Optimal detuning for quantum filter cavities

TL;DR

This paper analyzes the optimal operating conditions for quantum filter cavities in gravitational-wave detectors, aiming to enhance sensitivity by mitigating quantum noise through frequency-dependent squeezing.

Contribution

It provides a detailed model and numerical analysis to identify the optimal parameters for filter cavities in future gravitational-wave observatories.

Findings

Optimal filter cavity parameters improve quantum noise reduction.

Design considerations for upcoming A+ LIGO upgrade.

Insights into optomechanical effects on filter cavity performance.

Abstract

Vacuum quantum fluctuations impose a fundamental limit on the sensitivity of gravitational-wave interferometers, which rank among the most sensitive precision measurement devices ever built. The injection of conventional squeezed vacuum reduces quantum noise in one quadrature at the expense of increasing noise in the other. While this approach improved the sensitivity of the Advanced LIGO and Advanced Virgo interferometers during their third observing run (O3), future improvements in arm power and squeezing levels will bring radiation pressure noise to the forefront. Installation of a filter cavity for frequency-dependent squeezing provides broadband reduction of quantum noise through the mitigation of this radiation pressure noise, and it is the baseline approach planned for all of the future gravitational-wave detectors currently conceived. The design and operation of a filter cavity requires careful consideration of interferometer optomechanics as well as squeezing degradation processes. In this paper, we perform an in-depth analysis to determine the optimal operating point of a filter cavity. We use our model alongside numerical tools to study the implications for filter cavities to be installed in the upcoming "A+" upgrade of the Advanced LIGO detectors.