Coherent versus incoherent excitation dynamics in dissipative many-body Rydberg systems

We study the impact of dephasing on the excitation dynamics of a cloud of ultracold two-level Rydberg atoms for both resonant and off-resonant laser excitation, using the wave function Monte Carlo (MCWF) technique. We find that while for resonant laser driving, dephasing mainly leads to an increase of the Rydberg population and a decrease of the Mandel Q parameter, at off-resonant driving strong dephasing toggles between direct excitation of pairs of atoms and subsequent excitation of single atoms, respectively. These two excitation mechanisms can be directly quantified via the pair correlation function, which shows strong suppression of the two-photon resonance peak for strong dephasing. Consequently, qualitatively different dynamics arise in the excitation statistics for weak and strong dephasing in off-resonant excitation. Our findings show that time-resolved excitation number measurements can serve as a powerful tool to identify the dominating process in the system's excitation dynamics.Comment: 10 pages, 10 figure

Pulse-splitting in light propagation through NN-type atomic media due to an interplay of Kerr-nonlinearity and group velocity dispersion

We investigate the spatio-temporal evolution of a Gaussian probe pulse propagating through a four-level $N$-type atomic medium. At two-photon resonance of probe-and control fields, weaker probe pulses may propagate through the medium with low absorption and pulse shape distortion. In contrast, we find that increasing the probe pulse intensity leads to a splitting of the initially Gaussian pulse into a sequence of subpulses in the time domain. The number of subpulses arising throughout the propagation can be controlled via a suitable choice of the probe and control field parameters. Employing a simple theoretical model for the nonlinear pulse propagation, we conclude that the splitting occurs due to an interplay of Kerr nonlinearity and group velocity dispersion.Comment: 9 pages, 7 figure

A hybrid model for Rydberg gases including exact two-body correlations

A model for the simulation of ensembles of laser-driven Rydberg-Rydberg interacting multi-level atoms is discussed. Our hybrid approach combines an exact two-body treatment of nearby atom pairs with an effective approximate treatment for spatially separated pairs. We propose an optimized evolution equation based only on the system steady state, and a time-independent Monte Carlo technique is used to efficiently determine this steady state. The hybrid model predicts features in the pair correlation function arising from multi-atom processes which existing models can only partially reproduce. Our interpretation of these features shows that higher-order correlations are relevant already at low densities. Finally, we analyze the performance of our model in the high-density case.Comment: significantly expanded and revised version (more observables, high-density regime); 9 pages, 8 figure

Mustererkennung zur Detektion von Rehkitzen in Thermalbildern

During pasture mowing 25% of the newborn fawns are killed [Jar02]. They are born in the meadows in the months May and June, the time of pasture mowing. Because of their innate instinct to remain motionless on the ground in case of imminent danger, they are often overlooked by farmers and inadvertently killed during mowing. This creates the demand for systems capable to detect these hidden animals. The paper presents a functional model of such a system, consisting of an airborne platform (octocopter) equipped with a thermal camera and a miniature computer. While the octocopter flies GPS-controlled search missions above the field, thermal images are taken permanently. A pattern recognition algorithm scans each thermal image captured during the flight in order to automatically detect fawns. The algorithm is based on a compression method. During the compression of an image a dictionary is created containing only non-redundant information. The dictionaries of the images recorded are compared with those of the training set categorised by the classes of fawns and meadows. The tested image is assigned to the class whose dictionaries exhibit greatest similarity. The decision, whether a fawn is recognized or not, is based upon this assignment

Non-linear absorption and density dependent dephasing in Rydberg EIT-media

Light propagation through an ensemble of ultra-cold Rydberg atoms in electromagnetically induced transparency (EIT) configuration is studied. In strongly interacting Rydberg EIT media, non-linear optical effects lead to a non-trivial dependence of the degree of probe beam attenuation on the medium density and on its initial intensity. We develop a Monte Carlo rate equation model that self-consistently includes the effect of the probe beam attenuation to investigate the steady state of the Rydberg medium driven by two laser fields. We compare our results to recent experimental data and to results of other state-of-the-art models for light propagation in Rydberg EIT-media. We find that for low probe field intensities, our results match the experimental data best if a density-dependent dephasing rate is included in the model. At higher probe intensities, our model deviates from other theoretical approaches, as it predicts a spectral asymmetry together with line broadening. These are likely due to off-resonant excitation channels, which however have not been observed in recent experiments. Atomic motion and coupling to additional Rydberg levels are discussed as possible origins for these deviations.Comment: 10 pages, 8 figure

Sub-Poissonian statistics of Rydberg-interacting dark-state polaritons

Interfacing light and matter at the quantum level is at the heart of modern atomic and optical physics and enables new quantum technologies involving the manipulation of single photons and atoms. A prototypical atom-light interface is electromagnetically induced transparency, in which quantum interference gives rise to hybrid states of photons and atoms called dark-state polaritons. We have observed individual dark-state polaritons as they propagate through an ultracold atomic gas involving Rydberg states. Strong long-range interactions between Rydberg atoms give rise to an effective interaction blockade for dark-state polaritons, which results in large optical nonlinearities and modified polariton number statistics. The observed statistical fluctuations drop well below the quantum noise limit indicating that photon correlations modified by the strong interactions have a significant back-action on the Rydberg atom statistics.Comment: 7 pages, 4 figure

Designing wearables for use in the workplace: the role of solution developers

Wearables (such as data glasses and smartwatches) are a particularly visible element of Industrie 4.0 applications. They aim at providing situation-specific information to workers, but at the same time they can also be used for surveillance and control because they generate data on the work process and sometimes even on movement patterns and vital data of the employees. Wearables technology is at an early stage of development, in which the interests and perspectives of relevant stakeholders, especially technology developers and the management, are of particular importance. This article explores the role of solution developers and their understanding of work processes in which wearables are to be used. It is based on expert interviews with solution developers, academic and company experts. The analysis shows an ambivalent understanding of work: On the one hand, it is characterized by the perception of workers as potential sources of error. It focuses on the optimization of individual workplaces and their ergonomics, while broader questions of work design and work organization are ignored. On the other hand, the technology developers see and discuss the potentials and dangers of wearables technologies with regard to individualization, data protection and control in a differentiated manner