  We investigate an optomechanical system in which a cavity with a moving
mirror is driven by two external fields. When the field frequencies match
resonance conditions, we show that there exists a class of dark states of the
moving mirror in the single-photon strong-coupling regime. These dark states,
which cause the cavity to be decoupled from the external fields, is a
manifestation of quantum coherence associated with the mirror's mechanical
degrees of freedom. We discuss the properties of the dark states and indicate
how they can be generated by optical pumping due to the decay of cavity field.
