Input spectrum for heterodyne detection in advanced gravitational wave detectors without non-stationary shot-noise

TL;DR

This paper demonstrates that by modifying the laser input spectrum, heterodyne detection can achieve the same quantum-noise limited sensitivity as homodyne detection in advanced gravitational wave detectors, despite the typical advantages of homodyne detection.

Contribution

The study shows how to modify the input spectrum to enable heterodyne detection to match homodyne detection sensitivity in quantum-limited gravitational wave measurements.

Findings

Heterodyne detection can match homodyne sensitivity with input spectrum modification.

Quantum-noise limited sensitivity is achievable with heterodyne detection.

Input spectrum modification enables new readout strategies for gravitational wave detectors.

Abstract

Future interferometric gravitational wave detectors will make use of the coupling between shot noise and radiation pressure noise that produces a squeezed output for the quantum noise at the dark-port of the interferometer allowing these interferometers to operate with a sensitivity that exceeds the standard quantum limit at certain frequencies. The ability of the detector to take advantage of this squeezed output state depends in part on the readout system used. With the phase modulated laser input planned for these interferometers the quantum-noise limited sensitivity is slightly better when homodyne (rather than heterodyne) detection is used. We show that by modifying the laser input spectrum for these interferometers, readout with heterodyne detection can be made to have the same quantum-noise limited sensitivity as readout with homodyne detection.