Curdin Maissen

Ultrastrong coupling of the cyclotron transition of a 2D electron gas to a THz metamaterial

Quantum Hall Meets Metamaterial Controlling and tuning light-matter interaction is crucial for fundamental studies of cavity quantum electrodynamics and for applications in classical and quantum devices. Scalari et al. (p. 1323) describe a system comprising an array of metamaterial split-ring resonators and a series of two-dimensional electronic gases (2DEG) formed in GaAs quantum wells. In a magnetic field, the electrons in the 2DEG performed cyclotron orbits and formed Landau levels. Strong coupling was observed between photon and magnetic cyclotron modes, producing a tunable semiconductor system for studying the light-matter interaction of two-level systems. A system of terahertz resonators coupled to two-dimensional electron gases presents a tunable test bed for the study of two-level physics. Artificial cavity photon resonators with ultrastrong light-matter interactions are attracting interest both in semiconductor and superconducting systems because of 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 (THz) metamaterial where the cyclotron transition of a high-mobility two-dimensional electron gas (2DEG) is coupled to the photonic modes of an array of electronic split-ring resonators. We observe a normalized coupling ratio, Ωωc=0.58, between the vacuum Rabi frequency, Ω, and the cyclotron frequency, ωc. 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.

Low-bias active control of terahertz waves by coupling large-area CVD graphene to a terahertz metamaterial

We propose an hybrid graphene/metamaterial device based on terahertz electronic split-ring resonators directly evaporated on top of a large-area single-layer CVD graphene. Room temperature time-domain spectroscopy measurements in the frequency range from 250 GHz to 2.75 THz show that the presence of the graphene strongly changes the THz metamaterial transmittance on the whole frequency range. The graphene gating allows active control of such interaction, showing a modulation depth of 11.5% with an applied bias of 10.6 V. Analytical modeling of the device provides a very good qualitative and quantitative agreement with the measured device behavior. The presented system shows potential as a THz modulator and can be relevant for strong light-matter coupling experiments.

Ultrastrong coupling in the near field of complementary split-ring resonators

Ultrastrong coupling of split ring resonators to the cyclotron transition in two-dimensional electron gases is studied in the terahertz regime, clarifying the importance of the resonator geometry. The use of the complementary type of resonator allows removal of the signal from the uncoupled areas. The experimental results are of spectacular quality and quantity. A record high light-matter coupling ratio (normalized vacuum Rabi frequency) of 0.87 is achieved.

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

Graphene-based plasmonic structures feature large tunability, high spatial confinement, and potentially low loss, and are therefore an emerging technology for unconventional manipulation of light. In this paper, we demonstrate electrically tunable terahertz plasmonic crystals consisting of square-lattice graphene periodic anti-dot arrays on a SiO2/Si substrate. Transmission spectroscopy reveals multiple distinct resonances arising from excitations of graphene surface-plasmon–polariton (SPP) modes on different branches of the SPP dispersion curves inherent to the periodic structures. The resonance frequencies are readily tuned electrostatically with the Si back-gate and exhibit the dependency on the carrier density unique to SPP in graphene. Simulations show excellent agreement with the experiments and further illustrate the symmetry-based selection rule for the excited graphene SPP modes. Such graphene plasmonic crystals may lead to a broad range of applications including plasmonic waveguide and transformation optics. Exploiting higher-order graphene SPP modes is an effective way to further facilitate field localization and enhancement.

High quality factor, fully switchable terahertz superconducting metasurface

We present a complementary THz metasurface realised with Niobium thin film which displays a quality factor Q = 54 and a fully switchable behaviour as a function of the temperature. The switching behaviour and the high quality factor are due to a careful design of the metasurface aimed at maximising the ohmic losses when the Nb is above the critical temperature and minimising the radiative coupling. The superconductor allows the operation of the cavity with high Q and the use of inductive elements with a high aspect ratio. Comparison with three dimensional finite element simulations highlights the crucial role of the inductive elements and of the kinetic inductance of the Cooper pairs in achieving the high quality factor and the high field enhancement.

Superconducting complementary metasurfaces for THz ultrastrong light-matter coupling

A superconducting metasurface operating in the THz range and based on the complementary metamaterial approach is discussed. Experimental measurements as a function of temperature and magnetic field display a modulation of the metasurface with a change in transmission amplitude and frequency of the resonant features. Such a metasurface is successively used in a cavity quantum electrodynamic experiment displaying ultrastrong coupling to the cyclotron transition of two-dimensional electron gas. A finite element modeling is developed and its results are in good agreement with the experimental data. In this system a normalized coupling ratio of is measured and a clear modulation of the polaritonic states as a function of the temperature is observed.

Subcycle measurement of intensity correlations in the terahertz frequency range

The terahertz frequency range is lacking an experimental implementation of Hanbury Brown and Twiss photon correlation measurements with sub-cycle time resolution and high sensitivity. Such a technique would be needed, for example, to observe photon pairs predicted to be released in a nonadiabatic modulation of an ultrastrongly coupled light-matter system. In this paper, we propose a room-temperature measurement of photon correlations in the THz range based on electro-optic sampling. We apply this technique to a THz quantum cascade laser and measure below and above threshold first- and second-order degree of coherence with a subcycle temporal resolution of 146 fs. The sensitivity of the proposed measurement scheme is so far limited to

Ultrastrong light-matter coupling at terahertz frequencies with split ring resonators and inter-Landau level transitions

\ensuremath{\sim}1500

Terahertz quantum Hall effect for spin-split heavy-hole gases in strained Ge quantum wells

photons. This technique can, in principle, be extended for ultrahigh bandwidth single-photon sensitivity in a wide range of frequencies.

Continuously tunable ultrastrong light-matter interaction

We study strong light-matter coupling at terahertz frequencies employing a system based on an array of deeply subwavelength split ring resonators deposited on top of an ensemble of modulation-doped quantum wells. By applying a magnetic field parallel to the epitaxial growth axis, at low temperatures, Landau Levels are formed. We probe the interaction of the inter-Landau level transitions with the resonators modes, measuring a normalized coupling ratio Ωωc=0.58 between the inter-Landau level frequency ωc and the Rabi frequency Ω of the system. The physics of the system is studied as a function of the metasurface composition and of the number of quantum wells. We demonstrate that the light-matter coupling strength is basically independent from the metamaterial lattice spacing.