Gravitational wave detectors use laser beams in tubes that span several kilometers.
Virgo Collaboration
Gravitational waves, which span thousands to billions of miles, can be rendered undetectable by detectors by the tiniest quantum fluctuations that permeate space-time, but now researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) have found a way to cancel out this quantum noise, and as a result, they’re discovering nearly twice as many cosmic phenomena as before.
“We’ve known for a long time that quantum noise is a limitation for us, it’s not just a fantasy. [quantum] “This is something that really has an impact on the actual detector.” Jia Wenxuan At Massachusetts Institute of Technology.
LIGO detects gravitational waves – ripples in the fabric of space-time created by dramatic cosmic phenomena like colliding black holes – by shining a laser beam along two four-kilometer arms that run perpendicular to each other. As gravitational waves pass through, the parts of space-time where these arms are located get squashed and expanded, causing the two beams to travel slightly different distances.
But the difference is so small that it’s hard to tell whether it’s due to gravitational waves or the nearly imperceptible flickering of quantum fields that permeate all of space, including the laser light itself.The researchers found that by altering the quantum properties of light, they can suppress the quantum field crackle and get a clearer gravitational wave signal.
They added a series of devices to the detector, including special crystals and several lenses and mirrors, all working together to “compress” LIGO’s light into a quantum state, one in which correlations between light particles reduce flicker.
LIGO completed its first experiment with squeezed light in 2020, but the method only worked for relatively high frequencies of gravitational waves; lower frequencies actually produced a noisier signal than before. Jia and his colleagues have modified the squeezing process ahead of LIGO’s 2023 experiment so that it works equally well for both high and low frequencies. The change had a surprising effect: it nearly doubled the number of gravitational waves detected, effectively allowing the machine to reveal a much larger portion of the universe.
“Pushing the limits of quantum measurement means pushing the limits of space-time measurement, which is really cool.” Chad Hannah researcher at Pennsylvania State University. This high level of precision will enable LIGO to observe black hole mergers “all the way back to the formation of the first stars,” he says.
Bruce Allen Researchers at the Max Planck Institute for Gravitational Physics in Germany say there are several new kinds of gravitational waves physicists are hoping to see with LIGO’s new precision, including gravitational waves emitted constantly by lumpy neutron stars as they spin, rather than the kind emitted when they collide with something, which accounts for most of the gravitational waves detected so far.
The upgrade could help probe the gravitational wave background that permeates space-time, opening the door to entirely new discoveries. [of your detectors]That way you’re more likely to encounter something unexpected,” Allen said.
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