Quantum metrology with one-dimensional superradiant photonic states

Photonic states with large and fixed photon numbers, such as Fock states, enable quantum-enhanced metrology but remain an experimentally elusive resource. A potentially simple, deterministic and scalable way to generate these states consists of fully exciting $N$ quantum emitters equally coupled to a common photonic reservoir, which leads to a collective decay known as Dicke superradiance. The emitted $N$-photon state turns out to be a highly entangled multimode state, and to characterise its metrological properties in this work we: (i) develop theoretical tools to compute the Quantum Fisher Information of general multimode photonic states; (ii) use it to show that Dicke superradiant photons in 1D waveguides achieve Heisenberg scaling, which can be saturated by a parity measurement; (iii) and study the robustness of these states to experimental limitations in state-of-art atom-waveguide QED setups.Comment: 17 pages, 3 figures. v2: substantially improved version with new result

Prediction of Electrolyte Distribution in Technical Gas Diffusion Electrodes From Imaging to SPH Simulations

The performance of the gas diffusion electrode GDE is crucial for technical processes like chlorine alkali electrolysis. The function of the GDE is to provide an intimate contact between gaseous reactants, the solid catalyst, and the liquid electrolyte. To accomplish this, the GDE is composed of wetting and non wetting materials to avoid electrolyte breakthrough. Knowledge of the spatial distribution of the electrolyte in the porous structure is a prerequisite for further improvement of GDE. Therefore, the ability of the electrolyte to imbibe into the porous electrode is studied by direct numeric simulations in a reconstructed porous electrode. The information on the geometry, including the information on silver and PTFE distribution of the technical GDE, is extracted from FIB SEM imaging including a segmentation into the different phases. Modeling of wetting phenomena inside the GDE is challenging, since surface tension and wetting of the electrolyte on silver and PTFE surfaces must be included in a physically consistent manner. Recently, wetting was modeled from first principles on the continuum scale by introducing a contact line force. Here, the newly developed contact line force model is employed to simulate two phase flow in the solid microstructures using the smoothed particle hydrodynamics SPH method. In this contribution, we present the complete workflow from imaging of the GDE to dynamic SPH simulations of the electrolyte intrusion process. The simulations are used to investigate the influence of addition of non wetting PTFE as well as the application of external pressure differences between the electrolyte and the gas phase on the intrusion proces

Algorithms and Bounds for Drawing Directed Graphs

In this paper we present a new approach to visualize directed graphs and their hierarchies that completely departs from the classical four-phase framework of Sugiyama and computes readable hierarchical visualizations that contain the complete reachability information of a graph. Additionally, our approach has the advantage that only the necessary edges are drawn in the drawing, thus reducing the visual complexity of the resulting drawing. Furthermore, most problems involved in our framework require only polynomial time. Our framework offers a suite of solutions depending upon the requirements, and it consists of only two steps: (a) the cycle removal step (if the graph contains cycles) and (b) the channel decomposition and hierarchical drawing step. Our framework does not introduce any dummy vertices and it keeps the vertices of a channel vertically aligned. The time complexity of the main drawing algorithms of our framework is $O(kn)$, where $k$ is the number of channels, typically much smaller than $n$ (the number of vertices).Comment: Appears in the Proceedings of the 26th International Symposium on Graph Drawing and Network Visualization (GD 2018

Investigating the electrowetting of silver based gas diffusion electrodes during oxygen reduction reaction with electrochemical and optical methods

Porous gas diffusion electrodes GDEs are widely used in electrochemical applications where a gaseous reactant is converted to a target product. Important applications for silver based GDEs are the chlor alkali and the CO2 electrolysis processes in which silver catalyzes the oxygen or carbon dioxide reduction reaction. The wetting of the porous GDEs is of utmost importance for the achieved performance of the electrode a completely dry electrode will result in low current densities due to the reduced active surface area while on the other hand, a completely flooded electrode will deteriorate the access of the gaseous reactant. Therefore, we investigated silver based GDEs for the oxygen reduction reaction with different amounts of the hydrophobic agent polytetrafluoroethylene PTFE and analyzed the potential induced wetting behavior electrowetting . The electrolyte breakthrough was recorded by a digital microscope and subsequently evaluated via imaging analysis of the observed breached electrolyte droplets. In order to characterize the wetting state during transition to the steady state, we applied electrochemical impedance spectroscopy measurements and retrieved the double layer capacitance. Our results indicate that a higher overvoltage facilitates the breakthrough of electrolytes through the gas diffusion electrode. Surprisingly, a faster breakthrough of electrolyte was observed for electrodes with higher PTFE content. Porometry measurements revealed that the GDE with low PTFE content has a monomodal pore size distribution, whereas electrodes with higher PTFE amount exhibit a bimodal pore size distribution. In GDEs with monomodal pore size distribution the time in which the double layer capacitance is leveling off correlates with the breakthrough time of the electrolyte. In summary, we emphasize that the wetting of GDEs is a complex interplay of the applied potential, electrode composition, and resulting porous structure which requires further advanced measurements and analysis considering the parameters affecting the wetting behavior as a whol

Compact and versatile neutron imaging detector with sub 4 mu m spatial resolution based on a single crystal thin film scintillator

