  Optimal control theory is usually formulated as an indirect method requiring
the solution of a two-point boundary value problem. Practically, the solution
is obtained by iterative forward and backward propagation of quantum
wavepackets. Here, we propose direct optimal control as a robust and flexible
alternative. It is based on a discretization of the dynamical equations
resulting in a nonlinear optimization problem. The method is illustrated for
the case of laser-driven wavepacket dynamics in a bistable potential. The
wavepacket is parameterized in terms of a single Gaussian function and field
optimization is performed for a wide range of particle masses and lengths of
the control interval. Using the optimized field in a full quantum propagation
still yields reasonable control yields for most of the considered cases.
Analysis of the deviations leads to conditions which have to be fulfilled to
make the semiclassical single Gaussian approximation meaningful for field
optimization.
