  A nanoscale object evidenced in a non-classical state of its centre of mass
will hugely extend the boundaries of quantum mechanics. To obtain a practical
scheme for the same, we exploit a hitherto unexplored coupled system: an atom
and a nanoparticle coupled by an optical field. We show how to control the
center-of-mass of a large $\sim500$nm nanoparticle using the internal state of
the atom so as to create, as well as detect, nonclassical motional states of
the nanoparticle. Specifically, we consider a setup based on a silica
nanoparticle coupled to a Cesium atom and discuss a protocol for preparing and
verifying a Schr\"{o}dinger-cat state of the nanoparticle that does no require
cooling to the motional ground state. We show that the existence of the
superposition can be revealed using the Earth's gravitational field using a
method that is insensitive to the most common sources of decoherence and works
for any initial state of the nanoparticle.
