LIGO team members (left-to-right: Fabrice Matichard, Sheila Dwyer, Hugh Radkins) install in-vacuum equipment as part of the squeezed light upgrade. Credit: Nutsinee Kijbunchoo, CGA

With the first detection of gravitational waves by LIGO, the quest to further improve the astrophysical range and the detector's sensitivity is in full swing. The ANU Centre for Gravitational Astrophysics is a key member of the LIGO Scientific Collaboration and continues to develop hardware and techniques for use at the LIGO observatories. We have developed and installed various hardware in the current advanced LIGO detectors, the most recent one being a ‘squeezer’ at LIGO-Hanford to improve the high frequency sensitivity [1].

The current generation of LIGO interferometers are limited by the quantum nature of the light at high frequencies, and the next-generation detectors are expected to be limited by quantum light noise across their entire measurement band. Squeezed light is used to reduce the noise of the vacuum field (zero-point energy) fluctuations below the standard quantum limit. The injection of squeezed states of light in advanced LIGO has improved the detector sensitivity by a factor of 2 thereby increasing detection rate of binary blackholes by 50%!! As a part of the next observing run (and for future gravitational wave detectors) advanced LIGO will implement a filter cavity [2-4] to rotate the injected squeezed states at the standard quantum limit to achieve a broadband reduction of quantum noise. As a part of OzGrav and the LIGO-Virgo-Kagra collaboration, we will continue to support the upgrade of the present detectors and help plan future detectors.

A squeezed light source (Optical Parametric Oscillator) similar to the one implemented in the advanced LIGO detectors. This cavity is pumped with 532 nm light to produce squeezed states at 1064 nm.Credit : Chathura Bandutunga,, CGA

Nutsinee Kijbunchoo and Dr Terry McRae at LIGO Hanford Observatory. Credit: Nutsinee Kijbunchoo, CGA

[1] Tse, M. and Yu, Haocun and Kijbunchoo, N. . et al. Quantum-Enhanced Advanced LIGO Detectors in the Era of Gravitational-Wave Astronomy. Phys. Rev. Lett. 123, 231107. https://doi.org/10.1103/PhysRevLett.123.231107

[2] N Kijbunchoo, T McRae, D Sigg, . et al. Low phase noise squeezed vacuum for future generation gravitational wave detectors. Classical and Quantum Gravity. Volume 37, Number 18, 2020. https://doi.org/10.1088/1361-6382/aba4bb

[3] Yu, H., McCuller, L., Tse, M. et al. Quantum correlations between light and the kilogram-mass mirrors of LIGO. Nature 583, 43–47 (2020). https://doi.org/10.1038/s41586-020-2420-8

[4] McCuller, L. and Whittle, C. and Ganapathy, D. et al. Frequency-Dependent Squeezing for Advanced LIGO. Phys. Rev. Lett. 124, 17, 171102, 2020. https://link.aps.org/doi/10.1103/PhysRevLett.124.171102