Wave-Mediated Random Walks of Bouncing Beads

A millimetric droplet bouncing on the surface of a vertically vibrated liquid bath constitutes an exotic active particle: at each impact, the droplet excites a localized standing wave that persists over many forcing periods. When the droplet’s vertical dynamics resonate with this wave field, the droplet can self-propel along a straight trajectory at nearly constant speed, forming the basis of pilot-wave hydrodynamics. We introduce a complementary experimental system in which drops are replaced by solid beads. Unlike walking droplets, the beads do not self-propel ballistically but instead execute a two-dimensional random walk on the surface, while remaining coupled through the underlying wave field. We characterize the resulting bouncing regimes and particle dynamics through detailed experiments.