Spontaneous parametric down-conversion is a non-linear optical process mediated by a crystal where an incident photon is converted into two or more outgoing photons. The theory describing...Show moreSpontaneous parametric down-conversion is a non-linear optical process mediated by a crystal where an incident photon is converted into two or more outgoing photons. The theory describing parametric down-conversion is studied; multi-photon correlations in a spatial basis and orbital angular momentum basis are studied theoretically and experimentally. For high intensity pump fields multiple photon pairs can be created. This is investigated experimentally and by simulation. Theory is developed to describe orbital angular momentum for multiple photon pairs and is applied to double photon pairs. Progress is made to differentiate between spontaneous and stimulated double photon pair emissions.Show less
We build a setup based on a paper of Pilnyak et al. PRA 95, 1 (2017) to cre- ate linear cluster states using a quantum dot cavity QED as photon source. We show that it is possible to create a two...Show moreWe build a setup based on a paper of Pilnyak et al. PRA 95, 1 (2017) to cre- ate linear cluster states using a quantum dot cavity QED as photon source. We show that it is possible to create a two photon cluster state, using a continuous wave laser to excite the quantum dot. Furthermore, we show g(2)measurements for distinguishable and indistinguishable photons.Show less
Localization of light and cavity modes play an important role in optics. In photonic crystals, localization occurs at defects to the periodicity of the structure. Recently, twist in a coreless...Show moreLocalization of light and cavity modes play an important role in optics. In photonic crystals, localization occurs at defects to the periodicity of the structure. Recently, twist in a coreless photonic crystal fibre was shown to confine an optical mode. In this project, the analogous system of a rotating two-dimensional photonic crystal has been investigated. Building upon previous work by Götte, Barnett and Padgett, a wave equation for a rotating photonic crystal is derived. Although no explicit solutions have been found yet, several solving procedures are proposed. In addition, the effect of elastic deformations resulting from rotation-induced centrifugal force is investigated theoretically. We report the emergence of localized modes in a circular Bragg deformed by rotation. The wavelength of these modes is found to be proportional to the magnitude of the deformations. The localized modes reported here present a first step towards highly tunable cavity devices.Show less
Can fluctuations be found in visible thermal light? To answer this three sections of literature research are included in which the following subjects will be explored: Spatial/temporal modes...Show moreCan fluctuations be found in visible thermal light? To answer this three sections of literature research are included in which the following subjects will be explored: Spatial/temporal modes/coherence, stellar interferometry and the second order correlation function (g(2)) for thermal light. The insights gained in these sections will be used for two experiments. The first experiment is designed to detect spatial fluctuations, which was achieved by a simple setup involving a double slit and two pinholes. The second experiment, designed to detect temporal fluctuations using the g(2) of a quasi-thermal light source, did not find significant results, which contradicts the results of a simulation of g(2) for thermal light.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
In this thesis I explore the possibility of excitation with a single photon source for biomicroscopy purposes. In biomicroscopy the fluorescent properties of molecules are used to label proteins or...Show moreIn this thesis I explore the possibility of excitation with a single photon source for biomicroscopy purposes. In biomicroscopy the fluorescent properties of molecules are used to label proteins or molecules of interest. A key limitation is the effect of photobleaching: after some time all fluorescent molecules are irreversibly converted to a dark state. Photobleaching processes involve highly reactive excited states of molecules and formation of radical oxygen. Excitation with single photons represses multiphoton processes and it is therefore expected that this will reduce the photobleaching rate. So far no experiments have been done with bright cavity based single photon sources. If the cavity based single photon source at our disposal is integrated in the microscopy setup, this could be a first test system for single photon microscopy.Show less
Over the last few decades, several methods have been explored and applied to circumvent the Abbe-Rayleigh diffraction limit, probably most importantly, stochastic super-resolution fluorescence...Show moreOver the last few decades, several methods have been explored and applied to circumvent the Abbe-Rayleigh diffraction limit, probably most importantly, stochastic super-resolution fluorescence microscopy methods. Another possibility, relying only on linear classical optics, is to exploit optical superoscillations, and is far less explored to date. In this project we explore the use of optical vortices for super-resolution far-field imaging. For this, we investigate strongly focused optical fields using a number of theoretical methods, we implement an experiment where a micro-pinhole is scanned through the focus, and, explore spin-orbit interactions of strongly focused optical fields. We find that our micron-sized pinhole is able to discern structures much smaller than its own size and leads to an enhancement of the spin-orbit interaction. Our method can be implemented as a simple and fast tool for characterizing the intensity distribution of a focused field with high resolution.Show less
