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Tunable Coherence für Streulichtunterdrückung in Gravitationswellendetektoren
No full textLaser interferometers are highly sensitive to length deviations, making them ideal for detecting gravitational waves. The kilometer-scale detectors used for this are reaching their incredible sensitivity by tackling many different noise sources. One such noise that is gaining more relevance with the increasing detector sensitivities; even beyond quantum mechanical limitations; is induced by straylight. Because it accumulates additional phase by traveling along unintended paths before reentering the readout, it introduces noise limiting the sensitivity, especially at frequencies below 30 Hz. In current detectors, scattered light mitigation is thus already a major effort; achieving even higher sensitivities with future detectors is inconceivable without new straylight mitigation techniques.
In this thesis, Tunable Coherence is introduced as a possible new strategy against straylight noise. Further, by conveying white-light characteristics to continuous-wave lasers, it advances a nearly unexplored sub-discipline of laser interferometry. The underlying technique, pseudo-random-noise phase modulation, is actively used in ranging and digital interferometry. Employing it at GHz-frequencies on the main laser of a gravitational wave observatory is, however, an audacious proposal. Tunable coherence intentionally breaks and controls the coherence of a continuous-wave laser. This leads to coherence loss for unwanted light fields differing in propagation delay, which suppresses their interference. However, it also complicates aspects like resonant power build-up and adds tight constraints on optical layouts. It therefore needs to be demonstrated and verified meticulously that the detectors operation is not negatively impacted by tunable coherence.
With this work, initial milestones of this process were achieved, as well as future challenges and opportunities identified. Experimental validation in a Michelson interferometer showed straylight suppression exceeding 40 dB while reducing the coherence length to a few centimeter. Compatibility of tunable coherence with optical cavities was then demonstrated with the artificial coherence length reduced down to the wavelength-scale. Optical layouts of gravitational wave detectors combine an interferometer with cavities used to reduce shot noise and increase sensitivity. Tunable coherence was demonstrated with such combinations by investigating a power-recycled Michelson interferometer. Here, general compatibility but also first limitations in its current implementation were observed.
The obtained results demonstrate tunable coherence as a promising tool for straylight suppression in high precision interferometers. Thus prompting the provided initial study of a possible implementation in current or planned gravitational wave detectors for helping advance low-frequency sensitivity. As these advances enable earlier, longer and more numerous detections, they open new opportunities for e.g. multi-messenger astronomy.Laser Interferometer sind aufgrund ihrer hohen Sensitivität gegenüber Längenänderungen ideal für die Detektion von Gravitationswellen geeignet. Um die hierfür benötigten besonders hohen Sensitivitäten zu erreichen, müssen die kilometerlangen Detektoren viele verschiedene Rauschquellen überkommen. Eine dieser Rauschquellen wird von Streulicht verursacht und gewinnt durch die immer besser werdenden Sensitivitäten; sogar über quantenmechanische Limitierungen hinaus; immer mehr Relevanz. Da Streulicht auf ungewollten Wegen durch den Detektor zusätzliche parasitäre Phaseninformation aufsammelt, bringt es Rauschen in die Auslesung ein, wenn es in diese gelangt. Dieses Rauschen ist insbesondere im Bereich der Messbandbreite unterhalb von 30 Hz limitierend. In aktuell betriebenen Detektoren ist Streulichtunterdrückung daher bereits eine enorme Herausforderung; das Erreichen der noch höheren Sensitivitäten in geplanten Detektoren ist ohne neue Konzepte hierfür undenkbar.
Mit dieser Arbeit wird das Konzept Tunable Coherence als mögliche neue Strategie gegen Streulicht vorgestellt. Durch das Übertragen von Weißlichteigenschaften auf einen Dauerstrichlaser erweitert es außerdem ein nahezu unerforschtes Teilgebiet der Laserinterferometrie. Bisher wird das hierfür genutzte Prinzip, die Phasenmodulation des Lasers mit einer pseudo-zufälligen Sequenz, in Bereichen von Satellitenortung und digitaler Interferometrie eingesetzt. Der Vorschlag, es auch auf den Hauptlaser eines Gravitationswellenobservatoriums anzuwenden, ist hingegen eher gewagt. Mit Tunable Coherence wird die Kohärenz des Dauerstrichlasers gezielt gebrochen und die Kohärenzlänge präzise kontrolliert. Dies führt dazu, dass das Streulicht durch seine längeren optischen Wege nicht mehr kohärent mit dem Hauptlaser ist und daher nicht mehr mit der Auslesung interferieren kann. Es hat allerdings den Nachteil, dass der Betrieb eines optischen Aufbaus durch zusätzliche Einschränkungen für beabsichtigte Interferenzerscheinugen komplizierter wird. Deshalb muss der Einfluss, positiv und negativ, von Tunable Coherence auf einen Gravitationswellendetektor vor einem potenziellen Einbau gründlich geprüft werden.
