The Nitrogen-Vacancy (NV) center has demonstrated great potential as a quantum networks platform. While many milestones have been reached, the current hardware implementations have reached their limit in terms of remote entanglement generation rates, which hinders the scalability of the platform. The most dominant limits are that only ∼ 3% of the emission is coherent, and the outcoupling efficiency in state-of-the-art network experiments is ∼ 15%. The coherent emission can be increased via the Purcell effect, which can be achieved by the use of an open Fabry-Pérot microcavity. In such a setup the NV center is embedded in a micrometer-thin diamond membrane, thereby retaining its favourable optical properties. The open microcavity has the ability of in situ spectral and spatial tunability. However, this is accompanied by a high susceptibility to vibrations, which needs to be considered in the experimental design. The goal of this thesis is to simultaneously increase the coherent emission and the outcoupling efficiency by coupling NV centers to an open Fabry-Pérot microcavity. An optimized cavity is found by characterizing different fiber tip mirrors, reaching a bare cavity finesse of 9500. The vibrations in the bare cavity are analyzed, revealing a root mean square cavity length detuning of 22 pm while operating at low temperature. A hybrid cavity is formed with a diamond membrane with NV centers, resulting in cavity with a finesse of 2100, quality factor of 266000, mode volume of 108 λ 3 , and outcoupling efficiency ∼ 30%. Due to a different setup configuration, an increased root mean square cavity length detuning of 190 pm is measured, resulting in a lowered Purcell factor. Off-resonant measurements demonstrate the coupling of NV centers to the cavity. Moreover, excited state lifetimes are measured to obtain a Purcell factor of 2.6 ± 0.5, with a corresponding enhanced coherent emission ratio of 0.07 ± 0.01. This result is in good agreement with simulations that include the effect of vibrations. The ZPL branching ratio and outcoupling efficiency are improved by a factor two compared to state-of-the-art confocal microscope setups. For the first time in open microcavities, the ability to drive the spin of NV centers is shown by an optically detected magnetic resonance measurement with a contrast of (28 ± 2)%. By improving the setup to the already obtained vibration level, and a realistic finesse of 5000, an expected Purcell factor of ∼ 15.7 and outcoupling efficiency of ∼ 80% can be reached, paving the way to the next-generation of quantum network nodes.

Humans are efficient at moving due to their exceptional mastery of bipedal locomotion. Several models have been made that attempt to model the motion of the centre of mass with a spring-mass system with various degree of success. For example, a two dimensional model tracks the height of the centre of mass well and a three dimensional model explains the normal force exerted on the ground.

In this report a three dimensional model is constructed to describe the motion of the centre of mass, with the purpose to determine the spring constant and the rest length in a simple prosthetic leg. The research question is: can a three dimensional spring-mass model accurately track the centre of mass and can this be used to determine the optimal properties of the spring of a simple prosthetic leg?

The spring mass model consists of two springs connected to the ground and the centre of mass. The springs do not exert a force on the centre of mass if they are extended. The model incorporates steps by moving the ground connection points instantaneously over fixed points on a rail. The model can be used in two distinct ways. The first generates a periodic trajectory by finding the optimal initial positions y₀ and z₀ (PPFA) and the second finds the optimal spring parameters k and u to fit a data set (DFA). The optimal conditions are found by discretizing the parameter space and using an iterative process. The space around the best parameters becomes the parameter space for the next iteration.

The PPFA shows that the initial lateral displacement is nearly constant with respect to the spring constant when the rest length is chosen such that the centre of mass is at constant height if the model is stationary. The PPFA also shows that there are two distinct y-trajectories possible for walking. Running, however, has only one trajectory. Several versions of the model are fit to the data: only discretised step widths, discretised step widths and a x₀-offset, and distinct legs. There is not much difference between these models. The x₀-offset is only Δs = -0.02m confirming that the position of the feet does align with the extreme values of the y- and z-position. The model fits the general characteristics well but fine details in the motion are lost. Future research should investigate how cumbersome these deviations of the data are perceived by people using a simple prosthetic.

In this thesis, a we have designed and fabricated a Josephson Parametric Amplifier (JPA) using a new double-angle evaporation method without a Dolan bridge. We have found and resolved several issues in the fabrication procedure, but it requires further tuning before being fully functional. We have also simulated the behaviour of a general parametric amplifier with an additional Duffing non-linear term, and found that this term appears to limit the oscillation amplitude. We have attempted to characterize Josephson junctions fabricated with the new double-angle evaporation procedure, but without much success. Using a different fabrication method, a JPA was made and successfully characterized. The maximum measured gain is 16 dB, with a bandwidth of 1 MHz. The noise temperature is comparable to the cryostat temperature of 250 mK, but it was not characterized accurately.