# Quantum correlation measurements in interferometric gravitational wave detectors

## TL;DR

This paper explores how quantum correlation measurements can distinguish quantum noise from classical noise in gravitational wave detectors, demonstrating experimental estimation of quantum radiation pressure noise in LIGO data.

## Contribution

It introduces correlation techniques to identify quantum noise components in gravitational wave detectors and provides the first experimental estimation of quantum radiation pressure noise in LIGO data.

## Key findings

- Quantum correlation techniques can distinguish quantum from classical noise.
- First experimental estimation of quantum radiation pressure noise in LIGO.
- Projections of detector sensitivity improvements in future science runs.

## Abstract

Quantum fluctuations in the phase and amplitude quadratures of light set limitations on the sensitivity of modern optical instruments. The sensitivity of the interferometric gravitational wave detectors, such as the Advanced Laser Interferometer Gravitational wave Observatory (LIGO), is limited by quantum shot noise, quantum radiation pressure noise, and a set of classical noises. We show how the quantum properties of light can be used to distinguish these noises using correlation techniques. Particularly, in the first part of the paper we show estimations of the coating thermal noise and gas phase noise, hidden below the quantum shot noise in the Advanced LIGO sensitivity curve. We also make projections on the observatory sensitivity during the next science runs. In the second part of the paper we discuss the correlation technique that reveals the quantum radiation pressure noise from the background of classical noises and shot noise. We apply this technique to the Advanced LIGO data, collected during the first science run, and experimentally estimate the quantum correlations and quantum radiation pressure noise in the interferometer for the first time.