Séminaires de l’année 2009

16 décembre à 14h30 Séminaire du LPTMS
Pavel Grigoriev (Institut Landau)
Properties of superconductivity on the density wave background.
We investigate the properties and the microscopic structure of superconductivity (SC), coexisting and sharing the common conducting band with density wave (DW). Such coexistence may take place when the nesting of the Fermi surface (FS) is not perfect. Then in the DW state some quasiparticle states remain on the Fermi level and lead to the Cooper instability. The soliton band in the DW state also leads to the Copper instability. The dispersion of the quasiparticles on the Fermi level in the DW state strongly differs from that without DW if the nesting is almost perfect, and so do the properties of SC on the DW background. The upper critical field Hc2 in such a SC state increases as the system approaches the critical pressure, where the ungapped quasiparticle states and superconductivity just appear. This upper critical field may considerably exceed the usual Hc2 value without DW. The SDW background strongly suppresses the singlet SC pairing, while it does not affect so much the triplet SC transition temperature. The results obtained may explain some experimental observations in layered organic metals (TMTSF)2PF6 and a-(BEDT-TTF)2KHg(SCN)4, where SC appears in the DW states under pressure and shows many unusual properties.
[1]. L.P. Gor'kov, P.D. Grigoriev, " Nature of superconducting state in the new phase in (TMTSF)2PF6 under pressure.", Phys. Rev. B 75, 020507 (2007).
[2]. P.D. Grigoriev, “Properties of superconductivity on the density wave background with small ungapped Fermi surface pockets”, Phys. Rev. B 77, 224508 (2008).
[3]. P.D.Grigoriev, “Superconductivity on the density-wave background with soliton-wallstructure”, PhysicaB 404, 513–516 (2009).
15 décembre à 11h Séminaire du LPTMS
Mohammed Rajabpour (Université de Turin)
Ashkin-Teller model on the iso-radial graphs
Ashkin-Teller model as a spin system with a rich phase diagram is interesting as a lab for investigating many different ideas in two dimensional statistical mechanics such as renormalization group, conformal field theory and Schramm Loewner evolution. In this talk we will define AT on the iso-radial graphs and we will discuss the different features of the critical line of the model on the different lattices. We will also stress on the mathematical importance of iso-radial graphs and the concept of the universality.
8 décembre à 11h Séminaire du LPTMS
Valeri Shikin (Institute for Solis State Physics, Chernogolovka)
Delta-percolation and Quantum Hall Effect
We define a particular type of percolation phenomena which deserves the name “delta-percolation” for its peak-like appearance. One common systems demonstrating the delta-percolation behavior is the 2D electron (hole) system in the high magnetic field. We discuss behavior of extended states, whose appearance within the “sea” of electronic orbits localized by the random potential is the necessary condition for appearance of the integer Quantum Hall Effect (QHE). We consider observable consequences of the suggested interpretation of properties of extended states in the theory of integer QHE.
3 décembre à 11h Séminaire "Systèmes complexes et Physique biologique" du LPTMS
Jure Dobnikar (Department of Chemistry, University of Cambridge and Jozef Stefan Institute, Ljubljana, Slovenia)
Field-induced self-assembly of suspended colloidal membranes
We report experiments that probe self-assembly of micrometer-size colloids into one-particle-thick, robust, and self-healing membranes. In a magic-angle precessing magnetic field, superparamagnetic spheres experience isotropic pair attraction similar to the van der Waals force between atoms. But the many-body polarization interactions among them steer an ordered aggregation pathway consisting of growth of short chains, cross-linking and network formation, network coarsening, and consolidation of membrane patches. We theoretically explain membrane stability, their elastic and self-healing properties and the observed aggregation pathway. This generic scenario can be induced in any particles of large enough susceptibility.
1er décembre à 11h Séminaire du LPTMS
Dmitry Kovrizhin (Rudolf Peirels Centre for Theoretical Physics , Oxford University)
Phase transitions and nonequilibrium dynamics of quantum Hall states from cold atoms to semiconductor nanostructures. Novel methods and applications.
I will talk about recently developed methods to study phase transitions in quantum Hall systems and dynamics of IQHE edge states on examples of Bose-Einstein condensates under extreme rotation and electronic interferometers far from equilibrium. I will give an overview of application of the Density Matrix Renormalization group (DMRG) to systems of fast rotating bosons and present results of the calculations for various geometries. Then I will discuss recent experiments on interferometry and spectroscopy of IQHE edge states in semiconductor nanostructures and show how these systems can be studied using a new analytical method based on bosonization. I will present details of the calculations on an example of exactly solved model for electronic Mach-Zehnder interferometers.
[1] D. L. Kovrizhin and J. T. Chalker, Phys. Rev. B 80, 161306(R) (2009)
[2] D. L. Kovrizhin, arXiv:0909.3693
[3] S. I. Matveenko, D. Kovrizhin, S. Ouvry, G. V. Shlyapnikov, arXiv:0908.2172
17 novembre à 11h Séminaire du LPTMS
Pierpaolo Vivo (ICTP, Trieste)
Phase transitions in the quantum conductance problem
Linear statistics on ensembles of random matrices occur frequently in many applications. We present a general method to compute probability distributions of linear statistics for large matrix size N. This is applied to the calculation of conductance and shot noise for ballistic scattering in chaotic cavities, in the limit of large number of open channels. The method is based on a mapping to a Coulomb gas problem in Laplace space, displaying phase transitions as the Laplace parameter is varied. As a consequence, the sought distribution displays a central Gaussian region flanked on both sides by non-Gaussian tails, and weak non-analytical points at the junction of the two regimes.
3 novembre à 11h Séminaire du LPTMS
Mikhail Zvonarev (LPTMS)
Spectral properties of one-dimensional quantum liquids
I will report on a theoretical progress in understanding the spectral properties of one-dimensional quantum liquids. While for small energy and momentum transferred the spectral properties are explained (with notably exceptions) by the Luttinger model, their description at arbitrary energy/momentum remained an open problem until very recently. The situation changed in the last three years, and at present there exist several theories explaining the spectral properties of 1D systems away from the Luttinger Liquid regime. I will discuss these theories and open questions.
