  The synchronization of coupled oscillators is a phenomenon found throughout
nature. Mechanical oscillators are paradigmatic among such systems, but
realising them at the nanoscale is challenging. We report synchronization of
the mechanical dynamics of a pair of optomechanical crystal cavities that are
intercoupled with a mechanical link and support independent optical modes. In
this regime they oscillate in anti-phase, which is in agreement with the
predictions of our numerical model that considers reactive coupling. Finally,
we show how to temporarily disable synchronization of the coupled system by
actuating one of the cavities with a heating laser, so that both cavities
oscillate independently. Our results can be upscaled to more than two cavities
and are thus the first step towards realizing integrated networks of
synchronized optomechanical oscillators. Such networks promise unparalleled
performances for time-keeping and sensing purposes and unveil a new route for
neuromorphic computing applications.
