Entanglement study makes a quantum leap

Jul 09, 2012 By Monte Morin

Some scientists have likened it to voodoo, while Albert Einstein called it just plain "spooky." In the bizarre realm of quantum mechanics, entanglement is the phenomenon in which two seemingly distinct particles control each other in ways that defy common physical sense. For instance, when an atom located in Beijing is measured by an observer, it will exhibit the exact opposite qualities of its entangled counterpart in Boston.

In the 1930s, the idea of seemed so absurd that Einstein derided it as "spooky action at a distance" and argued that it revealed serious shortcomings in quantum theory.

Today, however, entanglement stands as the essential feature of quantum mechanics, and scientists say its exploitation could lead to extraordinary leaps in computing, communications and cryptology. A quantum computer, they say, would take seconds to solve problems that today's PCs would take billions of years to parse. Governments, financial institutions and armies, meanwhile, are intrigued by the potential for secure long-distance communications that would instantly reveal attempts at hacking.

Those technologies may still be sometime in the future, but researchers in Germany have taken a step closer to their realization. In a report Friday in the journal Science, at the Ludwig-Maximilians-University in Munich said they had demonstrated that two atoms separated by a distance of about 65 feet could become entangled and trigger an alert to announce that they had done so.

To visualize the phenomenon, imagine two boxes that each contain a single coin, said study co-author Wenjamin Rosenfeld. In , neither coin has a defined orientation - heads or tails - until an observer opens one of the boxes and sees which side is facing up. At that instant, the second coin will be found, without fail, to be lying in the exact opposite position, no matter how far away it is.

While other experiments have successfully entangled atoms, photons and diamond crystals, this was the first to do so at a long distance and include a signal, or herald, to let scientists know that entanglement had been achieved. Such a signal - in this case, a message on a computer screen - is crucial to the further study of entanglement and its future practical application, researchers said.

The experiment involved the capture of two rubidium atoms in separate "atom traps" located in different rooms. The traps used lenses and lasers to position each atom and prompt it to emit a stream of photons, or packets of light. The photons were inherently entangled with the atoms that emitted them.

Those photons sped through fiber-optic cables from the atom traps to a centralized measurement device at a rate of about 1,000 per minute. When photons from the two traps arrived simultaneously - an event that occurred roughly every 100 seconds - the atoms that sent the photons became entangled as well.

At that point, a computer heralded the achievement.

The physicists say they believe their experiment would work at distances up to about 1,000 feet. Beyond that, however, it becomes increasingly difficult to achieve the same effect due to photon loss over the length of the cable.

In an independent assessment that also appeared in Science, physicists Jurgen Volz and Arno Rauschenbeutel of the Vienna Center for Quantum Science and Technology said the study was significant.

"The experiment represents an important milestone toward the implementation of practical long-distance quantum communication protocols," they wrote.

Harald Weinfurter, the study's senior author, said he hoped the results would help address concerns raised by Einstein and others years ago. The question of whether needed revisions might soon be answered, he said.

Explore further: A new key to unlocking the mysteries of physics? Quantum turbulence

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User comments : 14

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virtualist
1.8 / 5 (10) Jul 09, 2012
"..To visualize the phenomenon, imagine two boxes that each contain a single coin, said study co-author Wenjamin Rosenfeld. In quantum mechanics, neither coin has a defined orientation - heads or tails - until an observer opens one of the boxes and sees which side is facing up. At that instant, the second coin will be found, without fail, to be lying in the exact opposite position, no matter how far away it is..."

NO ! NO ! NO ! .. bad example !
Ventilator
2.3 / 5 (3) Jul 09, 2012
"..To visualize the phenomenon, imagine two boxes that each contain a single coin, said study co-author Wenjamin Rosenfeld. In quantum mechanics, neither coin has a defined orientation - heads or tails - until an observer opens one of the boxes and sees which side is facing up. At that instant, the second coin will be found, without fail, to be lying in the exact opposite position, no matter how far away it is..."

NO ! NO ! NO ! .. bad example !


