The field of terahertz (0.1-10 THz) science and technology has had an exotic standing for a long time, due to the lack of performant sources and detectors. In this range, both electronics and optics fail to provide a performant solution. The scope of this work was to initiate experiments in quantum optics at terahertz frequencies, which lead to the exploration of the characteristics of quantum...
Positronium and Muonium are excellent systems to test bound-state QED theory to high precision. This has motivated numerous precise experiments aimed at measuring the hyperfine splitting and 1S-2S transition of these atoms.
Currently, there is some disagreement with the most recent bound-state QED calculations for the hyperfine splitting in positronium. Our approach to resolve this, PHySES,...
Spatial hole burning prevents single-frequency operation of thin-disk lasers when the thin disk is used as a folding mirror. We present an evaluation of the saturation effects in the disk for disks acting as end-mirrors and as folding-mirrors explaining one of the main obstacles towards single-frequency operation. It is shown that a twisted-mode scheme based on a multi-order quarter-wave plate...
The ground state of electromagnetic radiation is characterized by the presence of fluctuating zero-point electric fields. A direct method to characterize their spectral composition is still missing. In this work, we present the first direct electric field correlation measurement on the electromagnetic vacuum state at terahertz frequencies. It presents a peak value of 6.20 *10^-2 volts squared...
We study a paradigmatic quantum-optical model, where a collection of two-level systems interact with both quadratures of a cavity mode. The closed system exhibits rich physics, including discrete and continuous symmetry-breaking phase transitions. Exploring the dynamical response, we find an additional transition manifesting in the system's frequency response. Particle-hole like processes...
Low-temperature decoherence in many quantum systems, such as magnons or NV centers, is attributed to the interaction with the atomic impurities in the sample. We propose a model describing effective dynamics of a harmonic oscillator in the presence of impurities based on master equation formalism, to model such behaviour. Impurities are modelled as a bath of two-level atoms, which is a rather...
Elastic strain engineering utilizes stress to realize unusual material properties. Here we show that geometric strain engineering combined with soft-clamping can produce unprecedentedly high quality factor nano-mechanical resonators. Specifically, using a spatially non-uniform phononic crystal pattern, we co-localize the strain and flexural motion of a SiN nano-beam, while increasing the...
When particles with opposite spin scatter, momentum is transferred from one spin species to the other causing a spin drag - a friction between the relative motion of the two spin components. This phenomenon is relevant for spintronics devices, and has also been explored in experiments with ultracold atoms. Motivated by recent experiments [1,2], we consider spin drag in a one-dimensional...
By solving the Bogoliubov--de Gennes equations analytically, we derive the fermionic zero-modes satisfying the Majorana property that exist in vortices of a two-dimensional $s$-wave Fermi superfluid with spin-orbit coupling and Zeeman spin-splitting. The Majorana zero-mode becomes normalisable and exponentially localised to the vicinity of the vortex core when the superfluid is topologically...
The Pauli exclusion principle $0 \leq n_k\leq 1$ is a kinematical constraint on fermionic occupation numbers which strongly shapes fermionic quantum systems on all length scales. We demonstrate that this fundamental restriction can also be interpreted dynamically: the fermionic exchange symmetry manifests itself in the one-fermion picture in the form of an ``exchange force'' which repulsively...
We present the quantum master equation describing the coherent and incoherent dynamics of a rapidly rotating molecule in presence of a thermal background gas [1]. The master equation relates the rate of rotational alignment decay and decoherence to the microscopic scattering amplitudes, which we calculate for anisotropic van der Waals scattering. For large rotational energies, we find...
