There should be no remaining doubt regarding the validity of the Renormalization-Group theory, which stands as one of the pillars of modern physics. However, finite-size scaling theory, which is derived from it, remains unclear above the upper critical dimension dc. There, the violation of the hyperscaling relation is an example of how dangerous is the irrelevant variable of the self interaction φ4 term above dc. Such phenomena make the correlation length to play a pivotal role and it can be shown that it scales as a non-trivial power of the linear system size. This relaxation allows us to fix the break down in the finite-size scaling and hyperscaling, through a modified scheme. We investigate this scaling behaviour in low dimensional Ising ferromagnets with long-range interactions both with free and periodic boundaries. Additionally, we discuss the role played by the Fourier modes and we show that the current phenomenological picture is not supported for all thermodynamic observables.
 Thursday, 26th of May 2016 at 10:30, [SLIDES] Yaroslav Lutsyshyn, Quantum Monte Carlo study of
Mg-doped bulk helium-4 at zero temperature
, University of Rostock
Mg-doped helium droplets are believed to have an observable metastable state in which the alkali atoms remain separated by a considerable distance, thus forming so-called “atomic foam”. The exact nature of such a state is not well understood. I will describe our efforts to study the confinement-induced long-distance interaction between a pair of Mg atoms suspended in the superfluid.
 Wednesday, 16th of March 2016 at 11:30, [SLIDES] Carlos Lobo, Atoms in quadrupole traps:
some puzzling results from recent experiments, Mathematical Sciences,
University of Southampton, UK
Recent experiments in the group of C. Salomon (ENS-Paris) have shown some interesting behaviour for a classical gas of almost _non-interacting_ atoms trapped in a quadrupole potential, namely that when give a momentum kick to a 3D gas with very weak collision rate, it seems not to react along transverse directions, even though the quadrupole potential is not separable. Indeed the trajectories of individual atoms are highly complex but the gas as a whole seems to preserve a memory of the direction of the kick for very long (perhaps infinite) time. I will discuss the origin of the phenomenon and other issues related to classical irreversibility in the gas kinetics. An additional twist comes from considering a canonical transformation which maps the system onto that of a gas of Weyl fermions. This allows us to make nontrivial statements about the long term dynamics of these exotic particles in harmonic traps.
 Wednesday, 2nd of March 2015 at 11:30, [SLIDES] Petar Stipanović, Universality of quantum halo states, Faculty of Science,
University of Split,
The results of the recent research in quantum halo systems will be presented. Ground state of weakly bound systems consisting of few particles with a radius extending well into the classically forbidden region is explored, with the goal to test the universality of quantum halo states.
The focus of the study are clusters consisting of T↓, D↓, 3He, 4He and alkali atoms, where interaction between particles is much better known than in the case of nuclei, which are traditional examples of quantum halos. The study of realistic systems is supplemented by model calculations in order to analyze how low-energy properties depend on the interaction potential. The use of variational and diffusion Monte Carlo methods enabled very precise calculation of both size and binding energy of the trimers and tetramers.
Using dimensionless measures of the binding energy and cluster size, studied atomic clusters are compared to other known halos in different fields of physics. Characteristic scaling lengths, which make size-energy ratio to be universal, are selected. In the quantum halo regime, and for large values of scaled binding energies, all dimers and trimers follow almost the same universal line. As the scaled binding energy decreases, tango type trimers separate from Borromean type. Research is extended to tetramers. Furthermore, the structural properties of different trimers are compared with recently published experimental results obtained by Coulomb explosion imaging of diffracted clusters.
 Tuesday, 16th of February 2015 at 11:30, [SLIDES] Eduard Matito, Harmonium atom as a calibration
and development tool in DFT, Ikerbasque, Donostia International Physics Center (DIPC) and Kimika Fakultatea. Euskal Herriko
Unibertsitatea (UPV/EHU), 20018 Donostia, Spain
The construction of energy functionals in DFT is a complicated task because there are very few conditions known about the exact functional and they are diffcult to impose in functional expressions. Despite these difficulties in the last years quite many functionals have been put forward, broadening the choice of methods in computational chemistry. In this regard, new theoretical models to explore and calibrate the existing zoo of functionals and construct new expressions are required. Harmonium atom is a model system that replaces the usual electron-nuclear attraction by a harmonic interaction tuned with the confinement parameter strength (ω). The model is realistic as far as the electron correlation is concerned and presents a continuous transit from weak electron-correlation regimes (large ω) to strong-correlation regimes (small ω), thus being a formidable test bed for density functional methods. In this talk, several popular density functionals will be analyzed in the two lowest-lying energy states of three-electron harmonium atom. None of the functionals tested (including a wide variety of LDA, GGAs, meta-GGAs and range-separated functionals) are accurate in the whole range ω values, failing short in the description of the weak correlation limit. Finally, it is shown that new hybridized functional expressions can remedy this pitfall attaining ten μ-hartree accuracy for the whole range of confinement strength values.
 E. Matito and J. Cioslowski, in preparation.
 E. Matito, J. Cioslowski and S. Vyboishchikov, Phys. Chem. Chem. Phys. 12, 6712 (2010); J. Cioslowski and E. Matito, J. Chem. Theory Comput. 7 915 (2011)
 J. Cioslowski, K. Strasburger and E. Matito, J. Chem. Phys. 136 194112 (2012); ibid 141 044128 (2014)
 Wednesday, 3rd of February 2015 at 11:30, [SLIDES] Guillem Ferré, Phase diagram of a quantum Coulomb wire, Departament de Fisica, Universitat Politècnica de Catalunya
The quantum phase diagram of a one-dimensional Coulomb wire is obtained using the path-integral Monte Carlo method. The exact knowledge of the nodal points of this system permits us to find the energy in an exact way, solving the sign problem which spoils fermionic calculations in higher dimensions. The results obtained allow for the determination of the stability domain, in terms of density and temperature, of the one-dimensional Wigner crystal. At low temperatures, the quantum wire reaches the quantum-degenerate regime, which is also described by the diffusion Monte Carlo method. Increasing the temperature, the system transforms to a classical Boltzmann gas, which we simulate using classical Monte Carlo. At large enough density, we identify a one-dimensional ideal Fermi gas which remains quantum up to higher temperatures than in two-and three-dimensional electron gases. The obtained phase diagram and the energetic and structural properties of this system are relevant to experiments with electrons in quantum wires and to Coulomb ions in one-dimensional confinement.
