Quantum dots (QDs) are nm-size semiconductor structures that hold promise for applications in quantum information. One important requirement, however, is to achieve near-unity interaction between... Show moreQuantum dots (QDs) are nm-size semiconductor structures that hold promise for applications in quantum information. One important requirement, however, is to achieve near-unity interaction between photons and (singly charged) QDs. For this purpose, we make use of oxide-apertured micropillars that confine light in a small volume and thereby enhance the interaction. A QD transition coupled to the cavity mode can turn a transmittive cavity into a reflective one, and this property can be used to create entanglement between the spatial state of a photon and the spin state of a charge in the QD. This thesis consists of two parts: 1) in the first part we demonstrate techniques to monitor and fine tune the oxide aperture size and shape. By controlling the oxide shape we show we can fabricate polarization degenerate microcavities. 2) In the second part, perform cryogenic experiments with such a QD-cavity system. We investigate neutral and singly charged QDs as function of polarization and find this offers a way to assess the QD coherence. Next, we demonstrate a novel effect where charges around the QDs have a strong feedback with the QD properties. Finally, we present a homodyne detection technique of the QD coherence and phase shift. Show less
We investigate the detection mechanism in superconducting single photon detectors via quantum detector tomography. We find that the detection event is caused by diffusion of quasiparticles from the... Show moreWe investigate the detection mechanism in superconducting single photon detectors via quantum detector tomography. We find that the detection event is caused by diffusion of quasiparticles from the absorption spot, combined with entrance of a vortex. Moreover, we investigate the behaviour of superconducting single photon detectors in an external magnetic field. Show less
In this thesis we explore spatial quantum correlations of high-dimensional multi-photon states. These states are produced using the process of parametric down-conversion and are experimentally... Show moreIn this thesis we explore spatial quantum correlations of high-dimensional multi-photon states. These states are produced using the process of parametric down-conversion and are experimentally explored by measuring correlations with only two detectors. Compared to earlier investigations of multi-photon states, the correlations in this thesis are created in the spatial domain instead of the temporal domain. This has a distinct experimental advantage because it is much easier to measure the emission direction compared to a measurement of the arrival time of the photons. Show less
In this thesis we investigate diverse aspects of spatial coherence of light. Non-classical fields containing two photons can be generated by a nonlinear optical process known as spontaneous... Show moreIn this thesis we investigate diverse aspects of spatial coherence of light. Non-classical fields containing two photons can be generated by a nonlinear optical process known as spontaneous parametric down conversion (SPDC). Among the questions we consider are: What is so special about spatial entanglement? How is it revealed in the fourth-order correlations? What are the differences between a highly entangled and a classically correlated state? How can the number of modes be manipulated and measured? For a two-photon system, we measure both intensities and two-photon correlations. To get deeper insights into how coherence affects interference, we also investigate completely classical sources. Show less
This dissertation contains scientific research within the realm of quantum optics, which is a branch of physics. An experimental and theoretical study is made of two-photon interference phenomena... Show moreThis dissertation contains scientific research within the realm of quantum optics, which is a branch of physics. An experimental and theoretical study is made of two-photon interference phenomena in various optical systems. Spatially entangled photon pairs are produced via the nonlinear optical process of spontaneous parametric down-conversion. These entangled photons are then passed through different optical systems to study various aspects of two-photon interference. Firstly, an experimental analysis is made of the high-dimensional entanglement that is present in the orbital angular momentum of the photons. Secondly, we present a comprehensive description of two-photon quantum interference behind a double slit. We demonstrate how to control the quantum correlations and present the first observations of complete two-photon diffraction patterns behind a double slit. Finally, we present pioneering experiments on spatially entangled two-photon states that are scattered of random media. We have observed and theoretically analyzed the structure in the random two-photon interference patterns called two-photon speckle patterns. Spatial entanglement gives two-photon speckle a much richer structure than ordinary one-photon speckle. Our experiments also demonstrate a two-photon interference phenomenon that survives averaging over different realizations of disorder. The latter results are closely related to bosonic, fermionic, and anyonic particle exchange symmetries. Show less
