Electromagnetically induced transparency of ultralong-range Rydberg molecules

We study the impact of Rydberg molecule formation on the storage and retrieval of Rydberg polaritons in an ultracold atomic medium. We observe coherent revivals appearing in the retrieval efficiency of stored photons that originate from simultaneous excitation of Rydberg atoms and Rydberg molecules in the system with subsequent interference between the possible storage paths. We show that over a large range of principal quantum numbers the observed results can be described by a two-state model including only the atomic Rydberg state and the Rydberg dimer molecule state. At higher principal quantum numbers the influence of polyatomic molecules becomes relevant and the dynamics of the system undergoes a transition from coherent evolution of a few-state system to an effective dephasing into a continuum of molecular states.Comment: Submitted to PR

Cost-effectiveness of caries excavations in different risk groups − a micro- simulation study

Background Whilst being the most prevalent disease worldwide, dental caries is increasingly concentrated in high-risk populations. New caries treatments should therefore be evaluated not only in terms of their cost-effectiveness in individuals, but also their effects on the distribution of costs and benefits across different populations. To treat deep caries, there are currently three strategies: selective (one-step incomplete), stepwise (two-step incomplete) and complete excavation. Building on prior research that found selective excavation generally cost-effective, we compared the costs-effectiveness of different excavations in low- and high-risk patients, hypothesizing that selective excavation had greater cost-effectiveness-advantages in patients with high compared with low risk. Methods An average tooth-level Markov-model was constructed following the posterior teeth in an initially 18-year old male individual, either with low or high risk, over his lifetime. Risk was assumed to be predicted by several parameters (oral hygiene, social position, dental service utilization), with evidence-based transition probabilities or hazard functions being adjusted for different risk status where applicable. Total lifetime treatment costs were estimated for German healthcare, with both mixed public-private and only private out-of-pocket costs being calculated. For cost-effectiveness-analysis, micro-simulations were performed and joint parameter uncertainty introduced by random sampling of probabilities. Cohort analyses were used for assessing the underlying reasons for potential differences between strategies and populations. Results Selective excavation was more effective and less costly than both alternatives regardless of an individual’s risk. All three strategies were less effective and more costly in patients with high compared with low risk, whilst the differences between risk groups were smallest for selective excavation. Thus, the cost-effectiveness- advantages of selective excavation were more pronounced in high-risk groups, who also benefitted the most from reduced private out-of-pocket treatment costs. Conclusions Whilst caries excavation does not tackle the underlying sources for both the development of caries lesions and the potential differences of individuals’ risk status, selective excavation seems most suitable to treat deep lesions, especially in patients with high risk, who over-proportionally benefit from the resulting health-gains and cost-savings

Radiographic, antibacterial and bond-strength effects of radiopaque caries tagging

Selectively excavated carious lesions remain radiographically detectable. Radiopaque tagging could resolve the resulting diagnostic uncertainty. We aimed to evaluate if tagging depends on lesions depths, is antibacterial, or affects dentin bond-strengths. Artificial lesions (depth-range: 152–682 μm, n = 34/group) were induced in human dentin samples, evaluated using wavelength- independent microradiography, treated with one of two tagging materials (70% SnCl2, 30% SnF2) and re-evaluated. To evaluate antimicrobial effects, 40 dentin samples were submitted to a Lactobacillus rhamnosus invasion-model. Infected samples were treated with placebo, 0.2% chlorhexidine, SnCl2, SnF2 (n = 10/group). Dentin was sampled and colony-forming units/mg determined. Micro- tensile bond-strengths of adhesive restorations (OptiBond FL, Filtek Z250) to tagged or untagged, sound and carious dentin were assessed (n = 12/group). Tagged surfaces were evaluated microscopically and via energy-dispersive X -ray-spectroscopy (EDS). Tagging effects of both materials decreased with increasing lesion depths (p < 0.001). Un-/chlorhexidine-treated dentin contained significantly more viable bacteria (median 7.3/3.7 × 105 CFU/mg) than tagged dentin (no CFU detectable, p < 0.001). Tagging decreased bond strengths (p < 0.001) on sound (−22%/−33% for SnCl2/SnF2) and carious dentin (−50%/−54%). This might be due to widespread tin chloride or fluoride precipitation, as detected via microscopy and EDS. While radiopaque tagging seems beneficial, an optimized application protocol needs to be developed prior clinical use

