University of Siegen
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Publication Access status: Open Access , The structure of measurements and states in quantum theory(2019)Diese Arbeit behandelt die Struktur der Quantenmechanik mit Fokus darauf, was die Struktur von Zuständen und Messungen im Formalismus der Quantenmechanik auszeichnet. Ein sehr allgemeiner Formalismus um beide Begrifflichkeiten zu beschreiben ist durch den operationellen Formalismus der verallgemeinerten probabilistischen Theorien gegeben. Die Verallgemeinerung wird durch eine Abstraktion des reellen Vektorraums der hermiteschen Operatoren erreicht, sowie durch eine Abstraktion von positiv-Semidefinitheit. Beide Konzepte sind hinreichend um das Grundgerüst der Quantenmechanik zu erhalten, jedoch erweitern verallgemeinere probabilistische Theorien diese in einer solchen Weise, dass sie auf nahezu jede operationellen Theorie der Physik anwendbar sind. In dieser Arbeit wird die Rolle der Quantenmechanik innerhalb dieses Formalismus diskutiert, insbesondere bezüglich der Frage, welche Konzepte der Quantenmechanik eigen sind und welche Konzepte lediglich in der Tatsache gegründet sind, dass die Quantenmechanik ein Spezialfall der verallgemeinerten probabilistischen Theorien ist.Source Type:Habilitation5 13 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Cross-section measurement of tt̄γ production in pp collisions at √s = 8 and 13 TeV with the ATLAS experiment(2019)The cross-section measurement of top-quark pair production in association with a photon (tt̄γ) probes the electromagnetic coupling of the top quark. The inclusive and differential fiducial cross sections of tt̄γ are measured with the data collected by the ATLAS detector from proton-proton collisions at the Large Hadron Collider, at the centre-of-mass energy of √s = 8 TeV, with a corresponding integrated luminosity of 20.2 fb−1, and at the centre-of-mass energy of √s = 13 TeV, with a corresponding integrated luminosity of 36.1 fb−1. The measurements are performed in the single-lepton final state. Signal events in the √s = 8 (13) TeV measurement are selected by requiring one photon with a transverse momentum of pT > 15 (20) GeV, one isolated electron or muon, and at least four jets where at least one of them is originated from a b-quark. The fiducial region is defined to be close to the selection requirements. The inclusive cross-sections in √s = 8 and 13 TeV are measured to be 139 ± 7 (stat.) ± 17 (syst.) fb and 521 ± 9 (stat.) ± 41 (sys.) fb, respectively, in agreement with the corresponding next-to-leading-order theoretical predictions of 151 ± 24 fb and 495 ± 99 fb. The differential cross-sections are measured as a function of transverse momentum and absolute pseudorapidity of the photon, in both √s = 8 and 13 TeV data-sets, and as a function of the angular distance between the photon and the lepton in the √s = 13 TeV data-set. All differential measurements are in agreement with the theoretical predictions at next-to-leading-order accuracy.Source Type:Doctoral Thesis2 4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Characterization of Nb3Sn and multilayer thin films for SRF applications(2019)Basic R&D on materials for superconducting radio frequency (SRF) applications requires RF measurements on samples with high resolution. The Quadrupole Resonator (QPR) at Helmholtz-Zentrum Berlin is a dedicated test cavity, enabling RF characterization of samples in a wide parameter space of temperature and RF field strength at three frequencies. Thereby, the instrument covers typical real-life accelerator conditions without being limited to it. Within the scope of this thesis, the QPR measurement capabilities were continuously expanded and improved, allowing calorimetric measurements of RF surface resistance at all three operating frequencies. Furthermore, magnetic penetration depth, critical temperature (Tc) and the RF critical field can be studied. From those directly measured values, superconducting and normal conducting quantities such as DC critical fields, Ginzburg-Landau parameter, mean free path and normal state resistivity can be derived, yielding a multi-parameter characterization of the investigated sample. In this work, two superconducting coatings were characterized: One single layer of Nb3Sn and a NbTiN on Nb multilayer structure. Nb3Sn is one of the most promising alternative materials to niobium and already showed high quality factors in coated research cavities. The sample investigated here underscores the potential of this high-Tc material for low surface resistance. Ultimately, this could enable low-loss continuous-wave particle accelerators. However the SRF performance failed to reach theoretical values, presumably due to off-stoichiometric areas that were subsequently identified using surface analysis. Furthermore, the RF quench field measurement indicated practical difficulties in reaching the superheating critical field of Nb3Sn with the current coating process. Multilayer structures of superconducting thin films are expected to increase the superheating critical field of a bulk superconductor, corresponding to higher maximum achievable accelerating gradients. With the second sample characterized in this work, the theoretical descriptions of magnetic penetration depth and superheating field for multilayer structures can be confirmed. The observation of non-monotonic surface resistance as a function of temperature reveals additional contributions that are not included in current theories and