Tutelle du CNRSQuantum Matter group
led by Laurent Sanchez-Palencia

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Summer school Disorder in Condensed Matter and Ultracold Atoms

Annoucement: The Summer School, organized by Thierry Giamarchi, Giacomo Roati, and Laurent Sanchez-Palencia, will take place at the Institut d'Etudes Scientifiques de Cargčse. It is located on the west cost of the beautiful Corsica island in the south of France, near by the city of Ajaccio. The place enjoins a great landscape and a direct access to the sea. The wheather is usually fantastic in June and July.

Important dates:
____- Opening of applications: Mon, 8 Feb 2016
____- Deadline for application: Thu, 31 March 2015
____- Notification of acceptance: Mid-April
____- Deadline for registration: End of May

All information at http://dcmua2016.sciencesconf.org/.


Mott transition for strongly-interacting one-dimensional Bosons in a shallow periodic potential

January 2016: Rapid Communication by G. Boéris, L. Gori, M.D. Hoogerland, A. Kumar, E. Lucioni, L. Tanzi, M. Inguscio, T. Giamarchi, C. D'Errico, G. Carleo, G. Modugno, and L. Sanchez-Palencia published in Physical Review A.

We investigate the superfluid-insulator transition of one-dimensional interacting bosons in both deep and shallow periodic potentials. We compare a theoretical analysis based on quantum Monte-Carlo simulations in continuum space and Luttinger liquid approach with experiments on ultracold atoms with tunable interactions and optical lattice depth. Experiments and theory are in excellent agreement. Our study provides a quantitative determination of the critical parameters for the Mott transition and defines the regimes of validity of widely used approximate models, namely the Bose-Hubbard and sine-Gordon models.


Samuel LELLOUCH is awarded the 2015 PhD thesis prize jointly from IFRAF and GDR on Cold Atoms.

October 2015 Samuel Lellocuh has been awarded the 2015 PhD thesis prize from the French Institute of Research on Cold Atoms (IFRAF) and the Research Network on Cold Atoms for his work on . Click on text to read Samuel's PhD manuscript.


Protected quasi-locality in quantum systems with long-range interactions

October 2015: Rapid Communication by L. Cevolani, G. Carleo, and L. Sanchez-Palencia published in Physical Review A.

We study the out-of-equilibrium dynamics of quantum systems with long-range interactions. Two different models describing, respectively, interacting lattice bosons and spins are considered. Our study relies on a combined approach based on accurate many-body numerical calculations as well as on a quasiparticle microscopic theory. For sufficiently fast decaying long-range potentials, we find that the quantum speed limit set by the long-range Lieb-Robinson bounds is never attained and a purely ballistic behavior is found. For slowly decaying potentials, a radically different scenario is observed. In the bosonic case, a remarkable local spreading of correlations is still observed, despite the existence of infinitely fast traveling excitations in the system. This is in marked contrast to the spin case, where locality is broken. We finally provide a microscopic justification of the different regimes observed and of the origin of the protected locality in the bosonic model.


At the edge of mobility

July 2015: News and Views piece by L. Sanchez-Palencia published in Nature Physics.

The Anderson transition point between localization and diffusion - the mobility edge - has now been directly measured in an ultracold-atom experiment by the LENS group lead by G. Modugno and M. Inguscio.


Localization transition in weakly interacting Bose superfluids in one-dimensional quasiperdiodic lattices

December 2014: Rapid Communication by S. Lellouch and L. Sanchez-Palencia published in Physical Review A.

We study the localization of collective pair excitations in weakly-interacting Bose superfluids in one-dimensional quasiperiodic lattices. The localization diagram is first determined numerically. For intermediate interaction and quasiperiodic amplitude we find a sharp localization transition, with extended low-energy states and localized high-energy states. We then develop an analytical treatment, which allows us to quantitatively map the localization transition into that of an effective multiharmonic quasiperiodic system.


Marie PIRAUD is awarded the PhD thesis prize in physics of University Paris Sud.

June 2014 Marie Piraud has been awarded the 2014 PhD thesis prize in physics of the EDOM Graduate School of University Paris Sud for her work on Anderson localization of matter waves in correlated disorder: From 1D to 3D. Click on text to read Marie's PhD manuscript.


