  Cooling vibrational degrees of freedom down to ground states is essential to
observation of quantum properties of systems with mechanical vibration. We
propose two cooling schemes employing four internal levels of the systems,
which achieve the ground-state cooling in an efficient fashion by completely
deleting the carrier and first-order blue-sideband transitions. The schemes,
based on the quantum interference and Stark-shift gates, are robust to
fluctuation of laser intensity and frequency. The feasibility of the schemes is
justified using current laboratory technology. In practice, our proposal
readily applies to an nano-diamond nitrogen-vacancy center levitated in an
optic trap or attached to a cantilever.
