Enhancement of mobility by periodically modulating the slanting slope of a washboard potential

Average mobility of very feebly damped particles in tilted periodic potentials is considered. Under the combined action of thermal fluctuations and small temporal modulation of the tilt of the potential the particles, in the small tilt range, become more mobile than those without modulation. The enhancement of mobility depends (nonmonotonically) on the frequency of modulation. For small modulations the enhancement shows a peak as a function of frequency. This has an obvious implication, for instance, on the measured voltage across a Josephson junction driven by a small amplitude alternating current of suitable frequency. There is an intermediate range of the average tilt, say below about 0.16 times the critical tilt (at which the potential barrier to motion just disappears) the motion of the particle is slowed down as a result of modulation.