Exposing Gravitational Waves below the Quantum Shot Noise

TL;DR

This paper investigates a quantum correlation technique to improve gravitational wave detection sensitivity below shot noise levels, potentially enabling new astrophysical observations with single interferometers.

Contribution

It analyzes the feasibility and advantages of using quantum correlation in gravitational wave detectors to enhance detection capabilities beyond traditional shot noise limitations.

Findings

Quantum correlation can expose classical signals below shot noise.

The technique allows detection with a single interferometer, increasing duty cycle.

Potential to detect post-merger neutron star signals and set limits on pulsar emissions.

Abstract

The sensitivities of ground-based gravitational-wave (GW) detectors are limited by quantum shot noise at a few hundred Hertz and above. Nonetheless, one can use a quantum-correlation technique proposed by Martynov, et al. [Phys. Rev. A 95, 043831 (2017)] to remove the expectation value of the shot noise, thereby exposing underlying classical signals in the cross spectrum formed by cross-correlating the two outputs in a GW interferometer's anti-symmetric port. We explore here the prospects and analyze the sensitivity of using quantum correlation to detect astrophysical GW signals. Conceptually, this technique is similar to the correlation of two different GW detectors as it utilizes the fact that a GW signal will be correlated in the two outputs but the shot noise will be uncorrelated. Quantum correlation also has its unique advantages as it requires only a single interferometer to make a detection. Therefore, quantum correlation could increase the duty cycle, enhance the search efficiency, and enable the detection of highly polarized signals. In particular, we show that quantum correlation could be especially useful for detecting post-merger remnants of binary neutron stars with both short ($< 1\,{\rm s}$) and intermediate ($\sim 10-10^4\,{\rm s}$) durations and setting upper limits on continuous emissions from unknown pulsars.