Measurement of optical losses in a high-finesse 300 m filter cavity for broadband quantum noise reduction in gravitational-wave detectors

TL;DR

This paper reports the successful operation and loss measurement of a 300 m filter cavity designed for broadband quantum noise reduction in gravitational-wave detectors, demonstrating potential for at least 4 dB noise reduction.

Contribution

It presents the first measurement of optical losses in a high-finesse 300 m filter cavity for quantum noise reduction in gravitational-wave detection.

Findings

Round trip losses measured between 50 ppm and 90 ppm.

Achieved cavity resonance with multi-wavelength technique.

Demonstrated potential for at least 4 dB quantum noise reduction.

Abstract

Earth-based gravitational-wave detectors will be limited by quantum noise in a large part of their spectrum. The most promising technique to achieve a broadband reduction of such noise is the injection of a frequency dependent squeezed vacuum state from the output port of the detector, whit the squeeze angle rotated by the reflection off a Fabry-Perot filter cavity. One of the most important parameters limiting the squeezing performance is represented by the optical losses of the filter cavity. We report here the operation of a 300 m filter cavity prototype installed at the National Astronomical Observatory of Japan (NAOJ). The cavity is designed to obtain a rotation of the squeeze angle below 100 Hz. After achieving the resonance of the cavity with a multi-wavelength technique, the round trip losses have been measured to be between 50 ppm and 90 ppm. This result demonstrates that with realistic assumption on the input squeeze factor and on the other optical losses, a quantum noise reduction of at least 4 dB in the frequency region dominated by radiation pressure can be achieved.