Since all astrophysical objects spin, it is important to study the dynamics of spinning objects in curved space-time. The dynamics of spinning particles are described with a covariant Hamiltonian... Show moreSince all astrophysical objects spin, it is important to study the dynamics of spinning objects in curved space-time. The dynamics of spinning particles are described with a covariant Hamiltonian formalism. In this formalism, the closed set of equations of motion are obtained from Poisson-Dirac brackets. Since the brackets are model-independent, a large class of Hamiltonians are used to describe a variety of models. We apply our formalism to study the dynamics of spinning particles in Schwarzschild background, and establish a number of new results. First, we obtain the equations with minimal Hamiltonian for the circular orbit of the particle in the equatorial plane. By generalizing the method of geodesic deviation in General Relativity to world lines of particles carrying spin, we derive the complete first-order solution for the non- circular bound orbits. This solution leads to the surprising insight that the periastron is not only subject to an angular shift, but show radial variations as well. Then analyzing the stability criterion for circular motion we find the Innermost Stable Circular Orbits as a function of spin. Finally we show that the spin-orbit coupling leads to geodetic precession of the bound orbits. Show less
We developed a new FRET-based technique, “Fluredox”, which allows fluorescence readout of the redox state of oxido-reductases at single molecule level. Commercially available red-absorbing... Show moreWe developed a new FRET-based technique, “Fluredox”, which allows fluorescence readout of the redox state of oxido-reductases at single molecule level. Commercially available red-absorbing fluorophore ATTO655 was selected for labeling Azurin, a small blue mononuclear copper protein. Single molecule fluorescence correlation spectroscopy (FCS) of the fluorescently labeled Copper azurin in solution reveals how the position of the label in the 3-D structure of the protein affects the redox kinetics of the redox center as well as the label. Under certain redox conditions, we have been able to observe a microsecond dynamics for intramolecular ET reaction between the label and the metal center in azurin. Our results show that this FRET technique can be profitably used to study the enzyme activity of dye-labeled oxidoreductases. Show less
Catalysis is one of the most important technical and scientific developments, on which present-day society is based. For example, it is crucial to the production of fertilizers or clean... Show more Catalysis is one of the most important technical and scientific developments, on which present-day society is based. For example, it is crucial to the production of fertilizers or clean fuels and needed for the abatement of exhaust gases. Frequently, the employed catalysts are being discovered in a very empirical way; by trial and error. However, designing catalysts based on detailed understanding is preferred. Obtaining understanding is very difficult, because catalysts are very complex materials. Furthermore, its properties often depend on the atmosphere surrounding the catalysts, i.e., the temperature and pressure of reactants and products, which they are exposed to, and these properties also change over time. The major part of this thesis focuses on structural changes of Pt model catalysts exposed to high oxygen pressures at elevated temperatures. The changes were measured with a ReactorSTM, a special version of a scanning tunneling microscope (STM) adapted to operate at high pressure and temperatures. These observations show that various surface oxide with a single-layer thickness form under reaction conditions. These oxides are structurally and chemically different from the Pt bulk oxides. The second part describes a set of experiments to understand the role of low-coordinated atoms and water in Au-catalyzed CO oxidation. Show less
This thesis explores the basic mechanism of the CO oxidation reaction on a palladium catalyst. Two new setups are presented to investigate catalytic reactions in general. Using a variety of... Show moreThis thesis explores the basic mechanism of the CO oxidation reaction on a palladium catalyst. Two new setups are presented to investigate catalytic reactions in general. Using a variety of techniques, reaction oscillations are analysed and modeled to examine the basic structure of the palladium catalyst in operating conditions. Show less
