The term nonclassicality refers to fundamental features of quantum theory that are incompatible with the predictions of classical physics. This thesis explores several manifestations of nonclassicality, including the negativity of the Glauber-Sudarshan function of light and spin systems, quantum entanglement, and quantum memory effects in dynamical processes. Since these phenomena are responsible for the operational advantages of modern quantum technologies, their detection and characterization is a key challenge in both theoretical and experimental quantum science. A unifying theme throughout this work is the development of efficient, scalable methods to detect and quantify nonclassical features of quantum systems. Methodologically, the thesis is not only grounded on the formulation of nonclassicality in terms of abstract convex optimization problems, but also explores semidefinite programming relaxations, which provide tractable approximations for them. In the first part, we introduce detection methods for nonclassicality in single quantum systems, such as light modes. Here, we show how the theory of nonnegative polynomials can be used to optimally exploit data capturing the nonclassical nature of light. Specifically, we show that the convex cone of nonnegative polynomials can reveal nonclassicality in data even when it is hidden from standard detection methods up to now. Further, inspired by the nonclassicality of quantum particles, we introduce Wigner representations in generalized probabilistic theories and provide conditions under which they are unique. Turning to correlations between several systems, in the second part, we develop the polytope approximation technique for certifying separability and detecting entanglement in both bipartite and multipartite systems. This leads to an algorithm which, for practical purposes, conclusively recognizes bipartite separability for small and medium-size dimensions. For multipartite systems, the approach allows characterizing a range of different separability classes for up to five qubits or three qutrits. Finally, we systematically identify quantum states showing subtle forms of multipartite entanglement, such as strongly entangled three-qubit states which are separable in each bipartite split. In the last part, we turn to nonclassical phenomena in quantum systems that evolve in time. Specifically we investigate channel discrimination protocols under memory restrictions and the detection of quantum memory effects in quantum dynamical processes. By formulating these problems using the concept of convex optimization, we provide operational criteria to distinguish classical memory from genuine quantum memory. Practically, this allows us to systematically prove the presence of genuine quantum memory in spontaneous emission processes and to propose schemes for its experimental detection.

This collection provides an overview of various teaching methods that can be used in higher education. All entries are summarised according to the following three criteria: level of difficulty (easy, medium or difficult), estimated duration of use and recommended group size. Additional links and references to relevant tools are also provided for each method.

Die vorliegende Arbeit widmet sich der linguistischen Analyse von Medienkritik im digitalen Zeitalter am Beispiel des YouTubers Rezo. Im Fokus steht das im Jahr 2020 veröffentlichte Video „Die Zerstörung der Presse“, in dem Rezo etablierte deutsche Printmedien einer kritischen Betrachtung unterzieht. Auf Basis eines qualitativen Analyseansatzes werden drei Videos betrachtet: das Ursprungsvideo Rezos, die Reaktion der FAZ („Unsere Antwort auf Rezos „Zerstörung der Presse““) sowie Rezos Reaktionsvideo („Die dümmsten und lustigsten Reaktionen“). Die Analyse demonstriert, wie sich Rezo durch den Einsatz sprachlicher Kreativität und bewusster Inszenierung zwischen journalistischer Kritik und Politainment befindet. Im Rahmen der Analyse werden verschiedene Aspekte der Videos untersucht, darunter der Aufbau, die Verwendung von Anglizismen sowie der Pronomina-Gebrauch als Index einer adressatengerechten Gestaltung. Rezos Medienkritik ist gekennzeichnet durch jugendsprachliche Elemente, eine direkte Adressierung und diskursive Strategien, die auf eine junge Zielgruppe zugeschnitten sind. Die kontrastive Analyse mit dem FAZ-Video offenbart zudem Diskrepanzen in der sprachlichen Darstellung von Glaubwürdigkeit. Die vorliegende Arbeit leistet somit einen Beitrag zur Erforschung digitaler politischer Kommunikation aus sprachwissenschaftlicher Perspektive.

Advanced on-chip integrated photonic and electronic devices, such as hyperspectral photodetectors, depth sensors or memristors, obtain significant drawbacks with respect to performance and/or the technological integration effort. To overcome such limitations, optimized materials and innovative device concepts were developed to maximize performance and integration densities for specific applications. The selected thin and ultra-thin film material examples can obtain significant advantages and exhibit fundamentally different and adjustable material properties compared to their bulk monocrystalline counterparts. Exploiting the benefitial properties of two dimensional (2D) and amorphous semiconducting materials allows the development of high-performance optoelectronic devices, especially for sensing applications. The aim of this work is to demonstrate how novel 2D-material and conventional thin-film semiconductor processing platforms and technologies can be combined to enable a heterogenous device integration on top of chip electronics with enhanced performance. As device examples, 2D-material heterostructure photodetectors for enhanced sensing applications, nonlinear amorphous silicon and graphene photodetectors for depth sensing as well as thin-film memristors for the development of neuro-inspired “smart” cameras are presented, discussed and compared with the state-of-the-art.