  Ground-state cooling of mechanical resonators is an important task in quantum
optomechanics, because it is a necessary prerequisite for creation,
manipulation, and application of macroscopic mechanical coherence. Here, we
propose a transient-state scheme to accelerate ground-state cooling of a
mechanical resonator in a three-mode loop-coupled optomechanical system via
shortcuts to adiabaticity (STA). We consider four kinds of coupling protocols
and calculate the evolution of the mean phonon number of the mechanical
resonator in both the adiabatic and STA cases. We verify that the ground-state
cooling of the mechanical resonator can be achieved with the STA method in a
much shorter period. The STA method can also be generalized to accelerate other
adiabatic processes in cavity optomechanics, and hence this work will open up a
new realm of fast optomechanical manipulations.