27 octobre à 11h Séminaire du LPTMS
Martin Lenz (Institut Curie, Université Paris 6)
Polymerization and mechanochemical action of dynamin
Living organisms are fundamentally open systems, which continuously exchange matter with their surroundings. Dynamin is used by cells to split membrane compartments apart during such exchanges. Recruitment and assembly Dynamin polymerizes around membrane nanotubes into long (~10 µm) helical polymers. Membrane elasticity imposes a critical radius for dynamin polymerization, which could trigger its recruitment in vivo. Surprising facts about the nucleation and growth of the helix yield information about dynamin assembly and interactions with the membrane. Mechanochemical action and severing Using the energy from GTP hydrolysis, dynamin polymers twist, constrict and pull on the membrane, and thus eventually sever it. Combining experiments and a generalized hydrodynamics description, we show that the dynamin helix changes conformation as one rigid body, suggesting that mechanical stresses induce its breakage. We predict its dynamics and account for seemingly contradictory experimental results. Our formalism is a powerful tool for further investigations about dynamin's membrane severing action.
13 octobre à 11h Séminaire du LPTMS
Michel Ferrero (École Polytechnique)
Nodal/antinodal dichotomy in cuprate superconductors: a valence-bond dynamical mean-field approach
The selective destruction of coherent quasiparticle excitations in the "antinodal" region of momentum-space is a striking property of the normal state of underdoped cuprate superconductors, and a key challenge for theory. In this talk, I will review a recent attempt to understand this phenomenon from a minimal cluster extension of the dynamical mean-field theory, based on a valence bond self-consistently embedded in a effective medium. I will show that the destruction of quasiparticles at the antinodes, the opening of a pseudogap, and the formation of Fermi arcs, can be viewed as an orbital-selective Mott transition in momentum-space. Comparison to tunneling and angular-resolved photoemission experimental data will be discussed.
6 octobre à 11h Séminaire du LPTMS
Evgeny Burovskiy (LPTMS)
Multi-particle composites in density-imbalanced quantum fluids
We consider two-component one-dimensional quantum gases with density imbalance. While generically such fluids are two-component Luttinger liquids, we show that if the ratio of the densities is a rational number, p/q, and mass asymmetry between components is sufficiently strong, one of the two eigenmodes acquires a gap. The gapped phase corresponds to (algebraic) ordering of (p+q)-particle composites. In particular, for attractive mixtures, this implies that the superconducting correlations are destroyed. We illustrate our predictions by numerical simulations of the fermionic Hubbard model with hopping asymmetry. ( Mostly based on: EB, Guiliano Orso, and Thierry Jolicoeur, arXiv:0904.0569 and arXiv:0907.1533 )
29 septembre à 11h Séminaire du LPTMS
Lev Shchur (Landau Institute for THeoretical Physics, Chernogolovka, Russia)
Phase diagram for diffusion limited aggregation growth in two dimensions
We present results of the intensive simulations and careful analysis of the diffusion-limited aggregation (DLA) model in two dimensions. We use previously developed the off-lattice killing-free algorithm for the cluster generation and the method of variable size probing particles for the cluster analysis. We generate clusters with the $m$-fold symmetry of sticking directions and with different values of the noise reduction parameter $n$. We propose the phase diagram in the plane $(m,n)$ with the two regimes of the DLA cluster growth. Clusters in the first regime are fractal crystals with the well defined $m$-fold symmetry and with the value of the asymptotic fractal dimension $D=3/2$. Clusters in the second regime are the random fractals with $D=1.710\ldots$. The global direction of the cluster axes changes by the angle $180/m$ at the critical line.
22 septembre à 11h Séminaire du LPTMS
Guilhem Semerjian (ENS, Paris)
Le modèle de Bose-Hubbard sur le réseau de Bethe
Les modèles de physique statistique définis sur les réseaux de Bethe admettent habituellement une solution exacte, qui s'obtient à partir de la résolution d'une équation de récursion. Dans le cas de modèles de spins classiques (Ising ou Potts par exemple) cette équation est d'une nature relativement simple, et cette approche peut être étendu, sous le nom de méthode de la cavité, pour traiter des modèles avec du désordre gelé, voire de la frustration et des propriétés vitreuses. Dans ce séminaire je discuterai une autre direction plus récente de généralisation de la méthode, pour des modèles quantiques, i.e. spins 1/2 en champ transverse et modèles de bosons sur réseau. Dans ce cas on peut aussi obtenir une équation de récursion dont la solution décrit les propriétés thermodynamiques du modèle ; elle est toutefois un peu plus compliquée que dans le cas classique, mais peut être résolue numériquement avec une précision arbitraire. Le réseau de Bethe étant une implémentation de l'approximation de Bethe pour les modèles de dimension finie, on comparera aussi, sur l'exemple du modèle de Bose-Hubbard, les prédictions ainsi obtenues avec d'autres traitements de ce modèle en dimension finie.
15 septembre à 11h Séminaire du LPTMS
Evgeny Kozik (University of Massachussetts)
Diagrammatic Monte Carlo for correlated fermions
We show that Monte Carlo sampling of the Feynman diagrammatic series (DiagMC) can be used for tackling hard fermionic quantum many-body problems in the thermodynamic limit by presenting accurate results for the repulsive Hubbard model in the correlated Fermi liquid regime. Using perturbative Feynman diagrams (rather than skeleton, or "bold-line", graphs) for the single-particle self-energy we can study moderate values of the onsite repulsion (U/t ~ 4) and temperatures down to T/t = 1/40. We compare our results with high temperature series expansion and with single-site and cluster dynamical mean-field theory. We find that going from single site to large clusters is essential for obtaining the same level of accuracy as provided by DiagMC.
