Tunable $\varphi$ Josephson Junction ratchet
  We demonstrate experimentally the operation of a deterministic Josephson ratchet with tunable asymmetry. The ratchet is based on a $\varphi$ Josephson junction with a ferromagnetic barrier operating in the underdamped regime. The system is probed also under the action of an additional dc current, which acts as a counter force trying to stop the ratchet. Under these conditions the ratchet works against the counter force, thus producing a non-zero output power. Finally, we estimate the efficiency of the $\varphi$ Josephson junction ratchet. 
R. Menditto, H. Sickinger, M. Weides, H. Kohlstedt, D. Koelle, R.   Kleiner, and E. Goldobin
cond-mat.supr-con nlin.SI