Abstract
Mechanical resonators based on a singlecarbon nanotube are exceptional sensors of mass and force.The force sensitivity in these ultralight resonators is oftenlimited by the noise in the detection of the vibrations. Here,we report on an ultrasensitive scheme based on a RLCresonator and a low-temperature amplifier to detect nanotubevibrations. We also show a new fabrication process ofelectromechanical nanotube resonators to reduce the separation between the suspended nanotube and the gate electrodedown to ∼150 nm. These advances in detection and fabrication allow us to reach 0.5pm/ Hz displacement sensitivity.Thermal vibrations cooled cryogenically at 300 mK are detected with a signal-to-noise ratio as high as 17 dB. We demonstrate4.3zN/ Hz force sensitivity, which is the best force sensitivity achieved thus far with a mechanical resonator. Our work is animportant step toward imaging individual nuclear spins and studying the coupling between mechanical vibrations and electronsin different quantum electron transport regimes.