Gas bubbles in liquids are important in biomedical applications such as ultrasound imaging, drug release, or photothermal therapy. We create vapor nanobubbles in liquids around laser-heated gold... Show moreGas bubbles in liquids are important in biomedical applications such as ultrasound imaging, drug release, or photothermal therapy. We create vapor nanobubbles in liquids around laser-heated gold nanoparticles and investigate their time-dependent properties using optical techniques. Vapor nanobubbles can show explosive behavior on the (sub-)nanosecond (10^-9s) time scale, even under continuous heating. They are highly sensitivity to acoustic pressures. From our study, we conclude that vapor nanobubbles are very interesting systems for fast all-optical light modulation and for nanoscale acoustic-wave sensing. Conjugated polymers are important organic materials in organic light emitting diodes, thin-film transistors, solar cells, or as chemical sensors. We use photothermal microscopy to study the optical absorption of single conjugated polymer molecules (MEH-PPV). Immersing the molecules in supercritical xenon as the photothermal transducing medium, we detect single conjugated polymer molecules via their absorption, and correlate this signal with photoluminescence. We measure the number of monomers in individual polymer chains and the apparent quantum yield of single conjugated molecules. The information provided by our technique will generate a better understanding of trapping and non-radiative deactivation channels of optically-induced excitations in conjugated polymers and thus facilitate the design and optimization of devices based on this important class of materials. Show less
Nuclear magnetic resonance force microscopy (MRFM) is a technique which combines magnetic resonance imaging (MRI) with scanning probe microscopy (SPM). The final goal is to develop this technique... Show moreNuclear magnetic resonance force microscopy (MRFM) is a technique which combines magnetic resonance imaging (MRI) with scanning probe microscopy (SPM). The final goal is to develop this technique to such a level that the atomic structure of a virus or protein can be revealed by this microscope. This thesis shows nuclear magnetic resonance force measurements on copper in which the interaction of the magnetic moments of the nuclei of copper with a magnetic cantilever has delivered a detectable signal at a temperature of 50 millikelvin. Furthermore, we show measurements, which support a new theory where at low magnetic field and low temperature, non contact friction between the magnetic cantilever and paramagnetic electron spins is described. These measurements were enabled by technical improvements such as vibration reduction in a cryogen free dilution refrigerator. As a benchmark for the low vibration, we show atomic resolution scanning tunneling microscopy at 15 millikelvin temperature on graphite. We also show a method to create small magnets for MRFM from a thin magnet film. With these small magnets the field gradient and therefore the sensitivity may be significantly enhanced. Show less
In this thesis we study some aspects of the very early Universe. We focus on the period of inflation, and show how the presence of many fields during this period can affect its low energy... Show moreIn this thesis we study some aspects of the very early Universe. We focus on the period of inflation, and show how the presence of many fields during this period can affect its low energy description. We focus on the predictions for the two and three point correlation functions of the curvature perturbations, in the case in which apart from the inflaton field there is a very heavy isocurvature field participating in the dynamics. We also treat briefly the case in which the isocurvature field is light, in particular applied to the case of so-called natural inflation. Show less
For more than 65 years, scientists have been fascinated by the idea to miniaturize electrical circuits toward the smallest length scales. One particular way is inspired by nature itself,... Show moreFor more than 65 years, scientists have been fascinated by the idea to miniaturize electrical circuits toward the smallest length scales. One particular way is inspired by nature itself, specifically to assemble electrical components and switches from atoms and molecules. The molecules typically used have dimensions of the scale of a few nanometers (1 nanometer = 0,000000001 meter). The scientific research area that represents the study of electrical currents through molecules is called "molecular charge transport" or "molecular electronics". In this thesis, I have performed fundamental research on charge transport through various molecules. Specifically, I have investigated a special type of molecule that has the ability to change its spin state. To test these functional molecules, I have used a more robust type of molecular device that enables me to bridge the size gap mentioned above. This thesis has led to two important new insights. First, the properties of a switchable molecular device can be strongly enhanced artificially by making use of a charge transport mechanism called multiple inelastic cotunneling. Second, we show that the spin transition phenomenon can take place in a molecular-nanoparticle ensemble. Show less
