Efficient single photon sources, such as semiconductor quantum dots in micro-cavities, attracted attention not only for their fundamental properties, but also for wide use as resources of qubits...Show moreEfficient single photon sources, such as semiconductor quantum dots in micro-cavities, attracted attention not only for their fundamental properties, but also for wide use as resources of qubits for quantum communication and quantum computing. In this thesis, we study and optically characterize a device with QDs embedded in micro-cavities. By fitting the semi-classical model which describes QD-cavity interaction, we conclude that we observe trion transitions. A study of the second-order correlation function of one transition shows that it works as efficient single-photon source.Show less
Characterizing quantum states is a central, yet involved, task in quantum information processing. In experiments, the unknown quantum state of interest must be prepared and measured multiple times...Show moreCharacterizing quantum states is a central, yet involved, task in quantum information processing. In experiments, the unknown quantum state of interest must be prepared and measured multiple times to learn its properties. Unfortunately, a full tomographic description is prohibitive by the exponential scaling of the quantum state description with the system size. In practice, only a few quantities are of interest for which protocols involving informationally incomplete measurements are preferable. After studying existing data acquisition protocols, we discuss classical shadow estimation, a particular experimentally feasible method for estimating many system properties. We extend the applicability to quantum many-body systems with higher dimensional subspaces and derive similar performance guarantees to the qubit case. Ultimately we implement the generalized protocol in a modular and economic numerical framework and demonstrate the accuracy along with the favourable scaling of classical shadow estimation in unbiased numerical experiments. In particular, we suggest and discuss the near-term application to 4-photon OAM entangled systems.Show less
The hexapod made by Janssen Precision Engineering (JPE) is tested for optical purposes. Equations describing the movements of the platform are derived and tested using interferometric techniques...Show moreThe hexapod made by Janssen Precision Engineering (JPE) is tested for optical purposes. Equations describing the movements of the platform are derived and tested using interferometric techniques and imaging systems. A Python program for the hexapod motion control is developed and implemented, and its limitations are discussed. Several technical features, most notably the piezo actuators of the hexapod, are examined.Show less
This thesis gives insight into two photon quantum interference effects in quantum optics, with Hong-Ou-Mandel visibility detection. This is studied using a delay loop with different light...Show moreThis thesis gives insight into two photon quantum interference effects in quantum optics, with Hong-Ou-Mandel visibility detection. This is studied using a delay loop with different light polarizations. The single photons are created by exciting a quantum dot in a microcavity with a continuous-wave laser. We try to relate experimental results of the second order correlation function to a theoretical analysis of the obtained photon states in the system. As a result an insight into the creation of highly entangled qubit states, called cluster states, is given.Show less
For a phenomenological explanation of the absence of macroscopic superpositions, mass-dependent nonlinear and stochastic terms are added to the Schrödinger equation in some models of wave function...Show moreFor a phenomenological explanation of the absence of macroscopic superpositions, mass-dependent nonlinear and stochastic terms are added to the Schrödinger equation in some models of wave function collapse. This thesis describes a feasibility study of a microwave interferometer experiment with the purpose of falsifying the existence of spontaneous wave function collapse. Traveling wave parametric amplifiers in the interferometer arms effectively increase the mass of these superpositions, resulting in an interference visibility and an expected vanishing visibility in case of wave function collapse. The main question arises if the visibilities for these cases can be distinguished from each other in case of a gain of 20 dB and a (typical) insertion loss of 4 dB of the parametric amplifiers. Calculations of the interference visibilities were extended and performed by a Python program with the QuTiP module by using a Master Equation solver and Monte Carlo simulations on different computer infrastructures with up to 1.5 TB of RAM available. The limitations of the solvers were the QuTiP internals and computational time respectively. Visibilities are calculated using the Master Equation solver for gains up to 13.4 dB when neglecting losses, and for gains up to 5.3 dB and insertion losses up to 6.5 dB when including the effect of dissipation using both solvers. The differences between both visibilities appear to converge to constant values in the limit of large gain. Further calculations can be carried out on the Lisa Cluster to explore this promising observation. In addition, a cryogenic calorimeter for determining the insertion loss of an amplifier is characterized by its thermal time constants. Efforts were made to reduce the time constant attributed to a 3 dB attenuator, allowing for a precise determination of its power dissipation. On the basis of the results of this study, it can be concluded that significant steps in determining the feasibility of the proposed interferometer experiment are taken and future research is encouraged.Show less
We measured the homogeneous linewidth $\Gamma_h$ of ytterbium atoms inside a whispering gallery mode ring resonator. Using two-pulse photon echoes, we looked at the temperature dependence of $...Show moreWe measured the homogeneous linewidth $\Gamma_h$ of ytterbium atoms inside a whispering gallery mode ring resonator. Using two-pulse photon echoes, we looked at the temperature dependence of $\Gamma_h$ for an applied external magnetic field of $B=0$ and $B=0.3$ T. We found a clear narrowing of the linewidth at each temperature. Furthermore, we found saturation of $\Gamma_h$ for $T<30$ mK for both $B=0$ and $B=0.3$ T. At $T=10$ mK and $B=0.3$ T, we have observed a linewidth of 22 kHz, which is very near the lifetime limit of 1 kHz. Our results for the homogeneous linewidth of ions in glasses show that current theories have to be reconsidered. In addition, our results for $T_2$ ensure that rare earth element-doped cavities are a candidate for AFC quantum memory.Show less
