Ratchet with tunable asymmetry based on φ Josephson junction. Operation, loading and efficiency

We demonstrate experimentally the operation of a deterministic Josephson ratchet with tunable asymmetry. The ratchet is based on a φ Josephson junction with a ferromagnetic barrier operating in the underdamped regime. The ratchet operation with a load, i.e. in the presence of the additional dc counter current trying to stop the ratchet, is also demonstrated. Under these conditions the ratchet produces a non-zero output power. We estimate the efficiency of the ratchet using a general model for Josephson ratchets with hysteresis.