  We propose an efficient scheme for generating spin-squeezed states at steady
state in a spin-mechanical hybrid system, where an ensemble of SiV centers are
coupled to a strongly damped nanomechanical resonator. We show that,there
exists a collective steady state in the system, which is exactly formed by the
collective spin states plus the zero excitation state of the mechanical mode.
The generation of the steady spin-squeezed state is based on a dissipative
quantum dynamical process in which the mechanical dissipation plays a positive
role but without destroying the target state. We demonstrate that the
spin-squeezed steady state can be deterministically prepared via dissipative
means, with the optimal spin squeezing up to 4/N in the ideal case, where N is
the number of spins. This work provides a promising platform for quantum
information processing and quantum metrology.
