  We report on the efficient design of quantum optimal control protocols to
manipulate the motional states of an atomic Bose-Einstein condensate (BEC) in a
one-dimensional optical lattice. Our protocols operate on the momentum comb
associated with the lattice. In contrast to previous works also dealing with
control in discrete and large Hilbert spaces, our control schemes allow us to
reach a wide variety of targets by varying a single parameter, the lattice
position. With this technique, we experimentally demonstrate a precise, robust
and versatile control: we optimize the transfer of the BEC to a single or
multiple quantized momentum states with full control on the relative phase
between the different momentum components. This also allows us to prepare the
BEC in a given eigenstate of the lattice band structure, or superposition
thereof.