Maybe, however, this was the best the scientist could make to illustrate as an example. If you want better, I recommend Michio Kaku instead.
Sean_W
2.7 / 5 (10) Jul 09, 2012
I had always heard of entanglement as originating from an event (such as an atom releasing two photons) and being transferred to separate particles. I didn't realize that separate events (two atoms emitting photons which arrive at the same place and time could confer entanglement back to the separate events. The article makes it sound as if this was actually known to occur but the achievement was to do it to such distances. This would be the sort of thing I would be interested in knowing if the popular science press were not busy trying to educate me on how the latest computer model proves that ocean acidification was going to melt all the polar bears in the next five years.
Cynical1
1 / 5 (1) Jul 09, 2012
this article mentions only the two "trapped" atoms - are there any other atoms (NOT specifically observed) within the specified range that might also become entangled, as well?
We can use the "if a tree falls in the forest..." example.
ANd if there is randomly occurring entanglement, wouldn't there be entanglements that show an opposite reaction to the "first" one?
Noumenon
1.3 / 5 (27) Jul 09, 2012
I had always heard of entanglement as originating from an event (such as an atom releasing two photons) and being transferred to separate particles. I didn't realize that separate events (two atoms emitting photons which arrive at the same place and time could confer entanglement back to the separate events.


Yes. The reason is because it is not possible, (at the photon detector), to determine which photon came from which atom, even in principal. As far as the detector is concerned the two events are indistinguishable, and in all such QM cases the probabilities are determined as there are two possibilities in a single system.

i.e. to determine probabilities of two photons arriving (at same time and place), it is necessary that the amplitudes of the two events be added, and then squared,.... rather than as two independent events which would require both amplitudes to be squared and then multiplied (as in normal probability).
Noumenon
1.3 / 5 (28) Jul 09, 2012
,.... interestingly, if both photons are sent through polorizors before the detector, so that it is possible to determine which photon came from which atom, then there would be any entanglement, no correlation at all.
Noumenon
1.1 / 5 (27) Jul 09, 2012
,.... interestingly, of two photon polorizors were placed before the detector, so that it would be possible to determine which photon came from which atom, there wouldn't be any correlation, no entanglement.
daywalk3r
3.7 / 5 (12) Jul 09, 2012
So the computer evaluated, that at the instant of detecting an increased/decreased magnitude signal (eg. the result from constructive/destructive interferrence between 2 photons arriving at same time), the two emitting atoms were "in synch" (or exactly 180deg phase shifted), and displayed it on the monitor..

MIND = BLOWN

;-O

On a more serrious note:

Anyone else loves the new voting troll accounts? Like at most a few weeks old, with zero comment activity, and allready hundreds of up/down votes? The joy..

Accounts should not be allowed to vote until they (actively) participate, IMO. Else there is too much room for abuse.
Noumenon
1.4 / 5 (27) Jul 10, 2012
I've asked PhysOrg to disable comment ratings altogether many times. It doesn't work. Perhaps if others would email likewise, they would finally admit it is pointless, without moderators in place, and remove it.

Sock-puppet trolls like "pluton" have nothing to add, and think a 1 rating substitutes for their ignorance.
antialias_physorg
not rated yet Jul 10, 2012
I've asked PhysOrg to disable comment ratings altogether many times. It doesn't work. Perhaps if others would email likewise, they would finally admit it is pointless, without moderators in place, and remove it.

Just ask them to remove the voting troll (which automatically removes the votes, too). That usually happens within a day or two.
Noumenon
1.3 / 5 (26) Jul 10, 2012
I've never witnessed them ever removing a rating troll. If they would ditch the meaningless comment ratings, they would never have to deal with it.
antialias_physorg
not rated yet Jul 10, 2012
I've had a few. A nice mail to the physorg team solved the problem in no time. It's sort of funny to see all that effort they put into tracking down posts and downvoting them go to waste (along with all the trouble for registering a new sockpuppet) with the touch of a button.
Nerdyguy
2.8 / 5 (4) Jul 10, 2012
On a more serrious note:

Anyone else loves the new voting troll accounts? Like at most a few weeks old, with zero comment activity, and allready hundreds of up/down votes? The joy..

Accounts should not be allowed to vote until they (actively) participate, IMO. Else there is too much room for abuse.


You need to keep in mind that accounts are created for a variety of reasons. Many of us have more than one. Some may be used lots, and have lots of corresponding activity, while others may have very little.

However, I'm not sure I really get your point about "abuse". Frankly, who really gives a rat's ass what kind of "votes" you get (or give, for that matter)? It's absolutely meaningless and, IMO, if you're worried about what kind of votes you're getting on an internet site you've got bigger issues. I'd rather see PhysOrg, as I've suggested in the past, eliminate the whole silly, nonsensical thing.
antialias_physorg
5 / 5 (5) Jul 10, 2012
Many of us have more than one.

Sockpuppets are expressly forbidden in the site guidelines - so you'd better delete yours or get banned.

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