  The preparation of pure quantum states with high degrees of macroscopicity is
a central goal of ongoing experimental efforts to control quantum systems. We
present a state preparation protocol which renders a mechanical oscillator with
an arbitrarily large coherent amplitude in a manifestly nonclassical state. The
protocol relies on coherent state preparation followed by a projective
measurement of a single Raman scattered photon, making it particularly suitable
for cavity optomechanics. The nonclassicality of the state is reflected by
sub-Poissonian phonon statistics, which can be accessed by measuring the
statistics of subsequently emitted Raman sideband photons. The proposed
protocol would facilitate the observation of nonclassicality of a mechanical
oscillator that moves macroscopically relative to motion at the single-phonon
level.
