An off-board quantum point contact as a sensitive detector of cantilever motion

Recent advances in the fabrication of microelectromechanical systems and their evolution into nanoelectromechanical systems have enabled researchers to measure extremely small forces, masses and displacements(1). In particular, researchers have developed position transducers with resolution approaching the uncertainty limit set by quantum mechanics(2-5). The achievement of such resolution has implications not only for the detection of quantum behaviour in mechanical systems, but also for a variety of other precision experiments including the bounding of deviations from newtonian gravity at short distances(6) and the measurement of single spins(7). Here, we demonstrate the use of a quantum point contact as a sensitive displacement detector capable of sensing the low-temperature thermal motion of a nearby micromechanical cantilever. Advantages of this approach include versatility due to its off-board design, compatibility with nanoscale oscillators and, with further development, the potential to achieve quantum-limited displacement detection(8,9).