Equation of motion method for Full Counting Statistics: Steady state superradiance

For the multi-mode Dicke model in a transport setting that exhibits collective boson transmissions, we construct the equation of motion for the cumulant generating function. Approximating the exact system of equations at the level of cumulant generating function and system operators at lowest order, allows us to recover master equation results of the Full Counting Statistics for certain parameter regimes at very low cost of computation. The thermodynamic limit, that is not accessible with the master equation approach, can be derived analytically for different approximations.Comment: 7 pages, 3 figures, revised version, accepted by PR

Kollektive und kritische Effekte in bosonischem Transport

Mit dem in letzter Zeit erzieltem Fortschritt in der Detektion und Erzeugung von einzelnen Lichtteilchen geht ein stetiges Wachstum des Feldes der Kavitäts – Quantenelektrodynamik einher. Zusammen mit der alten Idee, die Quantenstatistik einer Quelle durch das Zählen der von ihr emittierten Teilchen zu bestimmen, führt dies natürlicherweise zu der Frage, ob durch die Anwendung der Methode der vollen Zählstatistik (Full Counting Statistic) neue physikalische Aussagen getroffen werden können. Als einen ersten Ansatz in diese Richtung behandelt das erste Kapitel dieser Arbeit das Dicke-Modell. Dieses beschreibt den Effekt einer erhöhten Abstrahlung aus einer Atomwolke, welcher auf die Kollektivität zurückgeht, die durch die Kopplung der Atome mit einer Kavitätsschwingung entsteht. Dieser Effekt ist in seiner zeitabhängigen Form zu Genüge studiert worden. Diese Arbeit richtet ihren Fokus daher auf die kontinuierliche Abstrahlung, die durch ein zusätzliches kollektives Pumpen der Atome entsteht. Im Rahmen der vollständigen Zählstatistik kann für den zeitabhängigen Effekt eine Entsprechung in der kontinuierlichen Abstrahlung gefunden werden. Zudem ist es möglich zu zeigen, dass höhere Kumulanten des Transportvorgangs sensitivere Indikatoren für die Kollektivität sind, als der Strom selbst. Zum Messen dieses Effektes wird ein Experiment mit einer Laser-gepumpten Kavität vorgeschlagen, indem die Atome in einer Nano-Zelle eingeschlossen sind. Der vorgeschlagene Aufbau sollte das einfache Manipulieren der relevanten Parameter erlauben. Im zweiten Teil der Arbeit wird die grundlegende Idee auf ein anderes System angewandt, dass einen rein quantenmechanischen Effekt zeigt. Die Quanten-Ising- Kette in einem transversalen Magnetfeld zeigt einen Quantenphasenübergang, eine grundlegende Änderung in Systemeigenschaften bei verschwindender Temperatur. Während diese Temperatur offensichtlich nicht in einem bosonischen Transportexperiment erreicht wird, stellt sich dennoch die Frage, ob der bosonische Strom durch solch ein quantenkritisches System Eigenschaften des Null-Temperatur-Verhaltens zeigt. Diese Frage kann mit Hilfe von Mastergleichungen beantwortet werden, die das analytische Herleiten des durch die Bosonen getragenen Energiestromes erlauben. Dieser Strom übernimmt nicht nur alle Eigenschaften des Null-Temperatur-Systems, sondern zeigt diese bereits bei endlichen Temperaturen. Durch die vielen bereits verfügbaren Quantensimulatoren für die Quanten-Ising-Kette sollte dieser Effekt mit modernen Technologien gemessen werden können. Der dritte Teil dieser Arbeit behandelt ein konzeptionell anderes Thema. Die ersten beiden Teile zeigten, das analytische Herleitungen von höheren Kumulanten in den benutzen Formalismen nicht möglich sind. Die Anwendung einer Bewegungsgleichungsmethode in der vollständigen Zählstatistik erlaubt die zumindest teilweise Umgehung dieses Problems. Für die Fragestellungen aus den ersten beiden Teilen ist es möglich, analytische Ausdrücke für das Rauschen des bosonischen Stromes herzuleiten. Die Herleitung noch höherer Kumulanten mit dieser Methode bleibt ein interessantes Ziel für die Zukunft.The recent progress in the detection and generation of single photons led to a growing interest in the field of cavity quantum electrodynamics. Together with the old idea of counting all photons emitted from a source to characterize its quantum statistics, this naturally leads to the question, if interesting physics can be revealed with the method of Full Counting Statistics applied to bosonic transport setups. As a starting point to this aim, the first part of this thesis is dedicated to the Dicke model. This model describes an effect of increased emission out of an atomic cloud, arising due to the build-up of collectivity mediated via the coupling of the atoms to a cavity field. This effect has been studied in detail in the transient regime. The focus in this thesis is therefore on the steady-state emission that arises if the atoms are additionally pumped collectively. Within the framework of Full Counting Statistics it is possible to show that the transient behavior has its counterpart in the steady-state cumulants of the emission process. Moreover, it can be shown that higher cumulants of the transport process are more sensitive indicators for the collectivity, than the current itself. To measure this effects, a pumped cavity experiment is proposed where the atoms are confined in a nano-cell. The experimental setup should allow the convenient manipulation of all relevant parameters. The second part of the thesis extends the concept to a system showing another purely quantum mechanical effect. The quantum Ising chain in a transverse magnetic field shows a quantum phase transition, a fundamental change in system properties at absolute zero temperature. This regime is obviously not reached in thermal transport experiments. Nevertheless, the question arises if the bosonic current through such a quantum critical system inherits characteristics of the zero-temperature behavior. This question can be answered in a master-equation formulation, leading to expressions for the current of bosons through the system. This current does not only fully inherit all signatures of the zero-temperature behavior, but shows these already at finite temperatures. Due to the many available quantum simulators for the Ising chain, the findings should be addressable with current technology. In the third part of the thesis a conceptually different question is addressed. The first two parts showed, that analytic solutions for higher cumulants are lacking. The application of the equations-of-motion technique within the framework of Full Counting Statistics allows to fill this gap at least partly. For both the Dicke model as well as the quantum Ising chain it is possible to obtain analytic expressions for the noise of the bosonic emissions

