LIGO researchers surpass the quantum limit

Barsotti: “We are finally taking advantage of our gravitational universe”

Laster Interferometer Gravitational-Wave Observatory (LIGO) researchers at MIT, Caltech, and other institutions reported that they had surpassed the quantum limit on Oct. 23. This marks a significant advance in quantum squeezing, a method for reducing quantum noise to obtain more precise measurements. Researchers will now be able to measure a larger volume of the universe by analyzing gravitational frequencies. 

According to MIT News, LIGO is able to measure the “stretching and squeezing of the fabric of space-time on scales 10 thousand trillion times smaller than a human hair.” Its precision, however, has continued to be limited by the laws of quantum physics, namely the Heisenberg uncertainty principle. Heisenberg’s uncertainty principle states that one cannot determine the position and momentum of objects (or the frequency and power of light) at the same time.

Since 2019, LIGO’s twin detectors have been squeezing light in such a way as to improve their sensitivity to the upper frequency range of gravitational waves they detect. However, due to Heisenberg’s uncertainty principle, making LIGO’s measurements more precise at the high frequencies will lead to measurements becoming less precise at lower frequencies.

“At some point, if you do more squeezing, you aren’t going to gain much. We needed to prepare for what was to come next in our ability to detect gravitational waves,” Lisa Barsotti, a senior research scientist at MIT who oversaw the development of the new LIGO technology, said. The original project was spearheaded by Matt Evans, professor of physics, and Nergis Mavalvala, the Curtis and Kathleen Marble Professor of Astrophysics and the dean of the School of Science. 

LIGO’s partner observatory, Virgo, will likely also use frequency-dependent squeezing technology within the current run, which will continue until roughly the end of 2024. Next-generation larger gravitational-wave detectors, such as the planned ground-based Cosmic Explorer, will also reap the benefits of squeezed light.

The solution was to squeeze light in different ways depending on the frequency of the gravitational waves.This was accomplished by LIGO’s new frequency-dependent squeezing cavity, which allows researchers to selectively move the quantum noise into different features of light based on the frequency range of gravitational waves.

This breakthrough will enable LIGO to detect even more black hole and neutron star collisions. “We are finally taking advantage of our gravitational universe,” Barsotti said. “In the future, we can improve our sensitivity even more. I would like to see how far we can push it.”

A full press release can be found here.