  We study synchronization in bulk suspensions of spherical microswimmers with
chiral trajectories using large scale numerics. The model is generic. It
corresponds to the lowest order solution of a general model for self-propulsion
at low Reynolds numbers, consisting of a nonaxisymmetric rotating source
dipole. We show that both purely circular and helical swimmers can
spontaneously synchronize their rotation. The synchronized state corresponds to
velocity alignment with high orientational order in both the polar and
azimuthal directions. Finally, we consider a racemic mixture of helical
swimmers where intraspecies synchronization is observed while the system
remains as a spatially uniform fluid. Our results demonstrate hydrodynamic
synchronization as a natural collective phenomenon for microswimmers with
chiral trajectories.