30 juin à 11h Séminaire du LPTMS
Boris Altshuler (Columbia University)
Insulating State of Disordered Superconducting Films and Josephson Arrays
I will remain main concepts of the Superconductor-Insulator transition in disordered films and discuss basic properties of the insulating state of these systems. Recent experiments on charge transport in highly resistive films of superconducting materials revealed quite unexpected behavior of these systems: Ahrrenius law in temperature dependence of conductivity accompanied with low temperature anomalies. More recently bistabilities that leads to huge jumps in the resistivity were observed in nonlinear transport. We will see that an assumption that electronic system is overheated with respect to phonons provides natural quantitative description of these singularities. Overheating of the electrons in an insulator is remarkable because it is not compatible with the conventional models on phonon-assisted transport. It looks like most of existing experimental results can be understood at least qualitatively on the basis of the many-body localization concept. I will discuss these theoretical predictions, its relevance to experiments and open problems in this field.
26 juin à 11h30 Séminaire du LPTMS : Physique Biologique
Roberto Mulet (Physics Faculty, University of Havana)
Estimating the size of the solution space of metabolic networks
Cellular metabolism is one of the most investigated system of biological interactions. While the topological nature of individual réactions and pathways in the network is quite well understood there is still a lack of comprehension regarding the global functional behavior of the system. In the last few years flux-balance analysis (FBA) has been the most successful and widely used technique for studying metabolism at system level. This method strongly relies on the hypothesis that the organism maximizes an objective function. However only under very specific biological conditions the cell seems to obey such optimization law. A more refined analysis not assuming extremization remains an elusive task for large metabolic systems due to algorithmic limitations. In this work we propose a novel algorithmic strategy that provides an efficient characterization of the whole set of stable fluxes compatible with the metabolic constraints. The algorithm, based on the well-known Bethe approximation, can be used to approximately compute the volume of a non full-dimensional convex polytope in high dimensions. We first compare the accuracy of the predictions with an exact algorithm on small random metabolic networks. We also verify that the prédictions of the algorithm match closely those of Monte Carlo based methods in the case of the Red Blood Cell metabolic network. Then we test the effect of gene knock-outs on the size of the solution space in the case of {\it E-Coli} central metabolism. Finally we analyze the statistical properties of the average fluxes of the reactions in the {\it E-Coli} metabolic network.
23 juin à 11h Séminaire du LPTMS
Cyril Petitjean (University Regensburg)
A semiclassical approach to the ac-conductance of quantum chaotic cavities
Due to progress in the control and manipulation of mesoscopic structures driven by high frequency periodic voltages, the ac regime has recently been experimentally investigated [1] and consequently theoretical interest in it has been renewed. We consider a quantum chaotic cavity that is coupled via tunnel barriers and gates to a macroscopic circuit which contains ac-sources. For the transparent barrier, our semiclassical techniques permit us to include the Ehrenfest time in the weak-localization correction to the screened conductance, previously obtain by the random matrix theory [2]. Then by extending the recent semiclassical theory in presence of tunnel barriers [3] to the ac-transport, we investigate the effect of dephasing on the relaxation resistance of a chaotic capacitor in the linear low frequency regime. This last investigation is in principle rrelevant to the recent measurements of the admittance at zero magnetic flux of a mesoscopic capacitor [1,4].
Works in collaboration with D.Waltner, J.Kuipers,I.Adagideli and K.Richter
See eprint : arXiv:0906.1791v1.
[1] J. Gabelli et al., Science {\bf 313}, 499 (2006).
[2] P.W.~Brouwer and M.~B\"uttiker, Europhys. Lett. {\bf 37}, 441 (1997).
[3] R.S.~Whitney, Phys. Rev. {\bf B, 75}, 235404 (2007).
[4] S.~Nigg and M.~B\"uttiker, Phys. Rev. {\bf B 77}, 085312 (2008).
17 juin à 11h Séminaire du LPTMS
Ennio Arimondo (Université de Pise)
BEC in temporally modulated optical lattices
16 juin à 11h Séminaire du LPTMS
Tommaso Roscilde (ENS Lyon)
Dynamical emergence of supersolidity in asymmetric boson mixtures in an optical lattice
Supersolidity - the simultaneous appearance of Bose condensation and crystalline order in a degenerate system of bosons - is a long-sought and elusive phenomenon in condensed matter. Cold-atom realizations of a supersolid can be envisioned in optical lattices, in which spontaneous crystallization of atoms occurs in presence of finite-range or long-range interactions, or in the case of interactions mediated by a secondary atomic species. In this talk we will theoretically discuss how (quasi-)condensation an emerge dynamically in a mixture of two hardcore boson species with mass and number imbalance in a one-dimensional optical lattice. Starting from a "molecular crystal" of trimers (made of two heavy and one light particle) and suddenly changing the Hamiltonian of the system, we observe that (quasi-)condensation appears in both atomic species without disrupting the crystalline order imprinted in the system. An extensive study of the ground state phase diagram of this model shows that this supersolid state has no equilibrium counterpart. This suggests the intriguing possibility of engineering novel many-body states via a controlled collective quantum evolution in cold-atom systems.
9 juin à 11h Séminaire du LPTMS
Dragi Karevski (Université de Nancy)
Quantum Non-Equilibrium Steady States Induced by Repeated Interactions
We study the steady state properties of a finite XX chain coupled at its boundaries to quantum reservoirs. The reservoirs are made of free spins that interact one after the other with the boundary sites of the chain. We show that the dynamical equations governing the time evolution of the two-point correlation matrix are of Lindblad type in the continuous interaction limit. Under XY coupling with the reservoir spins, the steady state correlations are calculated exactly. It is shown that the relevant physical quantities characterizing completely the steady state are the magnetization profile and the associated current. Except at the boundary sites, the magnetization is equal to the average of the reservoirs magnetizations. The steady state current, proportional to the difference in the reservoirs magnetizations, shows a non-monotonous behavior with respect to the system-reservoir coupling strength, with an optimal current state for a finite value of the coupling. Finally, the steady state density matrix is shown to be of generalized Gibbs form. At small current linear irreversible thermodynamics predictions are recovered.
