*Adria.Palau@student.uib.no; Department of Physics and Technology, University of Bergen, Allégaten 55, 5007 Bergen, Norway; this author is included in the author list here because of his extensive contribution to the preparation of this Erratum.
Maximum net electrical power , overall efficiency at maximum power , and characteristic frequency of the noise at maximum power , as a function of and . In (b) the efficiency exceeds 1 as increases, due to the fact that the parameter values were chosen to be the same as in the original paper. As discussed in the text, the physically acceptable regime corresponds to .