We present a high-sensitivity measurement technique for mechanical nanoresonators. Due to intrinsic nonlinear effects, different flexural modes of a nanobeam can be coupled while driving each of them on resonance. This mode-coupling scheme is dispersive and one mode resonance shifts with respect to the motional amplitude of the other. The same idea can be implemented on a {\it single} mode, exciting it with two slightly detuned signals. This two-tone scheme is used here to measure the resonance lineshape of one mode through a frequency shift in the response of the device. The method acts as an amplitude-to-frequency transduction which ultimately suffers only from phase noise of the local oscillator used and of the nanomechanical device itself. We also present a theory which reproduces the data without free parameters.
@article{arxiv.1511.07273,
title = {Modal "self-coupling" as a sensitive probe for nanomechanical detection},
author = {M. Defoort and K. J. Lulla and C. Blanc and O. Bourgeois and A. D. Armour and E. Collin},
journal= {arXiv preprint arXiv:1511.07273},
year = {2015}
}