  We experimentally study stochastic resonance in a nonlinear bistable
nanomechanical resonator. The device consists of a PdAu doubly clamped beam
serving as a nanomechanical resonator excited capacitively by an adjacent gate
electrode and its vibrations are detected optically. The resonator is tuned to
its bistability region by an intense pump near a point of equal transition
rates between its two metastable states. The pump is amplitude modulated,
inducing modulation of the activation barrier between the states. When noise is
added to the excitation, the resonator's displacement exhibits noise dependent
amplification. We measure the resonator's response in the time and frequency
domains, the spectral amplification and the statistical distribution of the
jump time.
