<!doctype html public "-//w3c//dtd html 4.0 transitional//en"> <html> <head>    <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">    <meta name="GENERATOR" content="Mozilla/4.76 [en] (X11; U; Linux 2.4.2-2 i686) [Netscape]">    <title>S&Eacute;MINAIRE du LPTMS</title> </head> <body>  <h1> S&eacute;minaire du LPTMS</h1> Le s&eacute;minaire du <a href="../index.html">LPTMS</a> a lieu le mardi <blink>&agrave; 14:30&nbsp; </blink>en salle 201 du b&acirc;timent 100. <p><a href="#PROCHAIN SEMINAIRE"><img SRC="shadedSquare.gif" ALT="next" height=13 width=13 align=BOTTOM> Prochain s&eacute;minaire</a> <p><b>Organisateur</b> : <a href="../membres/pzinn/index.html">Paul Zinn-Justin</a> <br><b>Renseignements</b> : <ul> <li> <a href="mailto:pzinn@ipno.in2p3.fr">courrier &agrave; P. Zinn-Justin</a></li>  <li><a href="http://ipnweb.in2p3.fr/~lptms/presentation.html">Instructions pour venir au LPTMS</a></li></ul> <b>Autres s&eacute;minaires</b> <ul> <li> <a href="http://ipnweb.in2p3.fr/~PhT-IPN/sem_PhT.html">S&eacute;minaire de Physique Th&eacute;orique de l'IPN</a></li>  <li> <a href="http://www-spht.cea.fr/w3_sem.html">S&eacute;minaires de physique th&eacute;orique au CEA-Saclay</a></li>  <li> <a href="http://www.phys.ens.fr/dpt/seminaire.html">S&eacute;minaires de physique a l'ENS-Paris</a></li>  <li> <a href="http://www.lpthe.jussieu.fr/info_labo.html">S&eacute;minaires du LPTHE-Jussieu</a></li>  <li> <a href="http://qcd.th.u-psud.fr/">S&eacute;minaires du LPT-Orsay</a></li>  <li> <a href="http://www.fast.u-psud.fr/">S&eacute;minaires du FAST-Orsay</a></li>  <li> <a href="http://www.limsi.fr/Actualites/Smeca.html">S&eacute;minaires de M&eacute;canique-Energ&eacute;tique d'Orsay</a></li>  <li> <a href="http://www.lri.fr/Francais/vie-labo/grille.html">S&eacute;minaires du LRI-Orsay</a></li> </ul> <b>Ann&eacute;es pr&eacute;c&eacute;dentes</b> <ul> <li> <a href="seminaire0102.html">Ann&eacute;e 2001/2002</a></li>  <li> <a href="seminaire0001.html">Ann&eacute;e&nbsp; 2000/2001</a></li>  <li> <a href="seminaire9900.html">Ann&eacute;e 1999/2000</a></li>  <li> <a href="seminaire9899.html">Ann&eacute;e 1998/99</a></li>  <li> <a href="seminaire9798.html">Ann&eacute;e 1997/98</a></li>  <li> <a href="seminaire9697.html">Ann&eacute;e 1996/97</a></li> </ul> <a NAME="#premsem2000"></a><b><font size=+1>Premier semestre 2002-2003</font></b> <p><b>17 septembre 2002<blink>&nbsp;</blink></b><blink>&nbsp;<b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </b></blink><b>Pedro Fonseca (Rutgers University)</b> <br>&agrave; 14h30 <br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Titre: <b><i>Proprietes analytiques du modele Ising 2D</i></b> <br><b><i>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; en champ magnetique</i></b> <p><b>24 septembre 2002&nbsp;<blink>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; </blink>Paul Wiegmann (Chicago University)</b> <br>&agrave; 14h30 <br><b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  </b>Titre:<b>&nbsp; <i>Correlations in complex random matrices</i></b> <p><b>8 octobre&nbsp; 2002&nbsp;&nbsp;</b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  <b>Jan Myrheim </b>(The Norwegian University <br>&nbsp; &agrave; 14h30&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; of Science and Technology) <p>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Titre:&nbsp; <b><i>From PC to QC: a quantum leap in</i></b> <br><b><i>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; computing?</i></b> <blockquote> <blockquote>I want to give an elementary introduction to quantum computing by looking at two specific algorithms, the Fourier transform and Shor's factoring algorithm.