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This paper addresses the central question of what a coherent concept of probability might look like that would do justice to both classical probability theory, axiomatized by Kolmogorov, and quantum theory. At a time when quanta are receiving increased and expanded attention -- think, for example, of the advances in quantum computers or the promises associated with this new technology (National Academies of Sciences: Engineering, and Medicine, 2019) -- an adequate interpretation of probability, which is no less important, should be given due attention, particularly with regard to quantum theory., Comment: in German language

Fluctuations are ubiquitous in nature. They are one of the fundamental building blocks of quantum mechanics and are responsible for a wide variety of phenomena in many areas of physics, ranging from biology to cosmology. Far from any classical intuition, quantum fluctuations are for instance responsible for the appearance of forces between non-magnetic and electrically neutral objects in vacuum, which seem to arise out of nothing. Ever since, quantum fluctuations have fascinated basic research providing new insights into physics and their understanding is becoming increasingly important for various future technologies. -- Fluktuationen sind allgegenw\"{a}rtig. Sie bilden einen fundamentalen Baustein der Quantenmechanik und sind verantwortlich f\"{u}r die unterschiedlichsten Ph\"{a}nomene, angefangen in der Biologie bis hin zur Kosmologie. Fern jeder klassischen Intuition findet man zum Beispiel Kr\"{a}fte zwischen nichtmagnetischen und elektrisch neutralen Objekten. Einzig bedingt durch Quantenfluktuationen entstehen diese Kr\"{a}fte wie aus dem Nichts. Seit jeher begeistern sie die Grundlagenforschung mit neuen Einsichten und gewinnen immer mehr an Bedeutung f\"{u}r verschiedene Zukunftstechnologien., Comment: 8 pages, 4 figures, 4 pictures. Overview paper in German. Appeared in a modified form in the May issue of the Physik Journal (journal of the German Physical Society - DPG)

This work reports on setup, characterisation and data processing of a true quantum random number generator. As a randomness source a pure quantum vacuum state of light is used, which is amplified by a laser beam. Performance and behaviour of the system as well as parasitic errors are investigated. For an optimized exploitation of the data they are Fourier-transformed and processed further as frequency amplitudes. The extractable entropy in that data is calculated to allow for elimination of non-random signal contributions by hashing. The system is able to produce true and unique random numbers at a rate of 25 Gbit/s and thus outperforms previous implementations considerably., Comment: Bachelor thesis at Friedrich-Alexander-Universit\"at Erlangen-N\"urnberg from September 22nd 2011 (in German)

The aim of this work is to model the measurement of flux qubits using Quantum-Flux-Parametron (QFP) and to theoretically investigate and numerically simulate the fidelity of the measurement in different bases., Comment: in German language

Quantum mechanics describes the unitary time evolution of isolated systems. In reality, every quantum system interacts with its environment, leading to an irreversible loss of the phase relation. Path integral based methods provide a rigorous description of the process of decoherence. We provide an overview over recent numerical methods suited to describe the non-perturbative regime of system bath interaction. -- Quantenmechanik beschreibt die unit\"are Zeitentwicklung isolierter Systeme. In der Realit\"at interagiert jedes Quantensystem mit seiner Umwelt, was zu einem irreversiblen Verlust von Phasenbeziehungen f\"uhrt. Pfadintegralbasierte Methoden erlauben eine rigorose Beschreibung dieser Dekoh\"arenzprozesse., Comment: 2 figures, in German

Gravitation, according to General Relativity, is an attribute of space-time's geometry and hence not a force in the Newtonian sense. This is a consequence of Einstein's equivalence principle, which so far passed all experimental tests with high precision. However, the search for possible violations continues, for they, as the case may be, are expected to point towards more fundamental theoretical extensions of General Relativity. In particular, it is expected that useful insights are gained by studying the interaction between gravitational fields and genuine quantum-mechanical systems, like atoms or molecules. But this raises some fundamental issues, for General Relativity and Quantum Theory rest on partially incompatible sets of concepts. This article tries to explain in an elementary fashion how these issues recently entered modern research in atom interferometry. A shorter and editorially adapted version of this paper will appear in "Spektrum der Wissenschaft" -- the German edition of "Scientific American"., Comment: 18 pages, 7 figures, in german

Schroedinger's great discovery of wave mechanics in 1926 - his annus mirabilis - is discussed in detail. Beside the six most important papers that appeared during the first half of 1926, letters between Schroedinger and leading physicists at this time are main sources of this account., Comment: Invited talk at the symposium: "Schroedinger's Wavemechanics 75 Years After" (Universitaet Zurich, 24-25 April 2001), 26 pages, 2 figures, text in german