We discuss our experimental efforts for generating and measuring four-photon entangled states, entangled in the orbital angular momentum space (OAM). For OAM space photons can be described in a...Show moreWe discuss our experimental efforts for generating and measuring four-photon entangled states, entangled in the orbital angular momentum space (OAM). For OAM space photons can be described in a high-dimensional Hilbert space. In order to generate the four-photon states, we use the process of spontaneous parametric down-conversion (SPDC) in a PPKTP crystal. Further a theoretical description on entangled states, Gaussian modes and SPDC is stated.Show less
An analogy between positronium and quantum dot excitons is often invoked in the literature. The former consists of a bound electron-positron pair in vacuum, whereas the latter consists of a bound...Show moreAn analogy between positronium and quantum dot excitons is often invoked in the literature. The former consists of a bound electron-positron pair in vacuum, whereas the latter consists of a bound conduction band electron and valence band hole in a quantum dot. We investigate the extent of this analogy in terms of their atom-like properties. The properties under study are the fine and hyperfine structure, Zeeman effect, confinement, Rydberg states, Stark effect, and entanglement of decay products. In addition, we experimentally investigate the photoluminescence of InAs/GaAs microcavity quantum dots in cavity QED to illustrate the confined Stark effect. We find that several important analogies and differences exist.Show less
Cluster states are often investigated in the field of quantum information. We consider two photon interference and two photon entanglement in a setup consisting of linear optical elements in which...Show moreCluster states are often investigated in the field of quantum information. We consider two photon interference and two photon entanglement in a setup consisting of linear optical elements in which single photons are produced by a quantum dot in a microcavity. We measure correlations between two detectors for different polarizations which we compare with theoretical predictions. Understanding of the predictions and the experimental results should lead to an extension to three or more photon cluster states in the future.Show less
In this thesis we investigate multi-photon entanglement in high dimensions, where the high-dimensional Hilbert space is given by the transverse-mode space of photon fields. We first introduce the...Show moreIn this thesis we investigate multi-photon entanglement in high dimensions, where the high-dimensional Hilbert space is given by the transverse-mode space of photon fields. We first introduce the reader to the mathematical framework and the quantization of light fields. Thereafter we discuss the possible partitions of the transverse-mode space, and the generic structure of photons created via type-I collinear degenerate spontaneous parametric down conversion. Finally, we present to the reader strong evidence that such entangled photons can be generated by the experimental setup that we have created.Show less
A plane-concave Fabry-Perot micro-cavity model within COMSOL has been built. The design parameters, geometry and mesh of the 2D model have been successfully implemented and meet the design criteria...Show moreA plane-concave Fabry-Perot micro-cavity model within COMSOL has been built. The design parameters, geometry and mesh of the 2D model have been successfully implemented and meet the design criteria. he solution of analytic model which describe the system had determined the resonant frequencies. In the study of the model with the use of a frequency sweep a number of resonant modes were found. The modes corresponding to the integer value N=2 & N=6 displayed modes which mostly likely describe physical modes. In addition to the correct field distributions, they also display resonant peaks in the spectrum of the 2D model.Show less
Cluster states are a viable resource for quantum computing where information is stored in these states and one single-qubit measurement is performed at a time. In order to generate such states, we...Show moreCluster states are a viable resource for quantum computing where information is stored in these states and one single-qubit measurement is performed at a time. In order to generate such states, we use the quanta of light - photons - as our qubits. We generate them from a quantum dot in a microcavity which serves us as a deterministic single photon source. We explore a method of generating cluster states by entangling these photons with the means of linear optical elements and post-selection. We develop a theoretical model and show that it is in an agreement with our experimental data with single photons. From this agreement, we conclude that the cluster states arise in the experimental setup and the entanglement between the photons can be confirmed to be present with further analysis using our hypothesis and possibly even the quantum state tomography in the future.Show less
This thesis is concerned with the design of numerical methods for solving the Schrödinger equation for a system of two-electrons in a double quantum dot. Theoretical background is presented for the...Show moreThis thesis is concerned with the design of numerical methods for solving the Schrödinger equation for a system of two-electrons in a double quantum dot. Theoretical background is presented for the physics of a two-electron quantum dot. Implementation of the double dot system is via the QuTiP library is discussed and a numerical approach for the treatment of the system using the density matrix formalism is presentedShow less