 G. Ferré, G. E. Astrakharchik, and J. Boronat Phys. Rev. B 92, 245305 (2015)
 2nd of December 2015, [SLIDES] Alessio Recati, INO-CNR BEC Center and Dipartimento di Fisica, Università di Trento, 38123 Povo, Italy and Technische Universität München, James-Franck-Strasse 1, 85748 Garching, Germany
 15th of October 2015 , [SLIDES] Boris A. Malomed, Bright solitons from defocusing nonlinearities in optical and matter-wave media, Department of Physical Electronics, School of Electrical Engineering,
Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel
The talk aims to give a review of recently obtained results which demonstrate that defocusing cubic media with a spatially inhomogeneous nonlinearity, whose strength increases rapidly enough toward the periphery (faster than r^D in the D-dimensional space, D = 1,2,3, where r is the radial coordinate), give rise to stable solitons (self-trapped localized modes) in all three dimension. These are one-dimensional (1D) fundamental and multihump solitons, 2D dipoles and quadrupoles, including spinning ones, and vortex solitons with an arbitrary topological charge in 2D, and vortex tori (soliton gyroscopes and Hopfions, i.e., intrinsically twisted tori with two independent topological numbers) in 3D. Solitons maintain their coherence in the state of motion, oscillating in the effective nonlinear trapping potential as robust objects. The 3D vortex tori exhibit stable precession and rotation, induced by the application of external torque. In addition to numerically found soliton families, particular solutions can be obtained in an exact analytical form, and accurate analytical approximations are available for the entire families, based on variational and Thomas-Fermi methods. Essentially the same mechanism for the self-trapping of bright solitons under the action of the spatially growing repulsive nonlinearity works in nonlocal media, and in discrete systems too, including the corresponding version of the quantum Bose-Hubbard model. Spontaneous symmetry breaking of the solitons in the 1D and 2D local-nonlinearity modulation profiles with the double-wall structure has been found too. Furthermore, numerical and analytical results demonstrate the existence of stable solitons in a PT-symmetric extension of the 1D model, and of stable dissipative solitons in media combining a uniform linear gain and nonlinear loss whose local strength grows toward the periphery faster than r^D. Such 1D and 2D settings can be implemented both in nonlinear optics and Bose-Einstein condensates (BEC), while the 3D setting may be created in BEC.
 R. Driben, Y. V. Kartashov, B. A. Malomed, T. Meier, and L. Torner, "Soliton gyroscopes in media with spatially growing repulsive nonlinearity", Phys. Rev. Lett. 112, 020404 (2014)
 R. Driben, Y. Kartashov, B. A. Malomed, T. Meier, and L. Torner, "Three-dimensional hybrid vortex solitons", New J. Phys. 16, 063035 (2014)
 Y. V. Kartashov, B. A. Malomed, Y. Shnir, and L. Torner, "Twisted toroidal vortex-solitons in inhomogeneous media with repulsive nonlinearity", Phys. Rev. Lett. 113, 264101 (2014).
 R. Driben, T. Meier, and B. A. Malomed, "Creation of vortices by torque in multidimensional media with inhomogeneous defocusing nonlinearity", Sci. Rep. 5, 9420 (2015)
 R. Driben, N. Dror, B. Malomed, and T. Meier, "Multipoles and vortex multiplets in multidimensional media with inhomogeneous defocusing nonlinearity", New J. Phys. 17, 083043 (2015).
 14th of October 2015 , [SLIDES] Jean Kormann, 3D Elastic Full Waveform Inversion: Toward Reflection Based Inversion, Department of Computer Applications in Science and Engineering (CASE) Barcelona Supercomputing Center (BSC)
Full Waveform Inversion (FWI) is one of the most challenging procedures to obtain quantitative information of the subsurface. On land seismic surveys, obtaining information from the recorded seismograms requires a full elastic approach. This shortcoming has been reduced as high-performance computing makes 3D elastic FWI more affordable. However, there is still a key issue for overcoming its computational burden and mitigate the requirement of having long-offset data. Here we introduce a Dynamic Offset Control, that is a data selection method for adapting the longer receiver offset to the current inverted frequency. We exemplify our approach through 2D and 3D synthetics, and afterwards, the algorithm was used to invert a real line from a 3D high resolution seismic reflection dataset acquired to image a shallow subsurface. This high resolution dataset images a 500x500 m block located in the Zancara river basin (Spain). The study area is characterized by a relatively heterogeneous geology revealed by the borehole data available and features topographic variations on the order of a few meters. As it is a very shallow target, free-surface effects and topography are critical issues which the code needs to handle appropriately. The obtained 3D velocity models were contrasted with other geophysical data available.
 16th of September 2015, [SLIDES] Vladimir A. Yurovsky, "Abandoned symmetry", Tel Aviv University
First applications of the group-theoretical methods in quantum mechanics in works by Wigner, Heitler, and Dirac in 1926-1929 were devoted to the permutation symmetry. A general interest to this topic was lost after the discovery of the Pauli exclusion principle, which allows only permutation-symmetric or antisymmetric wavefunctions for bosons or fermions, respectively, and forbids non-Abelian irreducible representations of the symmetric group, where a wavefunction is transformed to a linear combination of several wavefunctions in the representation. Such representations can appear in physical systems with spinor and spatial degrees of freedom. In the talk I analyze the selection rules and conservation lows, related to the permutation symmetry, as well as the states of spinor gases, where the permutation symmetry properties are pronounced.
 3rd of July, [SLIDES] Alfredo Vidal Arias, "Quantum description of one-dimensional hydrogen" (TGF thesis directed by Gregory Astrakharchik and Jordi Boronat), Universitat Politècnica de Catalunya
 3rd of July, [SLIDES] Juan Sanchez Baena, Microscopic Description of Confined Bosonic Dipolar Quantum Gases in 2 Dimensions (TFG thesis directed by Ferran Mazzanti and Jordi Boronat), Universitat Politècnica de Catalunya
 3rd of July, [SLIDES] Aleix Gimenez Grau, "Dynamics of Many-Body Quantum Systems" (TFG thesis directed by Ferran Mazzanti), Universitat Politècnica de Catalunya
 Thursday, 27th of November 2014 at 16:00, [SLIDES] Andrii Gudyma, Quantum impurity in one-dimensional Bose gas, Université Paris-Sud, Laboratoire de Physique Théorique et Modèles Statistiques, UMR CNRS 8626, Orsay, F-91405, France
The problem of polaron in a one-dimensional Bose gas at ultralow temperature is addressed. When a single impurity moves in a background of interacting particles, its effective mass changes compared to the bare mass. We study how the effective mass depends on the interaction between the impurity and background. Diffusion Monte Carlo method is used in order to calculate the diffusion coefficient of the impurity in imaginary time.
We study system properties under the same conditions as in Florence experiment . The interaction between impurities (K atoms) and the bath (Rb atoms) were controlled by Feshbach and confinement-induced resonances. We find out that zero-temperature predictions agree with the experimental results. This has to be contrasted to the theory proposed in , in which the coupling constant had to be artificially corrected by a factor of 3.15.
We obtain the polaron mass both for repulsion and attraction with the bath. We explicitly show that the complete three-dimensional simulation and effective one-dimensional descriptions lead to the same result.
 J. Catani, G. Lamporesi, D. Naik, M. Gring, M. Inguscio, F. Minardi, A. Kantian, and T. Giamarchi
“Quantum dynamics of impurities in a one-dimensional Bose gas”
Phys. Rev. A 85, 023623 (2012).
 Thursday, 25th of September 2014, [SLIDES] Konstantin Krutitsky, “Propagation of quantum correlations after a quench in the Mott-insulator
regime of the Bose-Hubbard model.”
