• Séminaire LPMMC
• Personne à contacter :
• Salle MAG1, Maison des Magistères

Résumé : The effect of electron-electron interactions on the transport properties of a quantum point contact (QPC) is considered. The basic point is that a QPC breaks translational invariance and therefore the electron-electron interaction process does not have to conserve momentum. This leads to a suppression of the current though the QPC. At low temperatures or bias voltages, the suppression is found perturbatively, but at higher temperatures or bias voltages perturbation theory breaks down. Therefore, we use a numerical self-consistent non-equilibrium Green's function approach to reach this regime for a simplified model.

Liens :Matthias LundeDépartement de physique théorique, Université de Genève

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, Amphi MAG

Résumé : We investigate transport properties of a superconducting junction of one-dimensional quantum wires. We include the effect of electron-electron interaction within the one-dimensional quantum wires using a weak interaction renormalization group (WIRG) procedure. Due to the proximity effect, transport across the junction occurs via direct tunneling as well as via crossed Andreev channel. We find that the fixed point structure of this system is far more rich than the fixed point structure of a normal metal-superconductor (NS) junction, where we only have two fixed points - the fully insulating fixed point or the Andreev fixed point. Even a two wire system with a superconducting junction ie a normal metal-superconductor-normal metal (NSN) structure, has non-trivial fixed points with intermediate transmissions and reflections. We demonstrate possible scenarios for production of pure spin current through such junctions and show that there are fixed points in the theory which correspond to the case of pure spin current. We have also shown that (a) effects due to inclusion of electron-electron interaction induced back-scattering in the wire, and (b) competition between the charge transport via the electron and hole channels across the junction give rise to a non-monotonic behavior of subgap conductance as a function of temperature.

Liens :Harish-Chandra Research Institute, Allahabad

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG 1

Résumé : "Quantum impurity models", describing a tiny structure coupled to macroscopic ones, are having a second life. They are indeed well adapted to the description of situations where nanostructures are connected to macroscopic electronic reservoirs, a flourishing experimental field.
On the theoretical side, predicting the transport properties of those models requires taking into account strong correlations often in a non-equilibrium situation, a considerable challenge. In this talk, we will show how field theory and integrability can be used to investigate the far-from-equilibrium regime of a quantum impurity system, the Interacting Resonant Level Model. This approach allows to calculate the full I-V curve at arbitrary temperature, as well as the DC shot noise. We also present results of time-dependent DMRG, that are in full agreement with the analytical approach. A striking effect of interactions is the development of a negative differential conductance regime.

Liens :Édouard BoulatLaboratoire MPQ, Université Paris Diderot

• Séminaire interne LPMMC
• Personne à contacter :
• Maison des Magistères, salle lecture 2

Résumé : La réalisation expérimentale de réseaux optiques permet une étude approfondie de phases fortement corrélées dans les systèmes d'atomes froids. La dimensionnalité, l'intensité de l'effet tunnel comme celle des interactions sont autant de paramètres aisément contrôlables. De nombreux modèles théoriques, traditionnellement appliqués à la physique des solides, trouvent ici un nouveau champ d'application. Nous nous sommes particulièrement intéressés à l'étude d'un système d'atomes froids sur un réseau en forme d'échelle. Les échelles sont des systèmes quasi unidimensionnel ayant un diagramme de phase très riche, en fonction du champ magnétique et du remplissage. Je présenterai le calcul de plusieurs signatures expérimentales susceptibles d'être observées lors de mesures des corrélations de densité sur le nuage atomique, après relaxation du piège.