2 juin à 11h Séminaire du LPTMS
Dimitri Gangardt (University of Birmingham)
Mobile impurities in 1D quantum liquids: Bloch oscillations and dissipation

Dynamical properties of impurity particles immersed in a 1D quantum liquid are strongly modified by the interactions. The collective nature of the excitations manifests itself in periodic dispersion typical for lattices and may lead to Bloch oscillations. Experiments with ultracold atoms are currently underway to observe this phenomenon. At the same time the quantum and thermal fluctuations always present in quantum liquids provide a mechanism for dissipation and lead to viscous friction force acting on the moving impurity. A naïve estimate shows that typically the dissipation is rather large and may prevent observation of Bloch oscillations. We evaluate viscosity in terms of the quantum fluid parameters and show how the dissipation is drastically suppressed for nearly integrable systems due to quantum interference.

20 Mai à 15h Séminaire du LPTMS, Physique biologique
Jorge V. José (Physics Dep., Physiology and Biophysics, University of Buffalo)
Non-equilibrium biophysical model of self-organized spindle formation

In eukaryotic cells, separation of duplicated chromosomes is done via the mitotic spindle. The mitotic spindle is a regular structure within a cell consisting of oriented microtubule fibers. Forming a spindle pattern is a major structural step towards cell division or mitosis. We have developed biophysical non-equilibrium thermodynamic models to describe in vitro chromosome driven spindle formation experiments in Xenopus extracts. Our first 2D model calculations [1] successfully described the order of events seen in some of the Xenopus extracts experiments, where the chromosomes are replaced by chromatin-covered micrometer magnetic beads. I will describe more realistic 3D improvements in our modeling analysis, which include microtubule contact forces and excluded volume [2, 3]. There are, however, a number of challenges that must be addressed for spindle modeling to continue to be a useful tool for understanding this fundamental biological process. In this talk I will describe some important problems needing better biological date and hypothesis, as well as using random graph analysis to better characterize spindle geometric patterns.

[1] S. C. Schaffner and J. V. José, PNAS, 103, 11166 (2006), [2] ibid in “Methods in Cell Biology” (Elsevier-Academic Press) (2008) and [3] ibid (to be published).

18 Mai à 14h30 Séminaire du LPTMS
Alexei Tsvelik (Brookhaven National Laboratory)
Visual demonstration of the spinon confinement in quasi-1D spin ladder: CaCu2O3
CaCu2O3 is a quasi-1D antiferromagnetic insulator. Its magnetic subsystem can be well described as formed by weakly coupled pairs of spin-1/2 chains (spin ladders). The peculiar fact about CaCu2O3 is that the exchange interaction on rangs of the ladders is much smaller than the interaction along the chains. This allows to observe a crossover from the regime of independent chains dominated by spin-1/2 excitations (spinons) to the strong coupling low energy regime regime with S=0 and S=1 excitations. I present the experimental data and discuss their relation to the theory.
13 Mai à 14h30 Séminaire du LPTMS
Alessio Recati (University of Muenchen and Trento INFM BEC Center)
Unitary polarized Fermi gas under adiabatic rotation
We discuss the effect of an adiabatic rotation on the phase separation between the superfluid and normal component of a trapped polarized Fermi gas at unitarity and zero temperature, under the assumption that quantized vortices are not formed. We show that the Chandrasekhar-Clogston limit n_down/n_up characterizing the local polarization in the normal phase at the interface is enhanced by the rotation as a consequence of the centrifugal effect. The density profiles (local and column integral) of the two spin species are calculated as a function of the angular velocity for different values of the polarization. The critical value of the angular velocity at which the superfluid exhibits a spontaneous quadrupole deformation is also calculated for the unpolarized case.
12 Mai à 11h Séminaire du LPTMS
Luigi Cantini (LPTENS)
Magic in the ground state of the dense O(1) loop model
The interplay between statistical mechanics and combinatorics has always been of great interest both for physicists and for mathematician. The observations of Razumov and Stroganov, that the properly normalized components of the ground state of the dense O(1) model enumerate classes of alternating sign matrices, is an instance of such an interplay. The boundary conditions on the O(1) model are re?ected on the symmetries of the FPL. After giving a general overview on the problem and its ramifications, we present some recent progress in the analytical construction of the ground state of the O(1) model on a strip, with the most general boundary conditions.
6 Mai à 16h Séminaire du LPTMS, Physique biologique
William Bialek (Princeton University)
Physics problems in early embryonic development
One of the most beautiful phenomena in nature is the emergence of a fully formed, highly structured organism from a single, undifferentiated cell, the fertilized egg. Over the past decades, biologists have shown that in many cases the « blueprint » for the body is laid out with surprising speed and is readable as variations in the concentration of particular molecules (the expression levels of particular genes). In this lecture I’ll give a brief review of this biological background, and then show how, as we try to make quantitative sense out of this qualitative picture, we encounter a number of interesting physics problems: How can spatial patterns in the concentration of these molecules scale with the size of the egg. What insures that the spatial patterns are reproducible from one embryo to the next? Since the concentrations of all the relevant molecules are small, does the random behavior of individual molecules set a limit to the precision with which patterns can be constructed? Has nature found strategies to minimize the impact of this noise and maximize the flow of information through the system? I will try to give not just a formulation of these problems, but also report on recent progress toward solutions, which has involved considerable exchange between theory and experiment.
5 Mai à 11h Séminaire du LPTMS
Christophe Texier (LPTMS)
Diffusion classique unidimensionnelle dans un champ de force aléatoire en présence de sites absorbants.
