  A recently developed theory of stochastic swimming is used to study the
notion of coherence in active systems that couple via hydrodynamic
interactions. It is shown that correlations between various modes of
deformation in stochastic systems play the same role as the relative internal
phase in deterministic systems. An example is presented where a simple swimmer
can use these correlations to hunt a non-swimmer by forming a hydrodynamic
bound state of tunable velocity and equilibrium separation. These results
highlight the significance of coherence in the collective behavior of
nano-scale stochastic swimmers.
