Internal and external dynamics of a strongly-coupled atom-cavity system

A system comprised of a small number of neutral atoms coupled to the mode of a high finesse optical resonator is a model system to study light-matter interaction at the quantum level and to explore fundamental effects like the influence of the measurement process on the atomic state. Promising proposals to generate entangled states in such systems are based on the simultaneous coupling of two atoms to one resonator mode. In chapter 1 of this thesis I shortly summarise the experimental tools to capture, trap, and transport single atoms using a magneto-optical trap and an optical conveyor belt. I discuss theoretical foundations to describe our system and present numerical simulations, the results of which enter the analysis of our experimental data. The average atom-cavity coupling strength is deduced from the measured cavity transmission and compared to a model taking atomic motion into account. The dynamics of the hyperfine spin state of one and two coupled atoms is the focus of chapter 2. I describe a nondestructive cavity-based state detection method, quantify the state detection fidelity, and identify optimum experimental parameters. This method is then used to record random telegraph signals, exhibiting quantum jumps on a timescale of milliseconds. Telegraph signals for two atoms are analysed employing Bayesian statistics, yielding additional information on the evolution of the hyperfine states. A good localisation of the atom is necessary to achieve stable coupling to the cavity mode. In chapter 3, I discuss two different aspects of how the motion of the atom can be controlled. Firstly an intracavity dipole trap is characterised and it is shown that it results in improved confinement of the atom. Secondly I examine the dependence of cavity-cooling forces on our experimental parameters and compare two different cooling regimes.Interne und externe Dynamik eines stark gekoppelten Atom-Resonator-Systems Einige wenige Atome, die an das Feld eines optischen Resonators hoher Finesse gekoppelt sind, stellen ein Modellsystem zur Untersuchung von fundamentalen Prozessen der Licht-Materie-Wechselwirkung dar, wie etwa die Rückwirkung des quantenmechanischen Messprozesses auf den atomaren Zustand. Vielversprechende Vorschläge zur Erzeugung von verschränkten Zuständen in solchen Atom-Resonator-Systemen basieren auf der simultanen Wechselwirkung zweier Atome mit dem Resonatorfeld. Im ersten Kapitel dieser Arbeit fasse ich die wesentlichen Komponenten des experimentellen Aufbaus zusammen. Theoretische Grundlagen zur Beschreibung des Systems werden diskutiert, sowie darauf aufbauende numerische Simulationen, deren Ergebnisse in spätere Auswertungen von Messergebnissen eingehen. Den Abschluss des Kapitels bildet eine Bestimmung der mittleren Atom-Resonator-Kopplungsstärke und deren Vergleich mit einem theoretischen Modell, welches die atomare Bewegung berücksichtigt. Die Dynamik der internen Hyperfein-Spinzustände bildet den Schwerpunkt des zweiten Kapitels. Eine nicht-destruktive Methode zur Messung des Spins mit Hilfe der Cavity wird vorgestellt und charakterisiert; dabei werden optimale experimentelle Parameter identifiziert. Mit Hilfe dieser Methode wurden sog. Telegraphen-Signale aufgenommen, bei denen Quantensprünge auf der Zeitskala einiger Millisekunden beobachtet werden können. Im Falle zweier Atome werden derartige Signale zusätzlich mittels Bayes'scher Statistik analysiert um Informationen über die zeitliche Entwicklung der Spinzustände zu erhalten. Eine wichtige Voraussetzung für stabile Atom-Resonator-Kopplung ist eine gute Lokalisierung der Atome. Im dritten Kapitel werden zwei Phänomene diskutiert welche die Bewegung der Atome beeinflussen. Zum einen wird gezeigt, wie eine innerhalb des Resonators gebildete zusätzliche Dipolfalle zu einer verbesserten Lokalisierung führt. Des Weiteren wird theoretisch und experimentell untersucht, wie Kühleffekte, die ausschließlich auf der Atom-Resonator-Wechselwirkung basieren, von der Wahl der experimentellen Parameter abhängen

Analyzing quantum jumps of one and two atoms strongly coupled to an optical cavity