Als Teil dieser Arbeit wurden erste Meilensteine dieser Überprüfung erreicht und zukünftige Herausforderungen identifiziert. In experimentellen Demonstrationen konnte eine Streulichtunterdrückung von mehr als 40 dB in einem Michelson Interferometer gezeigt werden. In diesem Fall wurde die Kohärenzlänge auf wenige Zentimeter reduziert. Zusätzlich wurde gezeigt, dass Tunable Coherence auch mit optischen Resonatoren funktioniert. Hier wurde die künstlich eingeführte Kohärenzlänge auf wenige Wellenlängen reduziert. Da Gravitationswellendetektoren in ihrem optischen Aufbau aus einer Kombination eines Interferometers mit weiteren Resonatoren bestehen, wurde die Kompatibilität von Tunable Coherence in einem ähnlichen Aufbau demonstriert. Hierfür wurde ein Michelson Interferometer mit einem zusätzlichen Resonator zum Überhöhen der internen Lichtleistung genutzt. In diesem Aufbau konnte Tunable Coherence generell demonstriert werden aber es wurden erste Einschränkungen, verursacht durch die momentane Realisierung, beobachtet.
Die gesammelten Ergebnisse zeigen, dass Tunable Coherence ein vielversprechendes Mittel für Streulichtreduktion in hochpräzisen Interferometern sein kann. Es wurde daher ein vorläufiges Konzept erarbeitet wie eine mögliche Realisierung in derzeitigen oder zukünftigen Gravitationswellendetektoren aussehen könnte um die Sensitivität dieser im niedrigfrequenten Bereich zu verbessern. Solche Verbesserungen würden viele neue Möglichkeiten für zum Beispiel Multi-Messenger Astronomie bringen, da sie mehr Detektionen und diese früher und für längere Zeitspannen ermöglichen würden
Biologische und molekulare Charakterisierung der zellulären Ursprünge und Progression von atypischen teratoiden/rhabdoiden Tumoren (AT/RT)
No full textAtypical teratoid/rhabdoid tumors (AT/RT) are rare embryonal tumors of the central nervous system that affect very young children and have a poor prognosis. Based on DNA methylation profiles, the different subtypes AT/RT-SHH, AT/RT-TYR, AT/RT-MYC, and AT/RT-SMARCA4 were identified. Although the genetics of these tumors are known, targeted therapies are lacking. Therefore, we aimed to identify the cellular origins of AT/RT and to characterize the mechanisms of tumor progression and recurrence, including therapy resistance. Both should help to develop novel therapeutic approaches.
In the first part of the project, we investigated paired primary and recurrent AT/RT using DNA methylation profiling and bulk RNA sequencing, which revealed an increased chromosome 1q gain and chromosome 10 loss in recurrences and differential expression of cancer-associated genes. Single-nucleus RNA sequencing revealed an enrichment of CD1A+ CD207+ dendritic cells (DCs) in recurrences and a high number of AT/RT-MYC tumor cells undergoing partial epithelial-mesenchymal transition. Potentially therapy-resistant cells were identified in AT/RTMYC, which were characterized by increased extracellular matrix remodeling, among others. Overexpression of respective genes and occurrence of CD1A+ CD207+ DCs correlated with an inferior survival of AT/RT patients. All findings were associated with TGF-β signaling – a novel, promising therapeutic target.
The second part of this work deals with the identification of the cellular origins of AT/RTSMARCA4 and AT/RT-TYR, because these are completely unknown and mouse models are lacking. We generated different Smarca4-deficient mouse models that targeted distinct cell types at specific timepoints. These mice did not develop tumors, but an important role of Smarca4 in the embryonic development was demonstrated, because Smarca4 loss either
resulted in embryonic lethality or neuromuscular disorders. For AT/RT-TYR, we revealed that precursors of the choroid plexus (CP) of the fourth ventricle are potentially the cellular origin. A high proportion of AT/RT-TYR biopsies was intermingled with CP tissue, and immunohistochemistry and RNA sequencing showed that CP marker genes were predominantly expressed in AT/RT-TYR. Deconvolution analyses demonstrated the highest similarity of AT/RT-TYR to the CP. Finally, Foxj1-cre::Smarcb1fl/fl mice displayed a Smarcb1 loss in the CP, resulting in large, atypical, monociliary CP cells. These mice did not develop tumors but demonstrated high similarity to human AT/RT-TYR on gene expression level.
In conclusion, our work demonstrated insights into the development of AT/RT, as well as mechanisms of progression and recurrence, which both revealed novel potential therapeutic targets
Video tutorials in traditional classrooms: The effects on cognitive load and time on task
No full textThis cumulative dissertation comprises three papers, each examining the effectiveness of video tutorials (VTs) in the traditional classroom on different types of cognitive load and time-on-task. Each article explores specific research questions related to the use of video tutorials in the classroom and is already published in a peer-review journal or currently under review.
1. Video Tutorials in the Traditional Classroom: The Effects on Different Types of Cognitive Load. Published: June 2024,Technology, Knowledge and Learning.
2. Comparing cognitive load during video versus traditional classroom instruction based on heart-rate variability measures. Submitted: July 2024, Computers & Education (2nd revision Under Review).
