First Long-Term Application of Squeezed States of Light in a Gravitational-Wave Observatory

TL;DR

This paper demonstrates the first long-term use of squeezed light to enhance the sensitivity of a gravitational-wave detector, significantly increasing its observational volume and maintaining stability over months.

Contribution

It presents the first extended application of squeezed vacuum states in a gravitational-wave observatory, introducing new techniques for stable long-term operation.

Findings

Sensitivity increased by 26% (2.0dB) in the 3.7-4.0kHz band

Squeezing was applied for 90.2% of science-quality data

Detector glitch-rate remained unaffected by squeezing

Abstract

We report on the first long-term application of squeezed vacuum states of light to improve the shot-noise-limited sensitivity of a gravitational-wave observatory. In particular, squeezed vacuum was applied to the German/British detector GEO600 during a period of three months from June to August 2011, when GEO600 was performing an observational run together with the French/Italian Virgo detector. In a second period squeezing application continued for about 11 months from November 2011 to October 2012. During this time, squeezed vacuum was applied for 90.2% (205.2 days total) of the time that science-quality data was acquired with GEO600. Sensitivity increase from squeezed vacuum application was observed broad-band above 400Hz. The time average of gain in sensitivity was 26% (2.0dB), determined in the frequency band from 3.7kHz to 4.0kHz. This corresponds to a factor of two increase in observed volume of the universe, for sources in the kHz region (e.g. supernovae, magnetars). We introduce three new techniques to enable stable long-term application of squeezed light, and show that the glitch-rate of the detector did not increase from squeezing application. Squeezed vacuum states of light have arrived as a permanent application, capable of increasing the astrophysical reach of gravitational-wave detectors.