  Optical control over elementary molecular vibration establishes fundamental
capabilities for exploiting the broad range of optical linear and nonlinear
phenomena. However, experimental demonstration of the coherently driven
molecular vibration remains a challenge task due to the weak optical force
imposed on natural materials. Here we report the design of "meta-atom" that
exhibits giant artificial optical nonlinearity. These "meta-atoms" support
co-localized magnetic resonance at optical frequency and vibration resonance at
GHz frequency with a deep-sub-diffraction-limit spatial confinement
(${\lambda}^2/100$). The coherent coupling of those two distinct resonances
manifests a strong optical force, which is fundamentally different from the
commonly studied form of radiation forces, the gradient forces, or
photo-thermal induced deformation. It results in a giant third-order
susceptibility $\chi^{(3)}$ of $10^{-13}$ $m^2$/$V^2$, which is more than six
orders of magnitude larger than that found in natural materials. The
all-optical modulation at the frequency well above 1 GHz has thus been
demonstrated experimentally.