3. From Heartbeats to Actions: Multimodal Learning Analytics of Cognitive and Behavior Engagement in Real Classrooms. Submitted: December 2024, Learning and Instruction (Under Review).
Each article explores a specific research question relevant to the study. The contributions of each author are listed below:
- Enqi Fan: conceptualization and design of the study, literature review, development of research instruments, collection of data, data analysis, initial drafting of the manuscript, and final editing of the manuscript.
- Matt Bower: provide suggestions for improving the manuscript.
- Jens Siemon: support for the conception and design of the study, support for data collection, support for data analysis, especially database processing, review of manuscripts and providing advice.
Article 1 examines the effects of video tutorials on intrinsic, extraneous, and germane cognitive load. The study was conducted with 45 students in two vocational schools and one high school. The results found that video tutorials significantly reduced intrinsic cognitive load and increased germane cognitive load compared to traditional instruction. These results suggest that video tutorials facilitate deeper learning by optimizing cognitive resource allocation.
Article 2 compares cognitive load during video versus traditional classroom instruction using heart rate variability (HRV) measures, specifically the RMSSD indicator. The study, which surveyed 45 students from two vocational schools and one high school, showed that students experienced higher cognitive load during the developmental phase when using video tutorials. This increased cognitive load is associated with higher engagement and deeper processing of learning material.
Article 3 explores the dynamic relationship between student behavior and cognition through time-on-task and heart rate variability (HRV) data. An analysis of 45 students from two vocational schools and one high school found a significant negative correlation between time-on-task and HRV. In classrooms using videos, students’ cognitive changes were more stable. In contrast, students in traditional classrooms showed greater cognitive fluctuations.
The combined results of my three studies demonstrate the potential benefits of using video tutorials in traditional classrooms. The results showed that video tutorials can optimize cognitive load, increase student engagement, and potentially improve learning outcomes. However, there are some limitations, such as a small sample size, individual differences among participants, and insufficient control of variables. In future research these limitations should be solved, and video tutorials should be studied in more depth
Practicing Organizational Tensions: Towards an Understanding of Paradoxes of Legimaticy, Scaling and Temporality in Tackling Grand Challenges
No full textElektrophysiologische Indizes der Handlungsüberwachung innerhalb des Angst- und Zwangsspektrums
No full textErrors are a ubiquitous part of human experiences, associated with potential risks but also serving as resources for improving performance. The neural monitoring of performance can be measured through event-related brain potentials (ERPs), such as the error-related negativity (ERN) and the correct-response negativity (CRN). Meta-analyses have identified an altered ERN as a trait-like risk marker for both internalizing and externalizing disorders, with increased amplitudes observed in anxiety and obsessive-compulsive disorders. However, this association is not consistent across all related diagnostic categories, often attributed to differing underlying transdiagnostic factors (e.g., trait worry). Challenging the assumed trait-like nature of the ERN, symptom fluctuations (e.g., state worry) may also influence the ERN. Furthermore, there is limited understanding of how an increased ERN contributes to psychopathology, along with only few studies evaluating multiple disorder categories and testing for effect specificity. This dissertation aims to refine the understanding of electrophysiological indices of performance monitoring across the anxiety and obsessive-compulsive spectrum by employing a transdiagnostic and dimensional approach that includes various diagnostic groups and ERPs.
Disentangling the associations of the ERN/CRN with trait and state worry, the preregistered randomized-controlled longitudinal study 1 (n = 90) did not indicate intraindividual variability of the ERN/CRN due to the experimental manipulation of state worry. Instead, higher levels of trait worry were linked to an enhanced ERN/CRN, particularly in women. Study 2 investigated the role of the ERN/CRN as risk markers using a preregistered cross-sectional design (n = 156). This study found no significant ERN/CRN differences between participants with obsessive-compulsive disorder, social anxiety disorder, or specific phobia, as well as control participants. However, after reclassifying the sample, study 2 found trend-level significant larger ERN/CRN amplitudes in clinical compared to nonclinical participants, as well as significant larger amplitudes for those with a family risk for internalizing symptoms. Additionally, joint analyses of study 1 and 2 (n = 246) confirmed the ERN/CRN link with trait worry for women. Finally, the prospective study 3 addressed the pathways from an enhanced ERN/CRN to the development of internalizing psychopathology by employing mediation analyses during the COVID-19 pandemic (n = 113). Results indicated that an increased pre-pandemic ERN/CRN were indirectly linked to anxiety, obsessive-compulsive, and depressive symptoms during the pandemic, mediated by a heightened COVID-19 risk perception and increased stress.