Light-cone effect and supersonic correlations in one- and two-dimensional bosonic superfluids

March 2014: Rapid Communication by G. Carleo, F. Becca, L. Sanchez-Palencia, S. Sorella, and M. Fabrizio published in Physical Review A.

We study the spreading of density-density correlations in Bose-Hubbard models after a quench of the interaction strength, using time-dependent variational Monte Carlo simulations. It gives access to unprecedented long propagation times and to dimensions higher than one. In both one and two dimensions, we find ballistic light-cone spreading of correlations and extract accurate values of the light-cone velocity in the superfluid regime. We show that the spreading of correlations is generally supersonic, with a light-cone propagating faster than sound modes but slower than the maximum group velocity of density excitations, except at the Mott transition, where all the characteristic velocities are equal. Further, we show that in two dimensions the correlation spreading is highly anisotropic and presents nontrivial interference effects.


Universal superfluid transition and transport properties of two-dimensional dirty bosons

August 2013: Letter by G. Carleo, G. Boéris, M. Holzmann, and L. Sanchez-Palencia published in Physical Review Letters.

We study the phase diagram of two-dimensional, interacting bosons in the presence of a correlated disorder in continuous space, using large-scale finite temperature quantum Monte Carlo simulations. We show that the superfluid transition is strongly protected against disorder. It remains of the Berezinskii-Kosterlitz-Thouless type up to disorder strengths comparable to the chemical potential. Moreover, we study the transport properties in the strong disorder regime where a zero-temperature Bose-glass phase is expected. We show that the conductance exhibits a thermally activated behavior vanishing only at zero temperature. Our results point towards the existence of Bose bad-metal phase as a precursor of the Bose-glass phase.


Giuseppe CARLEO is awarded a Marie Curie fellowship

July 2013: Giuseppe Carleo has been awarded a Marie Curie fellowship from the European Union. He will work in the group on the dynamics of strongly correlated quantum systems.


Marie PIRAUD is awarded the poster prize at DCMUA2013

June 2013: Marie Piraud has been awarded the best poster presentation at the conference Disorder in Condensed Matter and Ultracold Atoms (Varennna, Italy; 2013). Two prizes, sponsored by EuroPhysics Letters, have been given by Graeme Watt, executive editor of EuroPhysics Letters. The committee was made of Tilman Esslinger and Thierry Giamarchi.


Matter wave transport and Anderson localization in anisotropic 3D disorder

September 2012: Letter by M. Piraud, L. Pezzé, and L. Sanchez-Palencia published in Europhysics Letters.

We study quantum transport in anisotropic 3D disorder and show that non rotation invariant correlations can induce rich diffusion and localization properties. For instance, structured finite-range correlations can lead to the inversion of the transport anisotropy. Moreover, working beyond the self-consistent theory of localization, we include the disorder-induced shift of the energy states and show that it strongly affects the mobility edge. Implications to recent experiments are discussed.


Three-dimensional localization of ultracold atoms in an optical disordered potential

March 2012: Article by F. Jendrzejewski, A. Bernard, K. Müller, P. Cheinet, V. Josse, M. Piraud, L. Pezzé, L. Sanchez-Palencia, A. Aspect, and P. Bouyer published in Nature Physics.

In disordered media, quantum interference effects are expected to induce complete suppression of electron conduction. The phenomenon, known as Anderson localization, has a counterpart with classical waves that has been observed in acoustics, electromagnetism and optics, but a direct observation for particles remains elusive. Here, we report the observation of the three-dimensional localization of ultracold atoms in a disordered potential created by a speckle laser field. A phenomenological analysis of our data distinguishes a localized component of the resulting density profile from a diffusive component. The observed localization cannot be interpreted as the classical trapping of particles with energy below the classical percolation threshold in the disorder, nor can it be understood as quantum trapping in local potential minima. Instead, our data are compatible with the self-consistent theory of Anderson localization tailored to our system, involving a heuristic energy shift that offers scope for future interpretation.


Contact

Laurent SANCHEZ-PALENCIA

lsp@cpht.polytechnique.fr

Center for Theoretical Physics

Ecole Polytechnique

F-91128 Palaiseau - France, EU

Office: 00.10.10 (ground floor)

Phone: +33 1 69 33 42 13

Fax: +33 1 69 33 49 49