The quantum theory of Ur-alternatives of Carl Friedrich von Weizsaecker tries to constitute general quantum theory based on the concept of logical alternatives in time. Based on this interpretation of quantum theory the existence of free objects in space, their symmetry properties and their interactions shall be inferred. The alternatives are represented by binary alternatives, which are called Ur-alternatives because of their logically fundamental character. Through Ur-alternatives as elementary quantum theoretical units of information the Copernican revolution with respect to the question of space is realized in a consequent way. This means that not the objects of nature are in a given space, but the existence of space arises as a kind of indirect representation of relations between abstract quantum theoretical objects. The Ur-alternatives do not exist in a given physical reality, but the existence of space is constituted by Ur-alternatives at all. Such a concept of reality is implicitly contained within the uncertainty relation and can be seen especially in the EPR-paradoxon. It is shown in this thesis in a mathematical consistent way that a state in the tensor space of many Ur-alternatives can directly be mapped into a real three dimensional space which means that together with the dynamics a representation in a (3+1)-dimensional space-time becomes possible. By considering the $G_2$ an approach for the incorporation of the internal symmetries can be suggested. Furthermore the Ur-alternatives enable the constitution of a concept of interaction, which is based on quantum theoretical entanglement. By using this concept it is tried to obtain a purely quantum theoretical description of electromagnetism and gravity. This corresponds to a much more principle and in a radical sense background independent way of quantization., Comment: 81 pages, in German

Introduction (in German) to a novel approach to sector analysis in theories with long range forces which avoids notorious infrared problems; cf. arXiv:1304.2794, Comment: 20 pages, in German, 11 figures, solicited by Ev. Studienwerk Villigst for the book project "Raum und Materie"

These lectures are intended for graduate students who want to acquire a working knowledge of path integral methods in a wide variety of fields in physics. In general the presentation is elementary and path integrals are developed in the usual heuristic, non-mathematical way for application in many diverse problems in quantum physics. Three main parts deal with path integrals in non-relativistic quantum mechanics, many-body physics and field theory and contain standard examples (quadratic Lagrangians, tunneling, description of bosons and fermions, quantization of gauge theories etc.) as well as specialized topics (scattering, dissipative systems, spin \& color in the path integral, lattice methods etc.). In each part simple Fortran programs which can be run on a PC, illustrate the numerical evaluation of (Euclidean) path integrals by Monte-Carlo or variational methods. Also included are the set of problems which accompanied the lectures and their solutions., Comment: 183 pages (in German), 28 figures, Latex with amsmath, amssym; v2: typos corrected, chapters 1.7 and 2.3 expanded, 187 pages (in German), 29 figures; v3: corrections, more "Vertiefungen" (details), 198 pages (in German), 31 figures; v4: English version with additional part (solution of problems), 211 pages, 31 figures

From its very beginning, Quantum Theory developed contrary to the intentions of its creators. For Max Planck it marks the failure of a long-term research program, in which he tried to understand the 2nd law of thermodynamics deterministically in terms of mechanics and electrodynamics. For Albert Einstein it meant a refutation of his scientific credo. I describe parts of the early stages of this most remarkable development, up to Einstein's light-quantum hypotheis and its unfavourable reception by most other physicists., Comment: 29 pages, 4 figures. Text in german. Contribution to the 2005-annus-mirabilis celebration at the Alte Kantonsschule Aarau

On December 14. 1900, Max Planck communicated his derivation of his radiation formula, which he later called ``an act of desperation''. This date is widely recognized as birthday of quantum theory. For Planck it meant the end of his carefully planned and ambitious research project, in which he wanted to establish the second law of thermodynamics as strictly deterministic law for systems of matter and electromagnetic radiation in interaction. He knew he could not succeed within classical mechanics, but had the somewhat strange hope that the inclusion of Maxwell's electrodynamics would change the situation. Later he always disagreed with Einstein's light-quantum hypothesis, because it implied a renunciation from Maxwell's theory, which in Germany gained full recognition and acceptance as late as the 1890's, mainly through the theoretical and experimental work of Heinrich Hertz., Comment: Text in german; LeTeX 2epsilon, 7 pages, no figures; to be published in Physikalische Blaetter, Dec. 2000

After some brief biographical notes, Wolfgang Pauli's main contributions to general relativity, quantum theory, quantum field theory, and elementary particle physics are reviewed. A detailed description is given how Pauli descovered - before the advent of the new quantum mechanics - his exclusion principle., Comment: Opening lecture at the symposium: Wolfgang Pauli And Modern Physics, in honor of the 100th anniversary of Wolfgang Pauli's birthday, ETH (Zurich), May 4-6 2000; in German

In 1923 Louis de Broglie (1892-1987) discovered the material waves and six years later received the Nobel price for this discovery. Apart these well known facts this French physicist nevertheless seems to be forgotten. Details of his life are as unknown as his efforts to describe quantum mechanics in a deterministic and objective way. Especially the actual discussion concerning the interpretation of quantum mechanics seems to justify a deeper occupation with the scientific work of Louis de Broglie. In this context the important influence of Albert Einstein is of special interest; for his photons announce the existence of material waves and it may surprise that Einstein himself did not postulate them. The basis of this short scientific biography are the publications of de Broglie (a complete bibliography is given at the end), some more or less short memories of his students and some unpublished documents found in the "Archives de l'Academie des Sciences" at Paris. The original text of the correspondence between de Broglie and Einstein is enclosed in German translation in the appendix., Comment: 87 pages, in german language, new PostScript file to fix problems with previous versions