Liens :LPS Orsay

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle lecture 2

Résumé : Consider a disordered medium at finite temperature, and the incoherent reflection of an impulse in and out through a single channel. An ensemble of such reflections r(t) may be constructed using simple thermodynamic arguments. In the absence of inelastic interior processes, such a reflection would be interpreted as a coherent 1x1 S-matrix, S(t), with the usual properties of causality and unitarity. It is amusing to imagine identifying the ensemble of such S matrices that, when garbled by inelastic scatterings, would lead to the stated ensemble of incoherent reflections r(t). If this could be done, we would then have a procedure for constructing maximum entropy S matrices (and therefore Greens functions too) and determining the corresponding features of mesoscopic transport and diffusion in systems with arbitrary internal structure.
We have not managed the above program, but we do argue that an ensemble of underlying S matrices can be reconstructed from the ensemble of incoherent reflections by an ad-hoc recipe that seeks to repair r(t) in the least invasive manner possible, consistent with unitarity and causality. The resulting ensemble of S matrices is shown, by numerical experiment, to manifest many of mesoscopic features. These include Coherent Backscatter Enhancement, (the familiar factor of two at short times), modal echo (CBE by a factor of three at late times), level repulsion, and power law decay of the probability of return. The recipe also predicts Thouless localization between two weakly coupled substructures, and Anderson localization in a multiply scattering structure. It is remarkable how much rich mesoscopic behavior follows from such simple principles.

Liens :Richard WeaverUniversity of Illinois

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle lecture 2

Résumé : The interplay between strong correlation and quantum fluctuations makes one dimensional (1D) systems very peculiar. Although a strict 1D system is an ideal case, recently it has been possible to reach and probe 1D physics both in semiconductor nanodevices and cold atom experiments. I will review two paradigmatic cases in both fields, namely the localization in parallel quantum wires[1], and the search for the FFLO state in very elongated traps with spin imbalance[2]. I will show how a quantum Monte Carlo approach to study these systems can predict accurately their phase diagram, particularly when non-homogeneous effects due to the experimental realization play an important role.

[1] Luke Shulenburger, Michele Casula, Gaetano Senatore, and Richard M. Martin, Phys. Rev. B 78, 165303 (2008);
[2] Michele Casula, D. M. Ceperley, and Erich J. Mueller, Phys. Rev. A 78, 033607 (2008).

Liens :

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle lecture 2

Résumé : Recent experiments have shown that cold atoms can be used as toy models to simulate complicated condensed matter systems, thus improving our understanding in terms of many-body theories.
In the first part of my talk I will present my theoretical work on interacting low dimensional fermions. In the case of attractive interactions, Fermi gases undergo pairing. I will focus on the interesting situation where the number of spin-up and spidown fermions is not the same, the population imbalance acting in the same way as the magnetic field f or usual superconductors. In my work, using Bethe ansatz, I have derived the exact quantum phase diagram for one dimensional gases. Moreover I also showed that, in the presence of a shallow longitudinal trap, the gas phase-separates in two shells, the partially polarized core being a Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superfluid.
In the second part of my seminar, I will present my recent results on the effect of disorder in Fermi gases. In the presence of a tunable s-wave scattering length, attractive fermions progressively form tightly bound pairs behaving as pointlike bosons. In my work I have generalized the Nozieres-Schmitt-Rink theory of superconducting fluctuations to investigate the effect of a weak static disorder throughout the crossover from Fermi to Bose superfluidity. In particular I have shown that Anderson's theorem, stating that nonmagnetic impurities do not affect the averaged superfluid order parameter, ceases to apply going towards the strong coupling molecular regime. Moreover I have found that resonant Fermi supefluids are the most robust against disorder. I will also briefly report on new exact results for disordered one dimensional bosons with strong repulsion.
In the last part of my seminar, I will present my contribution to the study of the Josephson tunneling in Fermi gases and its description in terms of hydrodynamic theories. In particular I have investigated the occurrence of dynamical instabilities when the gas is accelerated with respect to the optical lattice and the superfluid-Mott insulator phase transition in a chain of Josephson junctions.

Liens :Giuliano OrsoLPTMS, Universite Paris Sud

• Séminaire interne LPMMC
• Personne à contacter :
• Maison des Magistères, salle de conférences

Liens :Thierry ChampelLPMMC

• Séminaire interne LPMMC
• Personne à contacter :
• Maison des Magistères, salle lecture 2