As a synthesis of the available literature and the current results, this dissertation proposes an integrative model of error-related brain activity and psychopathology. This model identifies an altered ERN as a neural vulnerability marker linked to both the internalizing and externalizing spectrum through latent dimensions underlying multiple clinical phenotypes, such as trait worry for anxiety- and obsessive-compulsive symptoms or impulsivity for substance use and hyperactivity. Moreover, it considers potential moderators and mediators of these associations, such as biological sex, temperament, adverse life events, and interpersonal stress. However, given the heterogeneous CRN literature, it seems premature to incorporate an altered CRN as an additional model component. Nevertheless, the model offers a neuroscientifically informed framework with the potential to not only guide future research but also to facilitate the development of targeted interventions based on knowledge from brain potentials, ultimately aimed at preventing mental health impairments and reducing the risk of psychopathological conditions
CO2 Hydrierung zu Methanol in unterschiedlichen Reaktorkonzepten unter der Verwendung von Metall-dotierten Indium-basierten Katalysatoren
No full textCO2 hydrogenation with H2 from water electrolysis to methanol (MeOH) is a key strategy for chemical energy storage and for CO2 utilization. MeOH serves various applications and is an important feedstock for the chemical industry as well. This work investigates the application of indium-based catalysts for MeOH synthesis via the hydrogenation of CO2 in various reactor concepts focusing on the reaction conditions and catalyst properties necessary to achieve high activity and selectivity.
Industrial methanol production mainly uses two-phase (gas solid) or three-phase reactors (gas solid liquid). Two-phase reactors are categorized inro adiabatic an isothermal reactors based on the heat dissipation in the catalyst bed. Three phase reactors, such as slurry and trickle bed reactors, enable more efficiency in heat removal and minimize mass transport limitations.
First, the catalytic performance of In2O3 and In(OH)3 was studied in a fixed bed reactor. The impact of thermoelement positioning in the catalyst bed (top, middle or bottom position) was studied. Using catalytic data received at 200, 250 and 300 °C, along with material characterization (XRD and TGA) after the reaction, a catalytic model cycle was defined concerning the phase transition. CO2 hydrogenation produces water as a by-product, leading to the degradation of In2O3 to In(OH)3. The model postulates stable In(OH)3 at low temperatures and higher conversions. In contrast, In2O3 remains stable at higher conversions and temperatures. The separation of In(OH)3 into two identical segments, with a layer of glass wool between the segments, investigated the influence of the phase transition at 200, 250, 275 and 300 °C. Fresh gas flows through the top segment, being partially converted into MeOH, CO and water and flowing through the bottom segment. XRD and TGA analyses revealed an inversion of the trend between 250 °C and 275 °C, while the computational model predicts this occurrence at 285 °C. Lastly, the validated model was employed to predict the effects of hydrogen drop out in the feed due to fluctuating production from renewable energies on catalyst stability. In further studies within the fixed bed reactor, two different ZrO2 were used as catalyst support and impregnated with In2O3 using different synthesis methods. In detail, the combination of wetness impregnation according to Martin et al. (M) and the ZrO2 (SG) with a lager BET surface area and CO2 adsorption capacity exhibited the best catalytic performance. At 300 °C, 75 bar, CO2/H2 = 1/3 and 8600 h-1 the maximum MeOH production reached 4.25 g(MeOH)/(g(In)∙h). To increase the MeOH productivity, various metals (Cu, Ni, Mg, Ce) were investigated as promoters for the In2O3/ZrO2 (M-SG) catalyst. NiO In2O3/ZrO2 (M-SG) demonstrated an enhanced catalytic activity. Due to enhanced H2 uptake the H2 spillover effect increases, which promotes H2 dissociation and migration to the carrier surface and favors the formation of oxygen vacancies, the active centers for CO2. This was confirmed by chemisorptive analyses (H2-TPR and CO2-TPD). NiO on In2O3/ZrO2 prepared by wetness impregnation (WI) resulted in catalysts that were catalytically more active. NiO In2O3/ZrO2 (WI) with 0.76 wt.% Ni produced with 4.42 g(MeOH)/(g(In+Ni)∙h) more MeOH than pure In2O3/ZrO2 (M-SG) with 4.25 g(MeOH)/(g(In)∙h) at 300 °C, 75 bar, CO2/H2 = 1/3 and 8600 h-1. No methanation was observed. Over 100 h time on stream the NiO In2O3/ZrO2 (WI) remains stable and active.
In the Compact Profile Reactor (CPR), the reaction profiles of In2O3/ZrO2-based catalysts were investigated and compared with the industrially used Cu/ZnO/Al2O3 catalyst. The reactor design enables spatially resolved analysis of the reaction profile for every species and temperature inside the catalytic bed during high-pressure MeOH synthesis by the hydrogenation of CO2. The influence of reaction conditions, including total pressure, gas hourly space velocity (GHSV), and temperature, was studied using the most active catalyst, Ni-In2O3/ZrO2. In this study, higher pressures, temperatures, and GHSVs led to increase the MeOH productivity. Shorter residence times enhance MeOH selectivity. At 50 bar, 275 °C and 63,000 h-1, Ni-In2O3/ZrO2 produced 4.90 g(MeOH)/(g(In+Ni)∙h) with 73 % selectivity of MeOH. The remaining carbon is converted into CO via the rWGS. MeOH synthesis requires a lower activation energy (49 kJ mol-1) compared to the reverse water-gas shift reaction (71 kJ mol-1).