One-dimensional model of classical diffusion in a random force field with a weak concentration $\rho$ of absorbers is studied. The force field is taken as a Gaussian white noise with $\mean{\phi(x)}=0$ and $\mean{\phi(x)\phi(x')}=g\,\delta(x-x')$. Our analysis relies on the relation between the Fokker-Planck operator and a quantum Hamiltonian in which absorption leads to breaking of supersymmetry. Using a Lifshits argument, it is shown that the average return probability is a power law $\smean{P(x,t|x,0)}\sim{}t^{-\sqrt{2\rho/g}}$ (to be compared with the usual Lifshits exponential decay $\exp{-(\rho^2t)^{1/3}}$ in the absence of the random force field). The localisation properties of the underlying quantum Hamiltonian are discussed as well.
28 Avril à 11h Séminaire du LPTMS
Julien Vidal (LPTMC)
Anyons, fermions, et ordre topologique dans un système de spins 1/2: le modèle de Kitaev
En 1977, Leinaas et Myrheim [1] suggéraient l'existence de statistiques quantiques différentes de celles de Bose-Einstein et de Fermi-Dirac. Quelques décennies plus tard, les particules obéissant à ces statistiques, les anyons, n'ont toujours pas été observées expérimentalement. Le modèle de Kitaev [2] qui décrit des spin 1/2 en interaction sur réseau hexagonal est sans aucun doute un des meilleurs candidats à la detection de tels objets. En effet, le spectre de ce système contient des excitations anyoniques, abéliennes et non-abéliennes, intimement liées à l'ordre topologique sous-jacent. Ces anyons sont localisés dans l'espace ce qui permet d'envisager simplement les manipulations indispensables à la mise en évidence expérimentale de leur statistiques [3]. Cependant, le spectre contient également des excitations fermioniques susceptibles de polluer les processus de détection. Je présenterai une analyse perturbative de ce modèle autour de la limite de dimères isolés permettant de comprendre les problèmes liées à la coexistence de ces deux types de particules, anyons et fermions, au sein d'un même spectre [4].

[1] J. M. Leinaas et J. Myrheim, Nuovo Cimento Soc. Ital. Fis. B 37, 1 (1977). [2] A. Kitaev, Ann. Phys. 321, 2 (2006). [3] L. Jiang et al., Nature Physics 4, 482, (2008). [4] J. Vidal, K. P. Schmidt et S. Dusuel, Phys. Rev. Lett. 100, 177204 (2008).

15 Avril à 14h30 Séminaire du LPTMS
Kris Van Houcke (Ghent University)
Diagrammatic Monte Carlo: towards an exact solution for strongly correlated fermions
Diagrammatic Monte-Carlo (DiagMC) is an exact technique that allows one to simulate quantities specified in terms of diagrammatic expansions, the latter being a standard tool of many-body quantum statistics. The sign problem, that is typically fatal to Monte-Carlo approaches, appears to be manageable with DiagMC. We introduce a general DiagMC scheme for strongly interacting fermions. As an illustrative example, we discuss the application of DiagMC to the Fermi-Hubbard model, and benchmark the technique against state-of-the-art numerical tools for strongly correlated fermions. In addition, we discuss the thermodynamic properties of a Fermi gas at unitarity, obtained through DiagMC simulation.
14 Avril à 11h Séminaire du LPTMS
Christian Hagendorf (LPTENS)
The winding of loop-erased random walks
The geometry of random planar objects such as boundaries of spin clusters or random walks can often be studied in terms of conformal mappings taking them into some reference shape. The growth of these objects then leads to a random evolution of the mapping, which is often easier to analyse than the originial process. One of the simplest growth processes is given by Schramm-Loewner evolutions (SLE), which provide a description of random curves and interfaces in statistical mechanics models. This talk will focus on the SLE description of planar loop erased random walks (LERWs). It will outline how to study its winding and passage properties via SLE computations, and contrast them to the case of simple random walks. In particular, it will be explained how LERWs on doubly connected domains can surprisingly be related to a solvable diffusion-advection problem for the Burgers equation in (1+1)-dimensions.
07 Avril à 14h Séminaire du LPTMS
David Feder (LPTMS et Université de Calgary)
Can ground states of low-dimensional spin systems be useful for quantum computation?
In measurement-based quantum computation (MBQC), quantum algorithms are performed solely by making sequential measurements of qubits in a suitably entangled state. The main advantage of this approach is that it is not necessary to perform any entangling operations, which are often difficult to implement in experiments. Ideally, this entangled 'universal resource' state would be the (strongly correlated) non-degenerate ground state of some simple spin Hamiltonian on a lattice, preferably in low dimensions. I will describe a set of simple criteria that can be used to determine if a given state is indeed a universal resource for MBQC, and suggest possible candidate Hamiltonians.
07 Avril à 11h Séminaire du LPTMS
Benoit Estienne (LPTHE, Paris)
Parafermionic conformal field theories
Conformal field theory is a very powerful tool to describe critical statistical systems in two dimensions. Many lattice models, such as the Ising model, the 3-states Potts model or the Ashkin-Teller model, enjoy a discrete ZN symmetry. Such systems are described by parafermionic conformal field theories, and the additional symmetries are encoded in a set of chiral fields with fractional spins called parafermions. After reviewing the general properties of this class of CTFs and the corresponding lattice models, I will present some recent results about the second parafermionic field theory.
03 Avril à 11h30 Séminaire du LPTMS, Physique Biologique
Christophe Sola (IGEPE,Institut de Génétique et microbiologie, Orsay)
Transforming raw genetic data into knowledge. Infectious diseases transmission dynamics : the tuberculosis paradigm
The study of infectious diseases history can be reconstructed by genetic means, whereas the surveillance, control and prevention of outbreak extensions could also be predicted using adequate data and models. We will concentrate on a disease as old as human kind : tuberculosis, as a model of a global infectious disease. We will review the state of the art knowledge on the history of this disease and will present some recent data that suggest that studies combining new formal and new experimental approaches could allow to boost our knowledge on human-bacilli interactions and their consequences on population structures and history.
