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DY: Fachverband Dynamik und Statistische Physik
DY 33: Poster II
DY 33.1: Poster
Donnerstag, 14. März 2013, 17:00–19:00, Poster C
Efficiency of a Brownian information machine — •Michael Bauer, David Abreu, and Udo Seifert — II. Institut für Theoretische Physik, Universität Stuttgart, 70550 Stuttgart, Germany
The second law of thermodynamics forbids cyclic engines that extract work from a single heat bath when there is no other interaction with the surrounding medium. By making a gedankenexperiment with a Maxwell demon it became clear that with additional information on the system one can indeed extract work.
We investigate two types of an engine modelled by a Brownian particle in a time dependent harmonic trap [1]. In every cycle we perform a measurement with finite precision before we apply a feedback scheme which depends on the measurement outcome. Since the machine operates at finite time the distribution will not be in equilibrium after the measurement. Hence in every cycle the work will depend on all measurements before. We calculate analytically the average work in the steady state for a large number of cycles. To define a efficiency we calculate the information extracted from on the system by the measurements. In the first type of this engine only the center of the potential moves. Here, one extracts 1/2 kBT in a quasistatic case with perfect measurements. The maximal power is 1/2 for short cycle periods but then the efficiency goes to zero. In the second variant, additionally the strength of the potential changes which leads to efficiency 1 for precise measurements in finite time.
[1] M. Bauer, D. Abreu and U. Seifert. J. Phys. A: Math. Theor. 45, 162001 (2012).