Design and Validity of Randomized Controlled Dental Restorative Trials

Background: The evidence stemming from trials on restorative materials is shaped not only by trial findings, but also trial design and validity. We aimed to evaluate both aspects in randomized controlled dental restorative trials published from 2005–2015. Methods: Using systematic review methodology, we retrieved trials comparing restorative or adhesive dental materials. Two authors independently assessed design, risk of bias, registration status, and findings of trials. Descriptive and regression analyses were performed. Results: 114 studies on 15,321 restorations placed mainly in permanent teeth of 5232 patients were included. Per trial, the median number of patients was 37 (25th/75th percentiles: 30/51). Follow-up was 24 (20/48) months. Seventeen percent of trials reported on sample size calculations, 2% had been registered. Most trials (90%) used US Public Health Service (USPHS) criteria, and had a high risk of bias. More recent trials were more likely to have been registered, to have reported on sample size calculations, to be of low risk of bias, and to use other than USPHS-criteria. Twenty-three percent of trials yielded significant differences between groups. The likelihood of such differences was significantly increased in older studies, studies with potential reporting bias, published in journals with high impact factor (>2), longer follow-up periods, and not using USPHS-criteria. Conclusions: The majority of dental restorative trials published from 2005–2015 had limited validity. Risk of bias decreased in more recent trials. Future trials should aim for high validity, be registered, and use defined and appropriate sample sizes, follow-up periods, and outcome measures

Free-Space Quantum Electrodynamics with a single Rydberg superatom

The interaction of a single photon with an individual two-level system is the textbook example of quantum electrodynamics. Achieving strong coupling in this system so far required confinement of the light field inside resonators or waveguides. Here, we demonstrate strong coherent coupling between a single Rydberg superatom, consisting of thousands of atoms behaving as a single two-level system due to the Rydberg blockade, and a propagating light pulse containing only a few photons. The strong light-matter coupling in combination with the direct access to the outgoing field allows us to observe for the first time the effect of the interactions on the driving field at the single photon level. We find that all our results are in quantitative agreement with the predictions of the theory of a single two-level system strongly coupled to a single quantized propagating light mode. The demonstrated coupling strength opens the way towards interfacing photonic and atomic qubits and preparation of propagating non-classical states of light, two crucial building blocks in future quantum networks

