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Quantum 'kick' on big object measured for 1st time ever

The LIGO project operates two detector sites: one near Hanford in eastern Washington, and another near Livingston, Louisiana (shown here).
The LIGO project operates two detector sites: one near Hanford in eastern Washington, and another near Livingston, Louisiana (shown here).
(Image: © LIGO Collaboration)

Quantum effects are pushing us around all the time, and we now have observational evidence of this somewhat disconcerting fact.

Researchers with the Laser Interferometer Gravitational-wave Observatory (LIGO) Scientific Collaboration have measured the tiny kick imparted to their exquisitely sensitive equipment by quantum fluctuations, a new study reports.

And that kick is indeed tiny, moving LIGO's 88-lb. (40 kilograms) mirrors just 10^-20 meters, the scientists found.

Related: Hunting gravitational waves: The LIGO project in photos

"A hydrogen atom is 10^-10 meters, so this displacement of the mirrors is to a hydrogen atom what a hydrogen atom is to us — and we measured that," study co-author Lee McCuller, a research scientist at the Massachusetts Institute of Technology's (MIT) Kavli Institute for Astrophysics and Space Research, said in a statement.

Other research groups have measured such quantum effects before, but never on this scale. The LIGO mirrors are about 1 billion times heavier than previously observed "kicked" objects, study team members said.

The LIGO project hunts for gravitational waves — the ripples in space-time caused by the acceleration of massive objects — using two detectors, one in Livingston, Louisiana and the other in Hanford, Washington.

Each detector is an L-shaped facility with legs 2.5 miles (4 kilometers) long. A laser at the crux of the "L" shines light down these legs, and 88-lb. mirrors at the end of each bounce the beams back. If the reflected beams arrive back at the crux at slightly different times, it's potential evidence of a gravitational wave distorting the fabric of space-time in the legs.

The LIGO team has used this strategy to great effect. The collaboration now has about a dozen confirmed gravitational-wave detections under its belt, including the first-ever such find, made in September 2015. Most of these events involve merging black holes, but two were caused by the collision of superdense, city-size stellar corpses known as neutron stars.

The LIGO detectors are incredibly sensitive and profoundly shielded from noise; they have to be, or else they'd be incapable of picking up gravitational waves. Making the groundbreaking 2015 detection, for example, required measuring a distance change 1,000 times smaller than the width of a proton, team members have said.

The new study harnesses that sensitivity and takes it to another level. The researchers, led by MIT physics graduate student Haocun Yu, used a "quantum squeezer," an add-on instrument they recently built allowing them to "tune" the quantum noise inside the detectors. That noise is created by minuscule particles popping into and out of existence, a constant crackling that pervades the universe. 

"We think of the quantum noise as distributed along different axes, and we try to reduce the noise in some specific aspect," Yu said in the same statement.

The study team measured the total noise — both quantum and "classical," which is caused by ordinary vibrations — inside the detector. Then, with the aid of the squeezer, they subtracted out the classical noise during data analysis. This work revealed that quantum fluctuations in the laser light alone can move the detector mirrors, which hang from pendulums in a quadruple-suspension setup, by 10^-20 meters.

That number is in line with predictions made by theorists, team members said. 

The new study, which was published Wednesday (July 1) in the journal Nature, has more than just gee-whiz appeal. The quantum squeezer allows the LIGO team to "manipulate the detector's quantum noise and reduce its kicks to the mirrors, in a way that could ultimately improve LIGO's sensitivity in detecting gravitational waves," Yu said.

Mike Wall is the author of "Out There" (Grand Central Publishing, 2018; illustrated by Karl Tate), a book about the search for alien life. Follow him on Twitter @michaeldwall. Follow us on Twitter @Spacedotcom or Facebook. 

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  • Torbjorn Larsson
    Cool, and useful! I remember the demonstrator experiment https://arxiv.org/pdf/1812.09804.pdf ].
    Reply
  • TimLong
    Not only is the quantum charge interaction (in particular +/-) the basis of quantum motions, when charge and energy are balanced, it is possible for pair-formation at higher (1.0216 MeV) energies, when matter (as +/- electrons) is formed. These stable photon systems provide the original clock references which define "Time", and they even are the basis of our very existence. Not only is all matter composed of these stable particles, their spin interaction provides for the continuous evolution of larger and larger atomic structures -- from our scale to large scale astronomical structures.
    Reply
  • chemicalmicroscopist
    Can LIGO tell if one of the massive objects is a dark matter object? Apparently black holes, neutron stars etc can be distinguished. Why not dark matter objects?
    Reply
  • rod
    "And that kick is indeed tiny, moving LIGO's 88-lb. (40 kilograms) mirrors just 10^-20 meters, the scientists found."

    1E-20 meter is a very sensitive size measurement :)
    Reply
  • chemicalmicroscopist
    It is very sensitive. Some of the best transmission electron microscopes resolve 0.01 nm or 1E-11. Atomic Force Microscopes may reach 1E-12. If you hold your mouth right and the wind is blowing in the right direction.
    Reply
  • Torbjorn Larsson
    chemicalmicroscopist said:
    Can LIGO tell if one of the massive objects is a dark matter object? Apparently black holes, neutron stars etc can be distinguished. Why not dark matter objects?

    Dark matter objects are particles that interact gravitationally, as well as clumps of them that we now see by gravitational lensing.

    There isn't any localized dark matter clump mergers, say, that would generate strong gravitational waves.
    Reply
  • chemicalmicroscopist
    Torbjorn Larsson said:
    Dark matter objects are particles that interact gravitationally, as well as clumps of them that we now see by gravitational lensing.

    There isn't any localized dark matter clump mergers, say, that would generate strong gravitational waves.
    I don't see how it can be both ways: strong enough to hold galaxies together and make up more of the universes mass, then say there isn't enough gravity in the dark matter to clump dark matter together. This appears to be a contradiction. I would expect more black holes to form from dark matter than "regular" matter. How about dark matter solar masses? Nope. Too many contradictions. It either has gravitational force or it doesn't.
    Reply
  • chemicalmicroscopist
    Musing on this thread a bit. Is it possible dark matter only has gravitational pull on our regular matter, but little or none on itself? Would explain no clumps of dark matter, but seems ridiculous since this would muck with the space fabric explanation of gravity.
    Reply