Temporally Asymmetric Fluctuations are Sufficient for the Operation of a Correlation Ratchet

A number of recent attempts to understand broad priniples of energy transduction in biological systems have focused on correlation ratchets---systems which extract work out of fluctuations which are correlated in time.[1, 2, 3, 4, 5, 6] Correlation ratchets are ``information engines'' analogous to Maxwell's Demon. which extract work out of a barh by using information about thte system to ``choose'' only those fluctuations which are helpful to make the engine run.[7] This information, which can only be acquired if the Demon is not in equilibrium with the bath,[8] can be used to rectify the energy already available, but otherwise inaccessible in the thermal bath. Processes like this, in which the energy stored in a nonequilibrium bath is transformed into woek at the expense of increased entropy, are belived to be the basis of ``molecular motor,'' and are of great importance in biology, and a number of other fields. I thas been shown that the combination of a broken spatial symmetry in the potential (or ratchet potential) and time correlations in the driving are crucial, and enough to allow the transformation of the fluctuations into work. The required broken spatial symmetry implies a specific molecular arrangement of the proteins involved. Here we show that a broken spatial symmetry is not required, and that a temporally asymmetric deiving with mean zero can be used to do work, even when the retchet potential is completely symmetric. This type of temporal asymmetry is particularly common in bilogical systems.