, Physics Department, University of Duisburg-Essen, Germany
We have developed a new method which allows to study dynamics of quantum correlations in higher dimensional lattices of large size and gives reliable results for long times. The formalism is based on the equations of motion for the reduced density matrices. An infinite set of equations is truncated such that only two-point correlations are taken into account. This approximation is justified by exact diagonalization for small lattices in one and two dimensions.
Approximate analytical solutions of the resulting equations are obtained within the framework of a perturbative expansion in powers of the inverse coordination number. Exact solutions are obtained by numerical integration of the equations of motion and show qualitative agreement with the analytical approximations. On the other hand, numerical calculations allow to achieve higher accuracy which is confirmed by comparison with the exact diagonalization.
As an application we study the dynamics of interacting bosons in a lattice after quench within the Mott-insulator regime. It is shown that the time evolution of the local particle-number distribution is directly related to the propagation of correlations. In particular, we find the revival of oscillations of the local quantities after the propagation of correlations through the whole system. In two dimensions, the propagation of correlations is anisotropic with the minimal velocity along the lattices axes and maximal along the diagonals. Our method can be easily applied to inhomogeneous lattices which allows to include into consideration the harmonic traps as well as disorder potentials.
 Wednesday, 23rd of July 2014 at 11:30, [SLIDES] Boris A. Malomed, Stable two-dimensional composite solitons in spin-orbit-coupled self-attractive Bose-Einstein condensates in free space, Department of Physical Electronics, School of Electrical Engineering,
Faculty of Engineering, Tel Aviv University, Tel Aviv 69978, Israel
It is commonly known that two-dimensional mean-field models of optical and matter waves with cubic self-attraction cannot produce stable solitons in free space because of the occurrence of collapse in the same setting. By means of numerical analysis and variational approximation, we demonstrate that the two-component model of the Bose-Einstein condensate with the Rashba spin-orbit coupling and cubic attractive interactions gives rise to STABLE solitary-vortex complexes of two types in the FREE SPACE: semivortices (SVs, with a vortex in one component and a fundamental soliton in the other), and mixed modes (MMs, with topological charges 0 and ±1 mixed in both components). The SVs and MMs realize the ground state of the system, provided that the self-attraction in the two components is, respectively, stronger or weaker than the cross attraction between them. The SVs and MMs which are not the ground states are subject to a drift instability. The modes of both types degenerate into unstable Townes solitons when their norms attain the respective critical values, while there is no lower existence threshold for the stable modes. Moving free-space stable solitons are also found in the present non-Galilean-invariant system, up to a critical velocity. Collisions between two moving solitons lead to their merger into a single one.
Hidetsugu Sakaguchi, Ben Li, and Boris A. Malomed , “Creation of two-dimensional composite solitons in spin-orbit-coupled self-attractive Bose-Einstein condensates in free space”, Phys. Rev. E 89, 032920 (2014).
 Friday, 18th of July 2014 at 11:30, [SLIDES] Marta Abad, “Persistent currents in two-component condensates”, INO-CNR BEC Center and Dipartimento di Fisica, Universita di Trento, Italy
In this talk we address the stability of persistent currents in two-component Bose-Einstein condensates. We relate the instabilities shown by Bogoliubov excitations to the decay of persistent currents in the miscible regime of the binary mixture, finding a very good agreement with numerical simulations of the Gross-Pitaevskii equations. In particular, we analyze the presence of a partially stable region, where the superflow in the minority component decays while it remains stable in the majority component. The existence of this region could point out in the right direction to explain the experimental results. In addition, we study the behaviour of the system when a velocity difference between the two components drives a dynamical instability, known in the literature as counterflow instability. Finally, we comment on the stability of the currents in the phase separated regime of the binary mixture and also in the presence of a coherent coupling.
 Tuesday, 1st of July 2014 at 11:30, [SLIDES] Leonid Glazman, Nonlinear Quantum Liquids In One Dimension, Department of Physics, Yale University, USA
The conventional description of one-dimensional quantum fluids is based on the Luttinger liquid theory. In that theory, the true energy-momentum relation of particles making up the fluid is replaced by a linear one. This simplification is crucial for the theory, and abandoning it has proven to be difficult. The talk presents a breakthrough which allows one to circumvent the difficulty. The new theory describes dynamic responses of a fluid consisting of particles with a generic spectrum. It also provides a pathway for developing kinetic theory of a quantum fluid. The developed new description is applicable to a diverse group of systems, including, for example, electrons in quantum wires, one-dimensional spin liquids, and cold atomic gases in one-dimensional traps.
 Wednesday, 12th of March 2014 at 11:30, [SLIDES] Andrii Gudyma, LPTMS, Paris-Sud University
Breathing modes of one-dimensional trapped BEC One-dimensional ultracold atomic gas of bosons is considered. Frequencies of low-lying excitations are calculated for the parameters of the model relevant for the recent experiment from Innsbruck group [Science 325, 1224 (2009)]. Perturbative methods are combined with the exact Bethe Ansatz solution for the model. Analysis of results are made for both the weak coupling and the Tonks-Girerdeau regimes. Analytical calculations are complement with the results from the quantum Monte Carlo simulations. On the example of the two-particle system compared different methods of calculation of the breathing mode. Theoretical results confronted with data from experiment.
 Wednesday, 5th of March 2014 at 11:30, [SLIDES] Riccardo Rota, Dipartimento di Fisica e INO-CNR BEC center Universita` degli Studi di Trento
“Quantum Monte Carlo approach to dynamic properties of ultracold Bose systems”
Using quantum Monte Carlo methods, we perform zero-temperature calculations of the dynamic structure factor of a system of Bose particles interacting via a hard-sphere potential. The hard-sphere model is able to capture, in the dilute regime, the essential properties of ultracold atoms with positive scattering length, and, at higher densities, it can been used to characterize strongly interacting systems where the hard-core repulsion at short distances is the leading part of the interatomic potential, like superfluid helium.
With increasing density, we observe the appearance of an incoherent, multiphonon contribution in the spectral function at frequencies higher than the single quasi-particle peak and a crossover of the dispersion of elementary excitations from a Bogoliubov-like spectrum to a phonon-maxon-roton curve. The behavior of the dynamic structure factor at the same density in the stable solid and metastable gas phase above the freezing point is also discussed.
 Tuesday, 18th of February 2014 at 16:00, [SLIDES] Guido Pupillo, Université de Strasbourg and CNRS, Strasbourg, France
“Dynamics of blockaded Rydberg gases in low dimensions”
We discuss the quantum phases and dynamics of a gas of two-dimensional Bosons with finite-range soft-core interactions. For low densities, the system is shown to form a solid in which superfluidity is provided by delocalized zero-point defects. This provides the first example of continuous-space supersolidity consistent with the Andreev-Lifshitz-Chester scenario. We further discuss the connection between quantum mechanical supersolid behaviour and a novel mechanism for a glass formation.
