Chaotic Hamiltonian pumps

We present the results of a first exploratory survey of chaotic hamiltonian pumps, constructed as ratchets of finite extension. Two simple models are studied, composed of single or double square potential wells subject to a two-parameter driving that acts on the depth or the position of the wells. Binary spatio-temporal symmetries are broken by desymmetrizing the driving forces and/or the static shape of the potential. Numerical results indicate the existence of directed currents over wide ranges of the incoming energy and the model parameters, even after averaging over the relative phase of the two driving forces. They are not compatible with an adiabatic approximation.