Alignment sensing and control for squeezed vacuum states of light

TL;DR

This paper presents a novel automatic alignment sensing and control system for squeezed vacuum states of light, crucial for enhancing gravitational wave detectors' sensitivity over long periods.

Contribution

It introduces the first implementation of an automatic alignment system for squeezed vacuum states, enabling continuous optimal alignment in complex optical setups.

Findings

Successful demonstration of automatic alignment for squeezed vacuum at GEO 600

Maintains optimal alignment over long durations despite free-swinging optics

Enhances stability and sensitivity of gravitational wave detection

Abstract

Beam alignment is an important practical aspect of the application of squeezed states of light. Misalignments in the detection of squeezed light result in a reduction of the observable squeezing level. In the case of squeezed vacuum fields that contain only very few photons, special measures must be taken in order to sense and control the alignment of the essentially dark beam. The GEO600 gravitational wave detector employs a squeezed vacuum source to improve its detection sensitivity beyond the limits set by classical quantum shot noise. Here, we present our design and implementation of an alignment sensing and control scheme that ensures continuous optimal alignment of the squeezed vacuum field at GEO 600 on long time scales in the presence of free-swinging optics. This first demonstration of a squeezed light automatic alignment system will be of particular interest for future long-term applications of squeezed vacuum states of light.