• Séminaire LPMMC
• Personne à contacter : Nicolas Rougerie ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : Dans cet exposé, on considère le laplacien unidimensionnel agissant sur des fonctions définies sur un graphe métrique. En guise de condition aux sommets, analogue dans ce cadre des conditions au bord, on impose les conditions de Neumann, qui traduisent la conservation du courant à travers les sommets. Pour un graphe de départ donné, on s'autorise à faire varier les longueurs des arêtes tout en conservant la longueur totale du graphe. On cherche ensuite des bornes explicites sur la première valeur propre non nulle de cet opérateur (égale au trou spectral ici) en fonction de paramètres métriques, topologiques et combinatoires du graphe sous-jacent, que l'on souhaite optimales, ainsi que les graphes atteignant les valeurs extrêmes. On résout ainsi complètement le problème du minimum et l'on apporte également des réponses partielles au problème du maximum. On conclut en présentant une conjecture sur la forme générale des maximiseurs. Ce travail a été réalisé en collaboration avec Ram Band, du Technion (Haïfa).

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : Ultracold atom systems are well-controlled and tunable quantum systems, and thereby enable us to explore many-body quantum effects, such as BEC-BCS crossover, or superfluidity. In this talk, I will examine sound-propagation and superfluidity in ultracold quantum gases using analytical and simulation techniques. I will report on the second sound measurements in the BEC-BCS crossover and their theoretical analysis [1]. Here, I will demonstrate that the second sound velocity vanishes at the superfluid-thermal boundary, which is a defining feature of second sound. I will then study sound propagation in a uniform 2D Bose gas across the superfluid-thermal transition, motivated by the recent experiments in the Dalibard group. As a key result, I will show that the sound velocity undergoes a qualitatively different temperature dependence in the critical regime, which occurs due to an interplay between the superfluid and thermal mode [2]. In the second part of this talk, I will investigate superfluidity in ultracold quantum gases via laser stirring. I will present the stirring experiments in the BEC-BCS crossover and provide a quantitative analysis of the onset of dissipation associated with the breakdown of superfluidity [3]. I will then explore superfluidity across the Kosterlitz-Thouless (KT) transition with laser stirring and provide a quantitative understanding of the 2D stirring experiments performed in the Dalibard group [4]. I will also present the noise correlations of the time-of-flight images of 2D clouds and use them to determine the phase coherence of the recent experiments at Hamburg [5].

References

Liens :

• Colloque CPTGA
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Liens :

• Séminaire théorie
• Personne à contacter : Thierry Champel ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : This talk presents an overview of the theory of non-dissipative magnetoelectric effects in superconducting structures with spin-orbit coupling (SOC). I will emphasize a close connection between “classical spin-orbitronics” effects in normal systems and coherent transport phenomena mediated by SOC in superconductors. I start with an introduction to magnetoelectric effects in normal conductors with SOC, and to the standard quasiclassical theory of superconducting structures. By combining ideas from these two fields I will develop a theory of diffusive superconductors in the presence of SOC, and analyze a number of specific magnetoelectric effects. In particular we consider the generation of the long-range triplet condensate, the supercurrent induced spin/triplet accumulation, and the anomalous Josephson effect. We will see that these effects are the direct phase-coherent counterparts of the persistent spin helix, the spin Hall effect, the Edelstein effect, and the spin-galvanic effect, which are known for normal conductors.

References
1. F. S. Bergeret, I. V. Tokatly, Phys. Rev. Lett. 110, 117003 (2013)
2. F. S. Bergeret, I. V. Tokatly, Phys. Rev. B 84, 134517 (2014)
3. F. S. Bergeret, I. V. Tokatly, EPL 110, 57005 (2015)
4. F. Konschelle, I. V. Tokatly, F. S. Bergeret, Phys. Rev. B 92, 125443 (2015)
5. F. S. Bergeret, I. V. Tokatly, Phys. Rev. B 94, 180502 (2016)
6. I. V. Tokatly, Phys. Rev. B 96, 060502(R) (2017)

Liens :Ilya Tokatly

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire LPMMC
• Personne à contacter :
• Lieu : Salle de lecture 2

Résumé :

Liens :Jürgen BergesUniversity of Heidelberg

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Liens :

