  Experimental observation of the decoherence of macroscopic objects is of
fundamental importance to the study of quantum collapse models and the quantum
to classical transition. Optomechanics is a promising field for the study of
such models because of its fine control and readout of mechanical motion.
Nevertheless, it is challenging to monitor a mechanical superposition state for
long enough to investigate this transition. We present a scheme for entangling
two mechanical resonators in spatial superposition states such that all quantum
information is stored in the mechanical resonators. The scheme is general and
applies to any optomechanical system with multiple mechanical modes. By
analytic and numeric modeling, we show that the scheme is resilient to
experimental imperfections such as incomplete pre-cooling, faulty postselection
and inefficient optomechanical coupling. This proposed procedure overcomes
limitations of previously proposed schemes that have so far hindered the study
of macroscopic quantum dynamics.