 Tuesday, 18th of February 2014 at 16:00, [SLIDES] Guido Pupillo, Universite de Strasbourg and CNRS, Strasbourg, France
“Dynamics of blockaded Rydberg gases in low dimensions”
We discuss the quantum phases and dynamics of a gas of two-dimensional Bosons with finite-range soft-core interactions. For low densities, the system is shown to form a solid in which superfluidity is provided by delocalized zero-point defects. This provides the first example of continuous-space supersolidity consistent with the Andreev-Lifshitz-Chester scenario. We further discuss the connection between quantum mechanical supersolid behaviour and a novel mechanism for a glass formation.
 Wednesday, 5th of February 2014 at 11:30, [SLIDES] Robert E. Zillich, Institute for Theoretical Physics, Johannes Kepler University, Altenbergerstrasse 69, 4040 Linz, Austria
We approximate a dipolar Bose gas in a one-dimensional optical lattice as bosons residing on different 2D planes, thus effectively mapping the system on a multi-component 2D Bose gas. The long range of the dipole interaction can lead to appreciable inter-layer correlations up to the limit where dipoles from different planes form bound states. We study the dependence of these correlations on density, distance between layers, and polarization direction, and their effect on the excitation spectrum.
 Monday, 11th of November 2013 at 12:00, [SLIDES] Leticia Tarruell, ICFO-The Institute of Photonic Sciences, Barcelona (Spain)
"Exploring synthetic quantum materials with ultracold fermions in a tunable-geometry optical lattice" Ultracold atomic gases in optical lattices provide the opportunity of engineering synthetic quantum materials in a clean and highly controlled environment. On the one hand, these systems can be viewed as experimental quantum simulators for exploring challenging problems of condensed matter physics. On the other hand, they also allow for the realization of completely novel materials of interesting properties, without counterpart in solid-state systems.
In my talk, I will present recent experiments where an ultracold Fermi gas trapped in an optical lattice of tunable geometry is used to explore both aspects.
By loading non-interacting atoms into a honeycomb structure, we realize artificial graphene and observe the presence of two Dirac points in the band structure . The flexibility of our experimental approach allows us to adjust the properties of these Dirac points at will, moving them inside the Brillouin zone and changing the effective mass of the associated Dirac fermions. Furthermore, we observe how the two Dirac points annihilate each other when coming too close together, a situation which is presently out of reach in solid-state samples.
Preparing instead a repulsively interacting gas of atoms in two different internal states, we implement the Fermi-Hubbard model and aim at simulating quantum magnetism in this system. In particular, we explore experimentally how certain crystal geometries favor the emergence of short-range magnetic order, and directly probe the nearest-neighbor spin correlations of the system . In a dimerized lattice, the correlations manifest as an excess number of singlets as compared to triplets, whereas in an anisotropic simple cubic lattice we observe the appearance of antiferromagnetic correlations along one spatial axis.
 L. Tarruell, D. Greif, T. Uehlinger, G. Jotzu and T. Esslinger, "Creating, moving and merging Dirac points with a Fermi gas in a tunable honeycomb lattice", Nature 483, 302â€“305 (2012).  D. Greif, T. Uehlinger, G. Jotzu, L. Tarruell and T. Esslinger, "Short-range quantum magnetism of ultracold fermions in an optical lattice", Science 340, 1307-1310 (2013)
 Wednesday, 18th of September 2013 at 11:30, [SLIDES] Mikhail Zvonarev, Univ Paris-Sud, Laboratoire LPTMS, UMR8626, Orsay, F-91405, France; CNRS, Orsay, F-91405, France
"Dynamics of quantum particles in one-dimensional quantum liquids" What is the dynamics of a particle injected into a gas of quantum particles of other type? I will address this question in one spatial dimension in two different situations. In one case, an external particle is injected with a finite momentum, while as in the other the particle is subjected to a constant driving force. In the former case I will demonstrate that, contrary to conventional picture of relaxation dynamics, the particle never comes to a complete stop. Instead, for initially supersonic velocity long-lived oscillations develop and the velocity saturates to a value almost independent of initial conditions. In the latter case long-lived oscillations and velocity saturation take are also present, though their physical origin is different from the one in the former case. The methods used, namely Bethe Ansatz and numerics, will be discussed in detail along with the state-of-the-art experiments.
"Suppression of the quantum-mechanical collapse by repulsive interactions in bosonic gases" The quantum-mechanical collapse (alias "fall onto the center" of particles attracted by potential -V/r2) is a well-known issue in the quantum theory. We demonstrate that, in a rarefied gas of quantum particles attracted by the above-mentioned potential, the repulsive nonlinearity induced by collisions between the particles prevents the collapse, recreating the missing ground state. Further, a phase transition in the ground state is found at a critical value of V. The setting may be realized in the 3D gas of dipolar bosons attracted by a central charge, including the case of the binary gas. The addition of the harmonic trapping potential gives rise to a tristability, in the case when the Schroedinger equation still does not lead to the collapse. In the 2D setting, the cubic nonlinearity is not strong enough to prevent the collapse; however, the quintic term does it. The analysis is also extended to the 3D anisotropic setting, with the dipoles polarized by an external uniform field.
Results were partly published in: H. Sakaguchi and B. A. Malomed, Suppression of the quantum-mechanical collapse by repulsive interactions in a quantum gas, Phys. Rev. A 83, 013907 (2011); H. Sakaguchi and B. A. Malomed, Suppression of the quantum collapse in an anisotropic gas of dipolar bosons, Phys. Rev. A 84, 033616 (2011).
 Wednesday, 24th of April 2013 at 11:30, [SLIDES] Andrea Trombettoni, CNR-IOM DEMOCRITOS & SISSA - Trieste, Italy
"Quantum simulations with ultracold atoms in optical lattices" In this talk I will present two examples of quantum simulations with ultracold atoms in optical lattices. In the first part I discuss the properties of ultracold bosons in optical lattices at half-filling: using a similarity Hamiltonian renormalization procedure, we determine an effective spin-1/2 representation of the Bose-Hubbard model. This mapping allows to give analytical estimates of the correlation functions of the Bose-Hubbard model, which are in good agreement with DMRG results. The discussed analysis shows that, also at finite interaction, the 1D Bose-Hubbard model with suitably chosen parameters may be seen as a quantum simulator of the XXZ chain. In the second part I will discuss anisotropic Ginzburg-Landau and Lawrence-Doniach models describing a layered superfluid ultracold Fermi gas in optical lattices. We derive the coefficients of the anisotropic Ginzburg-Landau and the mass tensor as a function of anisotropy, filling and interaction, showing that near the unitary limit the effective anisotropy of the masses is significantly reduced. The anisotropy parameter is shown to vary in realistic setups in a wide range of values. We also derive the Lawrence-Doniach model - often used to describe the 2D-3D dimensional crossover in layered superconductors - for a layered ultracold Fermi gas, obtaining a relation between the interlayer Josephson couplings and the Ginzburg-Landau masses.
 Tuesday, 26th of February 2013 at 11:30, [SLIDES] Omjyoti Dutta, Institut de Ciències Fotòniques (ICFO)
"Beyond standard Hubbard models" A natural description of ultracold gases trapped in optical lattices is given by the so-called single-band Hubbard model. We will discuss the additional effects of interaction to induce intra- as well as inter-band scattering to neighbouring sites, which shows up as density dependent correlated tunneling processes. Such processes can spontaneously give rise to various exotic phases. As examples, we will present 1) spontaneous creation of non-Fermi liquid smectic metal phases in dipolar Fermions, and 2) dynamical generation of exotic lattices in Fermi-Fermi mixtures.
