  In this article we examine the dynamics of a colloidal particle driven by a
modulated force over a sinusoidal optical potential energy landscape. Coupling
between the competing frequencies of the modulated drive and that of particle
motion over the periodic landscape leads to synchronisation of particle motion
into discrete modes. This synchronisation manifests as steps in the average
particle velocity, with mode locked steps covering a range of average driving
velocities. The amplitude and frequency dependence of the steps are considered,
and compared to results from analytic theory, Langevin Dynamics simulations,
and Dynamic Density Functional Theory. Furthermore, the critical driving
velocity is studied, and simulation used to extend the range of conditions
accessible in experiments alone. Finally, state diagrams from experiment,
simulation, and theory are used to show the extent of the dynamically locked
modes in two dimensions, as a function of both the amplitude and frequency of
the modulated drive.

Soft Condensed Matter