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Scientists Teleport Information Between Ions a Meter Apart
Posted by
Soulskill
on Fri Jan 23, 2009 08:05 PM
from the perfecting-those-heisenberg-compensators dept.
from the perfecting-those-heisenberg-compensators dept.
erickhill writes with word that scientists from the University of Maryland have successfully transferred information from one charged atom to another without having it cross the intervening space of about one meter. The academic paper is available in the journal Science, though it requires a subscription to see more than the abstract.
Scientists have previously teleported unmolested qubits between photons of light, and between photons and clouds of atoms. But researchers have long sought to teleport qubits between distant atoms. Light's high speed of travel makes photons good transporters of information, but for storing quantum information, atoms are a much better choice because they're easier to hold on to. 'This is a big deal,' comments Myungshik Kim, a quantum physicist at Queen's University Belfast in the United Kingdom. 'To store information as it is in quantum form, you have to have a teleportation scheme available between two stationary qubits. Then you can store them and manipulate them later on.'"
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Scientists "Teleport" Quantum Information One Meter 107 comments
the4thdimension writes "While we may not be beaming up to the Enterprise anytime soon, a team of scientists from the University of Maryland and the University of Michigan have managed to teleport information between two atoms up to a meter apart. Until this point, only very tiny distances were able to be traveled. However, using a complicated system of photons, ions, lasers, and electromagnetics, scientists have managed to 'teleport' information contained on one atom to another atom that is in a separate sealed container. This can lead to a wide range of developments in computing and communications." Update: 01/29 22:29 GMT by T : Sorry, it's a dupe, but today's article in Time is better reading than the abstract anyhow.
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Scientists Teleport Information Between Ions (Score:5, Funny)
Are they positive?
Re: (Score:3, Insightful)
MPF. that's the most entertaining one-liner I've read in days...
Unmolested? (Score:5, Funny)
Qubit molester insists entanglement was consensual, stay tuned for details at 11.
Re:Unmolested? (Score:5, Funny)
In breaking news, the molester has been ordered to both sign and not sign the Atomic Sexual Deviancy Register at the same time.
Parent
Re:Unmolested? (Score:5, Funny)
Parent
Re:Unmolested? (Score:5, Funny)
Parent
Sounds neat, but I'm confused... (Score:5, Interesting)
All sources regarding quantum entanglement/teleportation are quite adamant that you can't use it to actually send information instantaneously. Despite there being "spooky action at a distance", any discernible information had to be transfered when you separated the photons themselves at sub-light speeds. In this case it would be atoms, but I assume it still applies? The article lists applications as super-fast quantum computers (I guess any functional quantum computer could be considered fast at what it does) and quantum encryption (a real application I've heard applied to quantum teleportation, though the encrypted data itself still has to travel at c or less).
So, am I right, and this is basically the same ol' non-instant-communication but still quite cool kinda teleportation, only using atoms instead of photons? I'm just checking.
Re: (Score:2, Interesting)
Re: (Score:3, Funny)
More importantly, does this kind of teleportation make the same cool sound as the teleportation the original "Star Trek"?
Re:Sounds neat, but I'm confused... (Score:5, Insightful)
The way I understand it:
* you generate two entangled quantum things
* you move them apart
* you look at one of them and figure out its state, by that you knock it out of the superposition
* magic happens and the (inverse of that) state is transported to the other thing
* you look at the other thing an confirm that the state is as expected
Since the stuff is in superposition you shouldn't be able to tell its state beforehand, but due to looking at the other thing an teleportation you can. The other thing has the inverse state thing since they must obey conservation of angular momentum (i.e. one spins up, then the other spins down).
Now what I don't get is why this involves any 'teleportation' or quantum weirdness at all. Analog experiment:
* you have two boxes
* you put into one of those boxes a ball at random
* you move them apart
* you look into your box and can now tell if a ball is in the other box or not
* no magic necessary, no teleportation happens, since the state of both boxes is fixed from the start
I don't get why this teleportation thing is anything special, since as far as I understand it, its completly normal and matches exactly what you would expect.
Parent
Good as far as it goes (Score:5, Informative)
Here's an illustration of the non-tranmission of information via entanglement.