Liens :Thierry ChampelLPMMC

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle lecture 2

Résumé : Interaction between nuclear spins in solids forces each spin to perform a complicated dance in a time-dependent field created by neighboring spins. This leads to spin-spin relaxation observed by nuclear magnetic resonance (NMR). I briefly discuss the efforts to calculate NMR spin-spin relaxation from first principles, and then argue that the main obstacle to these efforts is the lack of the proper understanding of microscopic chaos. I proceed with presenting a theory, which invokes the notion of chaos and thereby predicts that NMR free induction decay and spin echoes observed in the same system have identical exponential long-time behavior. This prediction was shown to be quantitatively correct by a very recent NMR experiment on hyperpolarized solid xenon. Such a lack of dependence of the long-time decay on the initial spin configuration reveals a new fundamental property of nuclear spin dynamics in solids. Namely, the quantum time evolution operator of a macroscopic system of nuclear spins 1/2 has isolated eigenmodes, which govern the long-time relaxation towards equilibrium. These eigenmodes decay on the ballistic microscopic timescale. Therefore, their existence cannot be predicted using the standard approximations of statistical physics. Such eigenmodes, however, are very reminiscent of Pollicott-Ruelle resonances in classical chaotic systems, and, in fact, were predicted on the basis of this analogy. Their discovery thus suggests that, even in the situations, when quasi-classical chaotic limit is not tenable, and the spacing between energy levels is not relevant to the observable properties, the notion of microscopic chaos can be defined for isolated many-body quantum systems at the level of Pollicott-Ruelle resonances.

References:
S.W. Morgan et al., Phys. Rev. Lett. 101, 067601 (2008)
B. V. Fine, Phys. Rev. Lett. 94, 247601 (2005)
B. V. Fine, Int. J. Mod. Phys. B 18, 1119 (2004)

Liens :Boris FineInstitute for Theoretical Physics, Heidelberg

• Séminaire interne LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG 1

Résumé : Recent calculations [1] have shown that the image of a Bose-Einstein condensate (BEC) expanding diffusively in a random potential exhibits a complicated irregular pattern of particle density. This phenomenon is reminiscent to what we know as speckle in optics. We consider a BEC expanding in a quasi-1D waveguide and show that such speckle patterns show up long-range density correlations. These correlations are accessible experimentally and exhibit remarkable features such as a strong enhancement at long times. They can even take negative values for sufficiently distant points [2].

[1] P. Henseler and B. Shapiro, Phys. Rev. A 77, 033624 (2008)
[2] N. Cherroret and S. E. Skipetrov, arXiv:cond-mat/0807.2954.

Liens :Nicolas CherroretLPMMC

• Séminaire LPMMC
• Personne à contacter :
• Salle MAG 1

Résumé : La physique dans son ensemble s'est construite sur une hypothèse de continuité de l'espace-temps dont les équations différentielles fondamentales sont l'expression. La tendance est aujourd'hui d'introduire un certain degré de discrétisation, comme dans la théorie des cordes, la théorie de la gravitation quantique à boucle etc. Mais ces tentatives sont basées sur la discrétisation d'un l'espace-temps supposé par ailleurs continu. Dans la présente approche l'univers physique est, dès l'origine, supposé être constitué d'éléments discrets si bien que tout doit être reconstruit, l'espace, le temps, les ondes, les particules etc. Dans ce séminaire on présentera un tel modèle d'univers discret et on discutera des hypothèses qui en forment la base. On évoquera, sans entrer dans les détails, les principales conséquences du modèle, reconstruction de l'espace-temps classique, justification de la mécanique quantique, explication du modèle standard, implications en cosmologie.

Liens :

• Séminaire théorie
• Personne à contacter :
• Maison des Magistères, salle de conférences

Résumé : Il y a 40 ans se déroulait une révolution scientifique: la fondation du modèle standard de la physique des particules. En son sein la très élégante chromodynamique quantique s'imposait comme la théorie des interactions fortes subnucléaires. Elle décrit le "confinement" des quarks et des gluons dans des états liés, neutres de "couleur", les "hadrons" (protons, neutrons, pions, etc.). A partir des quarks et des gluons elle promet, et souvent permet, de décrire de nombreuses expériences mettant en jeu ces "hadrons". La chromodynamique quantique sur réseau est la méthode de calcul la plus rigoureuse pour déduire les propriétés des hadrons de celles des quarks. Elle repose sur la discrétisation de l'espace-temps et est méthodologiquement proche de la physique statistique. Un petit échantillon de résultats sera montré. Cette discipline demandant de gros moyens de calcul, elle a donné lieu à des innovations dans le domaine des architectures d'ordinateurs.

