Unification of thermal and quantum noise in gravitational-wave detectors

TL;DR

This paper unifies the understanding of thermal, quantum, test-mass quantization, and optical thermal noises in gravitational-wave detectors using the quantum fluctuation-dissipation theorem, clarifying when certain noises can be neglected.

Contribution

It provides a unified theoretical framework for all four fundamental noises in gravitational-wave detectors, clarifying conditions under which some noises are negligible.

Findings

Unified description of four fundamental noises.

Conditions when test-mass quantization noise can be ignored.

Conditions when optical thermal noise can be ignored.

Abstract

Contemporary gravitational-wave detectors are fundamentally limited by thermal noise -- due to dissipation in the mechanical elements of the test mass -- and quantum noise -- from the vacuum fluctuations of the optical field used to probe the test mass position. Two other fundamental noises can in principle also limit sensitivity: test-mass quantization noise due to the zero-point fluctuation of its mechanical modes, and thermal excitation of the optical field. We use the quantum fluctuation-dissipation theorem to unify all four noises. This unified picture shows precisely when test-mass quantization noise and optical thermal noise can be ignored.