Squeezing the quantum noise of a gravitational-wave detector below the standard quantum limit

TL;DR

This paper demonstrates how the LIGO A+ upgrade successfully reduced quantum noise below the Standard Quantum Limit, enhancing gravitational-wave detection sensitivity by up to 3 dB across a broad frequency range.

Contribution

It presents the first broadband reduction of quantum noise below the SQL in a large-scale gravitational-wave detector using advanced quantum measurement techniques.

Findings

Quantum noise reduced by up to 3 dB

Broadband sensitivity improvement achieved

Demonstrates practical implementation of quantum noise reduction

Abstract

Precision measurements of space and time, like those made by the detectors of the Laser Interferometer Gravitational-wave Observatory (LIGO), are often confronted with fundamental limitations imposed by quantum mechanics. The Heisenberg uncertainty principle dictates that the position and momentum of an object cannot both be precisely measured, giving rise to an apparent limitation called the Standard Quantum Limit (SQL). Reducing quantum noise below the SQL in gravitational-wave detectors, where photons are used to continuously measure the positions of freely falling mirrors, has been an active area of research for decades. Here we show how the LIGO A+ upgrade reduced the detectors' quantum noise below the SQL by up to 3 dB while achieving a broadband sensitivity improvement, more than two decades after this possibility was first presented.