Liens :

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG1

Liens :Xavier BlaseInstitut Néel

• Séminaire interne LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG1

Résumé : We determine the phase diagram and the momentum distribution for a one-dimensional Bose-Hubbard model in the presence of an incommensurate potential, by using a combined numerical (DMRG) and analytical (low-energy) analysis. The system displays a delocalized (superfluid) phase at small values of the height V₂ of the second lattice and a localized (Bose glass-like) phase at larger strengths of the second lattice. We analyze the localization transition as a function of V₂ beyond the known limits of free and hard-core bosons. We also analyze the emergence of a Bose-glass phase by looking at the evolution of the Mott-insulator lobes at varying V₂. Finally, we characterize the superfluid phase by the momentum distribution.

Liens :Xiaolong DengLPMMC

• Séminaire théorie
• Personne à contacter :
• Maison des Magistères, salle MAG1

Résumé : We determine the ground state of the two-dimensional, fully polarized electron gas within the Hartree-Fock approximation without imposing any particular symmetries on the solutions. At low electronic densities, the Wigner crystal solution is stable, but for higher densities (r_s less than ~ 2.6) we obtain a ground state of different symmetry: the charge density forms a triangular lattice with about 11% more sites than electrons. We argue that this conducting state with broken translational symmetry remains the ground state of the high density region in the thermodynamic limit giving rise to a metal to insulator transition.

Liens :Bernard BernuLPTMC, UPMC, Jussieu, Paris

• Séminaire théorie
• Personne à contacter :
• Maison des Magistères, salle MAG1

Résumé : The physical behaviour of hydrogen under megabar compression is still largely unknown because experimental difficulties prevent a systematic investigation of the phase diagram in the interesting range of pressures and temperatures. Ab-initio theoretical methods have been exploited to interpret the scattered experimental data and to make predictions. However the problem is particularly difficult because the energy scales of several different phenomena, such as electronic correlations, protonic quantum effects, finite size effects in the metallic phase and in the metal-insulator transition region, becomes comparable and need to be considered together in a non perturbative manner. Quantum Monte Carlo methods are unique in their ability to treat all those effects with high accuracy in simple systems. In recent years we have developed a new QMC method, the Coupled Electron-Ion Monte Carlo (CEIMC) [C. Pierleoni and D. M. Ceperley, Lecture Notes in Physics vol 741 pp 641-683 (2006), xxx.lanl.gov/abs/physics/0510254], which is particularly suitable to study hydrogen under high pressure.
After a brief introduction to the physics of high pressure hydrogen, I will describe the main ingredients of the new method and present results from CEIMC. In particular I will discuss the metallic phase of hydrogen at pressures beyond the molecular dissociation threshold, including the melting of the proton crystal [C. Pierleoni, D.M. Ceperley and M. Holzmann, Phys. Rev. Lett. 93, 146402 (2004)], and the molecular dissociation phenomena in the liquid phase [K. Delaney, C. Pierleoni and D.M. Ceperley, Phys. Rev. Lett. 97, 235702 (2006)].

Liens :Carlo PierleoniDepartment of Physics, University of L'Aquila, Italy

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG 1

Résumé : Lymphnodes play a key role in the development of an appropriate and efficient immune response. Once an pathological entity (Antigen,Ag) is detected inside the host organism it must be presented to specific lymphocytes to trigger, if it is the case, an immune response that gets rid of it. Ag-scanning must be highly efficient: at most in few hours it is necessary to find specific lymphocytes inside a repertoire that includes 106 different receptors. The way Nature organized itself to accomplish this goal represents a charming fine-tuned mechanism, based on a careful balance between diffusion properties, chemotaxis and receptor expression. And the lymphnode is the scene of such mechanisms.
We present a simulator of the human immune system. It was born as the C-version of a program written by P. Seiden and F. Celada (Immunology today, 13,56 (1992)). Today the code is pretty different from the original one and it's able to handle a wide range of immunological phenomena: bacterial infection, cancer growth and viral infection. Our simulator can be seen as a generalization of cellular automata models. Time and space are discrete and the entities can be described in terms of internal states. Each cell is represented as a finite state machine that processes information and changes its state according to the results of the interaction with other cells, coded by probabilistic rules.
The version of the model we present here is customized to reproduce the characteristics of lymph node architecture and the details of the first hours of the immune response. Specific cells diffusion properties are taken into account using hybrid discrete/continuous approach. In particular, simulated lymphocytes, antigens and immunocomplexes are treated as stochastic discrete entities whereas interleukins, chemokines and in general small signalling molecules are described as continuous variables ruled by differential equations. Lymphocytes are endowed with a pool of receptors that make them able to feel the concentration of specific chemokines and move accordingly towards the direction of the increasing gradient (chemotaxis). We investigate the role of chemotaxis and the impact of the different chemokines on the timing of lymphocytes encounters and thus on the efficiency of the resulting immune response.