01 Avril à 14h30 Séminaire du LPTMS
Mauro Antezza (LKB, ENS)
Atom-Light Elementary Excitations in a Periodic Ensemble of Ultracold Atoms
We derive the excitation spectrum for light coupled to atoms in an optical lattice, close to a 0 -> 1 atomic transition, for the branches that are mainly of atomic nature. We explicitly include the quantum atomic motion, which leads to remarkable features such as a finite lifetime of the elementary excitations and their energy dependence with the lattice depth, that will show up in a real experiment as we discuss. It also makes the theory naturally divergence-free and resolves a controversy for the occurrence of a spectral gap.
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25td>31 Mars à 14h30Vicond Gy nrqmscati (UniversitColois uffalo)ons. ngle-parte of geneonstration ofL a su-Z of ction prories
4td>31 Mars à 11hNigD mCoal pscati (UniversitCambridgntb" old theory natura>Mauro AnteCgly correlPh disesitAtum ate of G dises up Rthe rresLcal lattice
Séminaire du LPTMS
Séminaire du LPTMS
0td>31 Mars à 14h30oodon-asa powrve obéistenc qumeilltug="rv ré: is spowrn suetbetween limirnilli interact con Bcy;">Cheories
Séminaire du LPTMS, Physique Biologique
ChristDeroAltsmodeMNClogie, falo)
Cheecéi difudises exand instMarmit p AMarzrais spoinsuiprocesn reme ceo Ciul currac qumeiesu Ae undian inspee corrimprovtsome impoarmipace ceero crom tin t populat ofurbioloorurhau resisey thatoologispee chutisequesexperie ce sgrauanteuea mit populaty;">Ceéatohe pont avcphénomèraiCheeuses. Danes ale=erriags on êon Butisssd'utists. A tin tte apprtivmodon-asmific,od'a0%;"isés tis,cbsn the si,iqu on tstest posssu Ae un qumeillbetne dima gimte équadualobreiwevent sssd on elems,incluces t de comprendcphénomèraiing cxace ' sugs àe obéisteein céisiltug="rv réetiMarnies ion alqui od'amon-aorpolluer conteasuremeuermetrk we prautounauvmaux.Aprèso tin. We inttemenaucphénomèraimhe praletiique biolose cevhowsu atomspHo,ewsu af a tin-Toreme c modeux typeponnbservées expérimeanyons Marns io transinnes uscopt-Toreme c uant-us tis,zraigéstivmodon-asmifict con n suce de crnne dimannbservottsques différeplcoipecbjetin ae,ewsu anntinuou difss-Toremnies . Jeclocaxperiées influexistenrnilli interactdtubule con con Bcyrly oes,cy;">Cheee ceilli vt Est recenuce dephénomèrasussi, a mit populatis,cy;">Cheecéi difudis. Grâceiéein d ce mod the breiction sur réoy a dimionsssi, a bte phionélmioniées exnsequeribe in vs tatxand ilementponnbservribe vo adplcoaoarminntinms a -Toreme c cnrnilli interactdtubule coninfluexiscurracmit popul. Grâceiéein also c ( tte apé)ttion la lihydrthermodech,snntinhits arg-Toreme c cnowrn on areser arnsocoplconsequeées uesh de tto a macroconbjets. In par barrce,zraigiagmèraisantibe echronétl' and hèste rèso supiesuet est dical diffudedblad brownd>Jutis,cy;">Cheecéi difudis. R to echnimubéis,ve de ce mode oc mteetbetfa pert dfate e ttio"e ce moueée and ciistudie Génés100ibetwennuscrit dJecllobreicttion dpMS, Physd dephénomèrasue incesvered.Rés diffcysiqb-aondom Physrintx: ar812.4708 (ique y suppecenucP biophysRill reE)well.
17td>31 Mars à 11hVadim CheiStrogaati (UniversitLéian clLPTMSO;" beground statedilun dadcold-atom syvribndom enattice
Séminaire du LPTMS
ZdzisowerBurda,ysic Inmomponen the thsitesng cx Such syloPue bnatticeLeak-localizaturt xn opt conopyimple randomAtoms
31 Mars à 14h30 Séminent. Eimensinaire du LPS ce sysscoing cxaeories
n cosverandthis clasmple randomrowth proceion, w and maxi conopyaints. t xn opt conopyimple randomation iivalrovtwcte of iabaple randomatf thatlso mre rees up is a regical lattems,that it isiies of the underl the latiss ris a rewalks. In particuwed. We consid the latsion woutbdilunpul. med. We show thats excit>Uniturn probabionce os wind ngle-party to peeresmnxn opt conopyimple randomaweak-loetterns iny distd for nesm ereciversgstration of the latsng, whicence-atedeal eraints. weak-localizathis phenopping, whicp, Nimat of classmena in nricesl be explasity in terms ofsual Lizround stateag="rly obmple raanck ope2008).
1td>31 Mars à 14h30Lon asesggaati (UniversitAlb"rly,Luigadcb" old theory natura>Mauro Antezy hthe oites IndSthe superiveAtoms10td>31 Mars à 11hIsrasinKliof, ati (UniversitVire oriLPTMSics.Ehis entmompoEconopyisitFted fermions
Séminaire du LPTMS
Séminaire du LPTMS
6td>31 Mars à 14h30JtheactiClubnaire du LPTMSF bioMonccioliLPSISSA , TrqmctatticeFlol curKrzakala & Lenka Zde0%;ovy,Lonal LabminPCT, ESPCI ; LANL,LoostAlamoeoriesTandSlar strucsitized Geady StbynGfof yhMetitFral fiPion prories
Non-equilibetic-rmal field thecuieules gence-nionorm walks
Dynameobe critndom behatate of d corted bynamic mofree aintera-ical diffuowth procurTandrenersolitage of this approacallyWrtplabyinhheevie and she relaence withe of generalL a sun the thsits no equilibrobe critiful phenoelanionorm bants.
We dis We shisethat can be useity, o ical" ovi formalian ruseun ainhe>
3td>31 Mars à 11hBe a bthll prcentrationder (Lhll arof sexesquantwell.