 Thursday, 24th of January 2013 at 11:30, [SLIDES] Stephan Humeniuk, Institut de Ciències Fotòniques (ICFO)
"Introduction to Stochastic Series Expansion Quantum Monte Carlo" The seminar is intended to be a technical introduction into the Stochastic Series Expansion Monte Carlo method  which is an alternative to Path Integral Monte Carlo and a method of choice for lattice spin systems. I will review the SSE representation of the partition function and the different update mechanisms, i.e. diagonal and off-diagonal update as well as the worm algorithm that allows to calculate off-diagonal correlation functions. Finally, I will mention a scheme that allows to treat long-range and frustrated interactions in quantum Ising systems efficiently .  Phys. Rev. B 59, R14157 (1999)  Phys. Rev. E 68, 056701 (2003)
 Wednesday, 5th of December 2012 at 11:30, [SLIDES] O. N. Osychenko, Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya, Campus Nord B4-B5, E-08034, Barcelona, Spain
"Diffusion Monte Carlo study of phase transitions at zero temperature." This seminar is devoted to application of diffusion Monte Carlo method to quantum phase transitions. The first problem that we study is the phase diagram of Yukawa systems. It is known that in the case of a large mass imbalance, the light fermions introduce an effective Yukawa potential between the heavy fermions. It was predicted that this effective interaction might lead to crystallization in 2D systems, although no estimations were done in 3D case. For the first time a fully quantum mechanical calculation is done in order to find the exact zero-temperature phase diagram of Yukawa particles. The melting and solidification curves show that there is a possibility for a reentrant gas-solid-gas transition, caused by a competition between long-range Coulomb part of the Yukawa potential (melts at large densities) and exponential screening (melts at small densities). In order to localize more accurately the phase transition point in the high density regime we apply the Ewald summation technique.
As well, we present a quantum Monte Carlo study of a bulk system of bosonic Rydberg atoms, that is alkali atoms with a single electron residing on a very high orbital, interacting through van der Waals 1/|r|6 interaction potential. Our aim is to understand how much of the behavior of a real system comes from this leading term, and to which extent the 1/|r|6 interaction of the excited atoms in the cloud can describe crucial properties of experimentally relevant systems like mixtures of excited and ground state atoms.
It the last part we present the results of quantum Monte Carlo calculations of atomic para-hydrogen p-H2 zero temperature below its solidification curve in a range of densities. In this study our principal motivation was to understand better the properties of the metastable liquid/glass phase at low temperatures.
 Thursday, 15th of November 2012 at 12:00, [SLIDES] Miguel Angel García-March, Dept. d'Estructura i Constituents de la Materia Univ. de Barcelona
"Strongly correlated ultracold bosons as impurities immersed in a Bose-Einstein condensate." Impurities, such as fermions or ions, immersed in a cloud of weakly interacting bosons forming a condensate have attracted recent interest because they conform versatile, highly controllable, and experimentally feasible systems for studying quantum correlations. We present an exact many body description of a mixture of ultracold bosons in which a few strongly interacting atoms play the role of impurities immersed in a second species of a much bigger cloud of weakly interacting atoms. The latter species acts as a tunable environment, whose effect over the impurities can be controlled through the interspecies interactions. This framework permits us to describe the behaviour of the quantum correlations between both species through the process of phase separation or along with the dynamics of the impurities within the environment. We also assess the possibility of mimicking the tools of quantum optics to analyse these quantum correlations. Finally, we derive a semiclassical description of the system in terms of two non-linear coupled differential equations where the nonlinearity depends on the interaction strength. Experimental feasibility and technological applications are henceforth discussed.
 Wednesday, 17th of October 2012 at 11:30, [SLIDES] Natalia Matveeva, Dipartimento di Fisica, Università di Trento, Italy
"Liquid and crystal phase of dipolar fermions in two dimensions." The liquid and crystal phase of a single-component Fermi gas with dipolar interactions are investigated using quantum Monte Carlo methods in two spatial dimensions and at zero temperature. The dipoles are oriented by an external field perpendicular to the plane of motion, resulting in a purely repulsive 1/r^3 interaction. In the liquid phase we calculate the equation of state as a function of the interaction strength and other relevant properties characterizing the Fermi-liquid behavior: effective mass, discontinuity at the Fermi surface and pair correlation function. In the high density regime we calculate the equation of state of the Wigner crystal phase and the critical density of the liquid to solid first order phase transition. Close to the freezing density we also search for the existence of a stripe phase, but such a phase is never found to be energetically favorable.
 Wednesday, 10th of October 2012 at 11:30, [SLIDES] Krzysztof Jachymski, Faculty of Physics, University of Warsaw, Poland
"Localization of ultracold bosons in a quasiperiodic optical lattice." Ultracold gases provide a unique opportunity to study Anderson localization in disordered trapping potential. Both the properties of the trap and the strength of the interactions can be controlled during the experiment.
I will discuss the properties of ultracold bosons in a one-dimensional quasiperiodic optical lattice, where the localization occurs for sufficiently strong disorder. The transition can be detected with a nondestructive method using off-resonant light scattering.
 Friday, 7th of September 2012 at 10:30, [SLIDES] Gianluca Bertaina, Institute of Theoretical Physics, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
"Quantum Monte Carlo study of a resonant Bose-Fermi mixture." We study resonant Bose-Fermi mixtures at zero temperature, with different relative concentrations of the bosons. We use for the first time a Quantum Monte Carlo method with Fixed-Node approximation, to explore the system from the weak to the strong coupling limit. A repulsive interaction among bosons is introduced to provide stability to the bosonic component. Beyond the unitarity limit, the resonant attractive interaction supports a bound fermionic dimer. At the many-body level, increasing the boson-fermion coupling the system undergoes a quantum phase transition from a state with condensed polaronic bosons immersed in a Fermi sea, to a normal Fermi-Fermi mixture of the composite fermions and the bare fermions in excess. We obtain the equation of state and we characterize the momentum distributions both in the weakly and in the strongly interacting limits, finding interesting signatures of the different many-body ground states. We compare Quantum Monte Carlo results to T-matrix calculations and we draw a preliminary phase diagram as a function of the Bose-Fermi scattering length and the concentration of the bosons.
 Thursday, 26th of July 2012 at 10:30, [SLIDES] D. M. Gangardt, School of Physics and Astronomy, University of Birmingham, UK
"Bloch oscillations without lattice: dynamics of mobile impurities in one-dimensional quantum liquids." A quantum impurity, i.e. a particle different from the others, moving in quantum liquid in one dimension is an interesting many-body problem. The dynamics of such mobile impurity is very rich due to its strong interactions with collective degrees of freedom of the liquid. One of the manifestations of this is the periodicity of the dispersion law of the impurity, similar to that of a particle in a lattice. Under action of an external force the motion of the particle exhibits Bloch oscillations. We discuss the role of dissipative processes and show that as a result the Bloch oscillations become superimposed with a drift. Our main finding is that the drift velocity and the period of the oscillations are extremely sensitive to the temperature as well as the underlying microscopic interactions.
