title: First long-term application of squeezed states of light in a gravitational-wave observatory.
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 GEO 600 during a period of three months from June to August 2011, when GEO 600 was performing an observational run together with the French-Italian Virgo detector. In a second period, the 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 were acquired with GEO 600. A sensitivity increase from squeezed vacuum application was observed broadband above 400 Hz. The time average of gain in sensitivity was 26% (2.0 dB), determined in the frequency band from 3.7 to 4.0 kHz. This corresponds to a factor of 2 increase in the observed volume of the Universe for sources in the kHz region (e.g., supernovae, magnetars). We introduce three new techniques to enable the 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.
authors.affiliation: Max-Planck-Institut für Gravitationsphysik, Albert Einstein Institut und Leibniz Universität Hannover, Callinstraße 38, 30167 Hannover, Germany. hartmut.grote@aei.mpg.de
authors.forename: H
authors.initials: H
authors.lastname: Grote
authors.forename: K
authors.initials: K
authors.lastname: Danzmann
authors.forename: K L
authors.initials: KL
authors.lastname: Dooley
authors.forename: R
authors.initials: R
authors.lastname: Schnabel
authors.forename: J
authors.initials: J
authors.lastname: Slutsky
authors.forename: H
authors.initials: H
authors.lastname: Vahlbruch