  We analyze the requirements to test some of the most paradigmatic collapse
models with a protocol that prepares quantum superpositions of massive objects.
This consists of coherently expanding the wave function of a
ground-state-cooled mechanical resonator, performing a squared position
measurement that acts as a double slit, and observing interference after
further evolution. The analysis is performed in a general framework and takes
into account only unavoidable sources of decoherence: blackbody radiation and
scattering of environmental particles. We also discuss the limitations imposed
by the experimental implementation of this protocol using cavity quantum
optomechanics with levitating dielectric nanospheres.
