Gravitational wave detectors use laser beams in tubes that extend for miles
The collaboration of the Virgin
Gravitational waves that span thousands or even billions of kilometers can be masked in our detectors by the smallest quantum fluctuations that permeate spacetime. But now, researchers at the Laser Interferometer Gravitational-Wave Observatory (LIGO) have found a way to overcome this quantum noise. With this, they are detecting almost twice as many cosmic events as before.
“We’ve understood for a long time that quantum noise is going to limit us. It’s not just a fancy (quantum) thing to demonstrate, it’s something that actually affects the detector itself,” he explains Wen Xuan Jia at the Massachusetts Institute of Technology.
LIGO detects gravitational waves, ripples in the fabric of spacetime created by spectacular cosmic events like black hole collisions. It does this by firing a laser beam along each of its two 4-kilometer-long arms, which are perpendicular to each other. A passing gravitational wave crushes and expands the part of spacetime where these arms are located, introducing a small difference in the distances traveled by the two beams.
But this difference is so small that it can be difficult to determine when it is caused by gravitational waves and when this is due to the almost imperceptible flickerings of quantum fields which permeate the entire spaceincluding laser light itself. The researchers found that changing the quantum properties of light could help them suppress the crackles of quantum fields and obtain a more distinct gravitational wave signal.
They added a series of devices to the detector, including a special crystal and several lenses and mirrors, all of which work together to “squeeze” LIGO’s light into a quantum state where correlations between light particles diminish the flickering.
LIGO has completed its first run with compressed light in 2020, but the method only worked for gravitational waves at relatively high frequencies—lower frequencies actually produced noisier signals than before. Jia and his colleagues tweaked the compression process to work equally well at high and low frequencies ahead of LIGO’s 2023 test. The change had a surprising effect: The number of gravitational waves detected nearly doubled, allowing the machine to reveal a larger part of our universe.
“Pushing the boundaries of quantum measurement has pushed the boundaries of measuring spacetime, which is a really beautiful thing,” says Chad Hanna He explains that this advanced precision will allow LIGO to see black hole mergers “from the formation of the first stars.”
Bruce Allen According to a researcher at the Max Planck Institute for Gravitational Physics in Germany, physicists would like to see several new types of gravitational waves with LIGO’s newly acquired precision. This includes those emitted continuously by bumpy neutron stars as they spin, as opposed to those they emit while they are rotating. collide with somethingwhich is the origin of most of the gravitational waves detected to date.
The upgrade also opens the door to a new discoveries, because it could help probe the gravitational wave background that permeates space-time. “Any time you increase the sensitivity (of your detectors), you increase your chances of encountering the unexpected,” Allen says.
