to the cavity frequency. We find a significant coupling to the cyclotron dispersion even in presence of screening of the electric field by the plasmon.ISSN:1098-0121ISSN:0163-1829ISSN:1550-235XISSN:0556-2805ISSN:2469-9969ISSN:1095-379