On the choosability of claw-free perfect graphs

It has been conjectured that for every claw-free graph $G$ the choice number of $G$ is equal to its chromatic number. We focus on the special case of this conjecture where $G$ is perfect. Claw-free perfect graphs can be decomposed via clique-cutset into two special classes called elementary graphs and peculiar graphs. Based on this decomposition we prove that the conjecture holds true for every claw-free perfect graph with maximum clique size at most $4$

Coherent dipole-dipole coupling between two single atoms at a F\"orster resonance

Resonant energy transfers, i.e. the non-radiative redistribution of an electronic excitation between two particles coupled by the dipole-dipole interaction, lie at the heart of a variety of chemical and biological phenomena, most notably photosynthesis. In 1948, F\"orster established the theoretical basis of fluorescence resonant energy transfer (FRET), paving the ground towards the widespread use of FRET as a "spectroscopic ruler" for the determination of nanometer-scale distances in biomolecules. The underlying mechanism is a coherent dipole-dipole coupling between particles, as already recognized in the early days of quantum mechanics, but this coherence was not directly observed so far. Here, we study, both spectroscopically and in the time domain, the coherent, dipolar-induced exchange of electronic excitations between two single Rydberg atoms separated by a controlled distance as large as 15 microns, and brought into resonance by applying a small electric field. The coherent oscillation of the system between two degenerate pair states occurs at a frequency that scales as the inverse third power of the distance, the hallmark of dipole-dipole interactions. Our results not only demonstrate, at the most fundamental level of two atoms, the basic mechanism underlying FRET, but also open exciting prospects for active tuning of strong, coherent interactions in quantum many-body systems.Comment: 4 pages, 3 figure

Single-Atom Addressing in Microtraps for Quantum-State Engineering using Rydberg Atoms

We report on the selective addressing of an individual atom in a pair of single-atom microtraps separated by $3\;\mu$m. Using a tunable light-shift, we render the selected atom off-resonant with a global Rydberg excitation laser which is resonant with the other atom, making it possible to selectively block this atom from being excited to the Rydberg state. Furthermore we demonstrate the controlled manipulation of a two-atom entangled state by using the addressing beam to induce a phase shift onto one component of the wave function of the system, transferring it to a dark state for the Rydberg excitation light. Our results are an important step towards implementing quantum information processing and quantum simulation with large arrays of Rydberg atoms.Comment: 4 pages, 3 figure

Single-atom trapping in holographic 2D arrays of microtraps with arbitrary geometries

We demonstrate single-atom trapping in two-dimensional arrays of microtraps with arbitrary geometries. We generate the arrays using a Spatial Light Modulator (SLM), with which we imprint an appropriate phase pattern on an optical dipole trap beam prior to focusing. We trap single $^{87}{\rm Rb}$ atoms in the sites of arrays containing up to $\sim100$ microtraps separated by distances as small as $3\;\mu$m, with complex structures such as triangular, honeycomb or kagome lattices. Using a closed-loop optimization of the uniformity of the trap depths ensures that all trapping sites are equivalent. This versatile system opens appealing applications in quantum information processing and quantum simulation, e.g. for simulating frustrated quantum magnetism using Rydberg atoms.Comment: 9 pages, 10 figure

Géochimie, minéralogie et sélection altérologique des argiles alluviales de la vallée du Nyong à Akonolinga (Cameroun) en vue de leur utilisation dans la production des briques cuites

Trois puits ont été ouverts dans la vallée du Nyong à travers lesquels les échantillons d’argiles alluviales ont été récoltés. Ces échantillons ont été  soumis à l’analyse spectrométrique de rayons X et la méthode « altérologique normative » a été mise en oeuvre en vue de leur sélection dans la  production des briques cuites. Les résultats obtenus montrent que la silice (SiO2) est l’élément le plus abondant suivie par l’alumine (Al2O3). Les  autres éléments majeurs (TiO2, FeO3, K2O, MnO, NiO, P2O5, CaO, Cr2O3) ont des concentrations insignifiantes. Les paramètres altérologiques  révèlent que l’Indice de Lixiviation Potentielle (ILP) est important contrairement au Dégré Virtuel d’Altération de la Roche (DVAR) qui est faible. Le  milieu est ouvert et faiblement induré car les valeurs de l’Indice de Confinement Potentiel (ICP) et de l’Indice d’Induration Potentielle (IIP) sont  faibles. L’application du protocole de selection normative aux matériaux de la vallée du Nyong, les a proscrits pour la fabrication des briques cuites. Cependant, en prenant soin de fabriquer les briques cuites avec l’argile saine (100 wt%) ou avec des faibles ajouts de sable (5, 10, 15 wt%), les  résultats obtenus sont bons. In the Nyong valley, three wells were dug from which alluvial clay samples were collected. These samples were subjected to X-ray analysis and the  normative alterology” method was applied for their selection in the production of fired bricks. The results obtained show that silica (SiO2) is the  most abundant element followed by alumina (Al2O3). The other major elements (TiO2, FeO3, K2O, MnO, NiO, P2O5, CaO, Cr2O3) have insignificant  concentrations. The alterology parameters show that the Potential Leaching Index (PLI) is high in contrast to the Virtual Degree of Alteration of the  Rock (VDA) which is low. The environment is opened and weakly indurated as the Potential Containment Index (PCI) and Potential Induration Index  (PII) values are low. The application of the normative selection protocol to the Nyong Valley materials has prohibited them from being used for the  manufacture of fired bricks. However, if care is taken to make the fired bricks with 100% pure clay or with small amounts of sand (5%, 10%, 15%),  good results are obtained.&nbsp

Guide de droit d\u27auteur

Ce guide, à jour des textes en vigueur en cette année 2017, traite des questions juridiques soulevées en droit de la propriété intellectuelle. Il constitue l\u27outil indispensable à tous ceux qui sont amenés à utiliser ou à créer des ressources, quelles que soient leurs natures

Robust Deep Reinforcement Learning Through Adversarial Attacks and Training : A Survey

Deep Reinforcement Learning (DRL) is an approach for training autonomous agents across various complex environments. Despite its significant performance in well known environments, it remains susceptible to minor conditions variations, raising concerns about its reliability in real-world applications. To improve usability, DRL must demonstrate trustworthiness and robustness. A way to improve robustness of DRL to unknown changes in the conditions is through Adversarial Training, by training the agent against well suited adversarial attacks on the dynamics of the environment. Addressing this critical issue, our work presents an in-depth analysis of contemporary adversarial attack methodologies, systematically categorizing them and comparing their objectives and operational mechanisms. This classification offers a detailed insight into how adversarial attacks effectively act for evaluating the resilience of DRL agents, thereby paving the way for enhancing their robustness.Comment: 57 pages, 16 figues, 2 table

The development of advanced optical fibers for long-​wave infrared transmission

International audienceLong-​wave IR fibers are used in an increasing no. of applications ranging from thermal imaging to bio-​sensing. However, the design of optical fiber with low-​loss in the far-​IR requires a combination of properties including good rheol. characteristics for fiber drawing and low phonon energy for wide optical transparency, which are often mutually exclusive and can only be achieved through fine materials engineering. This paper presents strategies for obtaining low loss fibers in the far-​IR based on telluride glasses. The compn. of the glasses is systematically investigated to obtained fibers with minimal losses. The fiber attenuation is shown to depend strongly on extrinsic impurity but also on intrinsic charge carrier populations in these low band-​gap amorphous semiconductor materials