  We investigate a setup where a cloud of atoms is trapped in an optical
lattice potential of a standing wave laser field which is created by
retro-reflection on a micro-membrane. The membrane vibrations itself realize a
quantum mechanical degree of freedom. We show that the center of mass mode of
atoms can be coupled to the vibrational mode of the membrane in free space, and
predict a significant sympathetic cooling effect of the membrane when atoms are
laser cooled. The controllability of the dissipation rate of the atomic motion
gives a considerable advantage over typical optomechanical systems enclosed in
optical cavities, in that it allows a segregation between the cooling and
coherent dynamics regimes. The membrane can thereby be kept in a cryogenic
environment, and the atoms at a distance in a vacuum chamber.