</blockquote> </blockquote> <br> <b>15 octobre&nbsp; 2002&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; P. Cvitanovic </b>(Georgia Institute of Technology) <br>&agrave; 14h30<br> &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Titre:&nbsp; <b><i>Wave chaos in elastodynamic cavity scattering</i></b> <blockquote> <blockquote>Exact scattering resonances are calculated for a system of several cylindrical cavities in elastodynamics. In the high frequency limit both classical and complex periodic orbits contribute, with each complex orbit composed of sequences of classical particle trajectory segments with varying polarizations interspersed with surface wave segments. The shortest of these orbits suffice to interpret exact elastodynamic scattering resonances and Wigner time delays. <br>(nlin.CD/0108053) <br>&nbsp; <br>&nbsp;</blockquote> </blockquote> <b>17 octobre&nbsp;</b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <b>K. Takatsuka</b> (The University of Tokyo) <br>&agrave; 14h30&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Titre:&nbsp; <b><i>Energy quantization of chaos&nbsp; with a semiclassical</i></b> <br><b><i><font color="#FF0000">&nbsp;&nbsp;</font>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; amplitude-free quasi-correlation function</i></b> <br><font color="#FF0000"></font>&nbsp; <blockquote> <blockquote>A simple and practical semiclassical method based on an <br>amplitude-free quasi-correlation function is proposed to quantize <br>energy spectrum of classically chaotic systems, ranging from weak chaos to strong one. Since classical trajectories used in this quasi-correlation function are required to satisfy only a very simple condition (turn-back orbits with weak periodicity), the present method can be readily applied to a relatively large system. Both theory and numerical examples are presented.</blockquote> </blockquote> <br> <p><b>22 octobre&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; G. Akemann </b>(CEA Saclay) <br>&agrave; 14h30&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Titre: <b><i>New results on random matrix models with complex eigenvalues</i></b> <blockquote> <blockquote>Random matrix models with eigenvalues in the complex plane are introduced and solved using the method of orthogonal polynomials. The orthogonality of Laguerre and Hermite polynomials in the complex plane leads to new correlation functions for both weakly and strongly non-Hermitian matrices. <br>Here, we consider correlations of eigenvalues at the distance of the mean level spacing. In the weakly non-Hermitian limit we can proove the universality of these correlations for a large class of weights. Applications to Dirac Fermions with chemical potential as they occur e.g. in QCD are briefly discussed.</blockquote> </blockquote><br>  <br> 29 octobre &agrave; 14h30 <br> <blockquote><b> J. Jose </b></blockquote> <blockquote>( Northeastern University, Boston )</blockquote> <blockquote> Titre: <b><i> Driven by inhibition and the problem of attention </i> </b></blockquote> <blockquote><blockquote> The brain receives an enormous amount of information transduced by peripheral sense organs. This massive informational influx is coded and decoded in ways that are not yet fully understood in cognitive neuroscience. Many experiments have found synchronization present in neuronal spikings associated to different activities, but its nature and its presence in  different parts of the brain is only partly understood. Recent experiments have shown, however, that inhibitory interneurons in the hippocampus and the thalamic reticular nucleus can indeed induce synchronized neuronal discharges.   In this talk I will present a general introduction of the synchronization phenomena in the brain and different applications of information theory to analyze the transduction of synchronized entrained neuronal spikings. I will briefly mention a recent proposal that synchronization in the brain may be associated to the general paradigm of how we pay attention. </blockquote></blockquote><br> <br> 5 novembre &agrave; 14h30 <br> <blockquote><b> A. Garcia </b></blockquote> <blockquote> Titre: <b><i> Novel applications of critical statistics in quantum chaos and disordered systems </i> </b></blockquote> <blockquote><b> L. Benet </b></blockquote> <blockquote> Titre: <b><i> Integrability of two-level interacting bosons </i> </b></blockquote> <blockquote><b> D. Das </b></blockquote> <blockquote> Titre: <b><i> Glassy dynamics in a couple of fully packed loop models </i> </b></blockquote> <br> 19 novembre &agrave; 14h30 <br> <blockquote><b> N. Kirova </b></blockquote> <blockquote>( LPTMS )</blockquote> <blockquote> Titre: <b><i> Optics of polymers in light of solid state theory </i> </b></blockquote> <blockquote><blockquote> The interdisciplinary science of conducting polymers is still seeking its identity between fundamentals and applications, chemistry and physics, molecular and  condensed matter  physics, quantum chemistry and solid state  theory, fields of semiconductors and strongly correlated systems. Thus the major dispute on basic parameters and the very nature of the principle light emitting exciton has not been resolved during the last decade of intensive studies. We report on the recent progress in the unified theory for electronic and optical properties of conducting polymers. Bringing together languages of the solid state theory for polymers and the quantum chemistry of oligomers  allows us to take into account strong electronic correlations upon the semiconductor type approach. Our model combines the long range electron-hole Coulomb attraction  with a specific strong on-site e-h repulsion. The theory operates with a few parameters which can be determined experimentally or from ab initio calculations. The model explains, exploits and organizes various experimental and numerical findings. E.g. we connect such different questions as coexistence of shallow singlet  and deep triplet excitons in phenylenes, crossing  of optically allowed and forbidden transitions in polyenes, common 1/L energy dependencies in oligomers. We can interpret several observed time delay regimes in luminescence, fluorescence and phosphorescence due to conversion between various types of excitons. </blockquote></blockquote><br> <br> 26 novembre &agrave; 14h30 <br> <blockquote><b> S. Nechaev </b></blockquote> <blockquote>( LPTMS )</blockquote> <blockquote> Titre: <b><i> On simple construction of non-abelian flat connections for the braid group B_3: Geometry of conformal maps </i> </b></blockquote> <blockquote><blockquote> Our main goal consists in defining an explicit and simple geometrical construction of a non-abelian generalization of a Gauss topological invariant (i.e. a "linking number") for different groups $G$ using monodromy representations of $G$. In particular, we construct a complex flat connection (or a "nonabelian Bohm-Aharonov-like vector potential") for three particle moving in the plane. The answer depends on whether the particles are identical or not. </blockquote></blockquote><br> <br> 3 d&eacute;cembre &agrave; 14h30 <br> <blockquote><b> E. Bogomolny </b></blockquote> <blockquote>( LPTMS )</blockquote> <blockquote> Titre: <b><i> Spectral properties of distance matrices </i> </b></blockquote> <blockquote><blockquote> Distance matrices are matrices whose elements are the relative distances between points located on a certain manifold. All their eigenvalues except one are non-positive. When the points are uncorrelated and randomly distributed we investigate the average density of their eigenvalues  and the structure of their eigenfunctions. The spectrum exhibits delocalized and strongly localized  states which possess different power-law average behaviour. The exponents depend only on the dimensionality of the manifold. </blockquote></blockquote><br> <br> 10 decembre &agrave; 14h30 <br> <blockquote><b> Niels Sondergaard   </b></blockquote> <blockquote>( University of Nottingham   )</blockquote> <blockquote> Titre: <b><i> Elastic resonators from the point of view of semiclassics  </i> </b></blockquote> <blockquote><blockquote> Recently physicists have started to use closed orbits in elasticity inspired by the seminal work of Gutzwiller in solid state theory. Thus in several areas of physics this theory and its generalizations have led to qualitative and quantitive understanding of spectra. In this talk I shall  give an overview of known results for bulk elasticity restricted to two dimensions in the chaotic case. Next I shall discuss our own results for a regular geometry, the disc. </blockquote></blockquote><br> <br> 17 decembre &agrave; 14h30 <br> <blockquote><b> Jeremie Bouttier </b></blockquote> <blockquote>( CEA Saclay )</blockquote> <blockquote> Titre: <b><i> Les cartes planaires sont des