We successfully produce Josephson junctions by stacking NbSe2 flakes, where the twist angle and strain are responsible for a weak link. Field sweep measurements are taken to characterize these...Show moreWe successfully produce Josephson junctions by stacking NbSe2 flakes, where the twist angle and strain are responsible for a weak link. Field sweep measurements are taken to characterize these devices. These measurements highlight the importance of the direction of the applied magnetic field. Prompted by this, simulations of the critical current given an arbitrarily shaped interface area are presented and compared to measurements.Show less
This works investigates the possibility of building a full-field X-ray fluorescence microscope using Silicon Pore Optics (SPO) technology in the Advanced Kirkpatrick-Baez (AKB) configuration. AKB...Show moreThis works investigates the possibility of building a full-field X-ray fluorescence microscope using Silicon Pore Optics (SPO) technology in the Advanced Kirkpatrick-Baez (AKB) configuration. AKB system focuses the X-ray beam by reflection from four curved mirrors. Such an imaging system is an aberration-free and relatively easy to manufacture optics. We start with a simple two-mirror Kirkpatrick-Baez (KB) system as a first step and a basis for understanding and modelling of Advanced KB. Using the derived equations, a KB system is parameterized and characterized. A sensitivity study is conducted to find the optimal system parameters under constraints enforced by microscopy application and SPO technology. Performance of an optical system is assessed on the basis of solid angle, tightness of focal spot and field of view. The conclusions made for the KB system are relevant for the AKB system as well. SPO technology was initially developed to enable light-weight large area telescopes with resolution of a few arc seconds. It uses the concept of stacking of slightly curved reflective mirrors of high quality. We were interested to explore whether SPO can improve X-ray microscopy. However, it was found that using SPO technology for the case of full-field X-ray microscopy presents no benefits in terms of increase of solid angle. Nonetheless, the technology can be used to provide self-standing stacks with only upper reflecting plate for AKB-based microscopy setup.Show less
Within the diverse order of beetle species that produce color through structural coloration, some beetles produce light with a strong left-handed circular polarization caused by a chiral structure...Show moreWithin the diverse order of beetle species that produce color through structural coloration, some beetles produce light with a strong left-handed circular polarization caused by a chiral structure in their outer shells. From an evolutionary perspective, there should be no substan- tial benefit to left-handed over rather-handed polarization. This raises the question why no beetles have been found showing right-handed polarization. Large-scale beetle surveys are required to investigate this question further. A systematic beetle classification scheme based on polarization would aid in such a survey and highlight species with interesting optical prop- erties for further investigation. To this end we constructed a setup capable of measuring the Stokes parameters of a beetle specimen for angles of incidence and observation. We tested this setup on the beetle species protaetia speciosa jousselini and verified that the setup produces accurate results. We are however sceptical this method will result in identifying beetle-specific Stokes parameters, as their values vary with respect to both location on the beetle cuticle as well as observational angles. Furthermore we provide quantitative evidence for earlier re- ported inversion of the polarization handedness in beetle species jousselini at large angles of observation. We detect such inversion at angles of observation of at least 70◦.Show less
Superconducting nanostructures can be used to detect single photons. Here we propose to use electron-beam-induced deposition (EBID) of a superconducting tungsten-carbon alloy to create nanowires...Show moreSuperconducting nanostructures can be used to detect single photons. Here we propose to use electron-beam-induced deposition (EBID) of a superconducting tungsten-carbon alloy to create nanowires that can be used as a transition edge sensor (TES). Determining if these EBID-written nanowires can be used as an efficient TES requires an experimental characterization of its electrothermal properties. We demonstrate two key experiments to characterize a TES and introduce a numerical model to describe a TES with a nanofabricated constriction as a proof-of-concept. We characterize the low frequency impedance of a PTC thermistor and determine its electrothermal properties. We find a thermal conductance $G = 5.1 \pm 0.2 \text{ \textmu W/K}$ and a heat capacity $C = 0.48 \pm 0.03 \text{ \textmu J/K}$ and discuss how to extend these measurements to superconducting nanowires. A remotely controlled experiment is performed on NbTiN nanowires with a nanofabricated constriction. From the measured IV curves we determine the Joule heating and local temperature of the wire from an adapted Skocpol-Beasley-Tinkham model for a resistive transition. This model is valid for low values of the wire resistance. Together, these experiments and the model provide necessary infrastructure to characterize the electrothermal properties of EBID-written nanowires in the near future.Show less
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
We observe spatial bunching of four spatially entangled photons produced by parametric down-conversion in a single periodically poled KTP crystal. This effect involves an increased probability to...Show moreWe observe spatial bunching of four spatially entangled photons produced by parametric down-conversion in a single periodically poled KTP crystal. This effect involves an increased probability to generate all four photons in the same optical mode. To observe the effect we create entangled double pairs at 826 nm wavelength using a 5 mm long crystal and investigate their correlations by measuring three-fold coincidence counts. We demonstrate that two-fold and three-fold coincidence measurements are sufficient to experimentally distinguish a spatially entangled two-photon state from a four-photon state and a four-photon state from a six-photon state, respectively. This makes experimental observation of the effect feasible at moderately high pump-powers.Show less
In this thesis we study spatially entangled photon pairs created by frequency-degenerate parametric down-conversion from a 2 mm long type-I periodically poled KTP crystal pumped by 2 ps duration...Show moreIn this thesis we study spatially entangled photon pairs created by frequency-degenerate parametric down-conversion from a 2 mm long type-I periodically poled KTP crystal pumped by 2 ps duration laser pulses. We present measurements of spatial correlations between the entangled photon pairs and compare them to the same measurements performed with a 5 mm PPKTP crystal, shown in [1, paragraph 5.4.2]). For the 5 mm crystal, a peak of coincidences is observed in the collinear direction, which is not in accordance with theoretical predictions. The peak is attributed to quadruplets. We do not observe this extra peak for the 2 mm crystal. Furthermore, we find that the optical alignment is critical and depends on the type of fiber. We conclude that the collection efficiency of the detection units depends on the detection position and decreases away from the collinear direction. Although this observation is not understood, it may contribute to the extra peak. For further research, it is necessary to redesign the detection units to exclude the position dependence of the collection efficiency.Show less