Liens :Valentina BaldazziINRIA Grenoble

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG1

Résumé : We construct Hubbard-like models with general symmetries and super-symmetries; these models are integrable. Perturbative calculations in the large coupling regime show the connection with Heisenberg-like spin chains. The same regime is interesting in relation to a particular gauge theory in four dimensions. Integrability allows us to evaluate scattering properties and to work out energy eigenvalues. Methods of nonlinear integral equations are used to perform an accurate study of excitations of the antiferromagnetic vacuum.

Liens :Giovanni FeveratiLAPTH (Annecy)

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG 1

Résumé : L'océan est un exemple important de fluides stratifiés, à l'intérieur desquels peuvent se propager des ondes internes de gravité. L'émission et la réflexion de ces ondes sont des mécanismes qu'il est important de comprendre pour expliquer la conversion de l'énergie des marées, ainsi que les processus de mélange observés entre les régions proches des fonds marins et à l'intérieur de l'océan. Ces ondes sont aussi très intéressantes pour le physicien car certaines de leurs propriétés défient notre intuition des phénomènes ondulatoires. Après avoir présenté les propriétés tout à fait inhabituelles de ces ondes ainsi que quelques résultats théoriques que nous avons obtenus, j'illustrerai leurs conséquences à l'aide de plusieurs expériences que nous avons réalisées au laboratoire de Physique de l'ENS Lyon ou à la plateforme Coriolis de Grenoble.

Liens :Thierry DauxoisENS-Lyon

• Séminaire interne LPMMC
• Personne à contacter :
• Salle MAG 1

Résumé : The effects of zero-point fluctuations such as the Van der Waals force or the Casimir force between a plate and a sphere, which is now accurately measured (with the best one is in the Néel lab!), are well known. Recent publications (Feigel, PRL92, 020404) claim that it is possible to transfert momentum from the quantum vacuum fluctuations, to matter and obtain mesurable velocity. We investigate this possibility via the coupling of an electric dipole and the free field in presence of applied crossed fields - to break the symmetries. A semi-classical approach has been done but we need a fully quantum mechanical description to confirm the latest and to validate a future experimental confirmation.

Liens :Sébastien KawkaLPMMC

• Séminaire LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG1

Liens :Institute of applied physics, Chisinau, Moldavie

• Séminaire interne LPMMC
• Personne à contacter :
• Salle MAG 1

Résumé : One of the key questions in the field of nano-mechanical systems is the effect of mechanical motion on the electric properties of the devices. In this presentation, We present the case of a tunnel junction formed between a fixed electrode and an oscillating one. Accumulation of the charge on the junction capacitor induces a force on the nano-mechanical oscillator. The junction is voltage-biased and connected in series with an impedance. We discuss how the picture of Coulomb blockade is modified by the presence of the oscillator. Quantum fluctuations of the mechanical oscillator modify the I-V characteristics particularly in the strong Coulomb blockade limit. We show that the oscillator can be taken into account by a simple modification of the effective impedance of the circuit. We discuss in some details the case of a single inductance and of a constant resistance. With little modifications the theory applies also to incoherent transport in Josephson junctions in the tunneling limit.

Liens :Nicolas PaugetLPMMC

• Séminaire théorie
• Personne à contacter :
• Salle de conférences - Maison des Magistères

Résumé : I present tools and strategies for the control of atomic and molecular processes by external fields, such as laser and cavity fields, with parameters specifically designed to achieve particular goals. Applications to selective population transfer, tunneling effect, alignment of molecules, and quantum information processing are addressed.

