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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.
No. This article clearly means we'll be transporting ourselves to Mars before the week is out.
Exactly. We just need to make sure no flies get into the pods before the doors shut.
Given that none of the articles, as far as I saw, said anything about faster than light communication, and one explicitly disavowed the concept, I think you're projecting your own mistaken conceptions here.
And your friend is correct - quantum teleportation has nothing to do with faster than light communication, as you can neither determine to what form the waveform has collapsed, nor whether one side has already collapsed it. It's effectively** equivalent to having two identical letters containing a random message sealed in an envelope, taking them to different locations, and opening them at the same time. Both sides will get the same random message at the same time, but it provides no means for conveying information faster than light. It is however useful for keysharing.
** In the real world, what is written inside the "envelopes" isn't determined until it's actually observed. But it works out to the same net effect.
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
Elon, at least log in if you refuse to take your pills.
We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
Can someone spell this out for us lamens?
How does something teleport across a wire? By that logic, our current communication systems are "teleporting" information.
I thought Quantum Entanglement is instantaneous and void of any connecting wires, which fits my definition of "teleportation" a little better, but I still don't think of it as teleporting.
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.
If that random message is used as the key then it is transporting information since information is simply data that has a meaning or use.
Data that to an observer is 100% random is not "transmitted information" in a physics context. Or in an information theory context either
"You abandoned me! You abandoned my hatred!" "I... I have cuttlefish..."
I think you misunderstand.
The experiments that are discarded are where the two end points don't measure the same quantum variable.
For photons, for example, you can measure whether linear polarization is up-down/left-right or diagonal-left-up diagonal-right-down/diagonal-right-up diagonal-left down.
If both ends measure the up-down/left-right state then one will get up-down, one left-right. If both measure the diagonal polarization then again they will get complementary results. But if one measures up-down and the other measures diagonal then we cannot tell anything useful any more than trying to compare two sweets where one person says what shape it is and the other says what flavour it is so those results get discarded.
There is additional statistical analysis - due to the fact that these experiments are done on single photons and sometimes detectors fire when there is no photon and sometimes they don't fire when there is so we cannot expect 100% correlation - but that's nothing to do with discarding some of the results.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
I always thought that it would be apropros to use Bob, Carol, Ted and Alice as example names for sharing.
Ted and Alice broke up, though he doesn't know it yet.
What a rotten party, have we run out of beer or something?
Not really, but if you want a completely descriptive analogy for quantum entanglement... well, there isn't one.
Alice and Bob have two different ways of measuring particles, and each way can give two different results. They might do a "brightness" measurement (analogy) which returns either black or white. Or they might do a "colour" measurement, which returns either red or blue.
The trick is that, although you might think the results are predetermind, and therefore fixed, they're not. If Alice does a brightness measurement and Bob does a colour measurement, there is now no way for Alice to get a colour measurement that will definitely match Bob's. The information is gone. It might match by chance, but it equally might not.
So Alice and Bob measure at random - sometimes brightness, sometimes colour. Later they compare notes on which tests they made on which photons (they can do this in public), and discard any results where they didn't use the same test. The remaining results are what they use to make up their key - a 0 for black-or-red, a 1 for white-or-blue.
If they do a test encrypt, and find that it doesn't work, that indicates someone else was intercepting their photons and screwing up the entanglement (because that person would have no way of knowing whether to test for brightness or colour).
At least, that's my understanding. I could be wrong, and probably am.
systemd is Roko's Basilisk.
Umm, this is Slashdot!
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There's no need to be a nerd about it.
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.
Particle could be anything, probably sub-atomic to actually work, so it barely matters what atom is actually SENT down the wire. Most likely a photon, though, in these cases though you can do it with electrons and similar.
Information is probably not much per attempt. Maybe as low as a bit each time. But that's enough to form a bitstream. Slow, but a bitstream. That means you can send a conventional PKE key or DH exchange using it because they are small but need to be transmitted securely.
You're measuring a property of the photon. Most likely a particular Bell State (google it) that it falls into.
Measuring that is HARD.
Entangling it is harder.
Measuring the state actually destroys the "connection", as such - like ripping open the envelope means you can't reseal it without someone noticing something has changed.
Thus, you can't measure the state AND then pass it on as the original. Which means you can't interfere with a message without people knowing, and then they throw that message / key away and make a new one.
And quantum teleportation is when something is in an entangled state. You send it anywhere in the universe. You measure it. And THAT MEASUREMENT determines what the particle was all along, everywhere, in all the universe, immediately, without care of the speed of light (Quantum stuff is WEIRD).
