  We present a technique to control the spatial state of a small cloud of
interacting particles at low temperatures with almost perfect fidelity using
spatial adiabatic passage. To achieve this, the resonant trap energies of the
system are engineered in such a way that a single, well-defined eigenstate
connects the initial and desired states and is isolated from the rest of the
spectrum. We apply this procedure to the task of separating a well-defined
number of particles from an initial cloud and show that it can be implemented
in radio-frequency traps using experimentally realistic parameters.
