  Sub-nanometer displacement detection lays the solid foundation for critical
applications in modern metrology. In-plane displacement sensing, however, is
mainly dominated by the detection of differential photocurrent signals from
photodiodes, with resolution in the nanometer range. Here, we present an
integrated in-plane displacement sensor based on a nanoelectromechanical
trampoline resonator. With a position resolution of 4 $pm/Hz^{1/2}$ for a low
laser power of 85 $\mu$W and a repeatability of 2 nm after 5 cycles of
operation as well as good long-term stability, this new detection principle
provides a reliable alternative for overcoming the current position detection
limit in a wide variety of research and application fields.
