We’ve just doubled the number of gravitational waves we can find
Nearly imperceptible quantum flickers used to limit how precisely we could detect the way space-time ripples, but squeezing the laser light used in detectors overcomes this and doubles the number of gravitational waves we can see
By Karmela Padavic-Callaghan
19 September 2024
Gravitational wave detectors use laser beams in tubes that span kilometres
The Virgo Collaboration
Gravitational waves that span thousands to billions of miles can be obscured in our detectors by the smallest of quantum fluctuations that permeate space-time. But now, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) have found a way to beat this quantum noise. And as a result, they are finding nearly twice as many cosmic events as before.
“We realised that quantum noise will be limiting us a long time ago. It’s not just a fancy [quantum] thing to demonstrate, it’s something that really affects the actual detector,” says Wenxuan Jia at the Massachusetts Institute of Technology.
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LIGO detects gravitational waves, ripples in the fabric of space-time created by dramatic cosmic events like collisions between black holes. To do so, it fires a laser beam along each of its two 4-kilometre-long arms, which sit perpendicular to each other. A passing gravitational wave squashes and expands the part of space-time where these arms reside, introducing a small difference between the distances travelled by the two beams.
But that discrepancy is so tiny it can be hard to tell when it is caused by gravitational waves and when it is due to the nearly-imperceptible flickers of quantum fields that permeate all of space, including the laser light itself. The researchers found changing the quantum properties of the light could help them suppress the crackles of quantum fields and get a more distinct gravitational wave signal.
They added a series of devices to the detector, including a special crystal and several lenses and mirrors, which all work together to “squeeze” LIGO’s light into a quantum state where correlations between light particles diminish the flickering.
