Controlled dynamics of interfaces in a vibrated granular layer

We present an experimental study of a topological excitation, interface, in a vertically vibrated layer of granular material. We show that these inter faces, which separate regions of granular material oscillating with opposit e phases, can be shifted and controlled by a very small amount of additiona l subharmonic driving mixed with the harmonic driving signal. The speed and the direction of the interface motion depends sensitively on the phase and the amplitude of the subharmonic driving.