Multiport interferometers are an important tool in the emerging field of quantum information technologies. In theoretical work, we investigate implementing Haar-random unitary transformations in...Show moreMultiport interferometers are an important tool in the emerging field of quantum information technologies. In theoretical work, we investigate implementing Haar-random unitary transformations in increasingly large interferometers with realistic imperfections. We find that random matrices result in mostly low values of interferometer beam splitter reflectivities. We model production imperfections and we find that these severely limit the implementation of random matrices. We show the effects of the imperfection can be mitigated through optimisation of interferometer degrees of freedom and by adding additional beam splitters. In experimental work, we investigate the realisation of reconfigurable multiport interferometers in silica-on-silicon integrated photonics chips using a modular design. We show that individual modules are fully reconfigurable. We give a proof-of-principle of the design by connecting three modules for the first time and measure 5% transmission.Show less
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
To sense the movement or piling up of single charges, a system interacting strongly with these charges is required. An available system, having these properties, is a single electron transistor ...Show moreTo sense the movement or piling up of single charges, a system interacting strongly with these charges is required. An available system, having these properties, is a single electron transistor (SET). The electric fi eld caused by the charge, strongly changes the resistance of the SET. Yet experiments opt for a less invasive charge sensor. Such a proposed charge sensor is a single fluorescent dye molecule. The distinguishable zero phonon lines (ZPL's) of the fluorescence of the molecules shifts strongly by the Stark e ffect. The lineshift of each molecule can be tracked with an excitation laser, allowing to observe the change in charging. Tracking the ZPL's of multiple molecules allows the observation of slow charge movement. The optical charge sensing method needs to be tested on devices fabricated on a glass substrate. In particular devices, which exhibit single electron charging. These devices have been constructed with electron beam lithography (EBL). Nanoparticles, representing an island to hold the charge, have been trapped between nano-electrodes using dielectrophoresis. The nanogaps have been created by electromigration or by EBL. Eventually, nano-electrodes were also fabricated on glass by coating the glass with a 1,5 nm Cr layer. This coating was removed afterwards with plasma etching. The project focused on the fabrication of the devices. The deposition of fluorescent dye molecules and tracking the lineshifts was left for subsequent experiments. A fluorescence microscope, also necessary for the lineshift measurements, was used to observe quantum dots. Proposed experiments with quantum dots are the tracking of the movement of quantum dots in a strong alternating electric fi eld or the eff ect of a high electric field on the fluorescence of a quantum dot in a nano-electrode junction.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
This research explores the possibility of producing acrylic micro-structures for optical purposes with a Nanoscribe 3D-printer, which uses two-photon polymerisation. More specifically, it tries to...Show moreThis research explores the possibility of producing acrylic micro-structures for optical purposes with a Nanoscribe 3D-printer, which uses two-photon polymerisation. More specifically, it tries to characterise the effect of inherent flaws of the 3D-printing production method on far-field transmission optics. The studied samples are gratings with different periodicities ranging from 4 to 1 mm and samples with flat and tilted surfaces. The gratings show optical effects from variations in displacement, duty-cycle and height, and scattering effects from writing lines. Steps are taken towards 3D-printing multi-grating layer samples, with the end goal of producing a woodpile structure and other multi-layer photonic crystals.Show less
So far, most well-known helioscopes have to be aligned manually with the ever-changing position of the sun in the sky. In this project, it was assessed whether a gas- or liquid-filled transparent...Show moreSo far, most well-known helioscopes have to be aligned manually with the ever-changing position of the sun in the sky. In this project, it was assessed whether a gas- or liquid-filled transparent sphere has adequate potential to function as a helioscope. If this would be possible, this helioscope would allow for omnidirectional imaging, solving the problem of constant manual adjustment. The numerical assessment of this gas- or liquid-filled ball lens was done with the help of a ray-tracing simulation, which was tested and confirmed by comparison with analytical as well as experimental results. Then, the suitability of available materials for the experimental assessment was evaluated. The final experimental assessment of the ball lens functioning as a helioscope was done with the help of a miniature version of the envisioned helioscope. It was found that the resolution limit of the ball lens used for the experiments should be sufficient to image a sunspot of average diameter.Show less
