Long-term stable squeezed vacuum state of light for gravitational wave detectors

TL;DR

This paper demonstrates a long-term stable squeezed vacuum state of light with over 9 dB noise reduction in gravitational wave detectors, achieved through an extended control scheme ensuring stability over 20 hours.

Contribution

An extended coherent control scheme is introduced, significantly improving the long-term stability of squeezed light in gravitational wave detectors.

Findings

Achieved over 9 dB quantum noise reduction in 10 Hz - 10 kHz band.

Maintained stability over 20 hours with >99% duty cycle.

Identified and mitigated mechanisms causing squeezing fluctuations.

Abstract

Currently, the German/British gravitational wave detector GEO600 is being upgraded in course of the GEO-HF program. One part of this upgrade consists of the integration of a squeezed light laser to nonclassically improve the detection sensitivity at frequencies where the instrument is limited by shot noise. This has been achieved recently [1]. The permanent employment of squeezed light in gravitational wave observatories requires a long-term stability of the generated squeezed state. In this paper, we discuss an unwanted mechanism that can lead to a varying squeezing factor along with a changing phase of the squeezed field. We present an extension of the implemented coherent control scheme [2] that allowed an increase in the long-term stability of the GEO600 squeezed light laser. With it, a quantum noise reduction by more than 9 dB in the frequency band of 10 Hz - 10 kHz was observed over up to 20 hours with a duty cycle of more than 99%.