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 Ω ωc = 0.58 between the vacuum Rabi frequency Ω and the cyclotron frequency ω 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 highmobility 2DEG.

We present a heterogeneous terahertz quantum cascade laser that emits continuously between 2.2 and 3.2 THz, covering an emission range of over 40% around the central frequency. Devices were realized by stacking different active region designs into a double-metal waveguide. They operate up to 125 K with 15 mW peak power at 10 K in pulsed mode. Smaller devices show broadband emission also in continuous wave. Time-resolved measurements of the emission spectra were realized, confirming the broadband emission within a 5 ns time window.

We present the continuous tuning of a terahertz quantum cascade laser based on 3rd order distributed feedback. This source provides a single mode emission with low dissipation power (∼400 mW) and milliwatt-level output power. The laser is tuned by nitrogen-gas condensation or by dielectric deposition. The former method offers a reversible, reproducible, and continuous mode-hop free tuning over 25 GHz at a frequency of ∼3.3 THz (Δf/f ∼ 0.75%). The latter is convenient for precise post-process targeting of a desired frequency.

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In this paper we show that by applying a perpendicular magnetic field to a quantum cascade structure it is possible to enhance the gain of different optical transitions. The combination of magnetic confinement with a broadband, cutoff-free optical resonator allows the demonstration of laser action over a large bandwidth, from 733 GHz to 1.38 THz together with the emission at 3.2 THz. A different lasing scheme is revealed that does not rely on resonant tunneling as the main injection mechanism. In combination with the magnetically enhanced gain laser emission at 1 THz is observed up to a temperature of 115 K, which corresponds to a ratio kBT/hν=2.3 between the lattice thermal energy and the laser photon energy.