opens a promising field for future studies.Source Type:Doctoral Thesis6 14 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , X-ray structural characterization of individual as-grown GaAs/(In,Ga)As/(GaAs) based core-multi-shell nanowires(2019)In recent years, owing to the major development of X-ray focusing optics such as fresnel zone plates and Kirkpatrick-Baez mirrors, highly intense and collimated X-ray beams with spot sizes in the range of a hundred nanometers and below can be achieved. Together with proper sample preparation such as selective area growth, X-ray diffraction techniques can be deployed to study single nanometer-sized objects, in particular nanowires. Typically, transmission electron microscopy based methods are used to investigate the thickness, crystal phase and alloy distribution in individual core-shell nanowires. These properties, if controlled precisely, play the key role in optimizing the optical emission of NW based devices. Nevertheless, in this work, using X-ray nano diffraction based techniques we demonstrate a new path to achieve the complete structural characterization of individual as-grown GaAs/(In,Ga)As/GaAs based core-shell nanowires in addition to correlating their phase structure to their optical properties. In a first step, the spatial distribution of the In alloy within the (In,Ga)As shell of individual GaAs/(In,Ga)As based core-shell nanowires is inspected by means of nano-focused scanning X-ray fluorescence microscopy. In contrast to energy dispersive X-ray spectroscopy in transmission electron microscopy, using this fast probing technique one can probe several nanowires in their as-grown geometry without the need of a complicated sample preparation procedure. In a second step, high resolution X-ray nano diffraction is applied along and perpendicular to the NW [111] growth direction to measure the structural properties of individual GaAs/(In,Ga)As/GaAs core-shell nanowires grown by vapor liquid solid epitaxy. There, we were able to calculate the thickness of the core and shells and therefore reconstruct the full NW cross-section which is forever done by means of transmission electron microscopy of the nanowire basal plane. In a third step, monitoring the GaAs 111 Bragg reflection, scanning X-ray diffraction microscopy was used as a fast scanning technique to reveal the polytype distribution along the growth axes of several individual core-multi-shell nanowires. The phase distribution was then correlated with cathodolu-minescence measurements revealing an enhancement in the optical emission of a mixed phase formed of the cubic zinc blende crystal phase and its twin, the hexagonal wurtzite polytype and slabs of defects and stacking faults. Finally, we reveal induced structural and optical damage of individual semi-conductor nanowires, that are supposed to be resistant to radiation, for a threshold absorbed X-ray dose. This was demonstrated only for measurements that require fixing the X-ray nano beam to the same position along the nanowire growth axis. This study will spreads awareness regarding time consuming X-ray diffraction measurements performed on nano-structures.Source Type:Doctoral Thesis2 4 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Application of pn-CCD detector for imaging of nanowires using white synchrotron radiation(2019)The pnCCD detector became an instrument which shows wide applications in material research. Besides white-beam Laue diffraction von single and polychrystalline materials the multilayer analysis of hard coatings and soft matter we demonstrate first application for the analysis of semiconductor nanowires (NWs). For the first time, a frame-store pn-junction CCD has been applied for structure analysis of semiconductor nanowires by means of energy-dispersive Laue diffraction using white synchrotron radiation in the energy range of 8 to 120 keV. Here a white x-ray beam exposes the sample providing a number of Laue spots which fulfill the Bragg condition for different x-ray energies. The fast and precise characterization of any materials by this method requires a simultaneous position and energy resolved detection of X-rays. The aim of this project was to investigate the real structure of different semiconductor NWs using white beam and pn CCD detector. Firstly, we present X-ray diffraction pattern taken from a periodic GaAs NW array that was grown onto GaAs[111]B surface. The experiment was performed at the home laboratory at Siegen University using a coplanar Bragg reflection. The structural properties were probed by measuring reciprocal space by quasi single shot exposure. Besides the peak related to the reflection from GaAs substrate, we found a second peak referring to the reflection from NWs. Form the difference of peak positions and peak energies the lattice mismatch between the NWs and the substrate was deduced. Secondly, a more detailed analysis was performed on InAs NWs grown onto GaAs[111]B. The experiment was carried out at the EDR beam line of BESSY II synchrotron. Energy-dispersive X-ray diffraction techniques rely on a high usable photon flux in a wide energy range (5< E< 35 KeV) so that as many Bragg peaks as possible can be detected in a single X-ray shot without any sample rotation. In addition, the usage of high-energy X-ray diffraction enables to measure a large section of reciprocal space at the same time allowing for probe the real structure of the InAs NWs and substrate GaAs and insensitive reflections simultaneously. By this experiment we could