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Scientists Teleport Information Between Ions a Meter Apart
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.'"
Are they positive?
Qubit molester insists entanglement was consensual, stay tuned for details at 11.
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.
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My mother always knew what I had done without anyone telling her. Or whatever I was going to do before I took action. I hear other mothers have the same ability. Therefore, all mothers must exist in some state of constant quantum communication with each other.
Every mans' island needs an ocean; choose your ocean carefully.
You mean a qubit molester?
3laws: No freebies, no backsies, GTFO.
Adds a whole new meaning to the term: wireless.
"It's the height of ridiculousness to say for those 9 lines you get hundreds of millions."
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).
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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.
The nice thing about this is, that it is instantly. There is no measurable delay.
So you could theoretically entangle a ton of material with another ton of material, and then send the first ton up to some remote planet. (Which of course would take very long. But you could send it at very high speeds which no human could survive too. For example by using a rocket that uses nuclear explosions as propulsion.)
Say you have defined, that you can use 0.5 kg of material every year for each side, and split the ton in such "blocks". Then you just write the outgoing 0.5 kg block (you collapse the entanglement) over the year, and read the incoming 0.5 kg block at the end of every year. By using a special encoding, you can detect where the data ends, and where the data collapsed trough your measurement. Or you just pipeline the to-be-written data on both sides, and read at the end of every month, week, day, hour, minute, second... whatever is most reasonable. (Making it a buffered transfer of blocks.)
This would give you a thousand years of infinite-speed (depending on your read rate) communication with the bandwidth of 0.5 kg of material per year (~1,37 g per day). (The amount of bits depends on the material.)
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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.)
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).
They know it was entangled because they prepared the state way. For example, if you have a spin zero particle that splits up into two particles, and you measure one as spin up, the other must be necessarily spin down, no matter how far away it is, because of the conservation of angular momentum. Or you can think of a neutral particle splitting into positive and negative ones. So I guess it is ultimately the consequence of some conservation law.
Ok, who voted for the beammeupscotty tag?
I can't think of a worse place to be beamed, than 'up scotty'.
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... :-)
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.
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Bell's theorem (which is a logical argument) and common sense (which we base logical arguments upon) are at odds. So the physicists side with "spooky action at a distance" because it's more phun. They've been taking the "magic" path ever since Einstein and relativity came along and said reality is unintuitive (which it is, but it follows from his assumptions which were based on observation). Witness "dark matter" and "dark energy" and "string theory".
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.
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 experiments testing Bell's hypothesis. The logic is a bit trickier and my simple analogy isn't good enough to explain it, but in actual quantum mechanics if one flip caused the other, then certain experiments could be devised which would have different results than if the two flips are merely 'coincidence'.
This is one of the amazing things about QM. There is actually NO causality anywhere in QM, only a distribution of the probabilities in a particular special type of function space. Causality is an emergent phenomenon which only exists at the 'macroscopic' level. Even then it isn't absolute. I believe it was Stephen Hawking who once quipped that Cthulhu could materialize in the middle of the Pacific Ocean at any moment and no law of physics would be broken.
There are a LOT of other interesting ideas which come out of this, like questions about the meaning of entropy, which leads into questions like the Anthropic Principle.
"Malo periculosam, libertatem quam quietam servitutem." -- Jefferson