Diffusion of periodically forced Brownian particles moving in space-periodic potentials

The diffusion properties of overdamped particles moving in spatially symmetrical periodic potentials subject to both symmetrical time-periodic driving and stochastic forcing are investigated [the typical model formally reads x = -V'(x) + U(t) + Gamma(t), V(L +/- x) = V(x), U(T + t) = U(t), [Gamma(t)] = 0, [Gamma(t)Gamma(tau)] = 2D delta(t - tau)]. It is found that the diffusion rate can be greatly enhanced if the various forcings are chosen in an optimal matching. In particular, we may get a diffusion rate larger than the rate of free diffusion.