This thesis presents a detailed study into the development of a custom- made cryogenic sample stage which was designed, fabricated, and retrofitted in a Scanning Electron Microscope (SEM) for...Show moreThis thesis presents a detailed study into the development of a custom- made cryogenic sample stage which was designed, fabricated, and retrofitted in a Scanning Electron Microscope (SEM) for performing Cryo-EBID, a cryogenic variation of the microfabrication technique known as ’Electron Beam Induced Deposition’ (EBID). It provides an overview of all relevant aspects of the design process, from the concept design to a fully integrated and functional product. The goal of the project is to implement Cryo-EBID for the fabrication of nanowires using a tungsten hexacarbonyl (W(CO)6) precursor, offering an immense increase in deposition rate compared to traditional EBID. The setup’s efficacy in creating microstructures is eval- uated at various electron doses and a small set of prototype nanowires were fabricated and characterized. This project serves to provide valuable insights into the development process of a cryogenic sample stage and a method for creating nanowires using cryo-EBID while also setting the stage for future cryo-EBID experiments.Show less
Quantum computing is a new mode of computation that allows qualitative advantage over classical computers for certain tasks. One such task is calculating the lowest energy states of quantum systems...Show moreQuantum computing is a new mode of computation that allows qualitative advantage over classical computers for certain tasks. One such task is calculating the lowest energy states of quantum systems. In the near term, a promising quantum algorithm for this task is the variational quantum eigensolver (VQE). In order to realize a VQE, one needs to choose a good ansatz for the ground state. The accuracy of the approximation of the VQE essentially depends on the chosen ansatz. Motivated by unitary coupled cluster (UCC) theory in quantum chemistry, the UCC-ansatz has emerged as a standard in the context of VQEs. Implementation on a quantum circuit for this ansatz however, requires a Suzuki-Trotter approximation. In this thesis, we identify two key approaches in this ”Trotterization” method. We investigate the behaviors of the resulting Trotterization schemes. We found a drastic, system-dependent variation in the performances of the different Trotterization schemes. Therefore we recognize that the choice of Trotterization scheme might be crucial for quantum advantage in the near future. Based on the analysis in this research, we propose a system-adapted criterion for efficient Trotterization choice. On top of that, we suggest a new VQE ansatz. For certain systems, this ansatz approximates the ground state considerably more accurately than the other ansatzes considered in this project.Show less
TaS2 is a Van der Waals material which can exist in more than on crystal structure(polytypes). Different of these crystal structure can exist at once on a sample of TaS2 creating different domains...Show moreTaS2 is a Van der Waals material which can exist in more than on crystal structure(polytypes). Different of these crystal structure can exist at once on a sample of TaS2 creating different domains of crystal structures. In this work a Low Energy Electron Microscope is used to perform reflectivity measurements using Low Energy Electron Diffraction on different domains. The measured reflectivity of the domains is than compared to simulated reflectivity of different known polytypes of TaS2. A method on how to perform LEED reflectivity calculations is explored and used to compare to two LEED measurements on TaS2 and the crystal structures of the observed domains is analyzed.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
In the search for substrates used in the investigation of catalytic nanoparticles we have grown alumina films on NiAl(110) past 5.35 Å, the maximum thickness that can be obtained with molecular...Show moreIn the search for substrates used in the investigation of catalytic nanoparticles we have grown alumina films on NiAl(110) past 5.35 Å, the maximum thickness that can be obtained with molecular oxygen. A NiAl(110) sample was first oxidized to that thickness with molecular oxygen, after which it was stepwise oxidized with NO2. The film thickness, crystal structure and chemical composition were measured using Low Energy Electron Diffraction (LEED), X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM). We have confirmed that film grown with NO2 follows the theoretical model of Cabrera and Mott up to 6.9 Å. STM images show an increase in the number of islands and vacancies in the metal, indicating that this growth happened at the film-metal interface and not the film surface.Show less
Chromatin is a dense structure of DNA and histone proteins. DNA wraps in units of 147 bps around 8 histones forming the nucleosomes. Strings of nucleosomes stack into dense 30 nm fibers, but the...Show moreChromatin is a dense structure of DNA and histone proteins. DNA wraps in units of 147 bps around 8 histones forming the nucleosomes. Strings of nucleosomes stack into dense 30 nm fibers, but the structure of these fibers remains disputed. Force spectroscopy experiments show that the linker length affects the characteristic unfolding of nucleosome-arrays and suggests two alternative conformations. However, the precise influence of linker base pairs remains unclear. Here we use Monte Carlo simulations and show that DNA twist-energy largely determines whether nucleosomes stack in a 1-start or 2-start conformation. In addition, we show with Mutation Monte Carlo simulations that the sequence of the linker DNA may affect nucleosome stacking. Thus both the sequence and length of the linker DNA are important for the higher-order structure of 30 nm chromatin fibers. Furthermore, the simulations form a bridge between theory and experiment as predicted changes in chromatin folding can be verified experimentally.Show less
