Creating Quantum Entanglement

derubergeek writes "APS has a summary of a paper being published in the Dec. 30th Physics Review Letters on the possiblity of creating quantum entanglement of particles traveling at speeds less than the speed of light. They believe there may be practical applications in satellite synchronization, for example."

Gerard Milburn

[QuantumG]

is known around campus as the prof who traps ions in the basement of the physics building. Always funny to see someone from your own university quoted as an authority.

Re:Gerard Milburn

[jxliv7]

.
what i don't understand is that matter has three states -- like water has a solid, liquid, and gaseous state.

why isn't it possible that these 'particles' in tune with each other have 3 states as well -- like synched, synched opposite, and not synched...?

my guess is that when we finally discover the real synching going on, we'll see that it is independent of the speed of light (aren't they particles in themselves...?)

oh, well, such is the core of a good science fiction story... the kind that usually become science fact later on.

Re:Gerard Milburn

[dabacon]

Gerard Milburn is known around campus as the prof who traps ions in the basement of the physics building.

Funny, that, considering he is a theorist ;)

dabacon

from the article

[sydlexic]

A strong gravitational field can actually create entangled particles; those that break free of the field are called Hawking radiation. "It would be very nice if this could be turned around and Hawking radiation derived as a consequence of quantum information in curved spacetime,"

I say, that would be nice, indeed!

Abstract

[Henry V .009]

ABSTRACT:

We study the properties of quantum entanglement in moving frames, and show that, because spin and momentum become mixed when viewed by a moving observer, the entanglement between the spins of a pair of particles is not invariant. We give an example of a pair, fully spin entangled in the rest frame, which has its spin entanglement reduced in all other frames. Similarly, we show that there are pairs whose spin entanglement increases from zero to maximal entanglement when boosted. While spin and momentum entanglement separately are not Lorentz invariant, the joint entanglement of the wave function is. ©2002 The American Physical Society

What this is saying--I'm guessing--is that an entangled spin state for two particles wouldn't look as entangled anymore for a moving observer (relativity). A classical (relatively--ha ha, double pun) analogy would be how electric fields look like magnetic fields to moving observers.

The interesting thing is this "boosting". They're saying, I guess, that there are refrence frames from which particles look far more entangled than the rest frame.

I'd like to close this post by pointing out how highly unethical it would be for some slashdot poster with an account for Physical Review to post the full text of the article as an AC. It would be entirely wrong to think of that as "liberating" some piece of research funded by U.S. taxpayer dollars. Furthermore, those of us interested in the article but lacking accounts or easy access to a college library to read it would not be at all grateful.

Re:Abstract

[derubergeek]

I'd like to close this post by pointing out how highly unethical it would be for some slashdot poster with an account for Physical Review to post the full text of the article as an AC. It would be entirely wrong to think of that as "liberating" some piece of research funded by U.S. taxpayer dollars. Furthermore, those of us interested in the article but lacking accounts or easy access to a college library to read it would not be at all grateful.

Fine. Here's a link [lanl.gov] you ungrateful bastard.

Fast internet?

[SHEENmaster]

In 1997, Nicholas Gisin and colleagues at the University of Geneva used entangled photons to enable simple - but instantaneous - communication over a distance of seven miles.

Could this be used for extending the internet to other planets? When we do eventually colonize mars, some reliable and two-way form of communication will be needed. Could this be the basis for it?

I seem to remember reading (in "The Golden Compass" trilogy?) of a creature that played a violin bow over a rock causing an entangled rock to play the same tune reporting to his commander. I didn't realize at the time that it had a basis in real (if mostly theoretical) physics.

Re:Fast internet?

[Henry V .009]

I doubt that there is any way to use these measurements to transmit information. For all the 'instantaneous communications' stuff in the media over these sort of experiments, no one has been able to show mathematically how that would work--much less practically. The wave collapse is instantaneous, but all that means is that you can pool information later and violate Bell's Inequality with it.

But we might get bigger and better EPR experiments from this!

Re:Fast internet?

[hprotagonist0]

According to current theory, no information can be reliably transmitted faster than light. IIRC (and that's a big if), here's the argument: supposed you've got two quantum particles with entangled spin. You can then separate them, say, by sending one of them to Mars with the manned mission. The thing is, you can't actually transmit any information over these particles, because you can't find out what the spin of one is without observing it, and that ruins the entanglement.
I know that argument isn't really complete, and I know that the full thing is explained in the April 2000 issue of Scientific American, but I don't have the magazine handy and sciam.com won't let you view articles that far back without paying. I'm sure if you're curious, though, you could find it in the library.

"find it in the library"!?

[SHEENmaster]

You obviously haven't been to a Tennessean public library. We're lucky to have the latest harry potter; the chances of us having a subscription to a magazine are slim-none.

That's why I started my collection of electronics magazines including the "cold fusion in your home" issue of Radio Electronics. Funny how no one got that to work....

Re:Fast internet?

[Alsee]

Could this be used for extending the internet to other planets?

No.

Using entanglement two people can "aquire" identical information instantaneously no matter what the distance. The problem is that the information they both get is completely random. You can't "send" any sort of message. You can only both recieve identical random data. That makes it useless for communication but perfect for cryptography. You take the random data and use it to encrypt a message and send the encrypted message through normal channels.

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there's no such thing as "completely random"

[SHEENmaster]

That argument is used erroniously against crypto but the basis of it, that every effect has a cause, remains.

Do we all agree that there is a cause? Do we have any clue as to what that cause is?

Re:there's no such thing as "completely random"

[Alsee]

Do we all agree that there is a cause?

The current best understanding of quantum mechanics is that not only does god play dice with the universe, sometimes he rolls them where they can't be seen.

So for all intents and purposes quantum mechanics produces completely random results. You flip a quantum coin and you get a pure random head or tail with no cause for the difference.

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Re:Hmmm...

[shrikel]

Exactly. Tachyons, for example, are therefore out of the scope of this paper.

What it means

[Alsee]

The equations in the paper were totally over my head, but I know enough physics to "get" what it means.

There's one point in the article that is missleading, both the slashdot title and the ASP article. This does not CREATE entanglement. It changes the nature of the entanglement. They can take particles with a completely useless kind of entanglement and by looking at it in a different way see perfect entanglement of a usefull kind.

This might be very important because it is tricky to entangle things, and the methods of creating different kinds of entanglement are completely different. In some cases you might need one kind of entanglement, but you can only manage to create a different kind. This lets you take that "wrong kind" and convert it into what you DO need.

This cound be critical for figuring out a way to really build quantum computers.

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