In a suspension (slurry) reactor (SR), pure In2O3 and In2O3/ZrO2 was doped with nickel using different synthesis methods and used for three-phase MeOH synthesis. Ni-In2O3/ZrO2 prepared by co-precipitation (CP) and suspended in mineral oil achieved the highest catalytic activity and selectivity for MeOH for both CO and CO2 hydrogenation. Using synthesis gas with industrial combustion (H2/CO/CO2) and a molar ratio of 70/28/2, a very high productivity of MeOH (6.84 g(MeOH)/(g(cat)∙h)) was achieved, which is significantly more efficient than the productivity of the commercial Cu/ZnO/Al2O3 catalyst (1.25 g(MeOH)/(g(Cu)∙h)) in the SR related to the quantities of active metals. Finally, the catalyst and the mineral oil remained stable in a recycling study with four replicate runs.
Intensive catalyst material characterization using ICP-OES, XRD, XPS, N2-physisorption, CO2 TPD, H2-TPR and TEM or SEM-EDX mappings provide insights in the difference in catalytic activity of the catalysts in the various reactor concepts
Radiation tolerance and performance of planar pixel assemblies for the Phase-2 Upgrade of the CMS Inner Tracker
Get PDFThe aim of this work is to evaluate the performance of planar hybrid pixel detectors designed for the High-Luminosity (HL-LHC) Upgrade of the Inner Tracker of the Compact Muon Solenoid (CMS) experiment at CERN. The HL-LHC will deliver a peak instantaneous luminosity of 7.5 × 10^34 cm^−2 s^−1, resulting in a total expected fluence for planar sensors of around ϕeq = 1 × 10^16 cm^−2 after an integrated luminosity of 3000 fb^−1.
To operate under such extreme radiation levels and high track densities, the new n+-in-p sensors will feature pixels with pitches of 25 × 100 µm^2, covering an area six times smaller than their Phase-1 counterparts. This work focuses on the characterization of 150 µm thick planar sensors manufactured by Hamamatsu Photonics K.K. These sensors are bump-bonded to the RD53B CMS readout chip and tested using a 5.2 GeV electron beam at the DESY II test beam facility. Key observables such as cluster size, noise, threshold, hit efficiency, and spatial resolution are measured as a function of both the applied bias voltage and the beam incidence angle.
The modules are characterized before and after irradiation with 24 GeV/c protons to fluences up to ϕeq = 1 × 10^16 cm^−2. For perpendicular incidence, hit efficiencies exceeding the corresponding fluence-dependent benchmarks are achieved for bias voltages as low as 5 V before irradiation, and in the range of 400 V–500 V after irradiation, for all thresholds under study, while keeping the amount of disabled pixels below the 1% limit, fulfilling the requirements for the second layer of the Phase-2 pixel detector. These measurements reveal that the optimal efficiency is achieved for a charge threshold of 1200 e− and a bias voltage of 600 V for all investigated fluences.
A spatial resolution of circa 3 µm was measured before irradiation at the optimal track incidence angle, degrading to about 4 µm after irradiation to the highest fluence under exam.
The characterization of these assemblies included in-depth studies of the correlation between crosstalk and readout timing in the first half-size demonstrator (RD53A) and in the pre-series version of the chips (RD53B CMS). By using the integrated charge injection circuit, crosstalk levels well-below the established 10% limit were measured for the optimal readout scheme, meeting the associated requirement
Die heilige Kuh auf ihrem Höhenflug fängt zu lachen an, merkt dabei dass sie gar nicht fliegen kann und ... - Enthierarchisierungsstrategien im Musiktheater
No full textDas Musiktheater spiegelt wie vielleicht keine andere Theatergattung die gesellschaftlichen Beharrungskräfte auf starre Hierarchien und Machtkumulation wider. Dabei existiert mit dem postdramatischen Theater ein Diskurs, der eine Enthierarchisierung aller Theatermittel ins Zentrum stellt und der auch das Musiktheater zumindest peripher gestreift hat. Jedoch spart das postdramatische Theater ein wesentliches formales Werkzeug der Enthierarchisierung aus: die Komik. In dieser Arbeit wird über die Analyse einer auch die Komik einbeziehenden postdramatischen Theorie der Bogen zur historischen komischen Figur gespannt. Daraus ergibt sich eine Metatheorie von Enthierarchisierung als strukturelle Beweglichkeit, die mit dem Begriff des performativen Motivs schließlich Theatertheorie und politikwissenschaftliche Forschung verbindet.
Im Rahmen der künstlerischen Forschung erfolgt anschließend eine exemplarische Übersetzung des performativen Motivs in die dramaturgische Konzepte zweier musiktheatraler Versuchsanordnungen
From the efficient trapping and accumulation of cooled antiprotons towards the formation of a pulsed beam of antihydrogen atoms
Get PDFDie hier präsentierte Arbeit umfasst eine Anzahl maßgeblicher Beiträge zur Entwicklung eines gepulsten Strahls von Antiwasserstoff-Atomen im AEgIS Experiment in der Antiproton Decelerator-Anlage am CERN. Das Hauptziel von AEgIS ist eine präzise Messung der Gravitationsbeschleunigung von Antimaterie, um das Schwache Equivalenzprinzip zu prüfen und Einblicke in mögliche Erklärungen für die Materie-Antimaterie-Asymmetrie unseres Universums zu erhalten. Zu diesem Zweck werden Antiwasserstoff-Atome in gepulster Form durch eine Ladungsaustausch-Reaktion zwischen kalten, gefangenen Antiprotonen und Laser-angeregten Positronium-Atomen hergestellt. Die Anti-Atome sollen zu einem horizontalen Strahl geformt werden, der ein Deflektometer durchquert, um eine Ermittlung ihrer vertikalen Ablenkung aufgrund der Gravitation zu ermöglichen.
