Scattering approach to backaction in coherent nanoelectromechanical systems

We present theoretical results for the backaction force noise and damping of a mechanical oscillator whose position is measured by a mesoscopic conductor. Our scattering approach is applicable to a wide class of systems; in particular, it may be used to describe point contact position detectors far from the weak tunneling limit. We find that the backaction depends not only on the mechanical modulation of transmission probabilities but also on the modulation of scattering phases, even in the absence of a magnetic field. We illustrate our general approach with several simple examples, and use it to calculate the backaction for a movable, Au atomic point contact modeled by ab initio density functional theory.