DNA-hosted silver clusters (Ag:DNAs) have attracted a lot of attention due to their small size (~20 atoms), wide range of applications in chemistry and biology, and sequence-dependent optical... Show moreDNA-hosted silver clusters (Ag:DNAs) have attracted a lot of attention due to their small size (~20 atoms), wide range of applications in chemistry and biology, and sequence-dependent optical tunability. Most of the previous studies are focused on the ensemble of emitters in solution. However, little is known about the optical properties of individual emitters, which is a crucial step towards understanding of their real nature, otherwise lost in ensemble averaging. We show that the excitation and emission spectra of individual emitters are broad even at 1.7 K (FWHM ~25 nm). Also, polarization measurements indicate that the excitation is not strongly dependent on the polarization of excitation light, whereas the emission is highly linearly polarized. Furthermore, from time-resolved measurements, we can conclude that the emission of single emitters can be fitted with single exponential decay curve, whereas the emitters organized with nanometer precision on the DNA scaffolds show double–exponential decay. This indicates the interaction between densely packed Ag:DNAs. Finally, we show that the DNA tubes can be used as a nano-contact glue between the colloidal particles functionalized with short DNA strands. Show less
The thesis is devoted to applications of the anti de Sitter/Conformal field theory correspondence (AdS/CFT, also called holography) to various problems in different areas of theoretical physics. We... Show moreThe thesis is devoted to applications of the anti de Sitter/Conformal field theory correspondence (AdS/CFT, also called holography) to various problems in different areas of theoretical physics. We make use of AdS/CFT to get insights into the physics of superconductors, quark-gluon plasma, and to study properties of quantum field theories on non-causal backgrounds. In the first part of the thesis we construct a holographic model of a Bardeen-Cooper-Schrieffer-like superconductor and demonstrate that the Cooper instability of Fermi-liquids can be naturally described in holographic terms. We show that both the superconducting phase and the BEC/BCS crossover appear naturally. In the second part we address the problem of quark-gluon plasma formation in heavy ion collisions. We study the effect of finite chemical potential on this process and calculate physical properties of the resulting deconfined state. The third part is dedicated to study of evolution of a quantum system with violated causality. Using AdS/CFT we can map the complicated and poorly defined non-causal quantum dynamics onto a classical spacetime with closed timelike curves. Doing that we have derived the Green's function of the QFT and demonstrated that evolution of a quantum system can be consistent and non-pathological even at broken causality. Show less
Topological superconductors are a novel type of superconductors that carry Majorana particles at their boundary. These surface states are equal superpositions of electrons and holes, and hence are... Show moreTopological superconductors are a novel type of superconductors that carry Majorana particles at their boundary. These surface states are equal superpositions of electrons and holes, and hence are their own anti-particles. There has been a recent surge of theoretical and experimental effort to realize these special particles in the lab. While first observations support the theoretical predictions, fail-safe experimental evidence for Majoranas is still needed. Part of the challenge is that due to their vanishing charge they are not easily detected electrically. The topic of this thesis is the proposal and study of electrical signatures of Majoranas that are present in spite of their charge neutrality. By applying scattering and random matrix theory we first examine their generic properties. With the tool of numerical simulations we then put our predictions to test on realistic systems. Show less
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
A guaranteed source of neutrinos is the production in cosmic ray interactions with the interstellar matter in our Galaxy. The signal has never been detected however and only an upper limit on this... Show moreA guaranteed source of neutrinos is the production in cosmic ray interactions with the interstellar matter in our Galaxy. The signal has never been detected however and only an upper limit on this flux of neutrinos has been published by the AMANDA-II detector. The ANTARES neutrino telescope, located in the Mediterranean Sea, offers a high visibility of the central region of the Milky Way, from where the highest signal is expected. ANTARES data from 2007-2012 were used to compare the flux from a region extending 39 degrees in Galactic longitude and 4.5 degrees in Galactic latitude on either side of the Galactic centre, with the flux from multiple equivalent off-source regions. No significant excess has been observed, and upper limits have been placed on the neutrino flux. The flux limits produced with ANTARES are more than a factor of 10 above the model predictions, which means that a bigger neutrino telescope is needed to constrain the models further. The future KM3NeT telescope is well suited to perform this measurement. Simulations show that by using all neutrinos flavours, KM3NeT should be able to seriously constrain the neutrino flux after about 3 years of operation. Show less