Suppose we have a pair of 'magic coins'. Either coin can be flipped and come up either heads or tails, and the other coin will always come up the opposite.
Now, suppose 2 people meet in New York and agree that they will meet again in Oslo if Amy's coin comes up heads and Bill's coin comes up tails, or they will meet in Sidney if Bill's coin comes up heads and Amy's coin comes up tails. Then Amy goes to Peking and flips her coin. It comes up heads, so she meets Bill in Oslo.
The information, which city they will meet in, was AGREED ON BEFORE HAND, it wasn't 'transmitted' by the flip of the coins. The information was in Amy's head when she went to Peking, it traveled by a classical channel governed by relativistic limitations.
This can be seen explicitly if you assume that Amy and Bill DIDN'T agree on which face of the coins meant Oslo or Sidney. In that case when Bill and Amy flip their coins they DO know that their opposite number's coin came up the other way, but neither of them knows which city to go to! In other words, no information was conveyed between them BY the flip of the coins.
Parent
But they DON'T know (Score:3, Informative)
At no point can either Amy or Bill determine whether or not the other coin has been flipped. All they can say for sure is that WHEN IT IS, it will come up a certain way. Maybe it already has been flipped, maybe it hasn't. The only way to find out would be using a classical communications channel.
There is a CORRELATION between the two 'coins' with entanglement, but there is NO causality. Flipping one coin does NOT cause the other one to flip, this has actually been verified by various iterations of experimen
Re:Sounds neat, but I'm confused... (Score:4, Informative)
http://en.wikipedia.org/wiki/Bell's_theorem [wikipedia.org]
Parent
Yeah, Bells's theorem... (Score:4, Interesting)
Back to the topic at hand, no one can explain what is different about a particle whose wave function has "collapsed" and one that hasn't. If you can tell the difference, then you can use entangled pairs to communicate instantly at a distance. One person makes a measurement or not, and the other guy checks for the collapsed-ness of his particle - instant transmission. But since no one knows what the collapse means we just chalk it all up as magic - or unknowable, or parallel universes, etc... By the way, the collapsedness of the particles wave function is therefore a hidden variable that we don't have access to. This proves the existence of hidden variables in contradiction to Bell's theorem, and offers the distinct possibility that the spin is also there all along as a "hidden variable".
I thus predict that an overturn of at least one assumption in Bell's theorem will be one of the biggest headlines in physics some time this century.
Parent
Re: (Score:3, Informative)
Re: (Score:3, Interesting)
Re:Sounds neat, but I'm confused... (Score:4, Informative)
Say particles A and B are entangled, and you are in a position to observe B, but not A. You have no way to know whether A has already been observed, because B will look the same to you either way, unless you already know the state of A.
Parent
Re:Sounds neat, but I'm confused... (Score:5, Informative)
You can't determine if a particle is in a super-position or not, because any measurement of it will instantly collapse the waveform on both particles, and if you collapse yours first you will be unable to receive the information being transmitted by the other. You will need to know that the other entangled particle has already been collapsed, before you read yours, and that information still has to get to you by a conventional method.
Parent
Re: (Score:3, Interesting)
The 2-slit experiment observed quantum super-position, not entanglement. The quantum state was measured when the photons hit the opposite wall, and that measurement only measured the collapsed state, not the super-position. The super-position was only observed in the pattern of interference in the collapsed states.
The super-position being measured was caused by the photon passing through the two-slits, so even if you took an entangled photon, collapsed it's partner, and sent it through the double-slit, it
Mod patent up. (Score:3, Informative)
Yeah. I will try to give a simplified explanation to non-experts (I'm just a curious guy myself):
First you entangle two particles. Then you let one travel somewhere. (If at bumps into another particle on that way, the particle loses the entanglement.)
Now if you "measure" the first particle, the "wavefunction" (the entanglement) of both particles collapses in a specific way.
By measuring that traveled particle, you can get the information on how the other particle got manipulated when it lost the entanglement
Re:Mod patent up. (Score:5, Informative)
Parent
Re:Mod patent up. (Score:4, Informative)
Unfortunately, you can't do either of the things you want to do. Relativity says you can't have synchronized clocks and quantum mechanics doesn't give you any way to know when/if the wave was collapsed.
