'Muting Quantum Whisper' Improves Gravitational Wave Detector Sensitivity, Says Study

Quieting the 'quantum whisper' is essential to improving gravitational wave detector sensitivity.
Brad Bergan

Gravitational wave detectors may soon see a technological jump in sensitivity.

Typically, gravitational wave detector sensitivity are limited by quantum fluctuations caused via light reflecting off of mirrors, but a recent experiment explored a way of canceling this quantum backaction and improving detector sensitivity, according to a new paper published in the journal Physical Review X.


'Quantum Whisper' disrupts gravitational wave detectors

In the new paper, the investigators showed a method for removing quantum backaction via a simplified system employing a mirror roughly the size of a human hair — and found the mirror's motion was reduced according to theoretical predictions. This research received support from the National Science Foundation and was carried out by LSU physics alumnus Jonathan Cripe (a postdoctoral fellow), NIST, and Cripe's team of LSU researchers, reports SciTech Daily.

Typically, 88.1-lb (40-kg) mirrors are used to detect passing gravitational waves, but despite this relatively large mass quantum fluctuations of light disrupt the position of the mirrors when reflecting light.

Jonathan Cripe LSU
LSU's almumnus Jonathan Cripe completed a new experiment to improve the sensitivity of gravitational wave detectors. Source: LSU

Upgrading sensitivity of gravitational wave detectors

Gravitational wave detectors have seen increased sensitivity as they undergo continual upgrades, but this quantum backaction functions as an operational ceiling for detector sensitivity — binding their ability to measure astrophysical information amid active gravitational waves.

"We present an experimental testbed for studying and eliminating quantum backaction," said Cripe, SciTech Daily reports. "We perform two measurements of the position of a macroscopic object whose motion is dominated by quantum backaction and show that by making a simple change in the measurement scheme, we can remove the quantum effects from the displacement measurement. By exploiting correlations between the phase and intensity of an optical field, quantum backaction is eliminated," he said.

Elsa Hahne / LSU ORED
Thomas Corbitt, LSU associate professor, hard at work. Source: Elsa Hahne / LSU ORED

Quieting the 'quantum whisper' advances gravitational wave detection

Technology Manager Garrett Cole of Thorlabs Crystalline Solutions and his team built the micromechanical mirrors, which consist of epitaxial multilayer subsisting of alternative GaAs and AlGaAs.

The crystal structure itself was curated at an external foundry called IQE North Carolina. While this happened, Cole and his team constructed the devices within the University of California Santa Barbara's nanofabrication facility.

"By performing this measurement on a mirror visible to the naked eye — at room temperature and at frequencies audible to the human ear — we bring the subtle effects of quantum mechanics closer to the realm of human experience," said Torrey Cullen — an LSU doctoral candidate. "By quieting the quantum whisper, we can now listen to the more subtle notes of the cosmic symphony."

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This latest research is especially apt because it comes on the heels of the Laser Interferometer Gravitational-wave Observatory (LIGO) announcing observations of the effects of quantum radiation pressure noise at the LIGO Livingston observatory, according to Associate Professor Thomas Corbitt of LSU's Department of Physics and Astronomy.

Notably, reducing the quantum whisper is needed to make deeper astrophysical observations possible. With this great success, gravity wave detection has made yet another small step into the future of physics.