Strings of droplets propelled by coherent waves

Bouncing walking droplets possess fascinating properties due to their
peculiar wave/particule interaction. In order to study such walkers in a 1d
system, we considered the case of one or more droplets in an annular cavity. We
show that, in this geometry, walking droplets form a string of synchronized
bouncing droplets that share a common coherent wave propelling the group at a
speed faster than single walkers. The formation of this coherent wave and the
collective behavior of droplets is captured by a model.