  In this letter we consider the phase diffusion of a harmonically driven
undamped pendulum and show that it is anomalous in the strong sense. The role
played by the fractal properties of the phase space is highlighted, providing
an illustration of the link between deterministic chaos and anomalous
transport. Finally, we build a stochastic model which reproduces most
properties of the original Hamiltonian system by alternating ballistic flights
and random diffusion.