Prior research has demonstrated by theory and simulation that the creation of holes in two-dimensional superconductors by periodic nanopaterning can increase the critical temperature. To test this...Show morePrior research has demonstrated by theory and simulation that the creation of holes in two-dimensional superconductors by periodic nanopaterning can increase the critical temperature. To test this theory it must be implemented experimentally and the resulting critical temperature must be measured. Preceding the modification of these superconductors, the cryogenic resistance-temperature measurement must be tested and optimized. This thesis discusses the steps, and the problems in them, of the measurement process and provides possible explanations and solutions.Show less
The structure of chromatin fibers has been researched in different salt conditions with Magnetic tweezers. The drag force on the tether as a result of flowing in a new buffer into the flow cell...Show moreThe structure of chromatin fibers has been researched in different salt conditions with Magnetic tweezers. The drag force on the tether as a result of flowing in a new buffer into the flow cell resulted in structural changes of the chromatin and disassembly of the histone octamer. In a new flow cell design, the drag force was eliminated by changing the buffer conditions by diffusion through a permeable membrane made from PEG-DA 400. Furthermore, double stranded DNA was unzipped using Magnetic tweezers and the position of the melting force was correlated with the G-C content calculated from the sequence.Show less
We measure the temperature dependent resistance of a niobium nitride (NbN) from room temperature to 4 K. The increasing resistance with decreasing temperature can be explained by tunneling of...Show moreWe measure the temperature dependent resistance of a niobium nitride (NbN) from room temperature to 4 K. The increasing resistance with decreasing temperature can be explained by tunneling of electrons between grain boundaries. Once the detector is in the superconducting regime single photon counts can be registered. We find an optimal setting of the trigger level of 0.2 V to register detection events while minimizing the influence of amplifier noise. From the measured voltage pulses we estimate a kinetic inductance of 200 nH for our devices. We explore the regime of high photon energies by plotting the count rate vs optical power on a double logarithmic scale. For photons with 500 nm wavelength the highest initial slope is equal to 2.6, indicating that detector tomography with 3 photon events realistic. Unfortunately, higher slopes are not observed and makes looking into detection events with more than 10 eV total energy difficult if not impossible.Show less
Source-free Maxwell equations admit three-dimensional solutions with a knotted optical vortex structure. The theoretical evidence naturally gives rise to the question: Could such peculiar fields...Show moreSource-free Maxwell equations admit three-dimensional solutions with a knotted optical vortex structure. The theoretical evidence naturally gives rise to the question: Could such peculiar fields also exist in nature and in particular, could they be created in a laboratory? Our main objective is to provide an analytic investigation of their characteristic properties, which will provide an insight in how their experimental synthesis could be achieved. A close examination reveals a saddle-shaped local polarization pattern that is transverse everywhere to the vortex line and a broad spectral decomposition. Although the latter feature contradicts the current experimental techniques and therefore complicates their realization; this thesis aims to bring the theory in closer contact with the experiment so to ensure that in the coming years it will be possible to witness an experimentally created knotted optical singularity.Show less
Self-assembled InAs/GaAs quantum dots currently have the highest overall single photon source (SPS) performance, but one of the limiting factors for the brightness is the extraction of single...Show moreSelf-assembled InAs/GaAs quantum dots currently have the highest overall single photon source (SPS) performance, but one of the limiting factors for the brightness is the extraction of single photons from the excitation laser pulse. Since the SPS is excited resonantly for maximal indistinguishability, a difference in polarization is used to extract the single photons from the incident excitation laser light. In this work we studied ways to maximize the collection of single photons and the brightness of the SPS both experimentally and theoretically. The system of a quantum dot in an optical cavity was simulated semi classically. Two new brighter configurations for the input and output polarization were found, one through analytical analysis and one with an optimization algorithm. These two new polarization configurations were tested in the lab along with the configuration that is conventionally used, which resulted in an SPS which was {\em twice} (analytical analysis) and {\em three} times (optimization algorithm) as bright as the conventional configuration. We show that the brightness can be improved by another factor of three through optimizing one of the sample dependent parameters determined in sample fabrication.Show less
One of the limiting factors for improving the sensitivity towards single spin detection using Magnetic Resonance Force Microscopy is the working temperature. A component limiting this working...Show moreOne of the limiting factors for improving the sensitivity towards single spin detection using Magnetic Resonance Force Microscopy is the working temperature. A component limiting this working temperature is the radio frequent (RF) source. The use of a superconducting NbTiN instead of a copper RF-source improves this working temperature and theory suggests that the dissipation of such a NbTiN RF-source is geometry dependent. The dissipation of 9 NbTiN RF-sources with different geometries was measured using two different methods. First a four-point measurement was used that returned inductive effects obscuring the dissipation of the RF-source. Secondly a calorimetric measurement was tried that returned dissipation originating in the supply cables overshadowing the dissipation of the RF-source. The dissipation of these supply cables corresponds very well with the dissipation attributed to the RF-source by our predecessors. The dissipation of the RF-source is thus found to be much lower than previously thought.Show less
