title: Quantum enhancement of the zero-area Sagnac interferometer topology for gravitational wave detection.
abstract: Only a few years ago, it was realized that the zero-area Sagnac interferometer topology is able to perform quantum nondemolition measurements of position changes of a mechanical oscillator. Here, we experimentally show that such an interferometer can also be efficiently enhanced by squeezed light. We achieved a nonclassical sensitivity improvement of up to 8.2 dB, limited by optical loss inside our interferometer. Measurements performed directly on our squeezed-light laser output revealed squeezing of 12.7 dB. We show that the sensitivity of a squeezed-light enhanced Sagnac interferometer can surpass the standard quantum limit for a broad spectrum of signal frequencies without the need for filter cavities as required for Michelson interferometers. The Sagnac topology is therefore a powerful option for future gravitational-wave detectors, such as the Einstein Telescope, whose design is currently being studied.
authors.affiliation: Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut) and Institut für Gravitationsphysik der Leibniz Universität Hannover, Callinstraße 38, 30167 Hannover, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Eberle
authors.forename: Sebastian
authors.initials: S
authors.lastname: Steinlechner
authors.forename: Jöran
authors.initials: J
authors.lastname: Bauchrowitz
authors.forename: Vitus
authors.initials: V
authors.lastname: Händchen
authors.forename: Henning
authors.initials: H
authors.lastname: Vahlbruch
authors.forename: Moritz
authors.initials: M
authors.lastname: Mehmet
authors.forename: Helge
authors.initials: H
authors.lastname: Müller-Ebhardt
authors.forename: Roman
authors.initials: R
authors.lastname: Schnabel