Liens :Stéphane GuérinInstitut Carnot, Université de Bourgogne

• Séminaire interne LPMMC
• Personne à contacter :
• Maison des Magistères, salle MAG2

Résumé : In view of upcoming experimental determination of moment of inertia of rotating superfluid fermions at Innsbruck, I want to report on our work on this subject. We use a semiclassical approach to calculate currents and moment of inertia in such systems. A rich structure going from rigid rotation to ideal fluid flow is observed as a function of temperature and/or size of the system. The density profile of the superfluid component is determined. At low temperatures, due to superfluidity, the moment of inertia turns out to be quenched with respect to its rigid body value.

Liens :Peter SchuckLPMMC

• Séminaire interne LPMMC
• Personne à contacter :
• Salle MAG 1

Résumé : We investigate superconductor / insulator / ferromagnet / superconductor (SIFS) tunnel Josephson junctions in the dirty limit, using the quasiclassical theory. We formulate a quantitative model describing the oscillations of critical current as a function of thickness of the ferromagnetic layer and use this model to fit recent experimental data. We also calculate quantitatively the density of states (DOS) in this type of junctions and compare DOS oscillations with those of the critical current.

Liens :Andrey VasenkoLPMMC

• Séminaire LPMMC
• Personne à contacter :
• Salle MAG 1

Résumé : L'éclatement d'une bulle à la surface d'un fluide complexe peut produire des évènements violents, que ce soit la projection de purée ou de sauce lors d'expériences culinaires malheureuses, ou, à plus grande échelle et aux conséquences plus dramatiques, à la projection jusqu'à plusieurs centaines de mètres de fragments de lave, lors d'une éruption volcanique. Les signaux acoustiques émis par l'éclatement de la bulle en surface constituent un moyen non-intrusif (et, dans le cas des volcans, sécurisé) pouvant permettre d'accéder, en cas d'impossibilité de mesure directe, aux propriétés physiques du système. Mais quelles informations peut-on vraiment en tirer ?

Afin de répondre à cette question, je présenterai les résultats d'expériences de laboratoire, mettant en jeu l'explosion, à la surface libre d'un fluide non-newtonien, d'une bulle unique, ou d'une série de bulles générées par un flux d'air constant à la base de la colonne de fluide. Nous montrons que la géométrie particulière de la bulle, due aux propriétés non-newtoniennes du fluide, influence directement le contenu fréquenciel du son émis lors de l'éclatement. La fréquence du signal acoustique est fixée par la longueur de la bulle, présentant un comportement intermédiaire entre un cône et un tube résonnant. L'énergie acoustique libérée dépend de manière critique de la dynamique de rupture du film, et sa mesure n'est donc pas suffisante pour estimer l'énergie totale initialement stockée dans le système. L'analyse acoustique dans le cas d'un flux d'air continu fait apparaître un glissement du contenu fréquenciel au cours du temps, corrélé avec la présence d'un signal précurseur. Enfin, pour un flux d'air constant, on observe, sous certaines conditions, une alternance entre un régime d'émission de bulles isolées, et la formation d'un canal ouvert avec émission continue de gaz. Ces phénomènes se rapprochent des observations de terrain, encore inexpliquées, sur certains volcans tels que le Karymsky (Kamchatka), ou le Stromboli (Italie).

Liens :Valérie VidalENS-Lyon

• Séminaire théorie
• Personne à contacter :
• Maison des Magistères, salle de conférences

Résumé : In contrast with the core (which might consist of color superconducting quark matter) there is a consensus about the basic physics of the outer layers of a neutron star, which form a solid crust whose inner part is permeated by superfluid neutrons, whose local movement (describable in terms of nonrelativistic nuclear physics) relative to the metallic solid lattice can explain the rotation frequency glitches observed in pulsars (whose global description requires a general relativistic treatment).

Liens :Brandon CarterObservatoire de Paris-Meudon

• Séminaire interne LPMMC
• Personne à contacter :
• Salle lecture 2

Résumé : Starting from a quantum two-mode Bose-Hubbard Hamiltonian we determine the ground state properties, momentum distribution and dynamical evolution for a Bose Josephson junction realized by an ultracold Bose gas in a double-well trap. Varying the well asymmetry we identify Mott-like regions of parameters where number fluctuations are suppressed and the interference fringes in the momentum distribution are strongly reduced. We also show how Schroedinger cat states, realized from an initially phase coherent state by a sudden rise of the barrier among the two wells, will give rise to a destructive interference in the time-dependent momentum distribution.

Liens :LPMMC