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : In this talk, I will discuss how interesting features of topological origin in material band structures can be inferred by mapping the particle-hole continuum with spectroscopic probes. I will first highlight some simple geometric characteristics of the particle-hole continuum that arise due to nodal points in the electronic dispersion. These characteristics can be used to infer the presence of Weyl and Dirac nodes both below and above the Fermi level in bulk three-dimensional bands, and can thus serve as identifiers of topological content. I will then argue that resonant inelastic x-ray scattering (RIXS) is an appealing tool for directly accessing and studying the features of the particle-hole continuum of topological semimetals, especially in settings that preclude the use of other probes, such as, e.g., in magnetic fields. Going a step further, I will discuss how polarization-resolved RIXS can be used to visualize the Berry curvature distribution around Weyl nodes. Most importantly, I will show how this method can determine the topological charge of individual Weyl nodes, indicating its potential for a spectroscopic measurement of a quantized topological invariant. I will conclude with a quick overview of ongoing experimental and theoretical work.

Liens :

• Séminaire LPMMC
• Personne à contacter :
• Lieu : Salle de lecture 2

Résumé : We show how the recently developed generalized hydrodynamic theory - an exact hydrodynamic description of the inhomogenous non-equilibrium time evolution of integrable models - has been very efficient to

• a) determine the non-equilibrium steady states emerging from joining two different chains in two different equilibrium states,
• b) provide an exact value of Drude weights of integrable chains, including XXZ and Fermi-Hubbard, for any finite temperature state and also give a rigorous and group-theory related interpretation of ballistic transport at finite temperature,
• c) construct a theory for diffusive transport in integrable models, where two-body scatterings among the quasiparticles completely provide the diffusion terms, namely the Navier-Stokes corrections to the Euler-scale hydrodynamic equations.

Liens :

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : Condensate mixtures consist of two or more different species of identical bosons which undergo Bose-Einstein condensation. In a recent joint work with Alessandro Michelangeli and Phan Thành Nam, we rigorously proved that, for mixtures in the Gross-Pitaevskii regime, the ground state energy is captured by the minimum of a suitable effective functional. We also studied the time-dependent behavior, and proved that the effective dynamics of mixtures is ruled by coupled non-linear Schroedinger equations, one for each species. I will devote the initial part of the talk to introducing the mathematical description of BEC and the main features of the Gross-Pitaevskii scaling limit. Then, prior to presenting our results, I will also recall some important known results on single-species.

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : We reveal several distinct regimes of the relaxation dynamics of a small quantum system coupled to an environment within the plane of the dissipation strength and the reservoir temperature. This is achieved by discriminating between coherent dynamics with damped oscillatory behavior on all time scales, partially coherent behavior being nonmonotonic at intermediate times but monotonic at large ones, and purely monotonic incoherent decay. Surprisingly, elevated temperature can render the system “more coherent” by inducing a transition from the partially coherent to the coherent regime. We furthermore show that non-Markovian memory plays a prominent role in the time evolution after a quantum quench in such systems. This provides a refined view on the relaxation dynamics of open quantum systems.

Liens :

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Liens :

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Salle Lecture 2, maison des Magistères

Résumé : The structure of quantum fluids is nowadays well understood from modern methods of quantum many-body theory, until recently the understanding of dynamic features has been much more limited. For that purpose, we have introduced the concept of dynamic multiparticle fluctuations i.e. processes which describe the dynamics of the short--ranged structure of the liquid. These processes turn out to be essential for the correct description of the dynamics of He-4 and He-3 in 3D. Carrying out the same types of calculations in 2D leads to somewhat surprising results which permit, in He-3, a decisive identification of the relevant physical effects responsible for the energetics of excitations, and may, if experimentally confirmed, illuminate the nature of the ``roton minimum'' in He-4. Practically simultaneously with the theoretical developments, new high precision neutron scattering measurements have been obtained of the group of Henri Godfrin in Grenoble which show the effects of mode-mode coupling with unprecedented accuracy. Theoretical predictions and experimental results are in very satisfactory agreement.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : Nous aurons une discussion sur les différentes questions soulevées lors des journées hors-murs concernant la nomadisation des jeunes docteurs, les perspectives d'emploi etc.

