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MIT researchers reveal new technique for measuring gravity

"We know that very small things act quantum, but then big things like you and me don’t act very quantum," explained grad student William Burton.

By
Brooks Hays
Researchers at MIT have found a way to more precisely organize Bose-Einstein condensates with a standing wave laser. Photo by MIT News
Researchers at MIT have found a way to more precisely organize Bose-Einstein condensates with a standing wave laser. Photo by MIT News

BOSTON, Dec. 27 (UPI) -- Researchers have found a way to improve atom interferometers, the most common and precise tool for measuring gravity.

Atom interferometers measure difference in wave characteristics between atomic matter. They rely on an exotic state of matter called Bose-Einstein condensates. Researchers in MIT have found a way to improve the precision of atom interferometers by augmenting the condensates.

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"The idea here is that Bose-Einstein condensates are actually pretty big," William Burton, an MIT graduate student in physics, said in a news release. "We know that very small things act quantum, but then big things like you and me don't act very quantum. So we can see how far apart we can stretch a quantum system and still have it act coherently when we bring it back together. It's an interesting question."

Bose-Einstein condensates are clusters of atoms that occupy the same quantum state when cooled to absolute zero. As a result, they exhibit uniquely similar properties and respond uniformly to outside forces.

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Interferometers work by trapping and dividing cooled condensates into groups using a standing wave laser. The standing wave organizes 20,000 rubidium atoms, for example, into 10 groups of about 2,000. The atoms in each "well" are subjected to outside forces, but are prevented from moving by the laser trap. When released, the condensates respond to the forces they experienced. Their reactions are measured by analyzing the scattering pattern made when light beams are passed through the cloud of atoms.

While the technique is quite successful at measuring forces of gravity and inertia, the atoms aren't divided into perfectly even groups. One well might contain 1,950 atoms while another might hold 2,050.

MIT scientists developed a new technique using two types of condensates, spin-down atoms and spin-up atoms. The two condensates react differently to an applied magnetic field. The spin-down atoms remain frozen in the standing wave laser, while the spin-up atoms move from well to well until their perfectly distributed, correcting the imbalances between spin-down atoms.

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Researchers described their new and improved gravity-measuring technique in the journal Physical Review Letters.

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