Superconducting kinetic inductance detectors will play an important role in the future of exoplanet spectroscopy. Their low bandgap and the possibillity that they can be multiplexed into large arrays open up new opportunities where conventional semiconductors stop. A key requirement for the performance of these new detectors is the consistency of their quality factor (Q-factor). Variations in Q-factors, known as Q-scatter, result in nonuniform sensitivity and hold back scaling to larger systems.

In this thesis, detectors that differ in fabrication, pixel count and pixel spacing are analyzed and compared to find out what is the cause of Q-scatter. Possible causes include design errors, inaccurate fabrication, electromagnetic crosstalk, magnetic vortices and unbalanced transmission lines. Analysis showed Q-scatter is unlikely to be impacted by design, fabrication method, electromagnetic coupling or vortex forming. Also, no spatial relations, that indicated any transmission line effects, were observed. What is interesting however, is that the Q-factors of one of the chips seem to scatter all over again when measuring the chip again after trimming one of its components.

With the data available in this experiment it was not possible to give an concrete cause of Q-scatter. Furhter experiments, especially concerning the new scattering need to be conducted. Also, simulations using Sonnet v19 can give more insights in the origin of Q-scatter.

Single-photon emitters are at the heart of quantum optics and photonic quantum-information technologies. Identifying and characterizing such quantum emitters requires sophisticated experimental physics. In this experimental master end project, we aim to design and build an optical setup that allows for the characterization of single photon sources. More specifically, we aim to build a setup that allows for photoluminescence (PL) spectroscopy and second-order autocorrelation (g(2)) measurements of single-photon emission (SPE).
The initial design of the optical setup is based on that of a micro-photoluminescence setup and optimized for single-photon emission from indium arsenide phosphide (InAsP) quantum dots (QDs). This design therefore includes a continuous-flow liquid-helium cryostat, and a high resolution monochromator that can be used to extract the emission line of a single QD transition.
The final version of the experimental setup is demonstrated to be able to perform high resolution PL spectroscopy measurements. g(2) Measurements are performed on room temperature hexagonal Boron Nitride (hBN) SPE using a free-space Hanbury-Brown and Twiss (HBT) interferometer containing two geiger-mode avalanche photodiodes (APDs) indicating pronounced photon antibunching. Due to malfunctioning of the cryostat, however, measurements have exclusively been performed at room temperature.

Superconducting nanowire single-photon detectors (SNSPDs) are characterized by their quantum limited ability to accurately detect single photons, with low jitter, high detection efficiency and low dark count rate. To achieve this, the detector is cooled to 2-3K, bringing the device in a superconductive state, and is then biased with a direct current (DC) close to its critical current. When a photon impinges the detector, the depairing of Cooper-pairs by the photon leads to local destruction of the superconductivity. The growth of this non-superconducting area, first across and then along the nanowire, leads to the development of a measurable resistance and hence the production of detection pulses. Increasing system detection efficiency (SDE) of detectors has been a long-term goal in the community. Recently ultrahigh efficiency detectors (SDE>98%) have been demonstrated. It has also been shown that the wavelengths dependence of SDE, typically defined by a quarter wavelength cavity, is modulated by fiber-detector airgap (Fabry–Pérot). Measuring such modulations and finding the optimal operation wavelength manually is a time consuming and tedious process. In this thesis a setup for automatic measurement of SDE versus wavelength was developed and benchmarked. For the tested detector, efficiencies were found ranging between 22% and 95% in the wavelengths range between 1260nm and 1650nm. For the optical circuit using Single Mode (SM) fibers only, the automated SDE measurements were unreliable due to shifts in polarisation during measurements. Using PM fibers led to efficiencies very similar to the values measured manually.