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : We revisit the atom-plate quantum friction and Casimir force with a full-relativistic formalism for atoms modelled as Unruh-deWitt detectors [1] in exited, relaxed and coherent superposition close to a plate [2]. We show that, for relative velocities close to c, the quantum friction diverges while the Casimir force is almost independent of the velocity. We are able to include the effect of the finite size of the detector, then we also obtain quantum friction when the detector is isolated but follows a non-inertial trajectory and we obtain a more realistic result for short distance interactions. Those studies open the venue to understand the role of non-local response in quantum friction. [1] E. Martin-Martinez and P. Rodriguez-Lopez. Relativistic quantum optics: The relativistic invariance of the light-matter interaction models. Phys. Rev. D 97, 105026 (2018) [2] P. Rodriguez-Lopez and E. Martin-Martinez. Casimir Forces and Quantum friction of finite-size atoms in relativistic trajectories. Accepted in Phys. Rev. A

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : Anderson localization was first discovered for electrons in disordered solids but later was shown to take place for various types of waves in disordered media. For three-dimensional (3D) disorder, it takes place only in a restricted band of frequencies, separated from the rest of the spectrum by mobility edges, and only when the disorder is strong enough. Our recent results indicate that the vector nature of waves (microwaves, light, elastic waves) used in the experiments on Anderson localization, plays an important role. In particular, the transverse electromagnetic waves cannot be localized by a random 3D arrangement of resonant point-like scatterers (atoms), whereas the elastic waves, which have a longitudinal component as well, can be localized in a way very similar to scalar waves. However, the localization of light can still be made possible by putting the atoms in a strong external magnetic field. We will present a unified view on Anderson localization and compute the localization phase diagrams and the critical parameters (mobility edges and critical exponents) of Anderson localization transitions for elastic waves and light scattered by atoms in a strong magnetic field. Despite the differences between these two systems, they turn out to belong to the same universality class.

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : The spatial and temporal order of two-dimensional systems with a continuous U(1) symmetry is determined by the dynamics of vortices. At low temperatures, vortices of opposite charge form tightly bound pairs, while they are free to roam and destroy order as the temperature is increased. Interestingly, driving the system out of equilibrium alters the interaction of vortices in a drastic way: Instead of being long-ranged and thus capable of holding together pairs of vortices and anti-vortices in the ordered phase, out of equilibrium the interaction becomes screened, and defects proliferate. Here, we show that the structure of defects and their interaction can equally dramatically be modified by the breaking of rotational symmetry. For sufficiently strong spatial anisotropy, the force that binds pairs of defects can even be enhanced up to parametrically large scales. As a consequence, the vortex-unbinding crossover in such finite-size systems exhibits peculiar universal behavior. In the thermodynamic limit, we argue that the modified structure of defects renders a stable ordered phase possible. These results, which we obtain by analyzing the compact anisotropic Kardar-Parisi-Zhang (caKPZ) equation, are relevant for a wide variety of physical systems, ranging from strongly coupled light-matter quantum systems such as exciton-polaritons, to recently proposed classical time crystals.

Liens :

• Séminaire LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : We clarify the role of "quantum chaos" in the analysis of Bose-Hubbard circuits. Specifically we address themes that are related to thermalization and localization [1], quasi-static sweep processes [2], and meta-stability of condensates [3].

References

Liens :Doron CohenBen Gurion University

• Séminaire interne LPMMC
• Personne à contacter : Anna Minguzzi ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Liens :

• Séminaire LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :Center for quantum technologies

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Résumé : The onset of irreversibility in physics is one of the great questions at the heart of statistical mechanics. The second principle of thermodynamics in essence states that spontaneous processes happen in one direction. In classical physics irreversibility can only happen with some seed of randomness or coarse graining and topological mixing. Since coarse graining and the counting of micro states is arbitrary in classical physics, firmer grounds for statistical mechanics must be found in the quantum domain. At a first glance the quantum case looks even harder. In a closed system evolution is unitary, and therefore the entropy of a quantum state cannot increase. Moreover, unitary evolution is always reversible, so irreversibility is strictly speaking impossible. In classical mechanics irreversibility is due to chaos, that is, high sensitivity to initial conditions. But in quantum mechanics, unitarity implies that slightly different initial conditions do not evolve into highly different states. In this talk we take seriously the idea that the defining feature of quantum mechanics is entanglement. As such, irreversibility must be a consequence of entanglement. As we shall see, it is not the amount of entanglement per se that is important, but its complexity. We show that complexity of entanglement classifies the dynamical behavior of a isolated quantum many-body system and determines its irreversibility and the approach to thermalization.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Résumé : Over the past few years, several experimental platforms from Atomic, Molecular and Optical (AMO) physics have begun to be used as quantum simulators. These are devices where we have excellent microscopic understanding and control – allowing us to write down microscopic models under well-controlled approximations, and to adjust the parameters of these models to explore a wide range of phenomena arising from many-body physics. An important aspect of these systems that is often not widely discussed is that we also have excellent microscopic understanding of the dissipative dynamics of these systems, and means to engineer this dissipation (e.g., via controlled light scattering, or introduction of a reservoir gas). This provides new possibilities to observe the effects of dissipation on many-body dynamics, and also new tools to produce interesting many-body quantum states. I will discuss this, with examples from our recent theoretical work on dissipative engineering of spin-entangled states, and exploration of light scattering and its effects on the dynamics and decoherence of many-body states in optical lattices.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : - Anastasia - Frederick - candidat de Sergey - Théotime