 Friday, 11th of May 2012 at 11:30, [SLIDES] Yaroslav Lutsyshyn, Institute of Physics University of Rostock 18051 Rostock, Germany
"Fast quantum Monte Carlo on GPU." I will describe recent efforts to parallelize quantum Monte Carlo for use with graphical processing units (GPUs). Modern graphical cards often feature GPUs with several hundreds of single computing cores. Arrays of such cores are designed to execute in parallel using single instruction-multiple data parallel model. Such vector parallelization suits well the applications in scientific computing. GPUs produced by Nvidia, a market leader in such GPU products, may be conveniently programmed with an extensions of the standard programming languages called CUDA (Compute Unified Device Architecture) framework.
I will report my recent work in parallelizing variational Monte Carlo for use with the Nvidia GPU cards. Acceleration of up to fifty times was achieved when comparing GPU execution with a single-core CPU run. Thanks to such an improvement in speed, variational calculations of a liquid helium system with over ten thousand particles can be comfortably performed on a regular desktop workstation. The talk will focus on details of the NVidia GPU architecture and its relation to the CUDA programming model. I will also cover some practical considerations that are important for starting a new CUDA project.
 Wednesday, 7th of March 2012 at 15:00, [SLIDES] Leandra Vranješ Markić, Faculty of Science, University of Split, HR-21000 Split, Croatia
"Quantum Monte Carlo simulations of 4He clusters adsorbed on the surface of graphene." Graphene, a single layer of graphite, which has demonstrated many surprising physical properties, is also of interest as a novel adsorber.
The talk will give an overview of our recent study of 4HeN clusters adsorbed on one and both sides of a graphene sheet. Different models for the interaction potentials will be discussed. We have modelled interactions of 4He clusters with graphene using an averaged helium-carbon potential that depends only on the distance to the graphene sheet, and a potential constructed as a sum of individual helium-carbon interactions. That way, we assess the effect of corrugation on the binding properties of helium clusters, both using isotropic and anisotropic interaction potentials. In addition, we asses the influence of the substrate mediated McLachlan interaction.
All the calculations have been performed using quantum Monte Carlo methods. At zero temperature the ground-state properties of 4HeN for 2â‰¤ Nâ‰¤100 have been determined using variational and diffusion Monte Carlo calculations. We find that clusters adsorbed on both sides of graphene are correlated. In addition, we observe the changes in the size of the clusters. For selected clusters, calculations have been performed also at finite temperature by path integral Monte Carlo simulations.
 Tuesday 28th of February 2012 at 12:00, [SLIDES] Diana Hufnagl, Institut fur Theoretische Physik Johannes Kepler Universitat Linz - Austria
"Staibility and Excitations of Dipolar Quantum Gases" Due to the recent experimental advances in generating Feshbach-associated molecular quantum gases, the field of ultracold dipolar gases has become a topic of great interest. In this talk we present our current work in this field. We study polarized dipolar Bose systems in a pancake shaped trap, where we also introduce a tunnel barrier to go from the limit of a quasi-2D layer, to the limit of two quasi-2D layers. We discuss instabilities due to dimerization in one layer and the associated signature of a roton in the spectrum. For the case of two layers we investigate for example the dependence of the stability on the distance of these layers. Recently we also investigated quantum gases other than dipolar gases, namely Rydberg-dressed atoms in two dimensions, where we study instabilities caused by the formation of a droplet lattice. We will also briefly mention work on the BEC-BCS crossover and the effects of molecular rotation.
 Thursday, 19th of January 2012 at 11:00, [SLIDES] Sebastiano Pilati, The Abdus Salam International Center for Theoretical Physics Trieste - Italy
"Quantum many-body physics with ultracold gases in optical lattices." In experiments performed with ultracold gases one can manipulate the main parameters that characterize the sample. This allows to induce various intriguing quantum phenomena due to strong inter-particle correlations. In this talk, we will review some recent quantum Monte Carlo studies of Bose and Fermi gases with resonant inter-particle interactions. For bosonic systems in optical lattices, we investigate the superfluid to insulator transition by using a novel continuous-space quantum Monte Carlo technique, and compare our results with more conventional theories based on simplified discrete lattice models. For fermions, we apply Kohn-Sham Density Functional Theory to investigate quantum magnetism of repulsive Fermi gases in optical lattices. We discuss how these calculations could provide a new link between experiments with ultracold atomic gases and the simulation of strongly correlated materials.
 Wednesday, 26th of October 2011 at 12:00, [SLIDES] Konstantin Krutitsky, Physics Department, University of Duisburg-Essen, Germany
"Excitation dynamics in a lattice Bose gas within the time-dependent Gutzwiller mean-field approach." Studies of excitations of ultracold atoms in optical lattices play an important role in the understanding of their physical properties and dynamical behavior. For instance, the celebrated quantum phase transition from the superfluid into the Mott-insulator is accompanied by the opening of the gap in the excitation spectrum. We have studied the ground state, stationary excitation modes, as well as the dynamics of the lattice Bose gas using the time-dependent Gutzwiller mean-field approach valid in the superfluid as well as in the Mott-insulator phases.
The modes of collective excitations are calculated within the framework of the linear-response theory considering small perturbations of the many-body ground state. The lowest excitation modes of the Mott-insulator display energy gaps which become smaller when we approach the phase boundary. The lowest-energy excitation of the superfluid is a Goldstone mode that appears due to the spontaneous breaking of the phase symmetry. It has a phonon-like dispersion relation characterized by the sound velocity which is described by the hydrodynamic relation. In this mode, the condensate and the normal fractions oscillate in phase. The second mode of the superfluid has a gap and the oscillations of the condensate and the normal components are out-of-phase. We have performed simulations of the sound-wave propagation in the linear-response regime and beyond.
Dark solitons of ultracold bosons in the vicinity of the Mott-insulator -- superfluid phase transition are studied as well. Making use of the Gutzwiller ansatz we have found antisymmetric eigenstates corresponding to standing solitons, as well as propagating solitons created by phase imprinting. Near the phase boundary, superfluidity has either a particle or a hole character depending on the system parameters, which greatly affects the characteristics of both types of solitons.
 Friday, 16th of September 2011 at 15:00, [SLIDES] Miguel A. Cazalilla, Centro de Física de Materiales CSIC-UPV/EHU. Paseo Manuel de Lardizabal 5, E-20018 San Sebastian, Spain; Donostia International Physics Center (DIPC)
"Dynamical Theory of Superfluidity in One Dimension." A theory accounting for the dynamical aspects of the superfluid response of one dimensional (1D) quantum fluids is reported. In long 1D systems, the onset of superfluidity is related to the dynamical suppression of quantum phase slips at low temperatures. The effect of this suppression as a function of frequency and temperature is discussed within the framework of the relevant correlation function that is accessible experimentally, namely the momentum response function. Application of these results to the understanding of the superfluid properties of helium confined in nanometer-size pores, dislocations in solid 4He, and ultra-cold atomic gases is also briefly discussed.