arbres decores                                     </i> </b></blockquote> <blockquote><blockquote> Les cartes planaires interessent les physiciens notamment dans le cadre de modeles de surfaces aleatoires ou des integrales de matrices. Ces dernieres permettent ainsi d'enumerer de nombreuses classes de cartes par le calcul effectif des fonctions generatrices associees, mais sans offrir de comprehension de la nature combinatoire du probleme. Je presenterai une methode alternative d'enumeration n'utilisant que des arguments combinatoires, reposant sur une bijection entre cartes et arbres decores. Je discuterai ensuite quelques generalisations a des cartes coloriees. </blockquote></blockquote><br> <br> 14 janvier &agrave; 14h30 <br> <blockquote><b> Vladimir Korepin </b></blockquote> <blockquote>( YITP Stony Brook )</blockquote> <blockquote> Titre: <b><i> Correlations in XXX Heisenberg spin chain and Riemann zeta function.    </i> </b></blockquote> <br> 21 janvier &agrave; 14h30 <br> <blockquote><b> Dimitri Gangardt </b></blockquote> <blockquote>( LKB ENS )</blockquote> <blockquote> Titre: <b><i> Proprietes de correlations des gaz de Bose unidimensionnels </i> </b></blockquote> <blockquote><blockquote> The model of bosons interacting via delta-like potential in one spatial dimension is relevant to the current experiments with cold gases.  Being one of the first examples exactly soluble by using the Bethe Ansatz, this model exhibit interesting behaviour which, in particular, manifest itself in strong (beyond the mean field) correlations, as the strength of interaction increases.  In this seminar, we discuss various correlation properties of one-dimensional bosons and concentrate on the new results for the local density correlations which are crucial for the decay rates of 1D Bose gases. </blockquote></blockquote><br> <br> 28 janvier &agrave; 14h30 <br> <blockquote><b> Istvan Daruka </b></blockquote> <blockquote> Titre: <b><i> Grain Boundary De-faceting: A First Order Phase Transition by Atomic Shuffle  </i> </b></blockquote> <blockquote><blockquote> A multiscale theory of a grain boundary de-faceting phase  transition in aluminum has been developed. At an atomic scale,  molecular dynamics (MD) calculations revealed that the grain  boundary can move only by a concerted shuffle of several atoms.  This elementary excitation allowed rapid motion and  equilibration of the grain boundary. The atomic understanding  of the grain boundary motion then was mapped onto a simple  lattice model which exhibited a first order phase transition.  The results provide a detailed understanding of an  experimentally observed grain boundary de-faceting transition  including a statistical mechanical description. </blockquote></blockquote><br> <br> 25 fevrier &agrave; 14h30 <br> <blockquote><b> Andrea Pagnani </b></blockquote> <blockquote> Titre: <b><i> Universality in 2 dimensional spin glasses </i> </b></blockquote> <blockquote><b> Jesper Jacobsen </b></blockquote> <blockquote> Titre: <b><i> Theories conformes parafermioniques basees sur des algebres de Lie </i> </b></blockquote> <blockquote><b> Eugene Bogomolny </b></blockquote> <blockquote> Titre: <b><i> Matrices de distance et plongements isometriques </i> </b></blockquote> <br> 11 mars &agrave; 14h30 <br> <blockquote><b> Isabelle Bouchoule </b></blockquote> <blockquote>( Institut d'Optique, Orsay )</blockquote> <blockquote> Titre: <b><i> Fluctuations de phases introduites par les interactions dans un "laser a atomes" guide </i> </b></blockquote> <blockquote><blockquote> Recent progress on micro-fabricated magnetic guides for atoms  are stimulating  efforts to realize high precision  guided-atom interferometers. Phase coherence is a crucial property  of such interferometers, and it may be affected by interactions between atoms. In this paper, we determine the magnitude of phase fluctuations caused by atom-atom interaction in a one-dimensional beam of bosonic atoms. In our model the beam is created with a large coherence length, and that interactions only act in a limited section of the beam. Using the Bogolioubov theory,  we determine the magnitude and correlation length of the