Relative diffusion in a chaotic system: Capillary waves in the Faraday experiment

We present experimental results for the motion of particles moving on capillary ripples. The ripples are formed on the surface of a fluid undergoing vertical oscillations. We find an anomalous relative diffusion: particles initially close separate in time, moving more rapidly apart as their distance increases. This result is surprising, as self-diffusion measurements indicate that single particles essentially move like random walkers.