  The rigorous resource framework of quantum coherence has been set up recently
and excited a wide variety of interests. Here we show that a quantum cavity
optomechanical system, as an emerging platform, can behave with a certain value
of quantum coherence at a macroscopic scale. We also find that the difference
between the total optomechanical coherence and the sum of the optical and the
mechanical coherence just equals their mutual information. Motivated by the
detection of the optomechanical entanglement, an experimentally feasible scheme
to probe the optomechanical coherence is proposed.
