Umemura, Kurumi, Ishikawa, Tomohiro, Tsuji, Kenji, Iwaguchi, Shoki, Enomoto, Yutaro, Michimura, Yuta, Komori, Kentaro, Kokeyama, Keiko  ORCID: https://orcid.org/0000-0002-2896-1992 and Kawamura, Seiji
2026.
Quantum noise from vacuum field injection in optical cavities with diffraction-related loss.
Applied Optics
65
(12)
, pp. 4107-4116.
10.1364/ao.580911
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Abstract
The space-based gravitational wave detector DECIGO is designed to observe primordial gravitational waves with 1000 km Fabry–Perot cavities. Its sensitivity is limited by quantum noise, and although squeezing can suppress it, its effectiveness is reduced by diffraction-related loss, which leads to the injection of vacuum fields into the interferometer. This paper presents a rigorous treatment of quantum field propagation in the presence of diffraction and higher-order mode losses, deriving input–output relations and modeling their impact via an optomechanical block diagram. The analysis shows that diffraction-induced vacuum fields slightly increase radiation pressure noise, while shot noise remains unaffected. Nevertheless, cavity detuning with homodyne detection yields a dip in the noise spectrum. By accurately capturing these effects, this framework enables a detailed study of sensitivity improvements made by either just detuning the main cavity while implementing homodyne detection, or by combining this with optical-spring quantum locking using auxiliary cavities, laying a firm foundation for enhancing DECIGO’s capability to detect primordial gravitational waves.
| Item Type: | Article |
|---|---|
| Date Type: | Publication |
| Status: | Published |
| Schools: | Schools > Physics and Astronomy |
| Additional Information: | RRS policy applied. License information from Publisher: LICENSE 1: URL: https://doi.org/10.1364/OA_License_v2#VOR, Start Date: 2026-04-17 |
| Publisher: | Optica Publishing Group |
| ISSN: | 1559-128X |
| Date of First Compliant Deposit: | 11 May 2026 |
| Date of Acceptance: | 1 April 2026 |
| Last Modified: | 02 Aug 2026 07:30 |
| URI: | https://orca.cardiff.ac.uk/id/eprint/186709 |
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