Traditionally the charge ratchet effect is considered as a consequence of
either the spatial symmetry breaking engineered by asymmetric periodic
potentials, or time asymmetry of the driving fields. Here we demonstrate that
electrically and magnetically driven quantum dissipative systems with
spin-orbit interactions represent an exception from this standard idea. In
contrast to the so far well established belief, a charge ratchet effect appears
when both the periodic potential and driving are symmetric. We show that the
source of this paradoxical charge ratchet mechanism is the coexistence of
quantum dissipation with the spin flip processes induced by spin-orbit
interactions.Comment: 5 pages, 3 figure