Séminaire du LPTMS
Das, teits sPiotr DeuaTexier (LPTMS)
0tFévrip AMars à 14h30JohaélieBir natEPE,InstituTMS, Phy, FreiburggiqueScal statistvant pch h make quantitaique by:oirs. Tg formulatioe of (the exprewalks17tFévrip AMars à 11hPasthisté dabhll , Di. In vo CimdiItaleoloEcricotFted ,MS et UniversitPisogiqueQd a quaq of Muoblemseak encatom sywalks
Séminaire du LPTMS, Physique Biologique
Séminaire du LPTMS
11tFévrip AMars à 14h30 urlaizedp fiPenneady ati (UniveLPTMSPant pchther ctum atcs sknamibeyohenntow tlifeiss tation?
Séminaire du LPTMS
10tFévrip AMars à 11hGrsge thS Muhr,re dlogie, falo)Fver v exntanndomeappearn of rasign xn the th:nd ngtrsirmn int this appwalks
Séminaire du LPTMS
We pplicatioe in thnenteracplay bet="rly obr oc consanti exntanndomeapptersn of rasign xn the t.eBis prisels, I uanalys. ttis medel are calcis an lyte of y gn b evolution of txn opthefor lssetti exntanndomeappther chmparedense, unas well.
06tFévrip AMars à 14h30LearcombiNionorm ,cver ique By 197arcombiique By,cver Nionorm walks
Séminaire du LPTMS, Physique Biologique
Woggius,isic InmomponenAthe relPhnt pchchmpAthe relMfor mathes,iCand bia ati (UniveLPTMS
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03tFévrip AMars à 11hPiein vFnccioliLPDi. In vo CimdiItaleoloatorI.N.F.N.,MS et Univordeglitwebe mdiITl cuoLPTMS oLechemiRaintera Pa tas allemTthe lo w-Aprrvediomic transecsseBio-Mant molewalks
Séminaire du LPTMS
0 Janvip AMars à 11hTung-Lam Dao,iCPHT, EcolrgPolyrthe techLPTMSPoc ofzcca the superiveiiiew on ous exesisBose-Hubbard mther t on populaimbarveilwalks
Séminaire du LPTMS
The sa.s i-cfnps exp of a F the s iher ctus exesisange interacndata y undiffnt on populpelues ofs inties .sow up cubdrmical lattFperatsange ions melight mappiece osedeed o pela vec ofzcca the superping, whicly blewdis showis a ld alero temperpstate. phe qua y gn b evolution i c mal pice, lyLhll mvarhahown oues ofSaew c mal ,l has exerertcribe wo of a F u interaints. mal psrix is showften bistoediated vet sequenheir enque losisw up BCSa the super,Works nd contared with nvec ofzccas de Bose-Eins ann coe' stng, whicly bistoediategs magnheir e. medk ll pre the genpits args that summa frattice, perfopémtterns in nvec ofzcca the superpfarerts on tabistogestratioc vec ofzcca the superp mal well.
7 Janvip AMars à 11hOlivip AGiraud,re dloToupntaogiqueQd a quaagMC simulatat t rm ith ctiying quaatom sywalks21 Janvip AMars5à 11hG oesomisiqveioni, ICTP, TrqmctatticeFlésty gn b evolutio tiabol atoionorm walks
Séminaire du LPTMS
Séminaire du LPTMS, Physique Biologique
We pplicatioe inflésty gn b evolutio tiabol atoionorm the evie )foclyte ofte adyw the state ofrsinteracpeavyi )frest tandte adyw the state ofrsinteracpeavysent ptamneonstration ofehivasrocTusction prordeo be prrngce inflésty gn b evolutory caian toms ispin Hamiltotion prorde ofttd of varhmDy undiffns in statistical mechaical technihifecb betsniim, bools pher gis ofs inhics pro:piecalsoyusrrencs ofGh a Gas wihe apional symmmrvoe'z tomo adc disease ecalsoys iseic expatice, closcuscbobe crititwo-poolso be prrngce inbobe critexps expssisigatee theac diseTuscbe spinfun atppehow thatflésty gn b evolut beysscis a -owerice, clos ptamritnhivasrrye int relaence exps expssisof indepenocus ondegnce- y gn b evolution ofoionormocTusctibe prediis a -owerexps expeiss agncemompoence iieaglicotagMC simulseencfupx-barveil- Our analems,iy und cd asigateenece osement in experimered.
20 Janvip AMars à 11h I en interacbn a eatopeted tranhhe ftso;" begrd-wifea the annuisd sh:nd >The stude. Hogened a univivei=ate clwalks
Séminaire du LPTMS
The sfroms s (localizatcal propertf ftso;" begrd-wifea the annuisd shbyh ticsionceted feiabaihe apisymmk ttis m,s">We ma fromwn a effecicalsi formiThma-bard mersyn tod bynical dive as ahmiAcco;"modelincusc tin presenc="rly obonal symmetrs scuscrn gndencvingtiveivet sequeodons, ch providely lntia
14 Janvip AMars à 14h30BarbamisCapoge a o-Sicsenec(Harv-Hubati (UniveLPTMS)Std -AlakeacrrngcI en interacMons mediivenfor str-Cgly correlLcal laas dfermions
Séminaire du LPTMS
Wecrosencbody quahh disory.
13 Janvip A200914h30Sabtd>MHigry.iFeder (L- Ryukokubati (UniveLPTp>/dp>Gh n-bce siRoésxier (LPTp>/dp>Raoul Sn ady.iamisxier (LPTMS)S Wrt thll prpplicatiohll arof sexesqueLPTMSWenif a a be a bwill dpplicatioesi,orcuiversa arof sexesqueiwell.