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : Quantum Chromodynamics (QCD) -- the theory of strong nuclear forces -- has baffled the physics community and remains one of the poorly understood parts of the standard model. Its quintessential property: the confinement of quarks into protons, neutrons and mesons, while verified both experimentally and numerically, remains an elusive theoretical problem. The various cousins of QCD are however possible to understand to varying degrees and precision. In some of these theories the vacuum state is degenerate, and hence allows for domain walls -- a surface excitation which interpolates between two vacua of the theory. These domain walls have a remarkable property that quarks become liberated on them, and the domain wall excitation spectrum is very different from that of the bulk. Such QCD cousins are, unfortunately, not the physical theory, and they do not occur in nature. QCD however has another unlikely cousin: the Valence Bond Solid (VBS) state of the quantum anti-ferromagnet, where spin 1/2 excitations (or spinons) are bound into spin 1 excitations by a mechanism very similar to confinement of quarks. Perhaps surprisingly the low energy theory describing the behavior of the VBS phase is virtually identical to its QCD cousins under certain conditions. Further the VBS phase may have multiple vacua, and thus support domain walls, which in turn support liberated spinon excitations absent in the bulk. This has been verified numerically in the so-called J-Q model. These domain wall modes can in fact be seen as edge modes akin to those of the symmetry protected topological state. A multidisciplinary effort is slowly emerging to understand such phenomena, from the theoretical aspects of fundamental and condensed matter physics, to the numerical efforts in trying to understand QCD and quantum magnets.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : The study of strongly correlated quantum systems is one of the most interesting and intriguing research field in physics. The framework of ultracold gases in optical lattices allows to explore equilibrium and non-equilibrium properties of such systems. One example is the Tonks-Girardeau (TG) gas, in which the infinite repulsive delta- like interaction mimics the Pauli exclusion principle and is reflected into the well known mapping to non-interacting fermions. While local quantities are identical to the fermionic case, all non local ones, like correlations or momentum distribution, are significally different. We develop a powerful method to study the spectral function of the TG gas by using only single particle orbitals, and apply it to inspect the behaviour of ultracold gases in a periodic lattice with hard-wall confining. Moreover, the efficient implementation of the one body green’s functions provide an instrument to investigate energy and mass transport in periodic media and quasicrystals via the scheme of non equilibrium green’s functions.

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Markus Holzmann ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : We study the interaction between two quantum systems (A and B) that is mediated by their common linear environment. If the environment is out of equilibrium the resulting interaction violates Onsager relations and cannot be described by a Hamiltonian. In simple terms the action of system A on system B does not necessarily produce a back action. We derive general quantum equations describing the situation and analyze in details their classical correspondence. Changing the properties of the environment one can easily change and engineer the resulting interaction. It is tempting to use this for quantum manipulation of the systems. However the resulting quantum gate is not always unitary and may induce a loss of quantum coherence. For a relevant example we consider systems A and B to be spins of arbitrary values and arrange the interaction to realize an analogue of the two-qubit CNOT gate. The direction of spin A controls the rotation of spin B while spin A is not rotated experiencing no back-action from spin B. We solve the quantum dynamics equations and analyze the purity of the resulting density matrix. The resulting purity essentially depends on the initial states of the systems. We attempt to find a universal characteristics of the purity optimizing it for the worst choice of initial states. For both spins s_A=s_B=1/2, the optimized purity is bounded by 1/2 irrespective of the details of the gate. We also study in detail the semiclassical limit of large spins. In this case the optimized purity is bounded by (1 et Ï€/2)^-1 ≈ 0.39. This is much better than the typical purity of a large spin state ∼ s^-1. We conclude that although the quantum manipulation without back-action inevitably causes decoherence of the quantum states the actual purity of the resulting state can be optimized and made relatively high.