Parent
Re:Mod patent up. (Score:4, Insightful)
If you check to see if a block you have is collapsed, then suddenly it becomes collapsed, even if it wasn't before. That means you can't tell what it was supposed to look like before.
The other option is to only look at the entangled matter after you are sure it has collapsed, and see how the collapsing happened. However, this is also impossible. The way the qbits collapse is completely random, so you can't get any useful information out of reading them.
The best way to think about it is you have two coins taped to each other head to tail or something.
Then the coins are flipped, and separated without looking at them. Then take these coins to opposite ends of the universe.
Now, as soon as one coin is observed, the value of the other coin is known as well. However, looking at either coin does not help to relay information. The only way to do that would be to know how the coin was going to land before looking at it. Or to be able to somehow observe the coin and know if the other has been observed.
Parent
Re: (Score:2)
I think the way to think of it is this: there's another (or maybe many other) dimensions in the universe that our feeble minds can't perceive. They still exist, though, and things that may appear to be far apart in space (or even time-space) may be r
Re: (Score:2)
IANAPhysicist, but my understanding is that while light speed is still an issue in physical space, the information sharing is truly instantaneous in this sort of quantum entanglement. It's not a short delay as light travels that distance, but instantaneous.
Well the waveform collapse is instantaneous, yes, but as the WP [wikipedia.org] says, you can't actually use it to communicate information from one end to the other.
I really don't understand the physics of why you're not really sharing information when the waveform coll
Re: (Score:3, Informative)
Relativity implies that if information goes from A to B instantaneously for some observers, it also goes from A to B in finite time for some other observers. For all the other observers it goes from A to B in negative finite time, from B to A, in other words. For causality, for A to cause B, then information must always travel from A to B.
Any instantaneous wavefunction collapse cannot transmit information from distant locations, it must create new information for those locations, i.e. a random value.
Re: (Score:2)
I just don't get it.
You "entangle" two atoms creating the qubit. You separate the atoms, then read the qubit?
Isn't the information already present in the entanglement, prior to the separation? Isn't it like spray-painting two objects red, sending them to opposite parts of the world and then proclaiming you've got a way to teleport information across the world, but can only send one message, "red" ?
I'm sure with all the hype I must just misunderstand the whole thing.
Re: (Score:3, Insightful)
Well, I think that's roughly the essence of why you can't send information instantly. All information about the qubits is actually sent with the qubit itself as you separate them to whatever arbitrary distance you're going to do your 'teleportation' trick. It's a little less obvious to me exactly why that is... my understanding is that it's kinda like you have both a black and red marble and you send one around the world, well when one guy checks and sees that his marble is red, the other guy instantly k
Re:Sounds neat, but I'm confused... (Score:5, Informative)
you have both a black and red marble and you send one around the world, well when one guy checks and sees that his marble is red, the other guy instantly knows that his marble is black.
More to the point, the other guy can find out his marble is black, but only if you communicate to him that your marble was red. Thus information was transferred, but you have to communicate by other means to make it meaningful, which defeats the purpose. It's like sending someone an encrypted message over an insecure channel. Great until you realize you now have to send him the key over the same channel. Sure it's encrypted, but the means of making it useful renders it ineffective.
Parent
Re: (Score:3, Funny)
It's like sending someone an encrypted message over an insecure channel. Great until you realize you now have to send him the key over the same channel. Sure it's encrypted, but the means of making it useful renders it ineffective.
Sure you can, you just need to use public key encryption. So I guess you're saying we need public key quantum entanglement?
Just kidding, thanks for the clarification. :)
Re: (Score:3, Interesting)
So I guess you're saying we need public key quantum entanglement?
Wouldn't it be hilarious if that turned out to be the case? If you just knew enough about the other member of your pair, that you could actually transmit information? It would make your comment one hell of a Doug Adams-type footnote.
Re: (Score:3, Funny)
Which goes to prove that teleporting physicists have lost their marbles.
