  We propose and demonstrate a versatile technique to measure the lifetime of
the one-phonon Fock state using two-color pump-probe Raman scattering and
spectrally-resolved, time-correlated photon counting. Following pulsed laser
excitation, the $n=1$ phonon Fock state is probabilistically prepared by
projective measurement of a single Stokes photon. The detection of an
anti-Stokes photon generated by a second, time-delayed laser pulse probes the
phonon population with sub-picosecond time resolution. We observe strongly
non-classical Stokes--anti-Stokes correlations, whose decay maps the single
phonon dynamics. Our scheme can be applied to any Raman-active vibrational
mode. It can be modified to measure the lifetime of $n \geq 1$ Fock states or
the phonon quantum coherences through the preparation and detection of two-mode
entangled vibrational states.