Liens :Vincent MichalQutech - TU Delft

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Colloque CPTGA
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Liens :

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Résumé : Resonant inelastic X-ray scattering (RIXS) is a relatively new technique for probing low energy excitations in materials. In addition to traditional techniques, such as angle resolved photoemission, it has become an important, high precision characterization tool of strongly correlated electron materials. To calculate RIXS, and related core and valence level spectra, we solve the Bethe-Salpeter equation (BSE) based on a self-energy corrected density functional theory electronic structure. I outline our implementation of the BSE and use SrVO3 for demonstration. Non fluorescence features in RIXS arise from a dynamic response of the system to the intermediate state perturbation. Since the Bethe-Salpeter equation is typically reduced to the static limit in practice, these dynamic excitations are generally not reproduced. To include interactions beyond the static BSE I introduce the cumulant expansion. Spectral functions derived from a GW self-energy are typically inadequate when the dressed Green’s function is built via the Dyson equation. With the same GW self-energy, a superior Green’s function and spectral function, implicitly including vertex corrections, is obtained through the cumulant expansion. I consider application of cumulant spectral functions to photoemission, photoabsorption, and X-ray scattering. Lastly, vibronic coupling has important impacts on these spectra. I show how to calculation the phonon contribution to photoemission, absorption and scattering with a vibronic cumulant.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :ILL, LPMMC

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Résumé : One of the simplest examples of nonequilibrium dynamics varying in the presence of a conservation law is the coarsening process of the kinetic Ising model, whose exponent changes from 1/2 to 1/3 if the magnetization is conserved. We start showing that this difference may be strongly enhanced by increasing the interaction range of the ferromagnetic coupling, which determines a speed-up in nonconserved coarsening while it almost freezes conserved coarsening [1]. Conserved quantities are also relevant to obtain a condensation-like transition in non interacting systems: we will discuss the relaxation process of a simple model, which may be considered as a rough approximation of the Discrete Nonlinear Schroedinger Equation [2], whose dynamics is actually much, much slower. [1] Federico Corberi, Eugenio Lippiello and Paolo Politi Effective mobility and diffusivity in coarsening processes EPL 119, 26005 (2017) [2] Stefano Iubini, Antonio Politi and Paolo Politi Relaxation and coarsening of weakly-interacting breathers in a simplified DNLS chain J. Stat. Mech.: Theory and Experiments, 073201 (2017)

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Résumé : The Kitaev honeycomb model is one of the few exactly solvable models with a spin liquid ground state. Here I will discuss the dynamics of an initial antiferromagnetic state time evolved with the Kitaev model. I find a dynamic crossover to a valence bond solid. When the spin interactions are anisotropic, an exponentially long prethermalized regime appears. Reference: arXiv:1710.09761

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Résumé : By virtue of emergent gauge fields in quantum impurity problems, we demonstrate that in experimentally realized regime the angulon, a quantum rotor dressed by bosonic excitations, can be seen as a point charge on a two-sphere interacting with a gauge field of non-Abelian monopole. We find a topological transition associated with making the monopole Abelian, which takes place in the vicinity of the previously reported angulon instabilities. Furthermore, we show that identical impurities interacting with a two dimensional many-particle environment obey anyonic statistics. In particular, we find that due to the many-body interactions between impurities and the bath, each of the impurities can be viewed as a flux-tube-charged-particle composite described by fractional statistics. This amounts to a novel configuration with emerging anyons, which is fundamentally different from the previously studied fractional quantum Hall and Kitaev model settings.

Liens :

• Séminaire LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : We study the Josephson oscillations of two strongly correlated one-dimensional bosonic clouds separated by a localized barrier. Using a quantum-Langevin approach and the exact Tonks-Girardeau solution in the impenetrable-boson limit, we determine the dynamical evolution of the particle-number imbalance, displaying an effective damping of the Josephson oscillations which depends on barrier height, interaction strength and temperature. We show that the damping originates from the quantum and thermal fluctuations intrinsically present in the strongly correlated gas. Thanks to the density-phase duality of the model, the same results apply to particle-current oscillations in a one-dimensional ring where a weak barrier couples different angular momentum states.

