Catching a gravity wave in a tangle of photons

Lisandro Firman
Lisandro Firman
Joined: 17 May 06
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Topic 192751

New article in New ScientistTech

A quantum "ruler" could reveal gravitational waves fainter than we can now hope to detect.

Gravitational waves are ripples in the fabric of space-time that physicists are trying to detect with interferometers - devices that split a beam of light into two and then recombine them to create interference fringes. A gravity wave passing through the device would change the distance travelled by one beam relative to the other, and this effect would show up as a change in the interference fringes.

Current designs, though, have their limits. They can't measure a shift smaller than the size of the fringes; this in turn is limited by the wavelength of the light used.

This can be overcome using quantum entanglement, whereby the states of two or more particles remain linked no matter how far apart they are. Shigeki Takeuchi at Hokkaido University in Japan and colleagues used a beam of four entangled photons. "Effectively we have four photons passing through our apparatus where otherwise we would have only one," Takeuchi says. This halves the spacing between the fringes, he says (Science, vol 316, p 726).

"It is essential to increase the number of entangled photons," says Takeuchi. "There is really no other way to improve precision."

From issue 2603 of New Scientist magazine, 15 May 2007, page 19

tullio
tullio
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Catching a gravity wave in a tangle of photons

Quote:

New article in New ScientistTech

A quantum "ruler" could reveal gravitational waves fainter than we can now hope to detect.

Gravitational waves are ripples in the fabric of space-time that physicists are trying to detect with interferometers - devices that split a beam of light into two and then recombine them to create interference fringes. A gravity wave passing through the device would change the distance travelled by one beam relative to the other, and this effect would show up as a change in the interference fringes.

Current designs, though, have their limits. They can't measure a shift smaller than the size of the fringes; this in turn is limited by the wavelength of the light used.

This can be overcome using quantum entanglement, whereby the states of two or more particles remain linked no matter how far apart they are. Shigeki Takeuchi at Hokkaido University in Japan and colleagues used a beam of four entangled photons. "Effectively we have four photons passing through our apparatus where otherwise we would have only one," Takeuchi says. This halves the spacing between the fringes, he says (Science, vol 316, p 726).

"It is essential to increase the number of entangled photons," says Takeuchi. "There is really no other way to improve precision."

From issue 2603 of New Scientist magazine, 15 May 2007, page 19

Einstein would be glad. His Einsten-Podolski-Rosen paradox of 1935 would be again a source of new ideas. Unfortunately, he was awarded a Nobel prize for much less.
Tullio

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