Reversible fluctuation rectifier

The analysis of a Feynman's ratchet system [J. M. R. Parrondo and P. Espano l, Am. J. Phys. 64, 1125 (1996)] and of its electrical counterpart, a diode engine [I. M. Sokolov, Europhys. Lett. 44, 278 (1998)] has shown that "flu ctuation rectifiers" consisting of a nonlinear element (ratchet, diode) and a linear element (vane, resistor) kept at different temperatures always sh ow efficiency smaller than the Carnot value, thus indicating the irreversib le mode of operation. We show that this irreversibility is not intrinsic fo r a system in simultaneous contact with two heat baths at: different temper atures and that a fluctuation rectifier can work reversibly. This is illust rated by a model with two diodes switched in opposite directions, where the Carnot efficiency is achieved when backward resistivity of the diodes tend s to infinity. [S1063-651X(99)15510-7].