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Comment by ricardobeat | Hacker News Reader

But quantum teleporting does require a link between the two points. From the Wikipedia article:

    The prerequisites for quantum teleportation are a qubit
    that is to be teleported, a conventional communication
    channel capable of transmitting two classical bits (...)

There is no teleporting in the classical meaning of the word, just communication between two locations to make a remote qubit match the (unknown) state of the local one. That state is 'teleported'.

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There is no teleporting in the classical meaning of the word

So isn't it dishonest to call it teleportation? Even if all the scientists working in this area are calling it that?

No? How on earth is it dishonest to use the technical term for the thing? It doesn't seem any more dishonest than calling the constituent parts of matter "atoms" even though they can actually be split.

The discovery that atoms are not atomic (could be split) came after the term was coined.

On the other hand, in this case, a bunch of people decided to call something "teleportation" when it isn't teleportation.

AFAIK, it is teleportation -- something is going from one place to another without having to move through the space between them -- but it just isn't what you think of when you think of "teleportation".

If it is moving from A to B via some physical continuous medium, then it is not teleporting.

(Note: my full qualifications are an on-going Coursera course on quantum computing that covers quantum teleportation lightly. FWIW, I recommend the course.)

In vague terms, the process of quantum teleportation is the following:

* You have a qubit that you want to transmit to a friend and that you don't know anything about.

* create an entangled pair of qubits (such as photons) and separate them. Keep one yourself and give another to your friend.

* Now you have two qubits; one entangled with your friends and one that you want to transmit.

* Send your two bits through a quantum circuit (the main part being a 'controlled NOT gate').

* Your bit is now entangled with the bit that is entangled with your friends bit.

* Measure each of your bits, hence 'collapsing' them. Each measurement gives you a classical bit.

* Transmit your two classical bits to your friend over any classical connection.

* Your friend then performs an operation on his or her qubit depending on what you send him or her.

* Your friend's qubit is now in the state that your original qubit was in. Your original qubit is now in a different state.

Call it teleporation if you want; it's not that unlike some sci-fi teleportation constructs of 'beaming' things places.

Why bother with this?

* It lets you send qubits to distant places that you have only classical channels to (and previously close enough contact share two entangled qubits).

* It allows more error-resistant computations: if your qubit is difficult to construct and you wish to perform a difficult operation on it, you can actually have your friend perform the difficult operation on his or her bit - prior to teleportation - and, if it succeeds, you can then proceed with the teleportation. If it doesn't succeed, your friend may try again on another entangled qubit without messing up your difficult-to-prepare qubit. After a success and teleportation, you get the same result (up to a commutator which is usually relatively small and risk-free) as performing the difficult operation on the difficult-to-prepare qubit, but with less risk of messing it up.

Thanks, this is a pretty helpful summary.

Can you clairify the second reasons to "bother" with it? I mean, if it's difficult for me to perform the operation, it's presumably equally difficult for my "friend" to do it (and subsequently "teleport" the result to me), so why not just do it myself?

Perhaps, you are working on an important experiment with your qubit. However, you realize that that you need an expensive piece of lab equipment to follow through.

However, you remember that your "friend" has this equipment at his/her lab. You also happen to share an entangled qubit with your friend. And you know that you can call your friend on the phone.

Rather than mail the qubit to your friend's lab which could be in a very remote location, you use quantum teleportation to send its state.

This way your friend receives your qubit without the qubit having traveled through physical space.

What silverdrake said, but also it's a matter of error-tolerance. If we want to do a difficult two-step computation and know when each sub-step succeeds or fails, than:

1) Perform the first step on a qubit (repeat if failed)

2) Your friend performs the second step on their qubit (repeat if failed, but no need to repeat (1))

3) Teleport your qubit to your friend

4) Your friend performs a simply operation on their qubit

After this, the state of your friend's qubit is now the result of applying both operations. But each sub-step can be redone without affecting the result of the other, so mistakes are easier to correct. So in this case, "your friend" might refer to yourself - the important part isn't teleporting the qubit somewhere elses, it's that the computation is less error-prone.

In addition to the transportation benefit, it can be used for computation. The example given in the Coursera course was to suppose that we have a qubit (quantum bit) Y on which we wish to perform some unreliable computation. If it fails, then Y's state is lost. Further suppose that Y is costly (e.g. time consuming) to re-create.

Instead, we can create a pair of entangled qubits (which is easy to do - just a single quantum gate), as one would when teleporting a qubit. We then apply the computation to one of these qubits, and try again with a new pair of qubits if it fails.

Once we have successfully applied the computation, we can teleport our "expensive" qubit Y using this entangled pair. The result is that we now have Y with the computation applied, but there is no risk of losing Y's state.

