Posts Tagged ‘quantum’

Looking Beyond Space and Time to Cope With Quantum Theory

October 29, 2012 Leave a comment

ScienceDaily (Oct. 28, 2012) — Physicists have proposed an experiment that could force us to make a choice between extremes to describe the behaviour of the Universe.

Trying to explain quantum “spooky action at a distance” using any kind of signal pits Einstein’s relativity against our concept of a smooth spacetime. (Credit: Timothy Yeo / CQT, National University of Singapore)

The proposal comes from an international team of researchers from Switzerland, Belgium, Spain and Singapore, and is published October 28 in Nature Physics. It is based on what the researchers call a ‘hidden influence inequality’. This exposes how quantum predictions challenge our best understanding about the nature of space and time, Einstein’s theory of relativity.

“We are interested in whether we can explain the funky phenomena we observe without sacrificing our sense of things happening smoothly in space and time,” says Jean-Daniel Bancal, one of the researchers behind the new result, who carried out the research at the University of Geneva in Switzerland. He is now at the Centre for Quantum Technologies at the National University of Singapore.

Excitingly, there is a real prospect of performing this test.

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Strength in Numbers: Physicists Identify New Quantum State Allowing Three — But Not Two — Atoms to Stick Together

July 4, 2012

ScienceDaily (July 3, 2012) — A Kansas State University-led quantum mechanics study has discovered a new bound state in atoms that may help scientists better understand matter and its composition.

Abstract rendering. (Credit: © John Denison / Fotolia)

The yet-unnamed bound state, which the physicists simply refer to as “our state” in their study, applies to three identical atoms loosely bound together — a behavior called three-body bound states in quantum mechanics. In this state, three atoms can stick together in a group but two cannot. Additionally, in some cases, the three atoms can stick together even when any two are trying to repel each other and break the connection.

“It’s really counterintuitive because not only is the pair interaction too weak to bind two atoms together, it’s also actively trying to push the atoms apart, which is clearly not the goal when you want things to stick together,” said Brett Esry, university distinguished professor of physics at Kansas State University and the study’s lead investigator.

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Quantum Researchers Able to Stop and Restart Light

Wednesday, 27 June 2012

‘In two independent experiments that defy the notions of Einstein, researchers have been able to stop, then restart a beam of light.

Ordinarily, light travels at the speed of 186,282 miles per second, but the research team of Lene Hau, a professor of physics at Harvard, who in 1999 was able to slow light down to 38 miles per hour, has been able to trap light in a cloud of sodium atoms super-cooled to near ‘absolute zero.’’

Read more: Quantum Researchers Able to Stop and Restart Light

Chinese Physicists Teleport Photons Over 100 Kilometers

Teleportation is the extraordinary ability to transfer objects from one location to another without travelling through the intervening space.

The idea is not that the physical object is teleported but the information that describes it. This can then be applied to a similar object in a new location which effectively takes on the new identity.

And it is by no means science fiction. Physicists have been teleporting photons since 1997 and the technique is now standard in optics laboratories all over the world.

The phenomenon that makes this possible is known as quantum entanglement,  the deep and mysterious link that occurs when two quantum objects share the same existence and yet are separated in space.

Teleportation turns out to be extremely useful. Because teleported information does not travel through the intervening space, it cannot be secretly accessed by an eavesdropper.

For that reason, teleportation is the enabling technology behind quantum cryptography, a way of sending information with close-to-perfect secrecy.

Unfortunately, entangled photons are fragile objects. They cannot travel further than a kilometre or so down optical fibres because the photons end up interacting with the glass breaking the entanglement. That severely limits quantum cryptography’s usefulness.

However, physicists have had more success teleporting photons through the atmosphere. In 2010, a Chinese team announced that it had teleported single photons over a distance of 16 kilometres. Handy but not exactly Earth-shattering.

Now the same team says it has smashed this record. Juan Yin at the University of Science and Technology of China in Shanghai, and a bunch of mates say they have teleported entangled photons over a distance of 97 kilometres across a lake in China.

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In New Quantum Experiment, Effect Happens Before Cause

By Paul Adams Posted 04.24.2012 at 5:14 pm
Four Particles Jon Heras, Equinox Graphics Ltd.

A real-world demonstration of a thought experiment conducted at the University of Vienna, has produced a result that is somewhat befuddling to people with what the lead researcher calls a “naïve classical world view.” Two pairs of particles are either quantum-entangled or not. One person makes the decision as to whether to entangle them or not, and another pair of people measure the particles to see whether they’re entangled or not.

The head-scratcher is: the measurement is made before the decision is made, and it is accurate. “Classical correlations can be decided after they are measured,” says Xiao-song Ma, the writer of the study. Entanglement can be created “after the entangled particles have been measured and may no longer exist.”

The finding can be integrated into potential quantum computers, one hopes. Causality, clearly, is a quaint, irrelevant concept.