Die Grundlage dieser Arbeit bildet die Ausarbeitung und Einführung eines Kontrollsystems, CIRCUS, das seit 2021 zuverlässig alle AEgIS Experimente steuert. CIRCUS ermöglicht einen autonomen Betrieb und beinhaltet als ein Kernstück die AERIALIST Schnell-Kontroll-Einheit, die experimentelle Prozesse mit Nanosekunden-Genauigkeit synchronisiert. Es ist fundamental für alle kürzlichen Errungenschaften von AEgIS, wobei herausragend die erste erfolgreiche Laser-Kühlung von Positronium zu nennen ist.
Diese Arbeit schließt außerdem die Inbetriebnahme des neuen Elektronen-Systems von AEgIS ein, das ein essenzieller Bestandteil des Experiments ist, sowohl in der Vorbereitungsphase als auch für die Implementierung der Antiprotonen-Plasma-Routinen.
Ein Hauptergebnis dieser Arbeit ist die beispiellose Akkumulation von mehreren hundert Millionen kalten Antiprotonen in einer elektromagnetischen Falle. Dies wird durch die Entwicklung von Routinen für das Einfangen von rekordbrechenden 70% der vom ELENA Entschleuniger am CERN verfügbaren Antiprotonen sowie für effiziente Elektronenkühlungs- und Plasma-Kompressionstechniken und für das Ansammeln von mehreren Antiprotonen-Paketen in der Falle ermöglicht. Da Antiprotonen ein Kernbestandteil der meisten gebundenen Antimaterie-Systeme sind, öffnet dieser Erfolg die Tür zu einer Vielfalt an Antimaterie-Forschung, einschließlich einer stark erhöhten Antiwasserstoff-Produktion in AEgIS und der Herstellung und Untersuchung von antiprotonischen Atomen.
Die Formung der Antiwasserstoff-Atome zu einem horizontalen Strahl, entscheidend für die Gravitationsmessung, ist in dieser Arbeit durch die Beschleunigung der Antiprotonen in die Richtung des Positroniums mittels eines parabolischen Potentials umgesetzt, präzise synchronisiert mit der Positronium-Anregung. Die Funktionalität der Methode wurde erfolgreich durch eine ebenfalls im Zuge dieser Arbeit implementierte Analyse des Signals auf einem Szintillator/PMT Detektor verifiziert. Dieselbe Analyse stellt auch eine erste Untersuchung der Antiwasserstoff-Herstellung mit AEgIS Phase II dar, die auf die Transformation der Abläufe zu einer kollinearen Antiwasserstoff-Produktion und wesentliche Verbesserungen des Apparats folgt, von denen einige Teil dieser Arbeit sind. Während Evidenz eines Überschuss-Signals im relevanten Zeitfenster für solche Daten zu beobachten ist, in denen Antiwasserstoff-Herstellung erwartet wird, im Vergleich zu Kontroll-Daten ohne Positronium-Anregung, sind die erreichten Anzahlen zu gering um eindeutig signifikant zu sein. Diese Beeinträchtigung kann hauptsächlich auf die Leistungsschwäche der Positronium-Komponenten zurückgeführt werden, die aktuell verbessert werden.
Dank der Gesamtheit der durchgeführten Upgrades, zu vielen von denen diese Arbeit beigetragen hat, wird eine im Vergleich zu vorherigen Durchführungen um mehrere Größenordnungen gesteigerte Effizienz der Antiwasserstoff-Herstellung erwartet. Mit der resultierenden Statistik und der darüber hinausgehenden Prozedur für die Strahl-Formung wird eine Bestimmung der Fallbeschleunigung von Antimaterie mit einer relativen Genauigkeit von 1% realistisch innerhalb einiger Monate der Antiprotonen-Strahlzeit erreichbar.The work presented here comprises a number of significant contributions to the formation of a pulsed beam of antihydrogen atoms in the AEgIS experiment at CERN's Antiproton Decelerator facility. The main objective of AEgIS is a precise measurement of the gravitational acceleration of antimatter to probe the Weak Equivalence Principle and gain insight into possible explanations of our universe's matter-antimatter asymmetry. For this purpose, antihydrogen atoms are produced in a pulsed scheme through a charge exchange reaction of cold, trapped antiprotons and laser-excited positronium atoms. The anti-atoms are to be formed into a horizontal beam that passes through a deflectometer, enabling a determination of their vertical deflection due to the influence of gravity.
