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Quantum Teleportation Sends Information 143 Kilometers
SchrodingerZ writes "Scientists from around the world have collaborated to achieve quantum teleportation over 143 kilometers in free space. Quantum information was sent between the Canary Islands of La Palma and Tenerife. Quantum teleportation is not how it is made out in Star Trek, though. Instead of sending an object (in this case a photon) from one location to another; the information of its quantum state is sent, making a photon on the other end look identical to the original. 'Teleportation across 143 kilometres is a crucial milestone in this research, since that is roughly the minimum distance between the ground and orbiting satellites.' It is the hope of the research team that this experiment will lead to commercial use of quantum teleportation to interact with satellites and ground stations. This will increase the efficiency of satellite communication and help with the expansion of quantum internet usage. The full paper on the experiment can be found [note: abstract only, full article paywalled] in the journal Nature."
Seems like a strange place to do quantum research.
No. No it wouldn't. Quantum entanglement does not allow for faster than light communication. Common myth.
-- MyLongNickName
But it has been mathematically proven that quantum teleportation does not allow faster than light communication. So unless you are not willing to believe mathematical proof, you should believe the previous poster's comment
It's not quite as simple as teleportation, it's just given that name:
https://en.wikipedia.org/wiki/Quantum_teleportation
Most specifically:
"Suppose Alice has a qubit in some arbitrary quantum state
The components of a maximally entangled two-qubit state are distributed to Alice and Bob.
In the end, the qubit in Bob's possession will be in the desired state."
So what Alice is doing is actually modifying the REMOTE qubits to be identical to the LOCAL qubits AFTER the initial information exchange has occurred. You're now literally turning someone's remote blank paper into a copy of the document you have yourself by using a little set of numbers that you determined between yourself last week.
I've been watching this NOVA series on quantum mechanics - it's been an excellent primer on this stuff for me. It's hosted by Brian Greene, a prof at Columbia who wrote a book about it for a lay audience. I think it would be very approachable for anybody with an interest in science, but without a scientific background.
I was the AC who posted the first reply. Please read here for more info on why quantum entanglement does not imply FTL communication. http://curious.astro.cornell.edu/question.php?number=612
See my journal for slashdot ID's by year. Mine created in 2005. http://slashdot.org/journal/289875/slashdot-ids-by-year
One more thing (dammit Slashdot! Let me edit my damned posts already!!!) --
They just did a new series (the one I linked to above is a little dated - almost 10 years old at this point). You can see that one here. It covers cosmology as well as a bit of quantum mechanics. Still very approachable.
Essentially, the "sender" does not get to choose the message. The sender "observes" the state of a particle with a previously undetermined state. Upon observing the particle, the "sender" causes the particle to have a determined state but does not get to determine what state that paticle is in. The "receivers" particle then has the same state as the "sender's" particle.
So the "sender" doesn't get to choose what message he sends. He simply discovers (bad term, but trying to keep it simple) the state of the particle which becomes the same as what the "receiver" gets. This would not be useful for sending any type of communication.
See my journal for slashdot ID's by year. Mine created in 2005. http://slashdot.org/journal/289875/slashdot-ids-by-year
The Higgs was not a common myth. It was entirely expected to be there. That's a reason they spent a bazillion dollars on the Large Hadron Collider, because they expected it to be there. Yes, it was possible it wasn't there, but it fit the standard model and so it was like saying, the world could always end tomorrow, but there's no convincing reason to believe it won't be there when the sun comes up.
Quantum teleportation does not transmit information faster than light and it is not expected to. If there was a mechanism that could do that, it would probably get its own article... and a Nobel Prize for whoever figured it out.
You can't "send states" either. You measure on your own photon (or electron, or whatever) and if you find a value. The other guy measure his own photon (or whatever) and find a value. The two values, once you communicate with each other (slower than light) will always match (be the same, or be opposite, depending of the way you entangled them). But you don't send the value of your measurement, and you don't even send the fact you did a measurement.
It has uses, for example in cryptography. Or if you want to run a solar system wide lottery and have the people on Mars and Earth follow, exactly at the same time (warning: that's layman speach, it doesn't have any real meaning in GR), the outcome of the lottery, and no one having the result before the other. But not for communication.
Yes and no.
Probability is very important, but it is not the measurement, or at least not the initial measurements, which are the issue.
The measurements on the particles will actually be the spookily transmitted values that you would expect. If person A observes his particle and locks in a state, the particle of person B will instantly take on the mirror or opposite of what person A has measured. Until entanglement is broken, particle B will remain in that state for person B to discover almost at their leisure. So, you *can* measure two particles and get the same/mirror answer... but only once per particle.
Or in other words, if Person A observes a living Schrodinger's Cat in his box, Person B will get a dead one in his entangled box instantly, which will be there for him to see when he opens the box. It will not go back to being uncertain until the box is opened and then closed again. Person B does get the opportunity to see the state of his particle as changed by entanglement.
So what is the problem? Sounds like this is faster than light. And it is. However, Relativity does not state that nothing can happen faster than light, only that *information* cannot be transmitted faster than light. The problem is entanglement does not actually create a channel for passing information by itself.
For information to be passed one side must use a channel to send a message to the other. With entanglement you will have "sent" a state, but the other side has no way of knowing you actually sent a message, which in turn means that information is not passed.
Remember, collapsing the probabilities and killing/not killing a cat can be done by *either side*. That means that if you open your box and find a living cat, it could mean that your partner earlier opened his box and found his cat was dead (and is attempting to send you a message). Alternately, it might mean he hadn't gotten around to opening his box yet and you opened first, making you are responsible for killing his cat which he may soon discover (you monster).
This is *not* insurmountable normally. If you could, say, ensure that you always kill the cat in your box when you are sending a message, then I could use frequency analysis or some other algorithm on all of my living cat results because I know that only living cats can be message data. There would still be a ratio of noise to the signal due to the ever present possibility that I am killing his cat on the other side by looking before he does, but you should be able to wring data out of it. You would, of course, need multiple entangled boxes for this, but other than representing mass cat murder, this is not a major problem.
Unfortunately, this is where the Uncertainty Principle checkmates us. When you open a box, it is always completely random what you get. You can't force a result or know ahead of time what you will send, so pre-arranging to only accept one result is pointless. Even the smallest attempt to alter the box before opening it in a manner that would make the result even slightly more predictable counts as a measurement and trips the entanglement effect. Then when you go to look in the box afterward, you are simply looking at particle that is no longer entangled. In effect, altering the box in any useful way is the same thing as opening it.
So, to actually send a decipherable message, you need a classical, slower than light channel to decipher every bit of information you send via entangled particles. While it is technically true that your actual bits arrived faster than light, the information is 100% indecipherable until you get the decoder for each bit at light speed, and so there is no way to disseminate actual information faster than light in this way.