deduce the simultaneous appearance of wurtzite and zinc-blende phases in InAs NWs. Finally, we measured GaAs/InxGa1-x As/GaAs core-shell NWs grown by molecular beam epitaxy (MBE) onto a Si (111) substrate at the EDDI beamline of BESSY II. In this system, the incident x-ray beam energy ranges between 20 to 120 keV and illuminates the sample nearly parallel to the [111] direction. Due to the wide range of x-ray energies provided various Laue spots of few highly indexed {hkl} families with different lattice plane fulfill the Bragg condition simultaneous. After the evaluation the Laue spots and correction caused by the small misalignment of the incident beam with respect to [111] direction the pseudomorphic growth of the InxGa1-x As shell and the GaAs core has been verified. In summary, by using white synchrotron radiation the pnCCD provides a three dimensional intensity distribution composed by two pixel coordinates and an energy direction covering a 3D data volume in reciprocal space. In this sense, the system provides a good possibility to investigate the structure of semiconductor NWs (GaAs, InAs, GaAs/ InxGa1-x As /GaAs) because several Laue reflections can be probed simultaneous which is impossible using monochromatic radiation.Source Type:Doctoral Thesis3 2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Die Entwicklung der Sterne : eine elementarisierte Betrachtung(2019)This thesis is about ways of simplifying stellar physics and of transferring them into teaching concepts. The aim is to provide future or active teachers of physics with the means to gain an appropriate understanding of theory. The main goal is to present an essential research method of astrophysics - to model celestial bodies mathematically in such a way that observable phenomena are predicted on their surface - in teaching. Currently, many astrophysical phenomena are only dealt with phenomenologically in teaching literature, which results in the desideratum that the actual research methodology is only insufficiently conveyed. This doctoral thesis takes into consideration astrophysics being only a minor part of a physics course in the teaching-study program, therefore the material is condensed and can be accessed without deeper previous knowledge. Furthermore, the analysis of the tasks of two textbook series shows that quantitative work, especially in secondary level II, constitutes in a large part of physics teaching and that mathematical modelling therefore is suitable for exercises. Astrophysics has always been subject to a particularly critical, epistemological view, since it naturally has to largely dispense with the experimental investigation of its research objects and can only lead to findings based on passive observations. A meaningful occupation with modern research results of astrophysics is therefore hardly imaginable without a special integration into an epistemological framework. Thus, the presented paper shows epistemological fundamentals that allow a critical view on the development of an astrophysical theory. Variants are shown to view the stars both as quasi-static objects and to shed light their evolution. Particularly the conditions for the development of life on a planet and the existing connections to the central star are discussed, since the question of life on other planets is an interesting topic for learners. The presented models are based on basic mathematics and physics lectures, partly even high school level is sufficient.Source Type:Doctoral Thesis6 8 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Quantum hypergraph states and the theory of multiparticle entanglement(2019)This thesis is devoted to learning different aspects of quantum entanglement theory. More precisely, it concerns a characterization of certain classes of pure multipartite entangled states, their nonlocal and entanglement properties, comparisons with the other well-studied classes of states and, finally, their utilization in certain quantum information processing tasks. The most extensive part of the thesis explores an interesting class of pure multipartite entangled states, quantum hypergraph states. These states are generalizations of the renowned class of graph states. Here we cover their nonlocal properties in various scenarios, derive graphical rules for unitary transformations and Pauli bases measurements. Using these rules, we characterize entanglement classes of hypergraph states under local operations, obtain tight entanglement witnesses, and calculate entanglement measures for hypergraph states. Finally, we apply all the aforementioned analysis to endorse hypergraph states as powerful resource states for measurement-based quantum computation and quantum error-correction. The rest of the thesis is devoted to three disjoint problems, but all of them are still in the scope of entanglement theory. First, using mathematical structure of linear matrix pencils, we coarse grain entanglement in tripartite pure states of local dimensions 2 x m x n under the most general local transformations. In addition, we identify the structure of generic states for every m and n and see that for certain dimensions there is a resemblance between bipartite and tripartite entanglement. Second, we consider the following question: Can entanglement detection be improved, if in addition to the expectation value of the measured witness, we have knowledge of the expectation value of another observable? For low dimensions we give necessary and sufficient criterion that such two product observables must satisfy in order to be able to detect entanglement. Finally, we derive a general statement that any genuine N-partite entangled state can always be projected on any of its k-partite subsystems in a way that the new state in genuine k-partite entangled.Source Type:Doctoral Thesis12 31 - Some of the metrics are blocked by yourconsent settings