Robustheitskonzepte und -untersuchungen für Schätzer konvexer Körper

In dieser Arbeit werden Schätzer für konvexe Körper auf ihr Bruchpunktverhalten untersucht, sowie Schätzer für konvexe Körper vorgeschlagen, die einen hohen Bruchpunkt aufweisen. Der finite­sample Bruchpunkt für den Schätzer eines beliebigen Parameters gibt den kleinsten Anteil von Beobachtungen einer Stichprobe an, die ausgetauscht werdenmüssen, bevor dieser Schätzer 'zusammenbricht'. Der Zusammenbruch wird dabei basierend auf einer geeigneten Me­ trik auf dem Parameterraum definiert. In der hier betrachteten Situation sind die zu schätzenden Parameter der Verteilung konvexe Körper. Eine geeignete Metrik für konvexe Körper ist der Hausdorff Abstand. Entsprechend bricht ein Schätzer für einen konvexen Körper zusammen, wenn der Hausdorff Abstand zwischen den Schätzungen dieses konvexenKörpers basierend auf der regulären und der kontaminierten Stichprobe beliebig groß wird. Andererseits sollte ebenfalls von einem Zusammenbruch dieses Schätzers gesprochen werden, wenn er zu einem niedriger­dimensionalen Gebilde degeneriert. Dies geschieht, falls der Hausdorff Abstand zwischen denSchätzungen für die Polarmenge des konvexen Körpers basierend auf der regulären und der kontaminierten Stichprobe beliebig groß wird. Die in dieser Arbeit vorgestellte Definition betrachtet beide Arten des Zusammenbruchs und erlaubt somit die Untersuchung vorhandener Schätzer konvexer Körper bzgl. ihres Bruchpunkt­verhaltens. Beispiele konvexer Körper sind Liftzonoide und Zonoide von Verteilungen. Diese konvexenKörper weisen die Besonderheit auf, dass sie dem Erwartungswert eines zufälligen konvexen Körper ent­ sprechen. Sie können somit als Parameter einer Verteilung interpretiert werden. Liftzonoide erlauben zudem die eineindeutige Beschreibung einer Verteilung. Die bisherige Schätzung von Liftzonoiden bzw. Zonoiden basiert auf Polytopen, d.h. konvexen Hüllen einer endlichen Punktmenge. Es zeigt sich, dass bei dieser Art der Schätzung schon eine einzelne Beobachtung ausreicht, um die Schätzung im Sinne der vorgestellten Bruchpunktdefinition zusammen brechen zu lassen. Weiterhin werden zwei Arten von Kontur­Toleranzbereichen vorgestellt. Die so genannten Mahalanobis­Bereiche werden durch den Erwartungswert und der Kovarianz der zugrunde liegenden Verteilung eineindeutig bestimmt. Eine Schätzung dieser konvexen Körper ergibt sich basierend auf der Schätzung der entsprechenden Momente. Da es eine eineindeutige Zuordnung zwischen den ersten beiden Momenten der Verteilung und den Mahalanobis­Bereichen gibt, wird das Bruchpunktverhalten der Schätzung dieses konvexenKörpers durch das Bruchpunktverhalten der Lokations­ und Kovarianzschätzer bestimmt. Des Weiteren wird ein Kontur­Toleranzbereich eingeführt, der eng mit Liftzonoiden verbunden ist, die so genannten zonoiden Zonen. Auch hier 1 zeigt sich, dass die Schätzung der zonoiden Zonen gegenüber Ausreißern sehr anfällig ist, da schon eine einzelne Beobachtung ausreicht, um die Schätzung im Sinneder vorgeschlagenen Bruchpunktdefinition zusammen brechenzu lassen. Da keiner der betrachteten Schätzer die obere Bruchpunktschranke innerhalb seiner Schätzerklasse annimmt, werden vorhandene Schätzer konvexer Körper soweit modifiziert, dass sie den größten Bruchpunkt aufweisen. Dazu wird aus einer gegebenen Stichprobe eine geeignete Teilstichprobe bestimmt, die unter allen zulässigen Teilstichproben ein festgelegtes Variabilitätsmaß minimiert. Die so erhaltene Teilstichprobe wird zur Schätzung der interessierenden konvexen Körper verwendet. Dieses Prinzip ist anwendbar auf Schätzer, die auf Polytopen basieren. Die so erhaltenen Schätzer nehmen die obere Bruchpunktschranke innerhalb ihrer Schätzerklassen an. In dieser Arbeit wird außerdem ein weiteres Kriterium vorgeschlagen, welches auf dem Volumen des geschätzen Zonoids basiert (MZE­Kriterium). Dieses Volumen kann als Variabilitätsmaß aufgefasst werden. Wird ein konvexer Körper basierend auf derjenigen Stichprobe geschätzt, die das MZE­Kriterium minimiert, so weist auch dieser Schätzer den größten Bruchpunkt innerhalb seinerSchätzerklasse auf. Weiterhin wird das MZE­Kriterium zur Definition von Lokations­ bzw. Kovarianzschätzer benutzt.Die resultierenden Schätzer sind affin äquivariant undnehmen die oberen Bruchpunkt­Schranken innerhalb ihrerSchätzerklassen an.As notion for robustness, a finite sample breakdown point definition for estimators of convex bodies is presented by using ideas from convex geometry. The estimation of a convex body arises in variety of contexts, ranging confidence ellipsoids to the estimation of depth contours that emerge naturally out of the concept of data depth. It is frequently mentioned that the estimation of these convex bodies can be heavily influenced by outliers in the dataset. On the one hand, outliers may cause the estimated convex body to grow beyond any measure (explosion); on the other hand, the estimator may degenerate to a lower dimensional shape (implosion). Until now there has not existed a notion describing these e#ects appropriately. A new breakdown point definition is proposed. Based on the Hausdor#­metric, this definition simultaneously takes into account the explosion and implosion of a convex body estimator. The proposed definition is appropriate to calculate the breakdown point of location and scale estimators as well. The breakdown points for several convex body estimators are calculated, such as contour of depth estimators and polytope­based estimators. It turns out that for many estimators only one bad observation can cause breakdown. To attain estimators of convex bodies with high breakdown point, new estimators are introduced based on a new half sample criterion (Minimum Zonoid Estimation Criterion (MZE­Criterion)). The criterion seeks the subsample that minimizes the volume of the estimated zonoid. This subsample is used to estimate the convex body. New multivariate a#ne equivariant location­ and scatter estimators are also introduced by using this MZE­criterion. These estimators attain the highest possible breakdown point for location and scatter estimator

Photon Subtraction by Many-Body Decoherence

We experimentally and theoretically investigate the scattering of a photonic quantum field from another stored in a strongly interacting atomic Rydberg ensemble. Considering the many-body limit of this problem, we derive an exact solution to the scattering-induced spatial decoherence of multiple stored photons, allowing for a rigorous understanding of the underlying dissipative quantum dynamics. Combined with our experiments, this analysis reveals a correlated coherence-protection process in which the scattering from one excitation can shield all others from spatial decoherence. We discuss how this effect can be used to manipulate light at the quantum level, providing a robust mechanism for single-photon subtraction, and experimentally demonstrate this capability

Observation of three-body correlations for photons coupled to a Rydberg superatom

We report on the experimental observation of non-trivial three-photon correlations imprinted onto initially uncorrelated photons through interaction with a single Rydberg superatom. Exploiting the Rydberg blockade mechanism, we turn a cold atomic cloud into a single effective emitter with collectively enhanced coupling to a focused photonic mode which gives rise to clear signatures in the connected part of the three-body correlation function of the out-going photons. We show that our results are in good agreement with a quantitative model for a single, strongly coupled Rydberg superatom. Furthermore, we present an idealized but exactly solvable model of a single two-level system coupled to a photonic mode, which allows for an interpretation of our experimental observations in terms of bound states and scattering states