At the foundation of this work lies the development and implementation of a control system, CIRCUS, that has reliably run all experiments in AEgIS since 2021. CIRCUS has the capability of autonomous operation and comprises a core formed by the AERIALIST fast control unit that synchronizes experimental processes with nanosecond precision. It has been fundamental to any recent achievements of AEgIS, most prominently the first-ever successful laser cooling of positronium.
This work further includes the commissioning of the new electron system of AEgIS, which is a vital component of the experiment, both in the preparatory phase and for the implementation of the antiproton plasma routines.
A main result achieved in this work is the unprecedented accumulation of several hundred million cold antiprotons in an electromagnetic trap. It has become feasible thanks to the development of routines for the capture of a record 70% of the antiprotons available from CERN's ELENA decelerator as well as efficient electron cooling and plasma compression techniques and the stacking of multiple antiproton bunches inside the trap. Antiprotons being a core component of most bound antimatter systems, this achievement opens the door to a variety of antimatter research, including a strongly increased antihydrogen production in AEgIS and the formation and study of antiprotonic atoms.
The formation of the antihydrogen atoms into a horizontal beam, crucial to the gravity measurement, has been realized as part of this work through the forward-acceleration of the antiprotons towards the formed positronium via a parabolic potential, precisely synchronized to the positronium excitation. The functionality of the procedure has been successfully verified by an analysis of the observed signal on a scintillator/PMT detector, which has been implemented as part of this work as well. The same analysis also represents a first investigation of antihydrogen formation with AEgIS Phase II, following major upgrades to the apparatus, some of which are part of this work, and the transformation of the procedures to a collinear antihydrogen production. While evidence of an excess signal is observed in those runs expected to produce antihydrogen, compared to control runs without positronium excitation, in the relevant time window, the produced numbers are too low to be unambiguously significant. This impediment can be mainly attributed to the underperformance of the positronium line, which is currently being improved.
Thanks to the collectivity of the performed upgrades, many of which this work has contributed to, an antihydrogen formation efficiency boosted by several orders of magnitude is expected with respect to previous production runs. With the corresponding statistics and the beam formation procedure furthermore well in place, a determination of the gravitational acceleration of antimatter with a relative precision of 1% has become realistically achievable within a few months of antiproton beam time
Multdimensionale Phononik in getriebenem YBa2Cu3O6+x
Get PDFQuantenmaterialien weisen viele Phasenzustände mit exotischen und potenziell nützlichen Eigenschaften auf, darunter Supraleitfähigkeit, Ladungsordnung und verschiedene Formen von Magnetismus. In vielen Fällen konkurrieren diese exotischen Phasen auf vergleichbaren Energieskalen miteinander. Die enge Nachbarschaft der Energieskalen führt zu einem Szenario, in dem selbst kleine Störungen die dominante Phase ändern können. Diese energetische Nähe führt häufig auch zu großen Fluktuationen. Während diese Fluktuationen in der Regel ein Hindernis für die Etablierung eines bestimmten geordneten Gleichgewichtszustands darstellen, können sie auch der Schlüssel zur Erzeugung eines gewünschten Phasenzustands außerhalb des Gleichgewichts durch eine Form der gepulsten Anregung oder des periodischen Antriebs sein. Eine Reihe von Experimenten hat kürzlich gezeigt, dass es möglich ist, durch resonante Anregung der Normalmoden der Kristallstruktur (bekannt als Phononen) mit intensiven Lichtpulsen im mittleren Infrarot- oder Terahertzbereich die Fluktuationen aktiv zu stabilisieren und damit die gewünschten Zustände bei Temperaturen zu erzeugen oder zu verstärken, bei denen sie im thermischen Gleichgewicht nicht zugänglich sind, sogar weit oberhalb der kritischen Temperatur Tc. Nicht-Gleichgewichts-Ferroelektrizität, Magnetismus, Isolator-Metall-Übergänge und Supraleitung sind einige der wichtigsten Beispiele.
Diese Arbeit befasst sich mit YBa2Cu3O6+x, einem kupferbasierten Hochtemperatursupraleiter, bei der supraleitende Zustand durch dispersive Tunnelmoden von Cooper-Paaren durch die gestapelten CuO2-Schichten, die als Josephson-Plasmon-Polaritonen bekannt sind, gebildet wird. Im Gleichgewicht wurden supraleitende Fluktuationen weit über Tc festgestellt. Verschiedene Experimente haben gezeigt, dass in den unterdotierten Verbindungen dieser Familie die resonante Anregung von Phononen groß Amplitude zum Auftreten vorübergehender makroskopischer supraleitungsähnlicher Eigenschaften bei Temperaturen führt, die weit Tc und sogar Raumtemperatur liegen. Diese ersten Beobachtungen lösten eine Welle von Folgeexperimenten aus, die darauf abzielten, den vorübergehenden Zustand weiter zu charakterisieren und den mikroskopischen Mechanismus zu verstehen, der zu seiner Entstehung führt. Kürzlich durchgeführte eindimensionale Anrege-Abfrage-Experimente, mit optischer Anregung im mittleren Infrarot und Detektion der Zweiten Harmonischen nahinfraroter Lichtpulse, haben eine durch Phononen vermittelte Verstärkung der Josephson-Plasmon-Polaritonen nachgewiesen, ein Phänomen, das wahrscheinlich den mysteriösen supraleitungsähnlichen makroskopischen Eigenschaften zugrunde liegt. Diese eindimensionalen Experimente konnten jedoch kein schlüssiges Bild der Kopplung zwischen den optisch angeregten Phononen und den Josephson-Plasmon-Polaritonen liefern.