We investigated the largely unknown spectroscopic properties silicon nitride implanted with trivalent ytterbium ions. We found that annealing the implanted silicon nitride samples is essential to...Show moreWe investigated the largely unknown spectroscopic properties silicon nitride implanted with trivalent ytterbium ions. We found that annealing the implanted silicon nitride samples is essential to see the characteristic 980 nm Yb3+ peak in the photoluminescence spectrum. We also notice that the peak we measured in our spectrum is redshifted by 5 nm compared to other host materials, which is to be expected. Additionally, in our spectrum we measure a background that seems to be intrinsic to the host material or due to implantation damage, yet the exact cause is still to be found. We also estimated the density of excited Yb3+ in our samples which differed two orders of magnitude from our Yb implantation density which we deem a realistic result.Show less
We investigate photon counting properties in an NbN superconducting nanodetector, and succesfully do quantum detector tomography. We find qualitative similarities to an earlier tomography result on...Show moreWe investigate photon counting properties in an NbN superconducting nanodetector, and succesfully do quantum detector tomography. We find qualitative similarities to an earlier tomography result on the same detector, although a larger power range may eliminate anomalies in the numerical fit. Furthermore, we investigate the resistive properties of a MoSi superconducting nanodetector, observing finite resistance below the critical temperature. Measuring current as a function of voltage, we find indications that indeed imply a finite resistance below Tc. Obtaining the critical current for different temperatures and applying a Ginzburg-Landau fit, we find a lower critical temperature than obtained from measurements of resistance as a function of temperature. Finally, we observe that photon counts for MoSi are not possible above T > 3.85 K. We calculate that electronic noise is responsible for this absence of photon counts.Show less
Using an optical cavity, coupled to a micromechanical oscillator - a relatively heavy mass, double trampoline resonator - we will test whether we can, using the method proposed by Clerk et al. ...Show moreUsing an optical cavity, coupled to a micromechanical oscillator - a relatively heavy mass, double trampoline resonator - we will test whether we can, using the method proposed by Clerk et al. (2008), perform back-action evading measurements (BAE) in the optical domain on a single quadrature of the oscillator’s motion. We will do so by probing the oscillators motion with two optical drives spaced one mechanical resonance frequency above and below the cavity resonance frequency. We will then inject noise in the cavity and analyze the light leaving the cavity. This is intended to show that we can perform classical back-action evading measurements. The long term goal of this project is to find out if this system is capable of reaching or exceeding the standard quantum limit (SQL).Show less
Recently it was observed that laser-induced breakdown creates macroscopic rings of plasma. These rings are of interest because they can be used to construct inherently stable magnetized plasma...Show moreRecently it was observed that laser-induced breakdown creates macroscopic rings of plasma. These rings are of interest because they can be used to construct inherently stable magnetized plasma structures. The goal is to form a better understanding of the processes within and properties of these plasma rings. We study the different stages in the time-evolution of the plasma using an intensified CCD with nanosecond resolution exposure time. Furthermore, the spectrum of the emitted light is studied and through Boltzmann analysis the temperature is derived.Show less
Entangled photons are created by use of Parametric Down Conversion in a periodically poled KTP crystal. We rebuild and modified a previous set-up\cite{Yorulmaz2014} and characterised the phase...Show moreEntangled photons are created by use of Parametric Down Conversion in a periodically poled KTP crystal. We rebuild and modified a previous set-up\cite{Yorulmaz2014} and characterised the phase-matching conditions in a new set of crystals. First results with single photon counters and correlated photons are given. The goal is to understand the generation of 4-photon states expressed as a source brightness per optical mode.Show less
The purpose of this research is to investigate the performace of a prototype detector for a neutrino telescope built in the Mediterranean Sea. The telescope consists of photomultiplier tubes which...Show moreThe purpose of this research is to investigate the performace of a prototype detector for a neutrino telescope built in the Mediterranean Sea. The telescope consists of photomultiplier tubes which record the position and time stamps of Cherenkov light created by charged particles form e.g. neutrino interactions. This investigation is done to find neutrino sources in the cosmos which could lead to a better understanding of active galactic nuclei, supernova remnants, micro-quasars and gammaray bursts. We used the data of a prototype where most of the signals stem from muons created in atmospheric interactions of cosmic rays. In the first part the properties of the detected signals are being investigated and we look for a lower limit to have a noise free signal when looking for Cherenkov light created by charged particles between multiple digital optical modules. The last part of this project is devoted to calibrating the observed data with the simulated data so that in future experiments it could be seen at which time a particle is detected with nanosecond precision and thus with an angular precision of a tenth of a degree the direction and path of particles could be constructed.Show less
