  We study the hydrodynamic coupling of neighboring micro-beads placed in a
dual optical trap setup allowing us to precisely control the degree of coupling
and directly measure time-dependent trajectories of the entrained beads.
Average experimental trajectories of a probe bead entrained by the motion of a
neighboring scan bead are compared with theoretical computation, illustrating
the role of viscous coupling and setting timescales for probe bead relaxation.
The findings provide direct experimental corroborations of hydrodynamic
coupling at larger, micron spatial scales and millisecond timescales, of
relevance to hydrodynamic-assisted colloidal assembly as well as improving the
resolution of optical tweezers. We repeat the experiments for three bead
setups.