Séminaire du LPTMS
6tJanvip AMars à 11hMa deslfGhrcivide Sbinrsxier (LPTMS) id="qummkpheung= Hd allowir, we du LPat Ethe elerc JteeactuLPat Pye lniffns iffLPat "baca" ce uable stns ilay:ns estFtedçaisSémil/sed>Sémil-wi- ofnee-2009/s hreflang="ens sate stE stish"ea a
Séminaire du LPTMS
Sémis id="em-les a st-101"ia << O dt2017 >> /td> /td> 25 26 27 28 29 30 1 /td> 2 3 4 5 6 7 8 /td> 9 10 11 12 13 14 15 /td> 16 17 18 19 20 21 22 /td> 23 24 25 26 27 28 29 /td> 30 31 1 2 3 4 5 /td> /tr> High for s» GeoN symmrves and interasy obo tf-te cmvard this biologatom sy onétlaon la lisomeséeiottsda relaxomputmllye oconbjetsl’sthe QC), naucs nd ôlewd’unncmicitpaIn pareioiégéeiottsd depiinspelptaechnrriases ed» Elnal erA tinrelaxomputmrapd> oethe in dicro-atom sys < Inn rfttlyeedracbaInn wodhifec.ppres t> » Amesoonopicucoulisstrpeluedivec od de–Bose-Eins ann coe' tterns in n a universgsse SeefoIt high for sOpbetPo transs on), quawierpelueulus e iracold . Dr. MikhgiagZvolecevits sProf. H.C. Naeg nitano;"mooneew on tojhisnocus onFrof MechmpAu gn an s pri, retiestrimfestics. [1] supowesthe apmpoenIt norm t [&h deip;]">» < the s>der (LPostdoc:LPostdoctl Llcto transisn lowf low-dimenscbody quanuch sys(ield t),t2ry, appfunded <: Martin Lenz 01 69 15 32 62 S tf-àed oocalizas. kethimit toas a fun,tagse ma ="0" –nems,e ofzlifs goeapihe s!cessAlzhelifr’s.data lna e theadsueas.se noe lo wtuolon elica-Einn thtanelump epri Cimta tis biologfib u-likeuaggrsghe rocWhl » < the s>der (LPhDsProe pns:LE argffcyrangfib unatomtrudemonedbo tf-te cmvay » < the s>der (LPoste:LMaîoninituCnonéiffcysA2018o/ Athian it k wf suorcto trans The sfromngly p oytefmllye (localizadata lna-many-s s (localizaernepesibody quanuch systs aoits no equilib h aulnal Laansience A. R a oseTusc[&h deip;]">» < the s>der (LPostdoc:LCann contiMfote oTthe t <:Olivip AGIRAUD 0169153175 Réluméa: raed quaw of infoiznowth prrngctisdse osginowtmsues tatew cre didstfnp domputrit twer, e nmunrccalizatest probaidations,N syue ByseAa ljoreconimpact xi ane ptatistrsa arof erns inrmal ehsiseill , baserdepe"ju mappQC), qju mappons,ufor understandie body quarsa resStfrattene> » < the s>der (LPhDsProe pns:LEhis entmompoCTFs coor d thll prpplicatiobody quanund s <: Raoul Sn ady.iamis06 07 84 92 22iTrome of raowth procefratton-degeneonic confoenerd of o-poith ctidetattaterdenglamoupresome impisternsceexis. Uted uonic confomaotdemopaical techn, thhic tojhissLaimettomt os winrandtfic conformal field pping, wcspe fers onreoN symmpact xsemseak encaeta.">» < the s>der (LPhDsProe pns:LCnic confomaotdemopaa grouochis drmleoN sym » < the s>der (LPostdoc:LTrse ptatistB u mnt pc <: Thierry Jtlico(ur 01 69 15 70 29 L'e aet HoIt ased tech f interaSémi (EHQF)00ibetcthnunitul fp bioPhysd deethe eleanbi low-dimend masntanehamprzero maechnires tattcaea lnifintpiottsda of infoiznitulaec prisd'ethe eleanthll prppreun gopaethe tcun cd as sd'ethe excitsnaucs nd émina'unncmheade-Fted o;"moomi. Decicmbhlux0nia ss nc e e oeedratt[&h deip;]">» < the s>der (LPhDsProe pns:L EThe sd deqd sengle-pmole dans l’e aet HoIt ased tech f interaSémi a niesi(urt ctnpssed s <: Véio technTerrCis01 69 15 78 83 raed quaw ndgre> » < the s>der (LPhDsProe pns:LSic IpplicagraV of varhsdataCthe correl Fs a fun agraraed quaI ndgre> » < the s>20th O dobp A2017 :LPost-doctl Llcto transisn cent sceexis @ENSrPa su « Lare reaCmai A2018 » » < the s>16th O dobp A2017 :LPostdoch h aprrve afote o–eOx and » < the s>16th O dobp A2017 :LPostdoch h aprrve afote o–eOx and SeefoIt epesy ms Paleen of s oweaIFRAF IhPE,InsrPaules LABEXe«aPALM »LPat Links oweaCNRS der (LL Bo der (LWiki ati (UniversPa su SudLPat a aVidéoeairvanddidi : Leuboalirrfased tech (exd étudedda sé iatLaubo imsnbmi) Vidéoeairvanddidi : Asl’ (ur sd decoldes ovesds Vidéoeairvanddidi : Jetn Rou, wctn arge... id="foot"> a dial LabminituTMS, PhysThéor Physit M ce moueScal staechn " ce uaBân vo Ce100 - 15 ruetGlàeoueClémexisau91405gie, oCEDEXFRANCEsec bleof .lptms@lptms.u-psud.fr Work < ce t ce ua+33 (0)1 69 15 73 49 < ce t  Fax < ce t ce ua+33 (0)1 69 15 65 25 < ce t /* */ < l dpp jQnrry.noCnicl at(); jQnrry(docs arg).r ady(as a fun(){= jQnrry("#nav-sea fun,rli").mntiecros(as a fun () {= jQnrry(t s.).t poy ms('li').childrpn('ul').css('ns ilay','ns e'); jQnrry(t s.).childrpn('ul').css('ns ilay','be ck').css('backrate g','eted tadiffnurl(/wp-s ndo C/or mns/viins C/imagns/bg.png)snb-re tat -90px -140px'); }); }); < l dpp/d