  We use optimal control theory to construct external electric fields which
coherently transfer the electronic charge in a double quantum-dot system.
Without truncation of the eigenstates we operate on desired superpositions of
the states in order to prepare the system to a localized state and to
coherently transfer the charge from one well to another. Within a fixed time
interval, the optimal processes are shown to occur through several excited
states. The obtained yields are generally between 99% and 99.99% depending on
the field constraints, and they are not dramatically affected by strict
frequency filters which make the fields (e.g., laser pulses) closer to
experimental realism. Finally we demonstrate that our scheme provides simple
access to hundreds of sequential processes in charge localization while
preserving the high fidelity.
