Estimation error for blind Gaussian time series prediction

We tackle the issue of the blind prediction of a Gaussian time series. For this, we construct a projection operator build by plugging an empirical covariance estimation into a Schur complement decomposition of the projector. This operator is then used to compute the predictor. Rates of convergence of the estimates are given

Intergenerational altruism and neoclassical growth models

This paper surveys intergenerational altruism in neoclassical growth models. It first examines Barro's approach to intergenerational altruism, whereby successive generations are linked by recursive altruistic preferences. Individuals have an altruistic concern only for their children, who in turn also have altruistic feelings for their own children. The conditions under which the Ricardian equivalence (debt neutrality) theorem applies are specified. The effectiveness of fiscal policy is further analysed in the context of an economy populated by heterogeneous families differing with respect to their degree of intergenerational altruism. Other forms of altruism, referred to as ad hoc altruism, are also examined, along with their implications for fiscal policy. JEL Classification: E13, D64, E62, C60altruism, fiscal policy, Neoclassical general aggregative models

L'université et la ville, genèse et structuration d'un champ socio-spatial et politique

International audienceThe objective of this research on the topic of the university and the city and specifically on the relationship between the university and the city of Tours was not so much to understand the only geographical integration of the University of Tours in the city but to capture how representations of the university were enrolled in the image of Tours in action in municipal projectsSans doute, la relation de l'université et de la ville fut longtemps l'impensé de la recherche urbaine tourangelle. Alors que, tout au long des années 1970 et 1980, s'affirmaient et s'affinaient les études sur les dynamiques spatiales, les fonctions urbaines, les groupes sociaux, ou encore les grandes opérations d'aménagements, l'université restait cet étrange objet -- du désir ? -- dont on n'ignorait certes pas la présence, sans que pour autant on éprouvât le besoin d'en débattre -- si ce n'est sous la forme, déviée, de la question du rôle politique et social global de l'université et des universitaires dans la société contemporaine. Mais quant à son statut local et aux formes et modalités de son inscription dans le jeu tourangeau, s'affirmait l'idée qu'on n'en pouvait rien dire ou peu s'en faut. Dans ce contexte, l'appel d'offre Université et Ville provoqua un réel effet de surprise et fut salutaire puisqu'il obligea un groupe de chercheurs hétérogène et assez hâtivement constitué -- auquel s'adjoignirent des praticiens fort motivés -- à se poser enfin la question de la pertinence de la dialectique postulée par le texte de l'appel d'offre, et par suite à élaborer une problématisation susceptible de nourrir trois années de recherche. Bref, nous n'avons eu que très tardivement et presque brutalement le loisir et les capacités de construire le champ de la relation de l'université et de la ville ; en même temps, cette élaboration d'un nouvel objet cognitif a constitué une étape, un jalon dans l'histoire du phénomène de la rencontre ville-université. L'objectif du travail mené sur ce thème ne fut pas tant de comprendre la seule insertion géographique de l'université de Tours dans la ville que de saisir la manière dont les représentations de l'université se sont inscrites dans l'image de Tours en acte dans les projets municipau

Blind forecasting for Gaussian time-series

International audienceLe but de cet exposé est de fournir, dans le cadre des séries chronologiques, un estimateur "aveugle" de l'opérateur de projection sur le passé infini. Il s'agit de donner un prédicteur, lorsque la structure de covariance est inconnue, et qu'un unique échantillon est disponible pour simultanément estimer la covariance et prédire le processus. Nous obtenons la vitesse de convergence en erreur quadratique, en utilisant un résultat de concentration sur la covariance empirique, et une astucieuse décomposition de Schur donnant une forme alternative de ce projecteur. La vitesse est alors obtenue en fonction de la régularité de la densité spectrale

Optimization of the pump spectral shape in a parametric down conversion process to generate multimode entangled states.

Quantum optics has been, from its beginning, a driving force both for the exploration of fundamental limits of the quantum world and for conceiving seminal ideas and applications of the so-called quantum technologies. The last 20 years have seen a rapid development of ideas and proof-of-principle experiments involving the fields of quantum communication, quantum computation, quantum metrology and quantum simulation. The so called continuous variable (CV) approach to quantum optics, which uses many photon in collective states, and continuous observables like the quadratures of the electric field to encode information, has many interesting properties, especially from a communications perspective. It is inherently broadband and compatible with standard telecom infrastructures. Moreover, in CV, entanglement, one of the fundamental resource of quantum optics, can be generated deterministically. One of the main challenges for all quantum information technologies is scalability, being able to generate and manipulate a large number of quantum resources to achieve practical tasks efficiently. One approach to solve the issue of scalability is to use highly multimode quantum states. The quantum description of the electromagnetic field associate each photon (particle of light) with a mode (way for light to propagate). In a mutlimodal approach, we look at the quantum state bases and optical modes bases conjointly and tailor quantum fields not only in given modes, but also optimize the spatio-temporal shapes of the modes in which the state is defined. This opens wide perspectives for treating complex quantum states. In particular, using ultra-fast pulses of light which contain many temporal/spectral modes, we are able to generate large and complex entangled states of light using simple resources. In this thesis, we used an optical parametric oscillator pumped synchronously (SPOPO) with a frequency comb to generate multimode squeezed vacuum states which can be used to form cluster states: a large collection of modes (the nodes) entangled to each other in a certain way. These state are the basic resource for Measurement Based Quantum Computation (MBQC). This set-up has the advantage to generate entanglement in many mode with a single device. It is also highly tunable. Indeed, by tuning the spectrum of the OPO pump with a pulse shaper, one can tailor the properties of the generated quantum state. In this work, we focus on the optimization of the pump spectral shape to generate specific states. Using simulations based on Machine Learning Algorithms (MLA), we find optimal pump profile for typical target states. We then implement those shapes on the experimental set-up and measure the resulting states using multipixel homodyne detection. We also study intra-cavity dispersion effects. Dispersion inside the SPOPO cavity is indeed one of the main factor that limits the number of entangled modes in the generated quantum states. A systematic study of dispersion effects is therefore necessary to model the SPOPO output accurately. This works paves the way toward a fully tunable device that can be optimized in real time to generate specific quantum resources tailored for specific tasks

Quantum nonlinear optics using cold atomic ensembles

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 219-232).The fundamental properties of light derive from its constituent particles, photons, which are massless and do no interact with each other. The realization of interactions between photons could enable a wide variety of scientific and engineering applications. In particular, coherent interactions would open the path for the simulation of quantum systems with light. Photon-photon interactions can be mediated by matter, in our case cold atomic ensembles, which provide a nonlinear medium. In conventional nonlinear media, the nonlinearities are negligibly weak at intensities corresponding to single photons and nonlinear optics at the few-photon level is a long-standing goal of optical and quantum science. In this thesis, we report on two different experimental approaches to create optical media with giant nonlinearities. Both approaches rely on Electromagnetically Induced Transparency, in which photons traveling in the medium are best described as part-matter part-light quantum particles, called polaritons. In our first approach, we achieve low-light nonlinearities by loading ensembles of cold atoms in a hollow-core photonic crystal fiber to enhance the polariton-photon interactions. In our second approach, the photons are coupled to strongly interacting Rydberg atoms, which mediate large interactions between single quanta of light. Moreover, the intrinsic nature of these interactions can be tailored to take on a coherent dispersive form.by Thibault Peyronel.Ph.D