Quantum Measurement Theory in Gravitational-Wave Detectors

TL;DR

This paper reviews the application of quantum measurement theory to gravitational-wave detectors, focusing on quantum noise, the Standard Quantum Limit, and methods to surpass it, to enhance detector sensitivity.

Contribution

It provides a comprehensive overview of quantum measurement theory as applied to gravitational-wave detectors, including recent advances and techniques to overcome quantum noise limitations.

Findings

Quantum noise is a fundamental limit in gravitational-wave interferometers.

Methods to surpass the Standard Quantum Limit are discussed.

Theoretical framework aids in designing more sensitive detectors.

Abstract

The fast progress in improving the sensitivity of the gravitational-wave (GW) detectors, we all have witnessed in the recent years, has propelled the scientific community to the point, when quantum behaviour of such immense measurement devices as kilometer-long interferometers starts to matter. The time, when their sensitivity will be mainly limited by the quantum noise of light is round the corner, and finding the ways to reduce it will become a necessity. Therefore, the primary goal we pursued in this review was to familiarize a broad spectrum of readers with the theory of quantum measurements in the very form it finds application in the area of gravitational-wave detection. We focus on how quantum noise arises in gravitational-wave interferometers and what limitations it imposes on the achievable sensitivity. We start from the very basic concepts and gradually advance to the general linear quantum measurement theory and its application to the calculation of quantum noise in the contemporary and planned interferometric detectors of gravitational radiation of the first and second generation. Special attention is paid to the concept of Standard Quantum Limit and the methods of its surmounting.