Optical spring tracking for enhancing quantum-limited interferometers

Modern interferometers such as LIGO have achieved sensitivities limited by quantum noise, comprising radiation pressure and shot noise. To mitigate this noise, a static system is employed that minimizes the quantum noise within the measurement band. However, since gravitational wave inspiral signals are a single frequency changing over time, only noise at the chirp frequency needs to be minimized. Here we demonstrate a proof-of-principle experiment of dynamically tracking a target signal using an optical spring, resulting in an increased signal-to-noise ratio (SNR). By injecting white noise to simulate excess shot noise, we found the SNR increased by up to a factor of 40 via dynamical tracking when compared to a static configuration.