The research contained in this thesis lies at the interface between quantum phyiscs, nanotechnology and the theory of computation. Its goal is to design electronic circuits to realize computations... Show moreThe research contained in this thesis lies at the interface between quantum phyiscs, nanotechnology and the theory of computation. Its goal is to design electronic circuits to realize computations that follow the laws of quantum mechanics, and which would allow to execute some algorithms faster than their classical counterparts - for instance, algorithms to solve chemical problems. In particular, these circuits use Majorana modes, very special states which appear in superconductors and are theoretically predicted to protect information from the environment, so that the computation can be executed without errors. The role of my research was to design electronic circuits able to use this fascinating property. Hence, this work is a bridge between some very abstract mathematical ideas and the very concrete world of electronic circuits, made out of inductors and capacitors. Show less
Low Energy Electron Microscopy (LEEM) is a microscopy technique typically used to study surface processes. The sample is illuminated with a parallel beam of electrons under normal incidence and the... Show moreLow Energy Electron Microscopy (LEEM) is a microscopy technique typically used to study surface processes. The sample is illuminated with a parallel beam of electrons under normal incidence and the reflected electrons are projected onto a pixelated detector, where an image is formed. In the first part of this thesis, we use LEEM to study the behavior of submonolayers of gold on Si(111). After a thorough analysis of the Si-Au system, we describe the behavior of these (sub)monolayers when exposed to alkanethiols. In the second part of this thesis we move away from pure surface physics and introduce two new applications for LEEM. The first of these, Low-Energy Electron Potentiometry (LEEP), can be used to visualize electrical conductance. We show that for layered two-dimensional materials we can obtain a higher resolution in LEEP experiments. Finally, in chapter 6, we present a new method to measure the dispersion relation of unoccupied states in two-dimensional layered materials. Show less
This thesis focuses on the investigation of Majorana zero-modes and their quantum transport properties of topological insulators and topological superconductors in several low-dimensional systems,... Show moreThis thesis focuses on the investigation of Majorana zero-modes and their quantum transport properties of topological insulators and topological superconductors in several low-dimensional systems, i.e. 1D nanowire system (Chapter 2), 2D quantum spin Hall system (Chapter 3, 4) and 0D quantum dot system (Chapter 5, 6). Show less
This thesis consists of two different parts, separating research projects carried out in two different groups. In the first and longest part of this thesis, we attempt to fit the signal for a... Show moreThis thesis consists of two different parts, separating research projects carried out in two different groups. In the first and longest part of this thesis, we attempt to fit the signal for a reduction in the speed of sound of the inflaton. In chapter 1, we shortly introduce the topics discussed in this thesis, namely _CDM cosmology, transient reductions in the speed of sound during inflation, and Bayesian statistical inference. Afterwards, we attempt to fit a particular hypothesis for the speed of sound reduction using Cosmic Microwave Background data (chapter 2) and later adding Large Scale Structure data to the search (chapter 3). Finally, in chapter 4 we present two pieces of code that were elaborated for the research in this thesis, and later released to the community. In the second part, consisting solely of chapter 5, we present a classification of all possible 6-dimensional symmetric toroidal orbifolds over which Heterotic String Theory leads to a supersymmetric model. To do that, we made use of standard crystallographic tools. Show less
This thesis starts with an introduction to the quantum electrodynamical description of the interaction between light and matter. The role of optical cavities is discussed and the basic properties... Show moreThis thesis starts with an introduction to the quantum electrodynamical description of the interaction between light and matter. The role of optical cavities is discussed and the basic properties of rare-earth ions are reviewed. In Chapter 2 a bare ring resonator that is coupled to a waveguide is studied. Transmission spectra are measured, from which optical properties of the ring resonator and the waveguide are characterized. Chapter 3 addresses two technical issues that are essential for the research presented in this thesis: the implantation of rare-earth ions into the ring resonator and the permanent fiber connections to the waveguides. Chapter 4 is devoted to the research on the enhancement of the spontaneous emission rate in an ytterbium-doped ring resonator in the temperature range of 5.5-295 K as a result of the Purcell effect. Chapter 5 presents the results of measurements performed on an ytterbium-doped ring resonator in a dilution refrigerator in the range of 12 mK-4.7 K. In Chapter 6 collective effects of an ensemble of emitters in a cavity are theoretically studied with different initial states and pure dephasing rates by using the quantum Monte Carlo method. Chapter 7 concludes the thesis and presents an outlook for future work. 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
