Sensitivity of a micromechanical displacement detector based on the radio-frequency single-electron transistor

We investigate the tunneling shot noise limits on the sensitivity of a micromechanical displacement detector based on a metal junction, radio-frequency single-electron transistor (rf-SET). In contrast with the charge sensitivity of the rf-SET electrometer, the displacement sensitivity improves with increasing gate voltage bias and, with a suitably optimized rf-SET, displacement sensitivities of $10^{-6} {\rm\AA}/\sqrt{\rm Hz}$ may be possible.