The details are rather more tricky (only certain computations can be used, some require a correction after teleportation etc.), but this basis can (and has) be built on to develop, for example, fault tolerant quantum computing.

After this process is completed, can the entangled qubit pair be reused to transfer more information or is this a one off? That is, do you have to repeat the "give another to your friend" part in order to transmit more information?

This method requires the initial entangled qubits to be in a "Bell State" (equal superposition of both in 0 and both in 1). After teleportation, its no longer in that state. So it's not reusable by this method, but maybe by another that I don't know about (though I doubt it).

It may be that the information encoded in the spin of a photon or something has jumped non-continuously. But most people think of "teleportation" as transferring matter.

Here is what I take to be an acceptable definition of teleporatation, which comes from Wikipedia:

Teleportation is the transfer of matter from one point to another without traversing the physical space between them

So under this definition, would you agree that quantum teleportation is not "regular" teleportation, since although information is traversing space without moving "through" it, matter is not?

I'm not really arguing semantics anymore, I'm just unclear whether the latter part of that question ("since...") is factually true, since I don't understand quantum stuff.

I think term teleportation is still valid because they can entangle and teleport any kind of particles. Photons are merely used because of their convenience.

You can entagled protons, electorns. Hell, I think they managed to demonstrate entanglement on a larger scale.

It seems to me like no particles are being teleported, becuse no matter is being moved. It's just information (i.e, the state of a particle) that is being duplicated in the same kind of particle on the other end.

I guess the realization that energy/information and matter is the same thing came after the term teleportation was coined also?

Because the technical term is misleading and inaccurate.

If scientists started calling walking "human teleportation" tomorrow, they'd be wrong in that too. The term "teleportation" had a very well-established meaning before they appropriated it.

Scientists can make mistakes, labeling this process "teleportation" was one of those mistakes.

If it was a mistake, it wasn't dishonest. If it was dishonest, they were intentionally trying to deceive people.

Some of the claims people are making about the purported security advantages of quantum crypto are borderline dishonest, IMHO.

Are you referring to the potential weaknesses just discovered recently?

No, not specifically.

Uh huh.

  Scientist: "As you can see here, we've demonstrated quantum teleportation across an unprecedented--"
  Journalist: "Teleportation?! Like in Star Trek?"
  Scientist: "Uh, no. *Quantum* teleportation is a different--"
  Journalist: "So you didn't send anybody through a wormhole or anything?"
  Scientist: "No. What we've demonstrated is the ability to--"
  Journalist: "It just seems like a bit of a mistake to call it 'teleportation'."
  Scientist: "Yes, I can see that now."

As always, there's an xkcd for that: http://xkcd.com/465/

What do you imagine they thought teleportation meant when they appropriated it?

Do you also get upset when biologists talk about "cloning" because they don't mean duplicating an adult like in the movies?

No, because the differentia of the definition of cloning does not reference maturity (age).

So Wikipedia states the following:

"Quantum teleportation is unrelated to the common term teleportation – it does not transport the system itself, and does not concern rearranging particles to copy the form of an object."

So, in a nutshell, scientists aren't always incredibly creative when conducting nomenclature. Although some people do find subatomic particles quite strange.

Not in any sense is it dishonest to call it quantum teleportation, since the quantum state is precisely (and only) what is subject to the phenomenon. What is dishonest is the claim that F-T-L communication is possible.

The quantum state does not undergo travel during the transmission of the classical signal. The only thing that travels is the classical signal, which is needed to tell you how to read the message (and generally preserve causality in the universe.) The quantum state is teleported as though you had two objects with the selfsame quantum state. Poking one pokes the other.

Teleportation is teleportation of matter. So AFAIK you can't call it quantum teleportation, for the same reason you can't call travelling along the road "road flying," i.e., flying is travelling above the ground, not on it.

The human ability to generalize concepts is amazing, watch—I'll swap out your of matter for of quantum information and suddenly you're up to speed on subject of discourse: "The teleportation of quantum information." Magic!

Your language gives you away, you've already done this process in reverse to make your case, so I know you have the power to understand this concept.

So we can use any word to mean anything?

This kind of abuse of language has serious consequences in the long run. The language of modern physics is already way too muddled.

I don't understand what you're trying to say in the last sentence. But it seems like you're being derisive, which is utterly inappropriate.

You know, in a lot of sci-fis its not implied that teleportation is faster-than-light. Quantum teleportation does meet what does seem to be universal about "teleportation" though, which is that the "original" is necessarily destroyed. That is, it takes a thing, and moves it to another location, rather than copying it.

As far as I can tell, it just replicates the state of a particle in a remote location, using another particle of the same kind. So state is being transfered (i.e., information), but not matter, and nothing is being destroyed. I might be wrong about this, but that's what someone who explained it on hn said.

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