Publication Die Entwicklung der Sterne(2019-09-24)Astrophysik gilt unter Lernenden aller Altersstufen als einer der beliebtesten Teilbereiche der Physik, wird aber im Physikunterricht der meisten Bundesländer kaum behandelt. Das große Potential der Astrophysik hier zu nutzen, erfordert ein überblicksartiges und dabei fachliches komprimiertes und didaktisches Wissen von Lehrkräften. Die vorliegende Arbeit stellt – neben einigen notwendigen, erkenntnistheoretischen Grundlagen der Modellbildung – verschiedene mathematische Modelle vor, die die Entwicklung eines Sterns elementarisiert beschreiben, ohne dass über Grundvorlesungen hinausgehendes Wissen benötigt wird. Speziell eingegangen wird insbesondere auf verschiedene Entwicklungsstadien der Sterne, auf die numerische Verteilung der Sternmassen sowie auf den Einfluss eines Sterns auf die Möglichkeit von Leben in seinem Planetensystem.Source Type:Dissertation2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , System tests, initial operation and first data of the AMIGA muon detector for the Pierre Auger Observatory(2012)Investigating the energy region between 10^17 eV and 4 × 10^18 eV for primary cosmic particles will lead to a deeper understanding of the origin of cosmic rays. Effects of the transition from galactic to extragalactic origin are expected to be visible in this region. The knowledge of the composition of cosmic rays strongly depends on the hadronic interaction models, which are applied in the air shower reconstruction. Directly determining the number of muons from an air shower on ground level will improve the precision of the composition measurements by reducing the dependence on the models. The Pierre Auger Observatory is facing these challenges with an upgrade of the original detector setup. A denser sub-array of water Cherenkov detectors and a dedicated muon detector (MD) array constitute the AMIGA enhancement (Auger Muon and Infill for the Ground Array). Additional fluorescence telescopes constitute HEAT (High Elevation Auger Telescopes). Seven MD modules have been installed until mid 2012 in a first hexagon at the site of the Pierre Auger Observatory in Malargüe, Argentina. The corresponding readout electronics, and 19 more of these setups, were assembled and tested in Siegen to assure correct functionality. The detectors were incorporated in the trigger structure of the original surface detector (SD) array of the Pierre Auger Observatory and are now taking data synchronously. In the framework of this thesis, system tests have been developed, a pre-unitary cell (PUC) of seven modules has been successfully operated and their trigger has been synchronised with the SD trigger. First data from the MD have been analysed and have been combined with data from the SD.Source Type:Doctoral Thesis3 2 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , From pnCCD to pnCCD + CsI(Tl) scintillator: characterizations and applications(2019)The pnCCD is a special type of a charge coupled devices developed for spectroscopy and imaging of X-rays. Different from other CCD concepts, pnCCD is a four-dimensional detector, in which the data volume is spanned over two spatial, one energy, and one time coordinates, with fast frame rates up to 1000 images/sec, high energy resolution, low electronic noise and an excellent quantum efficiency at soft X-ray energy range. Considering these parameters, the pnCCD has been used for single crystal structure analysis in the soft X-ray energy range (5-35 keV) so far. In this thesis we demonstrate single grain analysis of a polycrystalline sample by means of an energy-dispersive Laue diffraction (EDLD) using white X-ray radiation in the hard energy range (35-130 keV). In particular we investigate the deformation behavior of individual grains under tensile loading. In addition to many other advantages of the pnCCD in material science applications, the use of hard X-ray radiation penetrates deeply inside the samples and examine a largest possible number of grains within the specimen. However, the detection of the high energetic photons by silicon-based detectors is limited by the detector quantum efficiency. This drawback can be overcome by combining a columnar scintillator with a pixelated silicon-based pnCCD detector. In this thesis we report on the characterization of a low noise, fully depleted pnCCD coupled to a columnar structure CsI(Tl) scintillator in hard X-ray range. The performance of the detection system in the energy range between 40 keV to 130 keV was tested by means of a Laue type X-ray diffraction experiment. Realized at the EDDI beamline of the BESSY II synchrotron we recorded Laue pattern of a set of several GaAs single crystals irradiated by white synchrotron radiation. The first application of this new system in crystallography is demonstrated by a crystal structure analysis of a tetragonal SrLaAlO4 crystal in which the lattice parameters and the cell orientation has been determined with an accuracy better than 0.7%. In addition, the structure factors moduli have been determined from the intensities of the Laue spots with a standard deviation of less than 2.5%.Source Type:Doctoral Thesis3 12
