  We present a generic quantum master equation whose dissipative dynamics
autonomously stabilizes a harmonic oscillator in the n=1 Fock state. A
multi-mode optomechanical system is analyzed and shown to be an example of a
physical system obeying this model. We show that the optomechanical setup
enables preparation of a mechanical oscillator in a nonclassical steady state,
and that this state indeed approaches a single phonon Fock state in the ideal
parameter regime. The generic model may be useful in other settings, such as
cavity or circuit quantum electrodynamics or trapped ion physics.
