LIGOs Quantum Response to Squeezed States

TL;DR

This paper analyzes how LIGO's quantum response to squeezed states affects gravitational wave detection, providing detailed metrics and physical descriptions to improve understanding and future enhancements of quantum noise reduction.

Contribution

It introduces frequency-dependent response metrics that describe LIGO's quantum interactions with squeezed light and optical cavities, advancing understanding of quantum noise in large-scale interferometers.

Findings

Metrics describe physical mechanisms of squeezing in LIGO.

Analysis of quantum radiation pressure noise interactions.

First comprehensive physical description of observed quantum noise features.

Abstract

Gravitational Wave interferometers achieve their profound sensitivity by combining a Michelson interferometer with optical cavities, suspended masses, and now, squeezed quantum states of light. These states modify the measurement process of the LIGO, VIRGO and GEO600 interferometers to reduce the quantum noise that masks astrophysical signals; thus, improvements to squeezing are essential to further expand our gravitational view of the universe. Further reducing quantum noise will require both lowering decoherence from losses as well more sophisticated manipulations to counter the quantum back-action from radiation pressure. Both tasks require fully understanding the physical interactions between squeezed light and the many components of km-scale interferometers. To this end, data from both LIGO observatories in observing run three are expressed using frequency-dependent metrics to analyze each detector's quantum response to squeezed states. The response metrics are derived and used to concisely describe physical mechanisms behind squeezing's simultaneous interaction with transverse-mode selective optical cavities and the quantum radiation pressure noise of suspended mirrors. These metrics and related analysis are broadly applicable for cavity-enhanced optomechanics experiments that incorporate external squeezing, and -- for the first time -- give physical descriptions of every feature so far observed in the quantum noise of the LIGO detectors.