Re:Sounds neat, but I'm confused... (Score:4, Informative)
"teleportation" always seems to lead people to the wrong conclusions. This is about transferring the informational content of a qubit. Which you can't perfectly represent with a classical system. I can see how this as the one commenting physicist claims is a "big deal" when it comes to building quantum computers. But it's not about instantaneous matter transport or superluminal communication.
I'm not sure what the article meant by ultra secure "quantum communication". Quantum teleportation *is* a quantum communication *channel* but it's unclear what kind of security they are talking about. Perhaps "Quantum Encryption" but that's another term that often sends people down the wrong track.
Parent
Re: (Score:3, Insightful)
Although the state of one atom, once measured, will affect the other atom instantaneously, there's no possibility for FTL communication.
The one part of that conclusion I don't get (and I've seen it several times to this point in the thread) is this: Why can't it relay binary information? If I entangle them, separate them, then either DO or DO NOT measure the first, and then measure the second, won't that tell me if the first one was measured or not?
Hmmm thinking on this I have to ask for clarification on t
Re: (Score:3, Informative)
No, it doesn't. View it from the perspective of the two measuring parties. We'll call them Abe and Bob.
Each particle has a 50% chance of being in one of two states, + or -. Entanglement means that if Abe's particle is +, Bob's is -, and vice versa.
Abe measures his particle. Regardless of if his particle is + or -, that doesn't tell him if Bob measured his particle or not. While the values of the measurements are dependent on one another, without information from the other measuring party, the measurer can't
Re: (Score:3, Informative)
Wrong.
The only way to tell if your waveform has collapsed is by measuring it. And measuring it collapses it.
Thus *every* time you check to see if yours has been collapsed, it will always show as collapsed.
Go look at yourself in a mirror.
Now close your eyes.
Now, you cannot tell when your reflection has opened its eyes, unless you open yours, and if you open yours, the reflection will have its eyes open.
Same with the waveforms. No matter what, if you look, it'll be collapsed, and you can't tell if it was coll
Re:Sounds neat, but I'm confused... (Score:5, Informative)
Sure, I'll try: A quantum 'entangled' state means that two systems are in an 'undefined' state in the quantum sense, that are interdependent.
When one is measured, the other one will _instantanously_ adopt whatever state is 'required' to complement the other one. So one 'knows' instantly what the other is doing, so to speak. Which means a sort of information has been transferred at FTL speed.
The reason why this can't actually be used for communication is twofold: One is exactly as you said: Because you can't know which state you'll measure, you can't transfer information through that alone. The second reason is that, an entanglement between two systems occurs only if there's an (unmeasured) interaction between them.
That means you either separate the two systems from each other (as in the classic example of entangled photons moving apart), or as in this case, by letting them interact with photons - that travel at light speed. Either way though, light speed is the best you can do.
Parent
Re: (Score:3, Interesting)
Hmm.
Is there any way this could be used, not for sending FTL messages, but exchanging a cipher? You said you can't know which state you'll measure, but if you can measure some as-yet-unknown random state at one end and measure the corresponding state at the other end, then you should be able to use this random pattern of bits to encode a message, which would then be transferred through traditional (light speed or slower) means. The message could be intercepted in transmission, but the cipher couldn't be.
Re:Sounds neat, but parent needs a MOD UP (Score:5, Informative)
Is there any way to know that measurement has taken place at the other end and your local qubit has collapsed?
Crash course in quantum mechanics, perhaps this explains it: a binary quantum mechanical system is in a linear superposition of states A and B. That is, it is either 100% A, or 100% B, or anything in between; for example 70% A and 30% B.
Now if you measure, you would only get "pure" results, i.e. purely A or purely B. If the system was pure (i.e. 100% B) before the measurement, you get what it was. If the system was mixed (say, 70-30), and you had the chance to measure the system more than once, then you get A in 70% of the cases, or B in 30%. For example: make 1000 copies of the system, and measure each of them. Roughly 700 (give/take a few) would be A, roughly 300 would be B.
The biggest problem is that you don't have 1000 exact copies -- unlike with classical information, basic QM forbids cloning of a system. So you basically have one shot, and if you happen to measure B, you'll never know whether it was because of a 100% pure B state, or simply because you "got lucky".
