Squeezed Light for the Interferometric Detection of High Frequency Gravitational Waves

TL;DR

This paper analyzes how injecting frequency-dependent squeezed light can significantly improve high-frequency gravitational wave detection sensitivity in interferometers like GEO600, surpassing quantum noise limits.

Contribution

It presents a theoretical analysis of implementing frequency-dependent squeezing in GEO600 to enhance high-frequency gravitational wave detection capabilities.

Findings

GEO600 can benefit from frequency-dependent squeezed light at 1-10 kHz.

Squeezing can reduce quantum noise by up to 6 dB, improving sensitivity.

Proposes a scheme to implement frequency-dependent squeezing in GEO600.

Abstract

The quantum noise of the light field is a fundamental noise source in interferometric gravitational wave detectors. Injected squeezed light is capable of reducing the quantum noise contribution to the detector noise floor to values that surpass the so-called Standard-Quantum-Limit (SQL). In particular, squeezed light is useful for the detection of gravitational waves at high frequencies where interferometers are typically shot-noise limited, although the SQL might not be beaten in this case. We theoretically analyze the quantum noise of the signal-recycled laser interferometric gravitational-wave detector GEO600 with additional input and output optics, namely frequency-dependent squeezing of the vacuum state of light entering the dark port and frequency-dependent homodyne detection. We focus on the frequency range between 1 kHz and 10 kHz, where, although signal recycled, the detector is still shot-noise limited. It is found that the GEO600 detector with present design parameters will benefit from frequency dependent squeezed light. Assuming a squeezing strength of -6 dB in quantum noise variance, the interferometer will become thermal noise limited up to 4 kHz without further reduction of bandwidth. At higher frequencies the linear noise spectral density of GEO600 will still be dominated by shot-noise and improved by a factor of 10^{6dB/20dB}~2 according to the squeezing strength assumed. The interferometer might reach a strain sensitivity of 6x10^{-23} above 1 kHz (tunable) with a bandwidth of around 350 Hz. We propose a scheme to implement the desired frequency dependent squeezing by introducing an additional optical component to GEO600s signal-recycling cavity.