  We propose the implementation of selective interactions of atom-motion
subspaces in trapped ions. These interactions yield resonant exchange of
population inside a selected subspace, leaving the others in a highly
dispersive regime. Selectivity allows us to generate motional Fock (and other
nonclassical) states with high purity out of a wide class of initial states,
and becomes an unconventional cooling mechanism when the ground state is
chosen. Individual population of number states can be distinctively measured,
as well as the motional Wigner function. Furthermore, a protocol for
implementing quantum logic through a suitable control of selective subspaces is
presented.
