Éclairage direct en temps réel avec sources surfaciques et BRDF quelconques

National audienceL'augmentation rapide de la flexibilité et des performances offertes par la nouvelle génération de cartes graphiques programmables permet d'envisager d'inclure dans des applications temps-réel des effets autrefois limités à des simulations d'éclairage caractérisées par de longs temps d'exécution. Parmi ces effets, on retrouve les ombres douces, des réflections réalistes ou l'anisotropie des matières comme l'aliminium brossé. Lorsque l'on travaille dans le domaine de la synthèse d'images réaliste et interactive, on recherche toujours le meilleur compromis entre qualité et rapidité. Il est donc nécessaire de réduire les calculs au strict minimum tout en conservant du réalisme. Toute la difficulté réside dans le fait que chaque effet nécessite des simplications et des optimisations spécifiques. Les sources surfaciques proches sont rarement considérées pourtant elles sont présentent dans de nombreuses scènes. Les reflets causés par une lumière de ce type sont particulièrement intéressants car ils prennent sa forme. Considérer ces sources lumineuses apporte plus de réalisme mais impose de nouvelles limitations et ce rapport propose une solution simple et efficasse pour y parvenir

LAD models, trees and an analog of the fundamental theorem of arithmetic

International audienceMotivated by applications of Logical Analysis Data (LAD) in medical contexts, original discrete optimization problems are proposed. When a patient arrives with a presumption of a disease, he is submitted to a sequence of tests. From one patient to another, the tests allowing to detect the disease may vary. A subset of tests whose results detect the disease in a given part of the population is called a pattern, which has its own prevalence in the population. If there is only a limited number of tests that can be done, which ones must be selected in order to maximize the number of spotted patients ? Or, if each test has a cost, in which order the tests have to be done, in order to minimize the cost ? It is the kind of questions that are investigated in this paper. For various special cases, polynomial algorithms are proposed, especially when the hypergraph whose vertices are the tests and whose edges are the patterns is a tree graph. One of these questions involves a criterion which is not a number but a sequence of numbers. The objective is then to find the best sequence for the lexicographic order. To solve this question, a new product on finite sequences is defined, namely the maximum shuffle product, which maps two sequences to their shuffle that is maximal for the lexicographic order. Surprisingly, this product leads to a theorem similar to the fundamental theorem of arithmetic: every sequence can be written uniquely as the product of prime sequences, with the suitable definition of prime sequences

Injection of a single electron from static to moving quantum dots

We study the injection mechanism of a single electron from a static quantum dot into a moving quantum dot created in a long depleted channel with surface acoustic waves (SAWs). We demonstrate that such a process is characterized by an activation law with a threshold that depends on the SAW amplitude and the dot-channel potential gradient. By increasing sufficiently the SAW modulation amplitude, we can reach a regime where the transfer is unitary and potentially adiabatic. This study points at the relevant regime to use moving dots in quantum information protocols.Comment: 5 pages, 4 figure

GI-1.0: A Fast and Scalable Two-level Radiance Caching Scheme for Real-time Global Illumination

Real-time global illumination is key to enabling more dynamic and physically realistic worlds in performance-critical applications such as games or any other applications with real-time constraints.Hardware-accelerated ray tracing in modern GPUs allows arbitrary intersection queries against the geometry, making it possible to evaluate indirect lighting entirely at runtime. However, only a small number of rays can be traced at each pixel to maintain high framerates at ever-increasing image resolutions. Existing solutions, such as probe-based techniques, approximate the irradiance signal at the cost of a few rays per frame but suffer from a lack of details and slow response times to changes in lighting. On the other hand, reservoir-based resampling techniques capture much more details but typically suffer from poorer performance and increased amounts of noise, making them impractical for the current generation of hardware and gaming consoles. To find a balance that achieves high lighting fidelity while maintaining a low runtime cost, we propose a solution that dynamically estimates global illumination without needing any content preprocessing, thus enabling easy integration into existing real-time rendering pipelines

Fast end efficient single electron transfer between distant quantum dots

International audienceLateral quantum dots are a promising system for quantum information processing devices. The required basic manipulations of a single electron spin have indeed been demonstrated. However, a stringent requirement is the ability to transfer quantum information from place to place within one sample. In this work, we explore and demonstrate the possibility to transfer a single electron between two distant quantum dots in a fast and reliable manner

Electrons surfing on a sound wave as a platform for quantum optics with flying electrons

Electrons in a metal are indistinguishable particles that strongly interact with other electrons and their environment. Isolating and detecting a single flying electron after propagation to perform quantum optics like experiments at the single electron level is therefore a challenging task. Up to date, only few experiments have been performed in a high mobility two-dimensional electron gas where the electron propagates almost ballistically. Flying electrons were detected via the current generated by an ensemble of electrons and electron correlations were encrypted in the current noise. Here we demonstrate the experimental realisation of high efficiency single electron source and single electron detector for a quantum medium where a single electron is propagating isolated from the other electrons through a one-dimensional channel. The moving potential is excited by a surface acoustic wave, which carries the single electron along the 1D-channel at a speed of 3\mum/ns. When such a quantum channel is placed between two quantum dots, a single electron can be transported from one quantum dot to the other, which is several micrometres apart, with a quantum efficiency of emission and detection of 96% and 92%, respectively. Furthermore, the transfer of the electron can be triggered on a timescale shorter than the coherence time T2* of GaAs spin qubits6. Our work opens new avenues to study the teleportation of a single electron spin and the distant interaction between spatially separated qubits in a condensed matter system.Comment: Total 25 pages. 12 pages main text, 4 figures, 5 pages supplementary materia