| Summary: | The structure and dynamics of colloidal particles in optical potential energy landscapes is studied. Experiments use paramagnetic or optically anisotropic colloidal particles interacting with lines or pairs of time-dependent optical traps. First, the pairwise interactions of the paramagnetic particles are measured using pairs of optical traps. We test a novel data analysis method under various conditions and calculate the magnetic susceptibility of the particles. Next, we measure the structure and dynamics of chains of paramagnetic colloids in a sinusoidal optical potential of varying depth. At well defined chain lengths, we observe a transition from an asymmetric, strongly pinned state to a free-sliding, symmetric state as the optical potential decreases. We then analyse the frictional dynamics of the same system under a constant driving force and observe a transition from low to high friction as the optical potential increases. We model the dynamics of the chains in the low and high friction regimes. The simple hard sphere model developed for the high friction regime is used to derive an equation which predicts the transition point from low to high friction. Next, we drive the chains through a time-dependent optical potential with an oscillating depth. We analyse the synchronisation of the chain’s motion to the oscillations of the potential and characterise the dynamics, observing a novel mode of motion involving the simultaneous nucleation of kinks and anti-kinks. Finally, we study the dynamics of a single optically anisotropic dumbbell particle interacting with a repulsive optical trap controlled by a time-delayed feedback protocol. We observe a transition from diffusive to driven dynamics which is modelled using delay-differential equations. We find that this transition coincides with the maximum work done on the particle and a local minimum in the mutual information between the particle and the trap.
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