 Wednesday, 23rd of March 2011 at 11:00, [SLIDES] Henry R. Glyde, Department of Physics and Astronomy University of Delaware Newark, Delaware 19711
"Bose-Einstein Condensation and Superfluidity in Nanoscale Liquid and Solid Helium." Helium was first liquefied in the famous Kamerlingh Onnes laboratories in Leiden, Holland in 1908. More than a century of fascinating discovery followed revealing many remarkable phenomena such as Bose-Einstein condensation (BEC), superfluidity and well defined phonon-roton modes. Superflow of helium confined in porous media has always been an important part of this history. In 2004 superflow behavior was observed in solid helium. In this talk we review neutron scattering measurements of BEC, phonon-roton modes and superflow in bulk liquid helium. We then focus on helium confined in porous media and make the case for the existence of a new insulating phase that contains localized regions of BEC in porous media. This "localized BEC" phase lies between the superfluid and normal liquid phase and is induced by disorder. Recent measurements of BEC in bulk liquid helium under pressure up to the liquid/solid interface will also be presented as well as earlier attempts to observe BEC in solid helium.
 Wednesday, 13th of April 2011 at 11:30, [SLIDES] O. N. Osychenko, Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya
"Monte Carlo study of quantum phase diagram of Rydberg atoms with repulsive 1/r6 interaction." Recently the methods of laser cooling of atoms have given rise to a new wave of experiments on ultracold (~100 ÂµK) Rydberg atoms [1,2], in particular on alkali bosonic atoms as Rb87. These experiments revealed a suppression of excitations, called "van der Waals blockade", that was proposed as a perspective means to implement quantum gates between atom qubits. We study the quantum phase diagram of bosons interacting via repulsive van der Waals 1/r6 potential. The critical density for zero temperature gas-crystal phase transition is obtained from diffusion Monte Carlo calculations. If effective mass entering in the kinetic energy were taken to be of the order of the mass of a Rb atom, then the typical experimental conditions would correspond to being deeply in the phase of a classical crystal. Effects of the temperature are studied in the classical crystal using path integral Monte Carlo and classical Monte Carlo methods.
 Axel Grabowski, Rolf Heidemann, Robert LÃ¶w, JÃ¼rgen Stuhler, Tilman Pfau "High resolution Rydberg spectroscopy of ultracold Rubidium atoms'", Fortschr. Phys., 54, 765, (2005).  Vera Bendkowsky, BÃ¶rn Butscher, Johannes Nipper, James P. Shaffer, Robert LÃ¶w, Tilman Pfau "Observation of ultralong-range Rydberg molecules", Nature, 458, 1005 (2009).
 Wednsday, 6th of April 2011 at 11:30 UPC Campus Nord, B4-212 (aula seminari), [SLIDES] Carles Calero, Institut de Ciència de Materials de Barcelona, ICMAB-CSIC
"Ionic transport through a biological nanochannel." Understanding transport of charged solutes across transmembrane channels is a problem of paramount importance in biophysics, since it is crucial to regulate many cell functions . An important property of biological nanochannels is their preference to the passage of either cations or anions through them, the so-called selectivity. New experiments on the selectivity of a biological nanochannel (the OmpF bacterial porin, a model channel) observe a reversal of selectivity in the presence of multivalent cations . In my talk, I will discuss the results of new high-performance all-atom molecular dynamics simulations of the ionic transport across this biological nanochannel in the presence of electrolyte which provide an explanation for the experimental observations . I will also discuss a method based on the calculation of first passage time quantities that was used to obtain macroscopic parameters which characterize the diffusive dynamics of the ions in the interior of the channel from the MD simulations' trajectories .
 B. Hille, Ion Channels of Excitable Membranes (Sinaure, Sunderland, 2001)  A. Alcaraz et al., Biophys. J. 96, 56 (2009)  M. Aguilella-Arzo, J. Faraudo, C. Calero, Soft Matter 6, 6079 (2010)  C. Calero, J. Faraudo, M. Aguilella-Arzo, Phys. Rev. E 83, 021908 (2011)
 Thursday, 31st of March 2011 at 11:00, [SLIDES] Lluís Masanes, ICFO - Institut de Ciències Fotòniques
"A system equilibrates when diagonalizing its hamiltonian is sufficiently hard." In classical systems there is a relation between integrability and thermalization, but this is not well understood in the quantum case. Closed quantum systems never equilibrate to a stationary state. However, in some circumstances, the system equilibrates locally: the reduced density matrix of a subsystem evolves to a stationary state. The lack of integrability of a quantum system can be quantified by the computational complexity of diagonalizing its hamiltonian. It can be shown that, if this complexity is at least quadratic then local equilibration holds. If this complexity is sublinear then local equilibration does not hold.
 Friday, 4th of March 2011 at 10:30, [SLIDES] Yaroslav Lutsyshyn, Departament de Física i Enginyeria Nuclear, Universitat Politècnica de Catalunya
"Quantum Monte Carlo calculations of point defect formation in solid helium." Interest in the influence of strong quantum effects on the properties of crystalline solids has rekindled since the recent discovery of supersolidity and a host of accompanying effects in solid helium-4. While the exact nature of these effects remains unknown, they are oft-believed to owe to defects populating the experimental samples. In this talk I will describe our efforts to characterize quantum solids with first principles quantum many-body methods, and will report the results for properties of vacancy formation in solid helium.
Y. Lutsyshyn et al., Phys. Rev. B 82, 180506(R) (2010)
 Monday, 14th of February 2011 at 11:00, [SLIDES] Prof. Andrey Mishchenko, Cross-Correlated Materials Research Group, RIKEN (The Institute of Physical and Chemical Research), Japan
"Sharp Transition for Single Polarons in the One-Dimensional Su-Schrieffer-Heeger Model" We study  a single polaron in the Su-Schrieffer-Heeger (SSH) model using four different techniques (three numerical and one analytical). Polarons show a smooth crossover from weak to strong coupling, as a function of the electron-phonon coupling strength, in all models where this coupling depends only on phonon momentum q. In the SSH model the coupling also depends on the electron momentum k; we find it has a sharp transition, at a critical coupling strength, between states with zero and nonzero momentum of the ground state. All other properties of the polaron are also singular. This result is representative of all polarons with coupling depending on k and q, and will have important experimental consequences (e.g., in angle-resolved photoemission spectroscopy and conductivity experiments).
. D. J. J. Marchand et al, Phys. Rev. Lett. v. 105, 266605 (2010).
 Tuesday, 22nd of September 2009 at 11:00, [SLIDES] Antun Balaž, Институт за физику, Универзитет у Београду (Institute of Physics, Belgrade - Serbia)
"High order actions in Path Integral Monte Carlo" Recently, we have developed an efficient recursive approach for analytically calculating the short-time expansion of the propagator to extremely high orders for a general many-body quantum system . Here we apply this technique for numerical study of thermodynamical properties of a rotating ideal Bose gas of 87Rb atoms in an anharmonic trap . First, the energy spectrum of the system is obtained by the exact diagonalization of the discretized short-time propagator. Then the condensation temperature, ground-state occupancy, density profiles and the time-of-flight absorption pictures are calculated for varying rotation frequencies, including the critical and over-critical regime. The obtained results improve previous semiclassical calculations and agree well with Path Integral Monte Carlo simulations.
