Europhys. Lett., 71 (4), pp. 536-541 (2005)
DOI: 10.1209/epl/i2005-10116-1

Closed-loop control strategy with improved current for a flashing ratchet

L. Dinis¹, J. M. R. Parrondo¹ and F. J. Cao<sup>1, 2

1</sup>  Grupo Interdisciplinar de Sistemas Complejos (GISC) and Departamento de Física Atómica, Molecular y Nuclear Universidad Complutense de Madrid - 28040 Madrid, Spain
²  LERMA, Observatoire de Paris, Laboratoire Associé au CNRS UMR 8112 61 Avenue de l'Observatoire, 75015 Paris, France

received 26 April 2005; accepted in final form 16 June 2005
published online 13 July 2005

Abstract
We show how to switch on and off the ratchet potential of a collective Brownian motor, depending only on the position of the particles, in order to attain a current higher than or at least equal to that induced by any periodic flashing. Maximization of instant velocity turns out to be the optimal protocol for one particle but is nevertheless defeated by a periodic switching when a sufficiently large ensemble of particles is considered. The protocol presented in this letter, although not the optimal one, yields approximately the same current as the optimal protocol for one particle and as the optimal periodic switching for an infinite number of them.

PACS
05.40.-a - Fluctuation phenomena, random processes, noise, and Brownian motion.
02.30.Yy - Control theory.

© EDP Sciences 2005