Liens :LPMMC

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : Consider quantum dots (or other nanostructures) which can convert a heat flow into electrical power, or can use power to move heat from a cold reservoir to a hot one. Do such systems obey the same laws of thermodynamics as macroscopic heat engines? How does one get the second law of thermodynamics when the Schrodinger equation is invariant under time-reversal? What approximations can one make on the dynamics without unphysical violations of the laws of thermodynamics? I consider these questions in the context of a real-time Keldysh theory of transport for a nanostructure coupled to reservoirs of electrons and phonons, with particular interest in the difficult case of strong system-reservoir coupling. I explicitly formulate how our lack of information leads to entropy production with what I call a "no Maxwell demons" assumption. I then show that a simple microscopic symmetry in the Feynman diagrams enables one to show that the first and second law of thermodynamics are obeyed on average, but that fluctuations violate them. I show that these fluctuations obey a variety of fluctuation theorems (Jarzynski equality, Crooks equation, etc). Finally I mention the well-known approximations that satisfy this symmetry, and thus will not lead to unphysical thermodynamics.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire théorie
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Annulé
Annulation des vols à Florence à cause de la neige

Liens :

• Colloque CPTGA
• Personne à contacter :
• Lieu : Amphithéâtre, maison des Magistères

Résumé : Interactions between atoms often introduce large amounts of complexity into many-particle systems, but they can also lead to new and interesting physical regimes. In this presentation I will discuss several examples of interacting ultra cold atomic systems, where tuneable interactions allow to access new dynamical situations or create new control techniques. The first example will be taken from our efforts towards a full set of techniques to coherently control the external state of small samples of ultracold atoms using spatial adiabatic passage, and in the second an increased interaction in a multicomponent BEC system is shown to lead to emergence of classical behaviour in a fully quantum mechanical system.

Liens :

• Séminaire théorie
• Personne à contacter : Serge Florens ()
• Lieu : Amphithéâtre, maison des Magistères

Résumé : Recent experiments on one-dimensional and two-dimensional materials have been very successful in realizing topological states of electrons, with one of ultimate goals being the creation of emergent Majorana particles. Such emergent particles can have fractional charge, spin, and/or quantum statistics, so they are interesting both fundamentally and for quantum computing applications, but remain hard to realize. We will discuss the use of topological defects as a way to realize fractional particles. By combining analytic and numerical approaches we predict Majorana particles, having favorable energetic properties, in certain vortices of two-dimensional superconductors. Our predictions fully explain puzzling features of recent experiments at INSP Jussieu. We will also focus on lattice dislocations in topological insulators as realizations of more complex fractional particles. General properties of fractionalized particles and open questions will also be discussed.

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : We explore static and dynamical properties of fermionic and hardcore bosonic cold atomic gas trapped by the combination of two potentials (bichromatic lattice) with incommensurate periods. Firstly we study the effect of the metal to insulator transition, and the presence of a mobility edge, into many-body measurable quantities, such as the momentum distribution. Then we study the long time dynamics of the gas, subject to a quantum quench, by looking at both single particle and global quantities, namely the single particle Green's function and the Loschmidt echo. In the case of a periodic lattice we show that the asymptotic dynamics manifests the Anderson Orthogonality Catastrophe (AOC) and we find a general analytic expression for the power law exponent which is then compared with our numerical results. On the other hand in the case of an incommensurate potential, which shows a mtal-to-insulator transition, we observe the suppression of the AOC and an anomalous spreading of correlations as the transition point is approached. We discuss these results from the point of view of the nature of the single particle energy spectrum and show that these anomalous features come from the particular geometry of the system.

Liens :

• Séminaire théorie
• Personne à contacter :
• Lieu : Salle de lecture 2, maison des Magistères

Résumé : Describing and understanding the motion of quantum gases out of equilibrium is a tremendous challenge for theorists. In 2006, the groundbreaking Quantum Newton Cradle experiment [1], where it was observed that two 1d clouds of cold atoms bounce against each other indefinitely without relaxation, provided impetus for many developments on the effects of low dimensionality in out-of-equilibrium quantum physics. But it is only thanks to the breakthrough of « Generalized HydroDynamics (GHD) » in 2016 [2] that one now possesses the adequate tools for an effective large-scale description of that experiment [3]. The purpose of this talk will be to give an introduction to those recent theoretical advances. Refs: [1] Kinoshita, Wenger and Weiss, Nature 440, 900, 2006 [2] Castro-Alvaredo, Doyon and Yoshimura, PRX 6, 041065, 2016 and Bertini, Collura, de Nardis and Fagotti, PRL 117, 207201, 2016 [3] Caux, Doyon, Dubail, Konik, Yoshimura, arXiv:1711.00873

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire interne LPMMC
• Personne à contacter : Vincent Rossetto ()
• Lieu : Salle de lecture 2, maison des Magistères

Liens :LPMMC

• Séminaire interne LPMMC
• Personne à contacter : Denis Basko ()
• Lieu : Salle Rémi Lemaire K223

Liens :