We induce quantum jumps between the hyperfine ground states of one and two Cesium atoms, strongly coupled to the mode of a high-finesse optical resonator, and analyze the resulting random telegraph signals. We identify experimental parameters to deduce the atomic spin state nondestructively from the stream of photons transmitted through the cavity, achieving a compromise between a good signal-to-noise ratio and minimal measurement-induced perturbations. In order to extract optimum information about the spin dynamics from the photon count signal, a Bayesian update formalism is employed, which yields time-dependent probabilities for the atoms to be in either hyperfine state. We discuss the effect of super-Poissonian photon number distributions caused by atomic motion.Comment: 12 pages, 13 figure

Multi-Agent Parking Place Simulation

Parking in large urban areas is becoming an issue of great concern with many implications (environmental, financial, societal, etc.). In our research we investigate automated dynamic pricing (adp) as a mechanism for regulating parking place allocation. Adp means that the price for staying in a parking facility for a certain amount of time will fluctuate depending on the day and time of the week. In this paper, such a scenario is explored using multi-agent based simulation. Two kinds of agents are considered: drivers and parking facilities. Experiments are conducted in a real city environment in order to observe the impact of dynamic pricing, competition and demand increase. Results show that dynamic pricing application leads to better results (in terms of profit margin) for the parking facilities while it decreases drivers’ utility

Climate and carbon cycle changes from 1850 to 2100 in MPI-ESM simulations for the Coupled Model Intercomparison Project phase 5

The new Max-Planck-Institute Earth System Model (MPI-ESM) is used in the Coupled Model Intercomparison Project phase 5 (CMIP5) in a series of climate change experiments for either idealized CO2-only forcing or forcings based on observations and the Representative Concentration Pathway (RCP) scenarios. The paper gives an overview of the model configurations, experiments related forcings, and initialization procedures and presents results for the simulated changes in climate and carbon cycle. It is found that the climate feedback depends on the global warming and possibly the forcing history. The global warming from climatological 1850 conditions to 2080–2100 ranges from 1.5°C under the RCP2.6 scenario to 4.4°C under the RCP8.5 scenario. Over this range, the patterns of temperature and precipitation change are nearly independent of the global warming. The model shows a tendency to reduce the ocean heat uptake efficiency toward a warmer climate, and hence acceleration in warming in the later years. The precipitation sensitivity can be as high as 2.5% K−1 if the CO2 concentration is constant, or as small as 1.6% K−1, if the CO2 concentration is increasing. The oceanic uptake of anthropogenic carbon increases over time in all scenarios, being smallest in the experiment forced by RCP2.6 and largest in that for RCP8.5. The land also serves as a net carbon sink in all scenarios, predominantly in boreal regions. The strong tropical carbon sources found in the RCP2.6 and RCP8.5 experiments are almost absent in the RCP4.5 experiment, which can be explained by reforestation in the RCP4.5 scenario

Developments in the MPI‐M Earth System Model version 1.2 (MPI‐ESM1.2) and Its Response to Increasing CO2

A new release of the Max Planck Institute for Meteorology Earth System Model version 1.2 (MPI-ESM1.2) is presented. The development focused on correcting errors in and improving the physical processes representation, as well as improving the computational performance, versatility, and overall user friendliness. In addition to new radiation and aerosol parameterizations of the atmosphere, several relatively large, but partly compensating, coding errors in the model's cloud, convection, and turbulence parameterizations were corrected. The representation of land processes was refined by introducing a multilayer soil hydrology scheme, extending the land biogeochemistry to include the nitrogen cycle, replacing the soil and litter decomposition model and improving the representation of wildfires. The ocean biogeochemistry now represents cyanobacteria prognostically in order to capture the response of nitrogen fixation to changing climate conditions and further includes improved detritus settling and numerous other refinements. As something new, in addition to limiting drift and minimizing certain biases, the instrumental record warming was explicitly taken into account during the tuning process. To this end, a very high climate sensitivity of around 7 K caused by low-level clouds in the tropics as found in an intermediate model version was addressed, as it was not deemed possible to match observed warming otherwise. As a result, the model has a climate sensitivity to a doubling of CO2 over preindustrial conditions of 2.77 K, maintaining the previously identified highly nonlinear global mean response to increasing CO2 forcing, which nonetheless can be represented by a simple two-layer model