ensuing phase fluctuations in the beam after the interaction zone. </blockquote></blockquote><br> <br> 18 mars &agrave; 14h30 <br> <blockquote><b> S. Bettelli </b></blockquote> <blockquote>( Univ. Paul Sabatier, Toulouse )</blockquote> <blockquote> Titre: <b><i> The simulation of chaotic quantum maps on quantum computers: entanglement and decoherence   </i> </b></blockquote> <blockquote><blockquote> The field of quantum computing studies the possibility of solving computational problems faster than with the classical Turing machine model. Although there is already a number of theoretical results for ideal (noiseless) quantum computers which prove the superiority of the quantum computational model over the classical one, no scalable quantum computer has been built so far, and the technological and (maybe) fundamental problems concerning their design indicate that in the foreseeable future the quantum computer community will not have access to devices with a memory larger than 10-15 qubits (the quantum "equivalent" of a bit). It is therefore interesting to try to design and  study quantum algorithms with very limited memory requirements, which can however be used as a test-ground for error correction strategies. In this context, the quantum algorithms for the  simulation of chaotic maps are ideal candidates, because they satisfy the previous requirement and have the ability to investigate  non-trivial physics. In this talk, after a brief introduction to the  quantum computational model and to the general approach for chaotic algorithms, a recent study about the links between the entangle- ment in the quantum computer memory and the properties of the underlying chaotic map will be illustrated (quant-ph/0301086). </blockquote></blockquote><br> <br> 25 mars &agrave; 14h30 <br> <blockquote><b> Carlos Lobo </b></blockquote> <blockquote>( LKB, ENS Paris )</blockquote> <blockquote> Titre: <b><i> Vortex Lattice Formation in Bose-Einstein Condensates </i> </b></blockquote> <blockquote><blockquote> The nonlinear Schrodinger equation can simulate the formation of a vortex lattice in a superfluid. Starting from the experimental procedure used recently by the LKB (ENS) team I will show that the turbulent dynamics of the field produces an effective dissipation that allows for the lattice to be formed. At T=0 this process can be triggered by a dynamical instability of the condensate. At finite temperatures turbulence is present from the beginning of the simulation. These two regimes have a very different vortex dynamics and phenomenology. </blockquote></blockquote><br> <br> <a NAME="PROCHAIN SEMINAIRE"></a><b><font color="#CC33CC"><font size=+1>PROCHAIN SEMINAIRE</font></font></b><br> 1er avril &agrave; 14h30 <br> <blockquote><b> Thierry Jolicoeur </b></blockquote> <blockquote>( ENS Paris )</blockquote> <blockquote> Titre: <b><i> Effet Hall quantique fractionnaire dans les gaz de bose pieges en rotation </i> </b></blockquote> <blockquote><blockquote> Il est possible de mettre en rotation les condensats de Bose d'atomes ultra-froids. Lorsque la force centrifuge compense la force de rappel harmonique du piege, les bosons ne subissent plus que la force de Coriolis qui est analogue a la force de Lorentz d'un champ magnetique fictif. Si les bosons vivent dans une galette quasi-bidimensionnelle du a un fort piegeage selon la direction perpendiculaire, il est possible d'observer l'effet Hall quantique fractionnaire des bosons. A fort remplissage du niveau de landau le plus bas la rotation conduit a la formation du reseau d'Abrikosov. Ceclui-ci peut (theoriquement) fondre en un liquide incompressible de Hall a faible remplissage. Nous montrons par des arguments spectroscopiques et des diagonalisations exactes la presence de la serie principale de fractions n/n +- 1 et l'appariement des fermions composites lorsqu'il y a un quantum de vorticite par boson. Nous donnons des valeurs approchees des gaps des excitations neutres et chargees pour les fractions nu =1/2 (l'etat de Laughlin pour les bosons) ainsi que nu =2/3 et nu =1 ou nu est le remplissage du niveau de landau le plus bas. </blockquote></blockquote><br> </body></html> 