I mean, I know the answer is you can't communicate instantly, I'm just figuring out why (mostly to help explain to people with roughly my same layman's understanding of physics why instant communication is impossible).
While the "quantum information" is being transfered instantaneously, the problem is that the quantum state is not transfered 1:1 onto the target. It is ... "twisted". Imagine that like x*A+y*B (-> teleport ->) y*A+x*B. Now you know that the numbers x and y mean the same in both systems -- you just don't know exactly how they would be twisted after the teleportation. There are 4 possibilities how they can be twisted, and all 4 are equally probable, there's nothing you can do to favor the one over the other.
However, after the teleportation, the guy at the source can tell how they have been twisted (because the teleportation act itself is a measurement, which's result tells him exactly what happened), but the guy at the target does not.
So at first, even if the guy at the target knows that the atom has been "teleported", he stil doesn't know which one of the 4 twisted flavors of the original atom he got. If he just takes a "wild guess" and tries to measure, he'll get a statistical result which reveals absolutely no information about the actual coefficients.
The target-guy needs the source-guy to tell him which of the 4 twists occured, or in short: needs an information transfer in order to be able to "untwist" his atom and have an exact copy.
Again, the important part is that if the target-guy does not "untwist" his atom, but instead decides to go away and measure it anyway, he'll have an overall chance of 50-50 (regardless of the original x and y) to measure either A or B, so there's no information whatsoever that he could gain, not even from repeating the experiment.
It's the "twist" that makes the twist with teleportation... :-)
Parent
Re:Sounds neat, but I'm confused... (Score:5, Funny)
Analogy:
I have two basket balls, one has a cat inside - I don't know which one.
I send one basket ball to you.
I open my basket ball (observation).
I find it empty so I can deduce the cat is in yours (no information is transfered to you).
I cannot tell if you have opened yours and observed the cat as dead or alive.
You open yours and find a dead cat (observation).
Information is transfered in the normal manner when you call me up and ask why I sent you a dead cat in a basketball.
Parent
Re: (Score:3, Informative)
I have two basket balls, one has a cat inside - I don't know which one.
The heavier one. Duh. :-)
How fast is it really? (Score:2)
TFA (The Science News article) states 'instantly' and I can't actually read the academic paper (bugmenot doesn't seem to have a working login) but does anyone who's more familiar with this area know whether or not it's actually limited to the speed of light, or if we're actually seeing something that's capable of moving faster.
The article makes it sound as though it's instantaneous, but has this actually been measured to show that it's instantaneous or is the relatively short distance at which the "teleport
Re: (Score:3, Informative)
Any use of the word "instantly" is, quite simply, hype. It's instantaneous like an "instant message" is instantaneous. Not that this isn't a cool discovery; it is. But it's not teleportation and it's not instant communication.
No, "spooky action at a distance" is indeed instantaneous. It's a quantum phenomena - it's not based on the information being transmitted (which would indeed be limited to the speed of light).
Re: (Score:3, Informative)
You most certainly can measure the propagation time of light over distances of one meter. It takes on the order of 10^-8 seconds for light to travel 1 m, and we have time measurement devices better than ns. (Actually, using clever techniques, you can do way better than meters.)
A question that maybe someone might answer... (Score:2)
From the article they are saying that the entanglement has occurred, etc.... they also say that they know the entanglement occurs 1/100M times or so.
My question... If observation destroys the situation they describe, how to they know the entanglement happened at all?
Anyone know?
Bah! (Score:5, Funny)
A New Form of Wireless (Score:3)
Damn... (Score:4, Funny)
Ok, who voted for the beammeupscotty tag?
I can't think of a worse place to be beamed, than 'up scotty'.
Re:A quantum physicist? (Score:5, Funny)
You mean a qubit molester?
Parent
Re: (Score:3, Insightful)
The teleportation is instantaneous. (A philosophy-inclined physicist might object to you applying the label "instantaneous", since it implies a signal is propagating instantaneously -- but there's no signal at all.) However, the teleportation cannot be used for communication without information transfer -- which means the communication is bound by the speed you can transfer that information (which is lightspeed).