Rabi oscillations between the excited state and the ground state of an exciton in a quantum dot can be used to coherently control the state of a two-level system. Manipulating the state of a two...Show moreRabi oscillations between the excited state and the ground state of an exciton in a quantum dot can be used to coherently control the state of a two-level system. Manipulating the state of a two-level systems has applications in quantum computing and creating single photon sources. Rabi oscillations have been amply observed in atoms, free-space quantum dots, and ion traps. However, observing this phenomenon in cavity quantum electrodynamics has shown to be much more demanding. In this thesis we show that Rabi oscillations can also be observed in polarisation non-degenerate cavity-quantum dot systems.Show less
In this bachelor research project, the thermal conductivity of very thin (50 nm) suspended Silicon Nitride (SiN) membranes is studied. These membranes are used as mechanical resonators in...Show moreIn this bachelor research project, the thermal conductivity of very thin (50 nm) suspended Silicon Nitride (SiN) membranes is studied. These membranes are used as mechanical resonators in optomechanical experiments where quantum decoherence properties are studied. When these optomechanical experiments are performed at low (mK) temperatures, heating of the membrane by laser absorption perturbs these measurements. Therefore, the thermal properties of these membranes are studied in this project at room temperature with a method which is in principle also applicable for cryogenic measurements. In this project different methods are studied and the 3w method is expected to be the best suitable method and is therefore investigated in this project. Using this method, measurements have been done and a signal containing thermal properties of the membrane is obtained. However, due to the sample preparation, no thermal conductivty could be extracted from this signal.Show less
It has been a long term goal of physicists to control macroscopic quantum superposition states - cat states - since these connect to a number of open fundamental questions in physics: the...Show moreIt has been a long term goal of physicists to control macroscopic quantum superposition states - cat states - since these connect to a number of open fundamental questions in physics: the transition from the quantum to the classical world, the quantum measurement problem, and the area between quantum physics and theory of general relativity. Optomechanics has been identified as a method for generating cat states, however, this is yet to be achieved. The scientific community has developed increasingly improved optomechanical systems. About a decade ago, a promising optomechanical system has been demonstrated that consists of a high-stress silicon nitride membrane in the middle of a Fabry-Pérot cavity. This project concerns the development of a membrane-in-the-middle device for our lab. Our main focus lies on developing an understanding about the connection between system design and optomechanical performance. In addition, we demonstrate optomechanics for our device, and show that the initial optomechanical parameters are good. The availability of clearly defined methods for improving upon the current system parameters implies that we are moving in the right direction towards quantum optomechanical experiments.Show less
High-fidelity single photon sources are required for quantum information technologies and fundamental research. Recently near-unity single photon purity and near-unity indistinguishability have...Show moreHigh-fidelity single photon sources are required for quantum information technologies and fundamental research. Recently near-unity single photon purity and near-unity indistinguishability have been shown in resonantly pumped quantum dots embedded in an optical cavity. In this thesis we provide a theoretical framework and experimental results on polarization non-degenerate self-assembled InAs/GaAs quantum dots inside a polarization non-degenerate cavity, and show that by filtering the polarization the brightness of the single photon source can be enhanced. We furthermore describe the resulting output light analytically as a mixture of single photons and coherent light and derive a simple expression for the purity of the single photon source. Lastly we present pulsed measurements of this quantum dot-cavity system, and show that the purity of the single photon source is 98%.Show less
The purpose of this research is to improve a quantum dot based single photon source (SPS) by double-pass filtering weak coherent light pulses. This means that a second excitation of the quantum dot...Show moreThe purpose of this research is to improve a quantum dot based single photon source (SPS) by double-pass filtering weak coherent light pulses. This means that a second excitation of the quantum dot is done with light that has previously been scattered off the quantum dot. A double pass through a quantum dot in a cavity has never been done before and this thesis provides the first steps towards this. This could eventually lead to improvements in photonic quantum gates and therefore also in the field of quantum circuits. The polarization configuration of the setup plays an important role because we have to excite the quantum dot efficiently, and we want to filter out all (coherent) background light. The measurements show evidence that this novel scheme is feasible, however we have not yet established a higher single photon purity with respect to the single pass system, which will be subject to future research.Show less