Think of it as not "putting a message into a particle" but as "revealing what universe you WERE already in". When you measure, you know EXACTLY what universe you are in NOW, for that time of measuring. But it could be any universe and you could end up measuring all kinds of values. But in YOUR universe, for THAT measurement, your special code is whatever you measured. There's no way to determine that before you measure.
But as soon as you know that, you know what everyone else sent too because of the universe you happen to be in.
It's like being at a murder mystery party and not knowing that the murderer was YOU until the very end. when you measure them all. Even though you've already killed the guy, you didn't know until that point.
Quantum stuff is weird. It's never going to be easy to understand.
Exactly. We just need to make sure no flies get into the pods before the doors shut.
And since we are beaming ourselves over fiber, pray that backhoe fade doesn't hit while transporting....
You're messin' with my Zen Thing, man.....
Oh well. I tried to write a comment with a diagram but hit submit instead of preview :-(
Consider four directions on a plane. x axis (we'll call that |+>), y axis (we'll call that |->) y=-x (we'll call that |0>) and y=x (we'll call that |1>)
Modulo some constant factors, I hope it's obvious that you can build up some of those vectors from others:
|1> = |+> + |->
|-> = |0> + |1>
etc.
These are the directions of a plane polarized photon.
We setup some photons that are polarized in the |1> direction and then pass them through a polarization filter.
If the filter points along the |1> direction then all of them pass. If the filter passes along the |0> direction then none of them pass.
Now we put the filter along the |-> direction. What happens.
|1> = s|+> + s|-> (s is 1/sqrt(2) - which can be deduced from standard trig - the lines must be the same length)
When we measure along the |-> direction the s|-> part will pass the filter but the s|+> part wont.
But an individual photon can't get dimmer therefore it must either pass or not. Half the photons do pass and half don't (and it's random whether any one photon gets through the detector)
The ones that do get through are now in state |-> which is also |0>+|1> (again with factors of sqrt 2)
If we now measure along the |1> direction again we now lose half the photons again (due to that |0> component)
Quantum teleportation involves taking a photon in state a|0> + b|1> (for unknown values of a and b) and taking very careful measurements that don't destroy a and b but instead transfer them to another photon without us actually knowing what they are.
God said, "div D = rho, div B = 0, curl E = -@B/@t, curl H = J + @D/@t," and there was light.
I know there's a black and a white ball in a box. I pick one of them without looking at it and transport it 10km away, then I check what colour it is. Now I also know the colour of the other ball, but is it fair to say that checking the colour "affected" the ball I left in the box over the distance of 10km? Obviously it's absurd. Why would quantum entaglement be any more mysterious than this?
What you describe here it the hidden variable theory, and it has been proven wrong using Bell's theorem.
Quantum entanglement really is mysterious. Mysterious enough to drive Einstein nuts. And while the maths work, there is currently no satisfactory interpretation.
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 Key Distribution: More expensive and less practical that putting the key on a USB stick and driving it to the other end.
I should use this sig to advertise my book ISBN-13 : 978-1501515132.
OK, slight background. Basic applied physics knowledge from 20+ years ago.
How does this qualify as teleportation if you have an optical particle, and a optical transport medium? Isn't this the photon hitting the surface of the fiberoptic transport medium, changing state to an optical waveform, traveling along the transport to the endpoint, exiting and changing state again, and then being detected as a photon?
Also somewhat confusing as photon's have no mass.
If this had been a neutron, or some other actual subatomic particle with mass, then I could certainly conceptualize it as teleportation. Couldn't this simply be the researchers finding a "sweet spot" in "transmission frequency" for said optical fiber to allow transmission nearer theoretical maximum (i.e. the speed of light). Have they tried the same experiment on a different optical fiber from a different vendor and achieved the same results?
SDLeary
My favorite way to explain the difference between something "happening" FTL and useful information not being able to travel FTL is this:
Imagine you've got a powerful laser aimed at a wall a few light-years away. You then sweep the laser beam along the wall's length. The illuminated area changes at several times the speed of light. But this is not information transfer, because each photon travelled a few years in a straigh(ish) line and hit the wall based on the angle of the laser at the time of emission. We "see" a moving spot, but what we're actually seeing is a progression of non-FTL arrivals. The photons carry information, but whatever knowledge is imparted at the point where the wall is illuminated is not transferred to any subsequently illuminated location.
https://app.box.com/WitthoftResume Code: https://github.com/cellocgw
Bell's theorem rules out local hidden variables. There might still be non-local hidden variables, but that's just as weird, if not weirder.
systemd is Roko's Basilisk.
One could easily sweep the spot of a laser across the surface of the moon faster than a light-speed signal would do so.
systemd is Roko's Basilisk.