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

We investigate the intrinsic noise of a micromechanical displacement detector based on the radio-frequency single-electron transistor (rf-SET). Using the noise analysis of a SET by Korotkov [Phy. Rev. B 49, 10381 (1994)] as our starting point, we determine the spectral density of the displacement noise due to the tunneling current shot noise. The resulting mechanical displacement noise decreases in inverse proportion to the increasing gate voltage. In contrast, the displacement noise due to the fluctuating SET island charge increases approximately linearly with increasing gate voltage. Taking into account both of these noise sources results in an optimum gate voltage value for the lowest displacement noise and hence best sensitivity. We show that a displacement sensitivity of about 10(-4) Angstrom and a force sensitivity of about 10(-16) N are predicted for a micron-sized cantilever with a realizable resonant frequency 100 MHz and quality factor Qsimilar to10(4). Such sensitivities would allow the detection of quantum squeezing in the mechanical motion of the micromechanical cantilever and the detection of single-spin magnetic resonance in magnetic resonance force microscopy. (C) 2002 American Institute of Physics.