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The Heisenberg uncertainty principle dictates that the position and momentum of an object cannot be simultaneously measured with arbitrary precision, giving rise to an apparent limitation known as the standard quantum limit (SQL). Gravitational-wave detectors use photons to continuously measure the positions of freely falling mirrors and so are affected by the SQL. We investigated the performance of the Laser Interferometer Gravitational-Wave Observatory (LIGO) after the experimental realization of frequency-dependent squeezing designed to surpass the SQL. For the LIGO Livingston detector, we found that the upgrade reduces quantum noise below the SQL by a maximum of three decibels between 35 and 75 hertz while achieving a broadband sensitivity improvement, increasing the overall detector sensitivity during astrophysical observations.
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Broadband quantum enhancement of the LIGO detectors with frequency-dependent squeezing
Quantum noise imposes a fundamental limitation on the sensitivity of interferometric gravitational-wave detectors like LIGO, manifesting as shot noise and quantum radiation pressure noise. Here we present the first realization of frequency-dependent squeezing in full-scale gravitational-wave detectors, resulting in the reduction of both shot noise and quantum radiation pressure noise, with broadband detector enhancement from tens of Hz to several kHz. In the LIGO Hanford detector, squeezing reduced the detector noise amplitude by a factor of 1.6 (4.0 dB) near 1 kHz, while in the Livingston detector, the noise reduction was a factor of 1.9 (5.8dB). These improvements directly impact LIGO’s scientific output for high-frequency sources (e.g., binary neutron star post-merger physics). The improved low-frequency sensitivity, which boosted the detector range by 15–18 % with respect to no squeezing, corresponds to an increase in astrophysical detection rate of up to 65%. Frequency-dependent squeezing was enabled by the addition of a 300-meter long filter cavity to each detector as part of the LIGO A+ upgrade.
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- Award ID(s):
- 1912598
- PAR ID:
- 10435873
- Date Published:
- Journal Name:
- Physical review X
- ISSN:
- 2160-3308
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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