Ultrasensitive measurement of MEMS cantilever displacement sensitivity below the shot noise limit
by Raphael Pooser, Benajmin Lawrie
The displacement of micro-electro-mechanical-systems (MEMS) cantilevers is used to measure a broad variety of phenomena in devices ranging from force microscopes to biochemical sensors to thermal imaging systems. We demonstrate, to the best of our knowledge, the first direct measurement of a MEMS cantilever displacement with a noise floor 4 dB below the shot-noise limit (SNL) at an equivalent optical power. By combining multi-spatial-mode quantum light sources with a simple differential measurement, we show that sub-SNL MEMS displacement sensitivity is highly accessible compared to previous efforts that measured the displacement of macroscopic mirrors with very distinct spatial structures crafted with multiple optical parametric amplifiers and locking loops. These results support a new class of quantum MEMS sensors with an ultimate signal-to-noise ratio determined by quantum correlations, enabling ultratrace sensing, imaging, and microscopy applications in which signals were previously obscured by shot noise.