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arXiv · 2511.03842

Quadrature-witness readout for backscatter mitigation in gravitational-wave detectors limited by back-action

Niels Böttner·Roman Schnabel·Mikhail Korobko
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Abstract

Disturbances in gravitational wave (GW) observational data are often caused by non-stationary noise in the detector itself, such as back-scattering of laser stray light into the signal field. Unlike GW signals, non-stationary noise can appear in both the GW-signal quadrature and the orthogonal quadrature, which is usually not measured. Simultaneous sensing of this orthogonal quadrature provides a witness channel that can be used to reconstruct the disturbance in the signal quadrature enabling a subtraction of non-stationary noise. Here, we present the concept of quadrature witness that is compatible with frequency-dependent squeezing, which is already used to simultaneously reduce photon shot noise and photon radiation pressure noise. We demonstrate that implementing this approach in a GW detector could reduce noise caused by loud back-scatter events, thereby improving the overall sensitivity and robustness of GW observatories.

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Niels Böttner, Roman Schnabel, Mikhail Korobko. 2025-11-05. Quadrature-witness readout for backscatter mitigation in gravitational-wave detectors limited by back-action. https://arxiv.org/abs/2511.03842

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