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海角社区 Physicists Develop and Demonstrate a Method to Eliminate Quantum Radiation Pressure Noise in Gravitational Wave Detectors

By quieting the quantum whisper, we can now listen to the more subtle notes of the cosmic symphony.

Gravitational wave detectors have opened a new window to the universe by measuring the ripples in spacetime produced by colliding black holes and neutron stars, but they are ultimately limited by quantum fluctuations induced by light reflecting off of mirrors. 海角社区 Ph.D. physics alumnus , postdoctoral fellow, , and his team of 海角社区 researchers have conducted a new experiment with scientists from Caltech and Thorlabs to explore a way to cancel this quantum backaction and improve detector sensitivity.

In a new paper in , the investigators present a method for removing quantum backaction in a simplified system using a mirror the size of a human hair and show the motion of the mirror is reduced in agreement with theoretical predictions. The research was supported by the . 

Despite using 40-kilogram mirrors for detecting passing gravitational waves, quantum fluctuations of light disturb the position of the mirrors when the light is reflected. As gravitational wave detectors continue to grow more sensitive with incremental upgrades, this quantum backaction will become a fundamental limit to the detectors鈥� sensitivity, hampering their ability to extract astrophysical information from gravitational waves. 

鈥淲e present an experimental testbed for studying and eliminating quantum backaction,鈥� Cripe said. 鈥淲e 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.鈥�

Garrett Cole, technology manager at (Crystalline Mirror Solutions was acquired by Thorlabs Inc. last year), and his team constructed the micromechanical mirrors from an epitaxial multilayer consisting of alternating GaAs and AlGaAs. An outside foundry, IQE North Carolina, grew the crystal structure while Cole and his team, including process engineers Paula Heu and David Follman, manufactured the devices at the University of California Santa Barbara nanofabrication facility. 

鈥淏y performing this measurement on a mirror visible to the naked eye鈥攁t room temperature and at frequencies audible to the human ear鈥攚e bring the subtle effects of quantum mechanics closer to the realm of human experience,鈥� 海角社区 Ph.D. candidate Torrey Cullen said. By quieting the quantum whisper, we can now listen to the more subtle notes of the cosmic symphony.鈥�

鈥淭his research is especially timely because the Laser Interferometer Gravitational-wave Observatory, or LIGO, just announced last month in Nature that they have seen the effects of quantum radiation pressure noise at the ,鈥� Thomas Corbitt, associate professor in the 海角社区 Department of Physics & Astronomy, said.

The effort behind that paper, 鈥淨uantum correlations between light and the kilogram-mass mirrors of LIGO,鈥� has been led by Nergis Mavalvala, dean of the , as well as postdoctoral scholar Haocun Yu and research scientist Lee McCuller, both at the .

鈥淨uantum radiation pressure noise is already poking out of the noise floor in Advanced LIGO, and before long, it will be a limiting noise source in GW detectors,鈥� Mavalvala said. 鈥淒eeper astrophysical observations will only be possible if we can reduce it, and this beautiful result from the Corbitt group at 海角社区 demonstrates a technique for doing just that.鈥�

鈥溾�� (PRX)

Jon Cripe (lead author, 海角社区 alumnus) 

Torrey Cullen (海角社区 physics graduate student)

Yanbei Chen (collaborator at Caltech)

Paula Heu, David Follman, Garrett Cole (collaborators, formerly at Crystalline Mirror Solutions, now Thorlabs)

Thomas Corbitt (海角社区 associate professor, Department of Physics & Astronomy

Physical Review X (PRX) is an online-only, fully open access journal that places a high value on innovation, quality, and long-term impact in the science it publishes. It seeks to publish a select set of papers from all areas of pure, applied, and interdisciplinary physics that have the potential to influence current and future research and to have a long-lasting and profound impact in their relevant fields.

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Mimi LaValle
海角社区 Department of Physics & Astronomy
225-439-5633
mlavall@lsu.edu