  The low quality factor (Q) of Single-walled carbon nanotube (SWNT) resonators
has limited their sensitivity in sensing application. To this end, we employ
the technique of parametric amplification by modulating the spring constant of
SWNT resonators at twice the resonant frequency, and achieve 10 times Q
enhancement. The highest Q obtained at room temperature is around ~700, which
is 3-4 times better than previous Q record reported for doubly-clamped SWNT
resonators. Furthermore, efficient parametric amplification is found to only
occur in the catenary vibration regime. Our results open up the possibility to
employ light-weight and high-Q carbon nanotube resonators in single molecule
and atomic mass sensing.
