  Mechanical systems are one of the promising platforms for classical and
quantum information processing and are already widely-used in electronics and
photonics. Cavity optomechanics offers many new possibilities for information
processing using mechanical degrees of freedom; one of them is storing optical
signals in long-lived mechanical vibrations by means of optomechanically
induced transparency. However, the memory storage time is limited by intrinsic
mechanical dissipation. More over, in-situ control and manipulation of the
stored signals--processing--has not been demonstrated. Here, we address both of
these limitations using a multi-mode cavity optomechanical memory. An
additional optical field coupled to the memory modifies its dynamics through
time-varying parametric feedback. We demonstrate that this can extend the
memory decay time by an order of magnitude, decrease its effective mechanical
dissipation rate by two orders of magnitude, and deterministically shift the
phase of a stored field by over 2$\pi$. This further expands the information
processing toolkit provided by cavity optomechanics.
