  A fully reconfigurable two-dimensional (2D) rocking ratchet system created
with holographic optical micromanipulation is presented. We can generate
optical potentials with the geometry of any Bravais lattice in 2D and introduce
a spatial asymmetry with arbitrary orientation. Nontrivial directed transport
of Brownian particles along different directions is demonstrated numerically
and experimentally, including on-axis, perpendicular and oblique with respect
to an unbiased ac driving. The most important aspect to define the current
direction is shown to be the asymmetry and not the driving orientation, and yet
we show a system in which the asymmetry orientation of each potential well does
not coincide with the transport direction, suggesting an additional symmetry
breaking as a result of a coupling with the lattice configuration. Our
experimental device, due to its versatility, opens up a new range of
possibilities in the study of nonequilibrium dynamics at the microscopic level.
