The control of transport is a recurrent topic in physics, chemistry and biology. Particles diffusing on a periodic substrate, according to the laws of Brownian motion, represent an archetype of the transport one would like to harness.
The present work demonstrates that a complete control of transport of Brownian particles can be achieved via ac fields. Experimental evidence is produced by using cold atoms in a dissipative optical lattice as a model system. Two different mechanisms are considered. In the first, the application of a multi-harmonic ac driving field leads to a “ratchet effect” with the appearance of directed motion in the absence of a net applied bias force. In the second, we address the possibility of tuning the periodic potential with an external drive. This is often considered the ultimate limit for the control of transport as in many cases, e.g. in solid state, direct tuning of the potential is not possible. We provide a proof-of-principle of how this limitation can be overcome, and demonstrate the renormalization of a periodic potential amplitude via a strong high-frequency oscillating field.