  Using the Pontryagin maximum principle, the generic structure of optimal
policies is deduced for typical quantum control tasks involving coherent
lasers, magnetic fields and reservoir engineering. In addition, the periodic
optimization is considered for the first time in view of prospective
applications. We proved that nearly all optimal policies are actively
constrained by technical bounds on control parameter but reduce to entirely
bang-bang sequences only in special cases, such as the environmental control by
random collisions. The results allow to arguably refute two generally accepted
and concurring conjectures regarding the structure of optimal controls.
