|13:30 to 15:30||David Lacoste (ESPCI, Paris, France)||Session Chair|
|13:31 to 14:10||J. M. R. Parrondo (Universidad Complutense de Madrid, Spain)||
The Irreversibility Problem Revisited: Objectivity and Gaint Fluctuations
Boltzmann’s explanation of irreversibility is based on the concept of macro-states and the definition of entropy as the logarithm of the volume in phase space of the region of micro-states compatible with a given macro-state. The explanation, however, lacks an objective (i.e. non arbitrary) definition of macro-states and of the crossover between micro- and macro-scales. Here we show that this problem can be solved by reformulating Boltzmann’s explanation in terms of observables relaxing from giant fluctuations. We show that the irreversible behavior of an observable is a fully objective property and has nothing to do with its micro- or macroscopic nature. In fact, we will show a situation where a system exhibits irreversibility at the micro-scale and reversibility at the macro-scale. In the second part of the talk, we propose a mechanism for creating giant fluctuations of an observable (hence, irreversibility) based on metastable states induced by symmetry breaking.
|14:10 to 14:50||R. Marathe (Indian Institute of Technology, Delhi, India)||
Simple models of Active Brownian Heat engines
(Passive) Brownian heat engines are popular systems where a single microscopic particle is confined with the help of an optical trap and cycled through a time dependent protocol and kept in contact with two heat baths of different temperatures alternately, to mimic the macroscopic engine cycles like Carnot or Stirling. Due to the minute size of the system the fluctuations dominate. Recently it has been observed that presence of so called Active entities like Bacteria or Janus particles in the heat bath may drastically alter the thermodynamic properties, especially the efficiency of the engine, when compared with their passive counterparts. These are termed as Active Brownian Heat engines. I will discuss a few simple models of active heat engines that we have developed recently. I will also discuss a few general results that allow us to map such active, non-equilibrium system to an effective equilibrium system in the quasi-static limit of the cycle time.
|14:50 to 15:30||S. Sabhapandit (RRI, Bangalore, India)||
Entropy production for partially observed systems
The probability distribution of the total entropy production in the non- equilibrium steady state follows a symmetry relation called the fluctuation theorem. When a certain part of the system is masked or hidden, it is difficult to infer the exact estimate of the total entropy production. Entropy produced from the observed part of the system shows significant deviation from the steady-state fluctuation theorem. This deviation occurs due to the interaction between the observed and the masked part of the system. A naive guess would be that the deviation from the steady state fluctuation theorem may disappear in the limit of small interaction between both parts of the system.
|17:09 to 17:50||J M R Parrondo (Universidad de Madrid, Spain)||Session Chair|
|17:10 to 17:50||E. Barkai (Bar-Ilan University, Israel)||
Non-Normalized Boltzmann-Gibbs Statistics
Fermi pointed out that the Hydrogen atom in a thermal setting is unstable, as the canonical partition function of this simple system diverges. We show how a non-normalised Boltzmann Gibbs measure can still yield statistical averages and thermodynamic properties of physical observables, exploiting a model of Langevin dynamics of a Brownian particle in an asymptotically flat potential . The ergodic theory of such systems is known in mathematics as infinite (non-normalisable) ergodic theory, time permitting we will discuss these isssues in the context of a gas of laser cooled atoms .
 E. Aghion, D. A. Kessler, and E. Barkai From Non-normalizable Boltzmann-Gibbs statistics to infinite-ergodic theory Phys. Rev. Lett. 122, 010601 (2019).
 E. Barkai, G. Radons, and T. Akimoto Transitions in the ergodicity of subrecoil-laser-cooled gases Phys. Rev. Lett. 127, 140605 (2021).
|13:30 to 15:30||Abhishek Dhar (ICTS, Bengaluru, India)||Session Chair|
|13:31 to 14:10||S. Still (University of Hawaii, Mānoa, USA)||Partially Observable Information Engines|
|14:10 to 15:30||-||Session in memory of Prof. A. M. Jayannavar|