A large and increasing number of scientific domains pushes for high neutron imaging resolution achieved in reasonable times. Here we present the principle, design and performance of a detector based on infinity corrected optics combined with a crystalline Gd3Ga5O12 Eu scintillator, which provides an isotropic sub 4 amp; 8201; m true resolution. The exposure times are only of a few minutes per image. This is made possible also by the uniquely intense cold neutron flux available at the imaging beamline NeXT Grenoble. These comparatively rapid acquisitions are compatible with multiple high quality tomographic acquisitions, opening new venues for in operando testing, as briefly exemplified her

Influence of binder content in silver based gas diffusion electrodes on pore system and electrochemical performance

The influences of the polytetrafluoroethylene PTFE content in silver based gas diffusion electrodes on the resulting physical properties and the electrochemical performance during oxygen reduction in concentrated sodium hydroxide electrolyte were investigated through half cell measurements. A systematic variation of the pore system was achieved by application of different silver PTFE ratios during the production of the gas diffusion electrodes GDE . In all electrodes, a silver skeleton structure with relatively constant properties was formed, while the PTFE fills up part of the open pore space. The resulting structures were characterized with a variety of methods for the physical properties supported by focused ion beam milling and scanning electron microscope FIB SEM tomography. It could be shown that variations in the obtained pore system strongly influence the electrochemical performance of the electrodes. Determination of the Tafel slopes revealed that this is not due to changes in the electrocatalytic activity but rather caused by variations in the electrolyte uptake. While too small amounts of PTFE 1 wt lead to decreased performance through electrolyte flooding, higher PTFE contents above about 5 wt also deteriorate the electrode performance because the extent of the three phase boundary diminishes. The decisive role of the electrolyte intrusion was confirmed by measurements at higher electrolyte pressure. While the best electrochemical performance was achieved with an electrode containing 98 wt silver, a slightly higher PTFE content is advisable to prevent breakthrough of the electrolyt

The influence of heat Treatments on the microstructure and the mechanical properties in Commercial 7020 alloys

The spatial distribution of Al in magnetron sputtered ZnO Al films has been investigated in depth. Two different kinds of inhomogeneities were observed an enrichment in the bulk of the film and an enrichment at the interface to the substrate. This has been correlated to the electrical properties of the films the former inhomogeneities can lead to trap states at the grain boundaries limiting the free carrier mobility. The latter can promote the formation of secondary phases, which leads to an electrical inactivation of the dopant. Furthermore, this effect can contribute to the thickness dependence of the electrical properties of ZnO Al film

Multi scale Analysis and Phase Segmentation of FIB and X ray Tomographic Data of Electrolyzer Electrodes Using Machine Learning Algorithms

An efficient conversion of electrical energy into hydrogen could be one of the most important key issues for future green energy supply. In case of electrolyzer cells, this can be achieved by increasing the active surface of Ni based electrodes. This is a crucial topic for the research of alkaline electrolyzer cells in terms of improving the cell performance. Typical coating processes are scalable and effective techniques that are well suited for this purpose. Variations of sintering process parameters i.e. duration or temperature ramps have a distinct impact on the homogeneity of the coating layer and its thickness as well as on possible media transport paths during cell operation. In this study, we analyzed the impact of the coating layers on the structure and morphology of the electrodes using laboratory X ray computer tomography. We introduce a workflow that is based on machine learning algorithms which enable to distinguish between substrate and coating layers. More detailed information was obtained using focused ion beam. This multi scale approach enhances the understanding of the sintering processes and serve as a basis for CFD simulation

Superresolution imaging of individual replication forks reveals unexpected prodrug resistance mechanism

Many drugs require extensive metabolism en route to their targets. High-resolution visualization of prodrug metabolism should therefore utilize analogs containing a small modification that does not interfere with its metabolism or mode of action. In addition to serving as mechanistic probes, such analogs provide candidates for theranostics when applied in both therapeutic and diagnostic modalities. Here a traceable mimic of the widely used anticancer prodrug cytarabine (ara-C) was generated by converting a single hydroxyl group to azide, giving “AzC.” This compound exhibited the same biological profile as ara-C in cell cultures and zebrafish larvae. Using azide-alkyne “click” reactions, we uncovered an apparent contradiction: drug-resistant cells incorporated relatively large quantities of AzC into their genomes and entered S-phase arrest, whereas drug-sensitive cells incorporated only small quantities of AzC. Fluorescence microscopy was used to elucidate structural features associated with drug resistance by characterizing the architectures of stalled DNA replication foci containing AzC, EdU, γH2AX, and proliferating cell nuclear antigen (PCNA). Three-color superresolution imaging revealed replication foci containing one, two, or three partially resolved replication forks. Upon removing AzC from the media, resumption of DNA synthesis and completion of the cell cycle occurred before complete removal of AzC from genomes in vitro and in vivo. These results revealed an important mechanism for the low toxicity of ara-C toward normal tissues and drug-resistant cancer cells, where its efficient incorporation into DNA gives rise to highly stable, stalled replication forks that limit further incorporation of the drug, yet allow for the resumption of DNA synthesis and cellular division following treatment