  We present measurements of the ac response of a single-electron box (SEB). We
apply an rf signal with a frequency larger than the tunneling rate and drive
the system out of equilibrium. We observe much more dissipation in the SEB then
one would expect from a simple circuit model. We can explain this in terms of a
mechanism that we call the Sisyphus resistance. The Sisyphus resistance has a
strong gate dependence which can be used for electrometery applications.
