Cavity-less Quantum Optomechanics with Nanostring Mechanical Resonators

Optical level detection is a simple and ubiquitous precision measurement technique, but has not been fully explored near the standard quantum limit. Cavity optomechanical systems usually require complex optical setups with high fitness optical resonators to reach this quantum enhanced regime. Here we aim to use a high-quality mechanical string resonator without an optical cavity to the beat standard quantum limit of detecting the string motion. A laser bounces off the center of the string, gets deflected by the string motion, and this scattered light creates an interference pattern that evolves along the propagation. This process produces correlation between quantum amplitude and phase fluctuations of the scattered light, leading to a suppression of the displacement noise floor as measured by a quadrant photodetector. The best suppressed occurs when the detector is placed at particular frequency dependent location along the propagation direction. We are currently attempting to measure such suppression in the classical and quantum regimes with SiN phononic crystal string resonators.