Broadband Optomechanical Sensing at the Thermodynamic Limit

TL;DR

This paper introduces a microfabricated optomechanical accelerometer that achieves near-thermodynamic-limit broadband sensitivity, enabling advanced measurements in physics and geophysics without the usual tradeoffs between sensitivity and bandwidth.

Contribution

The authors demonstrate a novel optomechanical sensing platform that attains the highest reported broadband sensitivity at the thermodynamic limit, overcoming traditional design tradeoffs.

Findings

Achieves broadband sensitivity of 314 nm/s^2/√Hz over 6.8 kHz

Operates at the thermodynamic limit set by Brownian motion

Applicable to diverse measurements including gravimetry and dark matter searches

Abstract

Cavity optomechanics has opened new avenues of research in both fundamental physics and precision measurement by significantly advancing the sensitivity achievable in detecting attonewton forces, nanoparticles, magnetic fields, and gravitational waves. A fundamental limit to sensitivity for these measurements is energy exchange with the environment as described by the fluctuation-dissipation theorem. While the limiting sensitivity can be increased by increasing the mass or reducing the damping of the mechanical sensing element, these design tradeoffs lead to larger detectors or limit the range of mechanical frequencies that can be measured, excluding the bandwidth requirements for many real-world applications. We report on a microfabricated optomechanical sensing platform based on a Fabry-Perot microcavity and show that when operating as an accelerometer it can achieve nearly ideal broadband performance at the thermodynamic limit (Brownian motion of the proof mass) with the highest sensitivity reported to date over a wide frequency range ($314\,nm \cdot s^{-2}/\sqrt{Hz}$ over 6.8 kHz). This approach is applicable to a range of measurements from pressure and force sensing to seismology and gravimetry, including searches for new physics such as non-Newtonian gravity or dark matter.