 A. Balaž, A. Bogojević, I. Vidanović, A. Pelster, PRE 79, 036701 (2009)  V. Bretin, S. Stock, Y. Seurin, J. Dalibard, PRL 92, 050403 (2004)
 Tuesday, 15th of September 2009 at 16:00, [SLIDES] Marvin D. Girardeau, School of Optical Sciences, University of Arizona, Tucson, AZ
"Fermionization, bosonization, and correlations in ultracold Bose and Fermi gases in tight waveguides " Ultracold gases in tight de Broglie waveguides provide highly controllable realizations of one-dimensional quantum gases. A historical overview of Tonks-Girardeau (TG) gas of impenetrable bosons: from analytic prediction a long time ago to recent experimental realizations is presented. Fermi-Bose mapping is constructed for the ground-state wave function permitting to find an exact many-body solution for TG gas. Another exactly solvable system of fermions with strong attractions is explained: fermionic Tonks-Girardeau (FTG) gas. Superconductive long-range order is discussed. Generalized FB mapping is introduced: Spin-aligned fermions <-> bosons. Finally, Bose gases A and B with FTG AB interactions are also studied.
 1st of June 2009, [SLIDES] Mikko Saarela, Department of Physics, University of Oulu, Finland
"Quasi-2D bosons in correlated random potentials" Laser speckles provide a unique possibility to create fully controlled two-dimentional disorder potentials for neutral atoms. This type of disorder has exponential probability distribution and finite spatial correlation length. In this talk, I shall present our resent results on the superfluidity and Bose-Einstein condensation of interacting bosons in the presence of the laser speckles at zero temperature obtained using Monte Carlo methods in continuum as well as Gross-Pitaevskii equation and Bogoliubov theory.
 22nd of July 2008, [SLIDES] Prof. Yurii E.Lozovik, Institute of Spectroscopy, Russian Academy of Sciences and Moscow Institute of Physics and Technology, Russia
Course "BOSE-EINSTEIN COHERENCE IN SEMICONDUCTORS AND GRAPHENE" : Lecture 3 "Physical properties, possible coherent phases and applications of graphene" - Moore law. - Allotrope forms of carbon - Discovery of graphene - Problem of existence of 2D membrane and 2Dcrystal - Orbitals and chemical bonds - Band structure and envelope function of graphene - Berry phase and absence of backscattering - Controlling by gate - Problems of quantum dot and transistor based on graphene - Optical properties of graphene - Pecularity of correlations in graphene - Coherent phases and collective properties - Peculiarities of coherent phase in graphene - Landau quantization and anomalous QHE in graphene - Magnetoexciton condensation - Possible applications. NEMS
 21st of July 2008, [SLIDES] Prof. Yurii E.Lozovik, Institute of Spectroscopy, Russian Academy of Sciences and Moscow Institute of Physics and Technology, Russia
Course "BOSE-EINSTEIN COHERENCE IN SEMICONDUCTORS AND GRAPHENE" : Lecture 2 "Bose condensation and superfluidity of cavity polaritons" - Exciton -polaritons in optical microcavity â€“ entanglement of cavity photons and 2D excitones - Bose-condensation and polariton laser - Gross-Pitaevskii-type system of equations for two-component entangled system - Landau method to calculate superfluid density Ï s - inapplicability to polaritons - Derivation of effective action of polariton system as system of two interacting Bose-field from linear response theory - Kosterlitz â€“Thouless transition of polariton system to superfluid state - Polariton traps "Smoking gun proofs" of polariton BEC
 20th of July 2008, [SLIDES] Prof. Yurii E.Lozovik, BOSE-EINSTEIN COHERENCE IN SEMICONDUCTORS AND GRAPHENE : Lecture 1, Institute of Spectroscopy, Russian Academy of Sciences and Moscow Institute of Physics and Technology, Russia
Course "BOSE-EINSTEIN COHERENCE IN SEMICONDUCTORS AND GRAPHENE" : Lecture 1 "Possible phases, Bose condensation and superfluidity of excitons in nanostructures: theory, present experimental status and problems" - Matter versus exciton matter - similarities and dissimilarities. - Short history of Bose condensate - Physical realizations. Coupled quantum wells. - Phases and regimes for exciton system in coupled quantum wells. - BCS regime - Rare exciton system - BEC-BCS crossover - Strongly correlated phenomena and phases in CQW - Exciton crystal and supersolid - Exciton traps. - Definition of superfluidity in finite system - Local density approximation. - Coherent phenomena - Present experimental status of exciton BEC
 19th of June 2008 at 11:00, [SLIDES] Gora Shlyapnikov, Laboratoire de Physique Théorique et Modéles Statistiques, Univ. Paris-Sud, Orsay, France
"Ultracold Quantum gases" Dmitry Petrov and Gora Shlyapnikov: Lecture 5 "Dipolar quantum gases. Bosonic dipoles" - Dipolar systems to be studied. Dilute regime. Scattering problem - Dipolar Bose-Einstein condensate. Dynamical instability - Trapped dipolar BEC. Gross-Pitaevskii equation. Stability diagram. - 2D and 1D dipolar BEC. Roton-maxon spectrum and instability - Can one obtain a supersolid state in free space?
 17th of June 2008 at 11:00, [SLIDES] Gora Shlyapnikov, Laboratoire de Physique Théorique et Modéles Statistiques, Univ. Paris-Sud, Orsay, France
"Ultracold Quantum gases" Dmitry Petrov and Gora Shlyapnikov: Lecture 4 "Strongly interacting Fermi gases" - Strongly interacting regime. Unitarity limit. - Universal thermodynamics - Experiments with two-species Fermi gases. Monte Carlo studies. - Strongly interacting regime in Fermi mixtures. What changes on the BEC and on the BCS sides of the resonance?
 13th of June 2008 at 11:00, [SLIDES] Dmitry Petrov, Laboratoire de Physique Théorique et Modéles Statistiques, Univ. Paris-Sud, Orsay, France
"Ultracold Quantum gases" Dmitry Petrov and Gora Shlyapnikov: Lecture 2 "Three-body problem" - Born-Oppenheimer approximation - Efimov effect - Three-body problem near a narrow resonance - Few-body problem in a lattice, exotic trimer states - Exact (not Born-Oppenheimer) approach to three-body problem
 10th of June 2008 at 11:00, [SLIDES] Dmitry Petrov, Laboratoire de Physique Théorique et Modéles Statistiques, Univ. Paris-Sud, Orsay, France
"Ultracold Quantum gases" Dmitry Petrov and Gora Shlyapnikov: Lecture 1 "Scattering theory" - Interatomic forces. Van der Waals potential. Length and energy scales - Ultracold scattering. Scattering amplitude, length and volume - Resonant scattering. Width of the resonance - Short-range pseudopotentials