Michael Jack
University of Otago

Loss processes and efficiency limitations of Brownian motors

M. W. Jack^{1}, J. Devine^{1}, C. Tumlin^{2} and K. J.Challis^{3}

^{1}Department of Physics, University of Otago, Dunedin, New Zealand
^{2}Department of Engineering Science, Uppsala University, Sweden
^{3}Scion, Private Bag 3020, Rotorua 3046, New Zealand

Molecular scale devices that transform energy at room temperature can be mathematically modelled as Brownian motion. Brownian motors have complex interactions with their environments that may or may not lead to dissipation and reductions in efficiency. We consider the loss processes and efficiency of a number of different types of Brownian motors within a consistent thermodynamic framework.
First, we consider the case of an isothermal motor with two degrees of freedom. We illustrate and interpret the loss processes and show that this motor is able to reach the dissipation-less limit and perfect efficiency despite constant exchange of energy with its environment.
Second, we consider a motor with two degrees of freedoms but in this case each degree of freedom is in contact with a reservoir of different constant temperature. We show that this motor displays non-vanishing probability current vortices that mean it is never able to reach perfect efficiency. Finally, we consider a Brownian motor strongly interacting with its local environment such that it creates self-induced temperature gradients. We show how these self-induced gradients lead to losses and efficiency limitations.