2 seminars coming up on Tuesday

[Cond.Matt. & Stat.Mech.Section]

JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR



Tuesday, 25 October   -   11:00 hrs.

 

Luigi Stasi Seminar Room, ICTP Leonardo Building - 1st floor

 



G. CARLEO   ( SISSA )

 

"Localization and glassy dynamics of many-body quantum systems"

 

Abstract

 

When classical systems fail to explore their entire configurationalspace, intriguing macroscopicphenomena like aging and glass formation may emerge. Also closed quanto-mechanical systems may stop wandering freely around the whole Hilbert space, even if they are initially prepared into a macroscopically large combination of eigenstates.  This phenomenon is actually known to occur in presence of disorder and manifests itself either by

single-particle [1] or many-particle  [2] wavefunction localization. However, alike classical models for glassy behavior, ergodicity breakdown may not necessarily require disorder.  [3] In this talk I will report numerical evidences that the dynamics of strongly interacting lattice bosons driven sufficiently far from equilibrium can be trapped into extremely long-lived inhomogeneous metastable states.  [4] The slowing down of incoherent density excitations above a threshold energy, much reminiscent of a dynamical arrest on the verge of a glass transition, is identified as the key feature of this phenomenon.  We argue that the resulting long-lived inhomogeneities are responsible for the lack of thermalization observed in large systems.  [5] Such a rich phenomenology could be experimentally uncovered upon probing the out-of-equilibrium dynamics of conveniently prepared quantum states of trapped cold atoms which I will discuss.  The approach used to extensively investigate this phenomenon is based both on the exact solution of the quantum dynamics and on a novel real- time variational Quantum Monte Carlo method we have introduced.  [4] The latter approach offers a reliable accuracy and stability in the study of 1-dimensional systems while also o_ering a seamless exploration of higher dimensional geometries.

REFERENCES

[1] P. W. Anderson, Phys. Rev. 109, 1492 (1958).

[2] D. Basko, I. Aleiner and B. Altshuler, Annals of Physics 321,1126 (2006)

[3] G. Biroli and M. Mezard Phys. Rev. Lett. 88, 025501 (2001).

[4] G. Carleo, F. Becca, M. Schiro and M. Fabrizio, arXiv:1109.2516 (2011).

[5] C. Kollath, A. M. Lauchli and E. Altman, Phys. Rev. Lett. 98, 180601 (2007).



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JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR



 Tuesday, 25 October   -   14:00 hrs.

 

 

Luigi Stasi Seminar Room, ICTP Leonardo Building - 1st floor

 

 

Yasser ROUDI   ( Kavli Institute, Stockholm )

 

"Mean field theory for   nonequilibrium network reconstruction"

  

Abstract

 

With the advancement of recording technology in various parts of biology, we can now observe many elements in a biological system at the same time.  For instance we can measure the expression level of many genes using gene microarrays or spike trains from many neurons using multi-electrode arrays.  Given this, an important and interesting question to ask is "can we use such data to infer interactions between elements of the system?".  In this talk, I will describe toy versions of this problem.  I will briefly describe how it can be done for an equilibrium Ising model, that is the inverse Ising problem; then I discuss inferring the interactions of a non-equilibrium Sherrington-Kirkpatrick model showing how Dynamical Mean-Field theory (naive mean field, TAP and exact MF) can be developed and exploited for inferring network connectivity.