Die in dieser Arbeit vorgestellte Studie hat zum Ziel, ein besseres Verständnis der mikroskopischen Dynamik im optisch angeregten Zustand von YBa2Cu3O6+x zu erhalten, und berichtet über die Entwicklung und Anwendung einer neuen Form der zweidimensionalen Spektroskopie. Bei dieser Methode werden die Phononen, welche die Bewegung der apikalen Sauerstoffatome der Kupratverbindung beinhalten, nacheinander mit zwei optisch phasenstabilen Lichtpulsen im mittleren Infrarot angeregt, und die zeitabhängige Änderung der nichtlinearen optischen Suszeptibilität zweiter Ordnung gemessen, die auf die kohärente Bewegung sowohl der infrarotaktiven Phonon- als auch der Plasmonmoden anspricht. Die Ergebnisse deuten darauf hin, dass die direkt angeregten Phononen kohärente Paare von Josephson Plasma Polaritonen mit entgegengesetztem Impuls über einen Vier-Moden Mischprozess verstärken und einen gequetschten Zustand der Phasenfluktuationen zwischen den Schichten erzeugen. Die Identifizierung dieses gequetschten Zustands der Zwischenschicht-Tunnelmoden bietet nicht nur einen potenziellen Weg zur Manipulation des supraleitenden Ordnungsparameters bei Temperaturen oberhalb von Tc, sondern liefert auch wesentliche Einblicke in die mikroskopische Physik, die der "photoinduzierten Supraleitung" in den Kupraten und ähnlichen Materialien zugrunde liegt.Quantum materials exhibit many phases with exotic and potentially useful properties, including superconductivity, charge ordering and various forms of magnetism. In many cases, these exotic phases compete with one another on comparable energy scales. The close proximity of the energy scales results in a scenario where even small perturbations can change the dominant phase. This energetic proximity also often gives rise to large fluctuations. Whilst these fluctuations typically act as a prohibiting factor in establishing a certain ordered state in equilibrium, they may also hold the key to establishing a desired state out of equilibrium through some form of pulsed excitation or periodic driving. In fact, a range of experiments have recently demonstrated that, by resonantly driving the normal modes of the crystal structure (known as phonons) with intense mid-infrared or Terahertz light pulses, it is possible to actively stabilize the fluctuations and hence induce or enhance desired orders at temperatures where they are not accessible in thermal equilibrium, even far above the critical temperature Tc. Non-equilibrium ferroelectricity, magnetism, insulator-to-metal transitions and superconductivity are some of the most relevant examples.
This thesis focuses on the case of YBa2Cu3O6+x, a high-Tc Cuprate compound, in which the superconducting state is formed by dispersive tunneling modes of Cooper pairs across the stacked CuO2 layers, known as Josephson plasmon polaritons. In equilibrium, superconducting fluctuations were found far above Tc. Various experiments have demonstrated that, in underdoped compounds from this family, large amplitude resonant phonon excitation results in the emergence of transient macroscopic superconducting-like properties at temperatures far exceeding Tc, and even up to room temperature. These initial observations sparked a wave of follow-up experiments aimed at further characterizing this transient state and understanding the underlying microscopic mechanism which leads to its formation. Recent one-dimensional mid-infrared pump and time-resolved second-harmonic generation-probe (tr-SHG) experiments have revealed phonon-mediated amplification of the Josephson plasmon polaritons, a phenomenon likely to underpin the mysterious superconducting-like macroscopic properties. However, these one-dimensional experiments could not provide a conclusive picture of the coupling between the optically excited phonons and the Josephson plasmon polaritons.
The study presented in this thesis addresses this problem by reporting the development and use of a new form of two-dimensional spectroscopy, with the aim of obtaining an improved understanding of the microscopic dynamics in the driven state of YBa2Cu3O6+x. This method involves sequentially exciting apical oxygen phonons with two carrier-envelope-phase-stable mid-infrared pump pulses and probing the time delay dependent changes in the second-order nonlinear optical susceptibility, which is sensitive to the coherent motion of both the infrared-active phonon and plasmon modes. The findings suggest that the driven phonons amplify coherent pairs of opposite-momentum Josephson plasma polaritons via a four-mode mixing process, generating a squeezed state of the inter-layer phase fluctuations. The identification of this squeezed state of the inter-layer tunneling modes not only offers a potential pathway towards manipulating the superconducting order parameter at temperatures higher than Tc, but also provides critical insights into the microscopic physics underpinning "photoinduced superconductivity" in Cuprates and similar materials