Controlling the way light interacts with material excitations is at the heart of cavity quantum electrodynamics (QED). In the strong-coupling regime, quantum emitters in a microresonator absorb and spontaneously re-emit a photon many times before dissipation becomes effective, giving rise to mixed light-matter eigenmodes. Recent experiments in semiconductor microcavities reached a new limit of ultrastrong coupling, where photon exchange occurs on timescales comparable to the oscillation period of light. In this limit, ultrafast modulation of the coupling strength has been suggested to lead to unconventional QED phenomena. Although sophisticated light-matter coupling has been achieved in all three spatial dimensions, control in the fourth dimension, time, is little developed. Here we use a quantum-well waveguide structure to optically tune light-matter interaction from weak to ultrastrong and turn on maximum coupling within less than one cycle of light. In this regime, a class of extremely non-adiabatic phenomena becomes observable. In particular, we directly monitor how a coherent photon population converts to cavity polaritons during abrupt switching. This system forms a promising laboratory in which to study novel sub-cycle QED effects and represents an efficient room-temperature switching device operating at unprecedented speed.

Sub-cycle switch-on of ultrastrong light–matter interaction

Photonic quantum technologies represent a promising platform for several applications, ranging from long-distance communications to the simulation of complex phenomena. Indeed, the advantages offered by single photons do make them the candidate of choice for carrying quantum information in a broad variety of areas with a versatile approach. Furthermore, recent technological advances are now enabling first concrete applications of photonic quantum information processing. The goal of this manuscript is to provide the reader with a comprehensive review of the state of the art in this active field, with a due balance between theoretical, experimental and technological results. When more convenient, we will present significant achievements in tables or in schematic figures, in order to convey a global perspective of the several horizons that fall under the name of photonic quantum information.

https://iopscience.iop.org/article/10.1088/1361-6633/aad5b2/pdf

Photonic quantum information processing: a review

The surface plasmon modes of periodic hole arrays in Ag and Al films enhance by one order of magnitude the conductivity and the carrier mobility of organic semiconducting films deposited on these structures.

Conductivity in organic semiconductors hybridized with the vacuum field

We provide an overview of recent developments of quantum cascade lasers (QCLs), from the mid-infrared (mid-IR) to the far-IR (THz) range, with a special focus on their metrological-grade applications in a number of fields. A special emphasis on the physics of the QCLs allows underlining peculiar effects and device features recently unveiled that pave the way to novel demanding photonics applications.

https://iopscience.iop.org/article/10.1088/0957-0233/25/1/012001/pdf

Quantum cascade lasers: a versatile source for precise measurements in the mid/far-infrared range

Researchers have fabricated an electrically powered semiconductor device that creates photon pairs

Electrically injected photon-pair source at room temperature.

We have realised an electroluminescent device in which electron are injected into intersubband polariton branches. We reproduce electroluminescence spectra by using a phenomenological model, in which a voltage dependent injection is taken into account.

/pdf/electrically-injected-cavity-polaritons-2ku3dxvn5c.pdf

Electrically injected cavity polaritons

We report the heterodyne detection and phase locking of a 2.5 THz quantum cascade laser (QCL) using a terahertz frequency comb generated in a GaAs photomixer using a femtosecond fiber laser. With 10 mW emitted by the QCL, the phase-locked signal at the intermediate frequency yields 80 dB of signal-to-noise ratio in a bandwidth of 1 Hz.

Phase-locking of a 2.5 THz quantum cascade laser to a frequency comb using a GaAs photomixer

We report on CW second-harmonic generation in selectively oxidized AlGaAs multilayer waveguides. Frequency doubling of a 1.55 μm pump is observed with 2.8% W−1 conversion efficiency and a maximum second-harmonic power around 0.3 mW. This is the strongest second-harmonic generation ever reported in semiconductor waveguides and an encouraging result toward integrated spontaneous parametric downconversion in the telecom range.

Large second-harmonic generation at 1.55 μmin oxidized AlGaAs waveguides.

We present an optimized technique for the measurement of gain and losses of semiconductor lasers. We optically inject the beam of a distributed feedback laser (DFB) inside the cavity of the lasers under study. The DFB laser operates in a pulsed mode and shifts its emission wavelength as a function of time. This frequency chirp creates the Fabry–Perot fringes of the transmitted intensity that contains all the information on the cavity losses. The setup has been validated by a quantitative study of the losses as a function of the injected current, for a quantum cascade laser emitting at 7.6 μm.

C. Manquest

Papers

Electrically injected photon-pair source at room temperature.

Electrically injected cavity polaritons

Phase-locking of a 2.5 THz quantum cascade laser to a frequency comb using a GaAs photomixer

Large second-harmonic generation at 1.55 μmin oxidized AlGaAs waveguides.

Measurement of gain and losses of a midinfrared quantum cascade laser by wavelength chirping spectroscopy