Dresden 2011 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 21: Thermodynamics and Statistical Physics of Small Systems (contributed talks)

DY 21.2: Vortrag

Mittwoch, 16. März 2011, 12:00–12:15, HÜL 186

Measurements in optimal finite-time thermodynamics — •David Abreu and Udo Seifert — II. Institut für Theoretische Physik, Universität Stuttgart, 70550 Stuttgart, Germany

The second law states the impossibility of extracting work from a system in a single thermal bath. However, as Sagawa and Ueda recently showed [1], this becomes possible if we extract information out of the system through measurements. We show here a basic example of an isothermal engine based on the conversion of information into work.

Our model system consists in a Brownian particle confined in a harmonic potential that we want to displace from its initial position to a fixed final position in finite time. Performing one or more measurements of the position of the particle at the beginning or during the process leads to work extraction from the thermal bath. We optimize the output work of such a process and build a cyclic engine based on it. We observe the presence of an optimal cycle-time which depends on the precision of the measurements.

We then quantify the information obtained during the measurements and show that we can transform it all into useful work in the quasistatic limit, given that we control not only the position but also the stiffness of the potential. We compare this result to a discrete two-level system, analogous to the Szilard engine, and show that the expressions of the total extractable work in both cases are similar and consistent with each other.

[1] T. Sagawa and M. Ueda. Phys. Rev. Lett. 104, 090602 (2010).