Charge sensitivity enhancement via mechanical oscillation in suspended carbon nanotube devices

Single electron transistors (SETs) fabricated from single-walled carbon nanotubes (SWNTs) can be operated as highly sensitive charge detectors reaching sensitivity levels comparable to metallic radio frequency SETs (rf-SETs). Here we demonstrate how the charge sensitivity of the device can be improved by using the mechanical oscillations of a single-walled carbon nanotube quantum dot. To optimize the charge sensitivity $\delta Q$, we drive the mechanical resonator far into the nonlinear regime and bias it to an operating point where the mechanical third order nonlinearity is cancelled out. This way we enhance $\delta Q$, from 6 $\mu e/\sqrt{\textrm{Hz}}$ for the static case, to 0.97 $\mu e/\sqrt{\textrm{Hz}}$, at a probe frequency of $\sim$ 1.3 kHz.