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Quantum Teleportation Achieved Over 7km of Cable (sciencealert.com)
An anonymous reader quotes a report from ScienceAlert: Quantum teleportation just moved out of the lab and into the real world, with two independent teams of scientists successfully sending quantum information across several kilometers of optical fiber networks in Calgary, Canada, and Hefei, China. Quantum teleportation relies on a strange phenomenon called quantum entanglement. Basically, quantum entanglement means that two particles are inextricably linked, so that measuring the state of one immediately affects the state of the other, no matter how far apart the two are -- which led Einstein to call entanglement "spooky action at a distance." In the latest experiments, both published in Nature Photonics (here and here), the teams had slightly different set-ups and results. But what they both had in common is the fact that they teleported their information across existing optical fiber networks -- which is important if we ever want to build useable quantum communication systems. To understand the experiments, Anil Ananthaswamy over at New Scientist nicely breaks it down like this: picture three people involved -- Alice, Bob, and Charlie. Alice and Bob want to share cryptographic keys, and to do that, they need Charlie's help. Alice sends a particle to Charlie, while Bob entangles two particles and sends just one of them to Charlie. Charlie then measures the two particles he's received from each of them, so that they can no longer be differentiated -- and that results in the quantum state of Alice's particle being transferred to Bob's entangled particle. So basically, the quantum state of Alice's particle eventually ends up in Bob's particle, via a way station in the form of Charlie. The Canadian experiment followed this same process, and was able to send quantum information over 6.2 km of Calgary's fiber optic network that's not regularly in use.
Someone explained this news to me recently, they said the scientists didn't send ~information~ over quantum entanglement, they sent the data across normal networking means and sent and a key to unlock the data via quantum entanglement. The method used has deep implications for security and encryption methods, but not faster than light data transfer. Just wanted to clear that up.
Quantum teleportation is instantaneous, but first the entangled particles must achieve some distance between them, and this is subject to the usual speed-of-light constraints. In this case the photons achieved that separation over a length of fiber, rather than being sent through free space. Fiber is likely to scale considerably better than line-of-sight transmission.
Entanglement won't survive optical repeaters, so I'm not sure just how well this actually will scale in the real world. Still, 6.2km is a useful distance for some limited applications.
How is the Riemann zeta function like Trump rallies? Both have an endless number of trivial zeros.
That's not quite the trick.
You have a box with black and white balls. You take two, X and Y. You throw X without looking at it to Bob. "Hey Bob what's the color of your ball?", Bob says its black. You open your hand and look at your ball,..... amazingly it's black too. No matter what color Bob says, yours is linked to his color!
The claim: The act of Bob looking at the color *sets* the color of his ball, and because they are linked by a mysterious spooky distance effect, it also sets the color of your ball. The balls normally have no color.
The reality: You take a photograph of the balls. You throw one, Bob looks at his, you look at yours. The photograph is checked to see if it the balls have the same color? Yes? Then you count the experiment. No? Then you discard the experiment as a failed entanglement.
EVERY entanglement experiment includes this filtering stage. Since the information on whether the entanglement was a 'success' or 'not' is sent along another line, it follows that you cannot use this "faster than light" communication until the fixup information arrives via normal communications.
Bob does not know if his ball is a valid entanglement until details of the outcome of the photograph are sent to him.
For the purposes of this experiment, we downplay the photograph, and we never count the photograph as a "detection". When the ball is measure by Bobs eyes, we count that as a detection, when the ball is photographed, we don't count that as a detection until someone looks at the photograph. I kid you not.
It's effectively** equivalent to having two identical letters containing a random message
No. you're describing entanglement.
Teleportation is subtly different.
Teleportation consists of transferring the quantum state of one particle to another particle via the use of entangled particles (and a classical channel)
The beauty of this is that the entangled state can be set up in advance. You then give me a particle that you might or might not know something about its quantum state (but importantly, I do not know what you know about it so cannot measure that quantum state in advance). I can transfer the state of that particle to another particle that Bob has via some entangled particles we exchanged earlier *plus* some standard classical information that goes over classical channels (it's this classical information that limits the teleportation to the speed of light)
The particle that Bob ends up with is in an identical state the the one you gave me (and which I still have).
N.B. This is quantum teleportation, not quantum cloning which is not possible. The act of getting the quantum state to Bob affects my particle in a way that means I cannot also extract any information from it about the original state of your particle.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
You got the first paragraph right. But then got sidetracked by tennis balls.
There are *two* complementary quantum states that you can measure. Measuring one destroys all knowledge of the other.
There is no classical system that behaves like this, therefore any analogy that doesn't invoke some magic artificial property of a classical object won't represent what happens in QM.
In your example you need tennis balls that randomly change colour when you measure their spin and can magically reverse spin when you look what colour they are.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.