Two seminars on Tuesday

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

JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR



Tuesday, 4 May   -   11:00 hrs.



SISSA, Santorio, Room 004



Udo SEIFERT    ( Universitaet Stuttgart )



"Stochastic thermodynamics"



Abstract



Stochastic thermodynamics provides a framework for describing small  
systems embedded in a heat bath and externally driven to non- 
equilibrium [1].  Examples are colloidal particles in time-dependent  
optical traps, single biomolecules manipulated by optical tweezers or  
AFM tips, and motor proteins driven by ATP excess.  A first-law like  
energy balance allows to identify applied work and dissipated heat on  
the level of a single stochastic trajectory.  Total entropy production  
includes not only this heat but also changes in entropy associated  
with the state of the small system.  Within such a framework, exact  
results like an integral fluctuation theorem for total entropy  
production valid for any initial state, any time-dependent driving and  
any length of trajectories can be proven [2].  These results hold both  
for mechanically driven systems modelled by over-damped Langevin  
equations and chemically driven (biochemical) reaction networks [3].   
These theoretical predictions have been illustrated and tested with  
experiments on a colloidal particle pushed by a periodically modulated  
laser towards a surface [4].  Key elements of this framework like a  
stochastic entropy can also be applied to athermal systems as  
experiments on an optically driven defect center in diamond show [5].   
Optimization within stochastic thermodynamics looks for the optimal  
protocols connecting two different states in finite-time with the  
least amount of dissipation [6].  For perturbations of non-equilibrium  
steady states, we have recently derived a generalized fluctuation- 
dissipation theorem and generalized Green-Kubo relations [7,8].

  [1] U. Seifert, Eur. Phys. J. B,  64 : 423, 2008.

  [2] U. Seifert, Phys. Rev. Lett. 95: 040602, 2005.

  [3] T. Schmiedl and U. Seifert, J. Chem. Phys. 126:044101, 2007.

  [4] V. Blickle, T. Speck, L. Helden, U. Seifert, and C. Bechinger,   
Phys. Rev. Lett. 96: 070603, 2006.

  [5] S. Schuler, T. Speck, C. Tietz, J. Wrachtrup, and U. Seifert,  
Phys. Rev. Lett. 94: 180602, 2005.

  [6] T. Schmiedl and U. Seifert, Phys. Rev. Lett. 98: 108301, 2007.

  [7] U. Seifert and T. Speck, EPL 89, 10007, 2010.

  [8] U. Seifert, Phys. Rev. Lett. 104, 138101, 2010.



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JOINT ICTP/SISSA STATISTICAL PHYSICS SEMINAR





Tuesday, 4 May   -   14:00 hrs.





SISSA, Santorio, Room 004





Marc MEZARD     ( Universite' XI Paris Sud )





"The cavity method for  quantum disordered systems"





Abstract



Motivated by the study of disordered superconductors, we develop an  
analytical theory, based on the quantum cavity method, describing the  
quantum phase transitions of disordered systems.  A connection to the  
classical problem of directed polymers in random media shows the  
relevance of replica symmetry breaking effects.  Because of these  
effects, various aspects of the zero temperature phase transition are  
very different from what is found in usual phase transitions, and  
strong inhomogeneities play a crucial role.