GWADW2026 - Gravitational-Wave Advanced Detector Workshop

Towards optimal, high-efficiency quantum enhancement in the LIGO gravitational wave detectors

Not scheduled

20m

Hotel Hermitage, La Biodola, Isola d'Elba

Poster Optical Design Poster Session

Speaker

Dr Maryrose Barrios (UC Berkeley)

Description

Key hardware improvements such as the upgrade to frequency-dependent squeezing for broadband quantum noise reduction [1] with quantum-limited sensitivities exceeding the Standard Quantum Limit [2] have made LIGO’s 4th observing run (O4) the most successful to-date [3]. Our newest astrophysical catalogue update (GWTC-4 [4]) more than doubles our gravitational-wave event count in about 1/3 of the observing time, and delivers high-fidelity population-scale studies of black hole astrophysics. Beyond the 6 dB of measured squeezing in O4, future observing runs of LIGO and future GW detectors target 10-dB of broadband measured squeezing to reach design sensitivity. Achieving this goal requires improved mode-matching and lower losses throughout the many optical cavities that comprise the LIGO detectors. Following O4, many changes as part of the “A+ upgrade” to LIGO are underway, including a change of the interferometer’s readout scheme to balanced homodyne detection. This installation includes lower loss output mode cleaner cavities with 98-99.5% power transmissivity to enable higher signal fidelity and squeezing levels. This talk will detail the design, fabrication, and installation of the new output mode cleaner cavities for LIGO A+, and highlight the collective impact of these changes on expanding the quantum-limited astrophysical reach of the LIGO detectors.

1. D. Ganapathy, LIGO O4 Detector Collaboration, “Broadband Quantum Enhancement of the LIGO Detectors with Frequency-Dependent Squeezing,” Phys. Rev. X 13, 041021 (2023).
2. W. Jia, LIGO O4 Detector Collaboration, “Squeezing the Quantum Noise of a Gravitational-Wave Detector Below the Standard Quantum Limit,” Science 385, 1318-1321 (2024).
3. E. Capote, LIGO O4 Detector Collaboration, "Advanced LIGO detector performance in the fourth observing run,” Phys. Rev. D 111, 062002 (2025).
4. LIGO-Virgo-KAGRA Collaboration, GWTC-4.0: Updating the Gravitational-Wave Transient Catalog with Observations from the First Part of the Fourth LIGO-Virgo-KAGRA Observing Run, arXiv:2508.18082 (2025).