  We study the localization and addressability of ultra cold atoms in a
combined parabolic and periodic potential. Such a potential supports the
existence of localized stationary states and we show that using a radio
frequency field allows to selectively address the atoms in these states. This
method is used to measure the energy and momentum distribution of the atoms in
the localized states. We also discuss possible extensions of this scheme to
address and manipulate particles in single lattice sites.
