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 $\dot{x}{=-V}^{\prime }\left(x\right)+U\left(t\right)+\gamma \left(t\right)$, $V(L\pm x)=V\left(x\right)$, $U(T+t)=U\left(t\right)$, $〈\gamma \left(t\right)〉=0\mathrm{}$, $〈\gamma \left(t\right)\gamma \left(\tau \right)〉=2D\delta (t-\tau )$]. 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.

• Received 26 January 1996

DOI:https://doi.org/10.1103/PhysRevLett.76.4874