The Network of Early Modern Printers and Its Impact on the Evolution of Scientific Knowledge: Automatic Detection of Awareness Relationships

This work describes a computational method for reconstructing clusters of social relationships among early modern printers and publishers, the most determinant agents for the process of transformation of scientific knowledge. The method is applied to a dataset retrieved from the Sphaera corpus, a collection of 359 editions of textbooks used at European universities and produced between the years 1472 and 1650. The method makes use of standard bibliographic data and fingerprints; social relationships are defined as “awareness relationships”. The historical background is constituted of the production and economic practices of early modern printers and publishers in the academic book market. The work concludes with empirically validating historical case studies, their historical interpretation, and suggestions for further improvements by utilizing machine learning technologies

I’m the One Building the Tool!

Abstract of paper 1095 presented at the Digital Humanities Conference 2019 (DH2019), Utrecht , the Netherlands 9-12 July, 2019

I’m the One Building the Tool!

Abstract of paper 1095 presented at the Digital Humanities Conference 2019 (DH2019), Utrecht , the Netherlands 9-12 July, 2019

White Paper of the ModelSEN Workshop (April 2022)

In April 2022, scholars from a variety of different disciplines and training met in Berlin for a workshop on historical networks organized by ModelSEN. This workshop brought together scholars, who have a joint interest in approaches drawn from multi-layer net- work analysis to investigate historical processes that involve layers of different kinds and include both social and epistemic components. This paper summarizes the outcomes and is intended to serve as a starting point for further discussions and the strengthening of a community in Historical Network Research

Impact of the COVID-19 Pandemic on Radiology in Inpatient and Outpatient Care in Germany: A Nationwide Survey Regarding the First and Second Wave

Objectives To find out the opinion of radiological inpatient and outpatient medical staff regarding the measures taken in relation to the COVID-19 pandemic during the first and second waves and to identify the measures that are still perceived as needing improvement. Materials and Methods We conducted an anonymous online survey among more than 10000 radiologists/technicians in Germany from January 5 to January 31, 2021. A total of 862 responses (head physicians, n =225 [inpatient doctors, n =138; outpatient doctors, n =84; N/A, n =3]; radiologic personnel, n =637 [inpatient doctor, n =303; outpatient doctor, n = 50; inpatient technician, n = 217; outpatient technician, n = 26; N/A, n =411) were received. Questions of approximation, yes/no questions, and Likert scales were used. Results During the first/second wave, 70 % (86/123)/43 % (45/104) of inpatient and 26% (17/66)/10%(5/52) of outpatient head physicians agreed that they received financial support from the authorities but the majority rated the financial support as insufficient. During the first and second wave, 33 % (8/24) and 80% (16/20) of outpatient technicians agreed that they were adequately provided with personal protective equipment. The perceived lack of personal protective equipment improved for all participants during the second wave. Inpatient [outpatient] technicians perceived an increased workload in the first and second wave: 72 % (142/198) [79% (19/24)] and 84% (146/174) [80% (16/20)]. Conclusion: Technicians seem increasingly negatively affected by the COVID-19 pandemic in Germany. Financial support by the competent authorities seems to be in need of improvement