Ensemble versus individual system in quantum optics

Modern techniques allow experiments on a single atom or system, with new phenomena and new challenges for the theoretician. We discuss what quantum mechanics has to say about a single system. The quantum jump approach as well as the role of quantum trajectories are outlined and a rather sophisticated example is given.Comment: Fundamental problems in quantum theory workshop, invited lecture. 11 pages Latex + 7 figures. To appear in Fortschr. d. Physi

Four-photon orbital angular momentum entanglement

Quantum entanglement shared between more than two particles is essential to foundational questions in quantum mechanics, and upcoming quantum information technologies. So far, up to 14 two-dimensional qubits have been entangled, and an open question remains if one can also demonstrate entanglement of higher-dimensional discrete properties of more than two particles. A promising route is the use of the photon orbital angular momentum (OAM), which enables implementation of novel quantum information protocols, and the study of fundamentally new quantum states. To date, only two of such multidimensional particles have been entangled albeit with ever increasing dimensionality. Here we use pulsed spontaneous parametric downconversion (SPDC) to produce photon quadruplets that are entangled in their OAM, or transverse-mode degrees of freedom; and witness genuine multipartite Dicke-type entanglement. Apart from addressing foundational questions, this could find applications in quantum metrology, imaging, and secret sharing.Comment: 5 pages, 4 figure

Multi-dimensional laser spectroscopy of exciton-polaritons with spatial light modulators

We describe an experimental system that allows one to easily access the dispersion curve of exciton-polaritons in a microcavity. Our approach is based on two spatial light modulators (SLM), one for changing the excitation angles (momenta), and the other for tuning the excitation wavelength. We show that with this setup, an arbitrary number of states can be excited accurately and that re-configuration of the excitation scheme can be done at high speed.Comment: 4 pages, 5 figure

Spontaneously Localized Photonic Modes Due to Disorder in the Dielectric Constant

We present the first experimental evidence for the existence of strongly localized photonic modes due to random two dimensional fluctuations in the dielectric constant. In one direction, the modes are trapped by ordered Bragg reflecting mirrors of a planar, one wavelength long, microcavity. In the cavity plane, they are localized by disorder, which is due to randomness in the position, composition and sizes of quantum dots located in the anti-node of the cavity. We extend the theory of disorder induced strong localization of electron states to optical modes and obtain quantitative agreement with the main experimental observations.Comment: 6 page

Feed-links for network extensions

Road network data is often incomplete, making it hard to perform network analysis. This paper discusses the problem of extending partial road networks with reasonable links, using the concept of dilation (also known as crow flight conversion coefficient). To this end, we study how to connect a point (relevant location) inside a polygon (face of the known part of the road network) to the boundary so that the dilation from that point to any point on the boundary is not too large. We provide algorithms and heuristics, and give a computational and experimental analysis

A Complexity View of Rainfall

We show that rain events are analogous to a variety of nonequilibrium relaxation processes in Nature such as earthquakes and avalanches. Analysis of high-resolution rain data reveals that power laws describe the number of rain events versus size and number of droughts versus duration. In addition, the accumulated water column displays scale-less fluctuations. These statistical properties are the fingerprints of a self-organized critical process and may serve as a benchmark for models of precipitation and atmospheric processes.Comment: 4 pages, 5 figure

Most vital segment barriers

We study continuous analogues of "vitality" for discrete network flows/paths, and consider problems related to placing segment barriers that have highest impact on a flow/path in a polygonal domain. This extends the graph-theoretic notion of "most vital arcs" for flows/paths to geometric environments. We give hardness results and efficient algorithms for various versions of the problem, (almost) completely separating hard and polynomially-solvable cases

Flexible, protokollbasierte Therapie auf Basis adaptiver Workflows

Viele medizinische Therapien basieren auf standardisierten Protokollen, z.B. Chemotherapien in der Onkologie. Die darin festgelegten Behandlungsprozesse sind stark strukturiert und sehr detailliert formuliert. So werden in typischen Chemotherapieprotokollen die Therapieschritte bis hin zu einzelnen Medikamentengaben spezifiziert. Workflow-Management-Systeme (WfMS) sind deshalb ein geeignetes Werkzeug, um die Durchführung solcher Protokolle zu unterstützen. In früheren Untersuchungen(3) wurde deutlich, dass die Therapien trotz der genauen Vorgaben einen gewissen Grad an Flexibilität besitzen. Bei einer signifikanten Anzahl von Fällen treten Ausnahmen auf, bei denen in vorgeschriebener, aber nicht im Workflow modellierter Weise vom geplanten Behandlungsverlauf abgewichen werden muss. Um Workflow-Systeme dennoch einsetzen zu können, ist es notwendig die laufenden Workflows zu adaptieren (d.h. zu verändern), um sie an die neue Therapiesituation anzupassen. Aufgrund der hohen Komplexität der Therapieprotokolle und der großen Datenmenge (10-30 Befunde pro Patient und Tag bei unterschiedlichen Protokollen) ist es außerdem notwendig, den behandelnden Arzt bei der Erkennung der Ausnahmen und der Auswahl der passenden Adaption zu unterstützen. Um das medizinische Personal von der manuellen Ausnahmebehandlung zu entlasten, ist ein System erforderlich, das Ausnahmen erkennt und durch automatische Adaptionen sicherstellt, dass laufende Therapien trotz Ausnahmen weiter durchgeführt werden können. Ein solches System ist insbesondere für den Einsatz in klinischen Studien geeignet, da dort die Protokoll-Konformität der Behandlung besonders wichtig ist. Infolge der Verbesserung der Protokoll-Konformität ist dann auch eine Erhöhung der Behandlungsqualität zu erwarten