First demonstration of 6 dB quantum noise reduction in a kilometer scale gravitational wave observatory

TL;DR

This paper demonstrates a 6 dB reduction in quantum noise in a kilometer-scale gravitational wave detector using squeezed light, marking a significant step towards improving future detector sensitivity.

Contribution

First successful application of 6 dB quantum noise reduction in a large-scale gravitational wave observatory, advancing the implementation of squeezed light techniques.

Findings

Achieved 6.03 dB quantum noise reduction at GEO 600.

Enhanced understanding of noise sources and mitigation strategies.

Demonstrated feasibility of integrating squeezed light in kilometer-scale interferometers.

Abstract

Photon shot noise, arising from the quantum-mechanical nature of the light, currently limits the sensitivity of all the gravitational wave observatories at frequencies above one kilohertz. We report a successful application of squeezed vacuum states of light at the GEO\,600 observatory and demonstrate for the first time a reduction of quantum noise up to $6.03 \pm 0.02$ dB in a kilometer-scale interferometer. This is equivalent at high frequencies to increasing the laser power circulating in the interferometer by a factor of four. Achieving this milestone, a key goal for the upgrades of the advanced detectors, required a better understanding of the noise sources and losses, and implementation of robust control schemes to mitigate their contributions. In particular, we address the optical losses from beam propagation, phase noise from the squeezing ellipse, and backscattered light from the squeezed light source. The expertise gained from this work carried out at GEO 600 provides insight towards the implementation of 10 dB of squeezing envisioned for third-generation gravitational wave detectors.