The distribution of "time of flight" in three dimensional stationary chaotic advection

The distributions of "time of flight" (time spent by a single fluid particle between two crossings of the Poincar\'e section) are investigated for five different 3D stationary chaotic mixers. Above all, we study the large tails of those distributions, and show that mainly two types of behaviors are encountered. In the case of slipping walls, as expected, we obtain an exponential decay, which, however, does not scale with the Lyapunov exponent. Using a simple model, we suggest that this decay is related to the negative eigenvalues of the fixed points of the flow. When no-slip walls are considered, as predicted by the model, the behavior is radically dfferent, with a very large tail following a power law with an exponent close to -3

Encoding many qubits in a rotor

We propose a scheme for encoding many qubits in a single rotor, that is, a continuous and periodic degree of freedom. A key feature of this scheme is its ability to manipulate and entangle the encoded qubits with a single operation on the system. We also show, using quantum error-correcting codes, how to protect the qubits against small errors in angular position and momentum which may affect the rotor. We then discuss the feasibility of this scheme and suggest several candidates for its implementation. The proposed scheme is immediately generalizable to qudits of any finite dimension.Comment: 11 pages, 5 figure

Conception rapide d'aides techniques pour personnes tétraplégiques

International audienceLes aides techniques permettent à de nombreuses personnes tétraplégiques d'accomplir des tâches qu'elles ne pourraient pas accomplir sans elles. Selon (Laffont, 2008), la possibilité de contrôler son environnement est d'ailleurs déterminante pour la qualité de la réinsertion sociale, familiale et professionnelle. En parallèle, nous pouvons constater qu'une grande proportion des aides techniques disponibles est peu ou pas utilisée. Ceci qui s'expliquer par de multiples raisons : manque d'écoute dans la sélection, difficulté d'obtention des aides techniques, des performances et du changement de besoins. Néanmoins, le développement récent de technologies à très bas coût, l'engouement du public pour le Do It Yourself et la diffusion des connaissances en interaction homme-machine permettent d'affirmer qu'il est possible de concevoir rapidement des aides techniques réellement adaptées. Nous illustrerons ces aspects au travers d'expériences menées de la conception à la réalisation de prototypes matériel et logiciels pour personnes tétraplégique

Optimal Unambiguous State Discrimination of two density matrices and its link with the Fidelity

Recently the problem of Unambiguous State Discrimination (USD) of mixed quantum states has attracted much attention. So far, bounds on the optimum success probability have been derived [1]. For two mixed states they are given in terms of the fidelity. Here we give tighter bounds as well as necessary and sufficient conditions for two mixed states to reach these bounds. Moreover we construct the corresponding optimal measurement strategies. With this result, we provide analytical solutions for unambiguous discrimination of a class of generic mixed states. This goes beyond known results which are all reducible to some pure state case. Additionally, we show that examples exist where the bounds cannot be reached.Comment: 10 page

Fisheye keyboard : whole keyboard displayed on small device

In this article, we propose a soft keyboard with interaction inspired by research on visualisation information. Our goal is to find a compromise between readability and usability on a whole character layout for an Ultra mobile PC. The proposed interactions allow to display all keys on a small screen while making pointing easier for the user by expanding any given key as a function of its distance from the stylus

Mutually unbiased bases for the rotor degree of freedom

We consider the existence of a continuous set of mutually unbiased bases for the continuous and periodic degree of freedom that describes motion on a circle (rotor degree of freedom). By a singular mapping of the circle to the line, we find a first, but somewhat unsatisfactory, continuous set which does not relate to an underlying Heisenberg pair of complementary observables. Then, by a nonsingular mapping of the discrete angular momentum basis of the rotor onto the Fock basis for linear motion, we construct such a Heisenberg pair for the rotor and use it to obtain a second, fully satisfactory, set of mutually unbiased bases.Comment: 9 pages, 4 figure

Optimal Lewenstein-Sanpera decomposition of two-qubit states using Semidefinite Programming

We use the language of semidefinite programming and duality to derive necessary and sufficient conditions for the optimal Lewenstein-Sanpera Decomposition (LSD) of 2-qubit states. We first provide a simple and natural derivation of the Wellens-Kus equations for full-rank states. Then, we obtain a set of necessary and sufficient conditions for the optimal decomposition of rank-3 states. This closes the gap between the full-rank case, where optimality conditions are given by the Wellens-Kus equations, and the rank-2 case, where the optimal decomposition is analytically known. We also give an analytic expression for the optimal LSD of a special class of rank-3 states. Finally, our formulation ensures efficient numerical procedures to return the optimal LSD for any arbitrary 2-qubit state.Comment: 7 pages. submitted to PR

Ysilex : a Friendly reading Interface for Dyslexics

International audienceIn this paper, we describe an interface to display texts in a fashion adapted to dyslexic readers. In order to help the reading task, we designed several tools geared towards the specific difficulties of this population, e.g. a tendency to lose one's place within the text, a fluctuating attention or a difficulty to access the syllable level of the words, a process known to be used with new or infrequent words. Preliminary results show that a pared down display coupled with a choice of tools available on demand could cater to the heterogeneity of difficulties displayed by dyslexics. Stepwise increments in design coupled with ongoing validation of the reading tools will insure the usefulness of the interface