  We propose a cascade-cooling method to realize simultaneous ground-state
cooling of a coupled mechanicalresonator chain through an optomechanical cavity
working in the unresolved-sideband regime. This dominoeffect cooling is
realized by combining the cold-damping feedback on the first mechanical
resonator with nearest-neighbor couplings between other neighboring mechanical
resonators. We obtain analytical results for the effective susceptibilities,
noise spectra, final mean phonon numbers, and cooling rates of these mechanical
resonators, and find the optimal-cooling condition for these resonators.
Particularly, we analyze a twomechanical-resonator case and find that by
appropriately engineering either the laser power or the feedback, a flexible
cooling switch between symmetric and asymmetric ground-state cooling can be
achieved. We also simulate the cooling performance of a coupled
N-mechanical-resonator chain and confirm that these mechanical resonators can
be simultaneously cooled to their quantum ground states in the
unresolved-sideband regime. This study opens a route to quantum manipulation of
multiple mechanical resonators in the bad-cavity regime.
