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Quantum-cascade lasers for the terahertz spectral region are promising light sources for several spectroscopic applications, despite currently only operating at cryogenic temperatures. The authors developed a local oscillator to be used in an airborne heterodyne receiver for the investigation of interstellar atomic oxygen. The challenge for the design consists in the simultaneous fulfilment of demanding specifications for a set of operating parameters.

The developed laser emits a single mode with an optical power of about 0.5 mW and an almost Gaussian beam shape. The laser mode can be tuned using the applied current to cover about 5 GHz in the vicinity of 4.745 THz. The local oscillator, which is based on a distributed-feedback laser combining a quantum-cascade laser with a single-plasmon waveguide and a lateral first-order grating, can be operated in a cryogen-free cooler in continuous-wave mode. The developed quantum-cascade laser exhibits large wall-plug efficiency over a wide range of current densities with a negligible spectral shift of the gain maximum in order to achieve the required tuning range.

Topologically protected states of matter are the focus of recent intensive research efforts. Such states may play an important role in future concrete implementations of devices for topological quantum computing. Prominent examples are incompressible 2D electron gases exhibiting the Quantum Hall effect or the spin Hall effect, 3D topological insulators and superconductors, etc. From a conceptual point of view it is important to note that the low-energy effective theories describing all these states can be derived, using only very general principles, from a unified theoretical framework which we have called “gauge theory of states of matter”.

A key idea underlying our framework is to promote fundamental or emergent global symmetries of idealized systems to local gauge symmetries of realistic systems, and to then study the response of such systems under variations of the corresponding gauge fields. For systems with a bulk energy gap, our theory predicts the general form of the response laws, transport equations, and the structure of gapless surface modes. It also elucidates how the structure of the ionic background, electromagnetic fields, velocity fields and curvature influence the properties of such systems.

In 2012 the experiments ATLAS and CMS discovered a new particle in proton-proton collisions at CERN's Large Hadron Collider (LHC). The measurements show that the properties of the particle are compatible with those predicted for the Higgs boson of the Standard Model. In the article we estimate the precision with which some of the fundamental properties of the particle, its couplings to other particles, can be measured including theoretical errors, at a high-luminosity LHC (HL-LHC), a linear electron-positron collider and the combination of the two. The uncertainties are expected to be better than 1% for a single parameter modifying all Higgs couplings simultaneously, and at the percent level if all relevant couplings are left free and independent of each other. The combination of the measurements at the two machines improves on the uncertainty of each one of these. Thus a HL-LHC and a linear collider form a dream team to study the properties of the Higgs boson with high precision.