Talk:Quantum teleportation/Archive 1

Problems with Protocol Description

I'd like to raise the following issues with the protocol description, particularly with the numbered list of protocol steps. Step 1 is clear. Step 2 has multiple problems. First, a punctuation error: "... of the EPR pair qubit ..." should be "... of the EPR-pair qubit ..." becaue "EPR pair" is being used as a quantitative adjective and quantitative adjectives must be hyphenated. Second, Step 2 says "At location A, A Bell measurement of the EPR pair qubit and the qubit to be teleported..." Ok, where did this "qubit to be teleported" come from? Is it the one that was sent to location B in step 1? Well, then it's no longer at location A, or is it still there? Is it a "copy" of the one sent to location B? Is it some other qubit? This ambiguity makes the rest of the protocol incomprehensible. Once it's resolved, I'll go on to my other issues with the protocol section.

References removed

On 20:08, 16 Jun 2004, the following user : 130.39.223.46, removed the references from this article. Does anyone have a clue why he did this ? I am a new user, so there might be a rule that I am not aware of. Maybe it was because the references had no direct connection with the content of the article ?

Also, now that teleportation has been demonstrated with atoms, maybe we should remove " It is not clear if such a procedure can be scaled up to larger systems"

user michaelmestre

it would seem this was Subhash Kak (see my comment on his Talk page; he had his own reference removed (for unnamed reasons) on 18 Mar 2004, (equally anonymously, by 218.22.21.27). We may be witnessing some sort of auctorial rivalry here ;)

Dbachmann 17:48, 28 Jul 2004 (UTC)

Rewrote and added details

I just went to a quantum computation seminar, and part of it was on teleportation. Rewrote part of the article and added more technical detail. I don't really know how to do LaTeX formatting though, so if someone can please help clean up the equations to make them look nicer, it would be appreciated.

Pkeck - teleporting someone's brain will involve getting information about both the electronic quantum states and the position / momentum quantum states of all the particles. Right now quantum teleportation only transfers electronic quantum states.

24.17.245.100 09:47, 20 May 2006 (UTC)

Is this true?

Is this part of the Star Trek beaming section true?

- So, we cannot move matter from one place to another with quantum teleportation. Biological functions, especially the thoughts in the brain (the mind), depend not only on the right positioning of the atoms but also on their correct internal quantum state. These, we cannot copy, due to the no-cloning theorem. But, we can teleport them from the original onto the replica, and afterwards, the replica would live and think, and the original would maybe "crumble to dust." So, we did not replicate the human being, but teleported it. -

As far as I know, the quantum state of particles in tissues has no known impact on thoughts or other biological functions, or at least not to the extent that they affect consciousness or anything like that. (Of course, I'm overlooking simple things like the ionic state/electron configuration of atoms so that they can bond correctly with other atoms, but I don't think this is what the passage is saying.)

Where/when has somebody teleported the contents of one persons brain onto another? I'm going to delete this section, and if someone can provide a more clear explanation of this subject along with some reputable references, maybe it can be added back in.Pkeck 16:59, 1 Apr 2005 (UTC)

I am a layman

Lets dumb this piece down a bit, I am a layman and I have only an average knowledge of mathematics (no more than community college level). I think this article is trying to say that we can transfer the state of one piece of matter to another over a distance by manipulating one of the entagled entities quantum state. I am probably wrong ,so if someone could dumb this down or provide a paragraph that gives us an anology to something more tangible I would appreciate it.--Mikeroodeus 17:16, 23 Jun 2004 (UTC)

Re : I am a layman

Sorry if I offend you, but you are not an idiot ; in fact, quantum teleportation has philosophical implications hardly understood by anyone. I doubt there is a good analogy for it. The summary, (without going into considerations of it being believable or not, or real or not), is that the state is indeed transferred from one particle to the other, over an arbitrary distance, at a speed limited by the speed of light (because of the mandatory presence of a classical communication channel). Entanglement is just the algebraic formalisation of the constatation that the event "measurement of a physical quantity in one element of the entangled pair" has, very often (and more often that what could be conceivable by just pure luck), a consequence on the event "measurement of a physical quantity in the other element of the entangled pair". Sorry, it is very hard to explain things simply when you (that is, the person who explains) don't understand them fully ! Hope this helps. michaelmestre 11:10, 24 Jun 2004 (UTC)

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On 2 Sep 2004, I have replaced the whole article by a complete rewrite. Here is the old text: Simon A. 08:12, 2 Sep 2004 (UTC)

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Quantum teleportation is a quantum information processing operation which can be summarized as follows:

Suppose Alice and Bob (arbitrarily named protagonists) are spatially separated. They have at their disposition a classical information channel and share a perfectly entangled bipartite quantum state. Alice has a quantum system in a particular quantum state which she wishes to transfer to Bob. She does not know what the state is. Because measurements disturb quantum information, she cannot just measure her state and send the result to Bob over the channel. She could simply send him the system, but this involves the use of a quantum information channel which she may not have.

However, there is a method which allows her to transfer the state over to Bob by performing a manipulation involving her quantum system and her part of the shared entangled state, then sending 2 classical bits over the classical channel. Once Bob has received the information, he knows how to manipulate his part of the shared state in order to recover the unknown state at his location.

Alice's manipulation destroys her copy of the unknown state (if it did not, it would violate the no-cloning theorem). Note that despite appearances, this scheme could not be used for superluminal communication, because a classical information transfer is an integral part of the procedure.

The first experimental verification of the teleportation of the polarization state of a photon was reported in 1997. It is not clear if such a procedure can be scaled up to larger systems.

As quantum teleportation of the quantum state of a qubit was expected to be a key element in quantum computing, it might be significant that BARETT et al. report (Nature 429, 737 - 739 (17 June 2004)) "unconditional teleportation of massive particle qubits using atomic (9Be+) ions confined in a segmented ion trap, which aids individual qubit addressing. We achieve an average fidelity of 78 per cent, ...).

Teleporting an atom

The following text has been removed from the article:

The New York Times June 17, 2004 p.A21, reports that two teams, one from NIST, Boulder, Colorado, another from University of Innsbruck, Austria, have teleported atoms of beryllium and calcium, respectively, as published in Nature, June 17, 2004. The setup involves triplets of charged atoms (A, B, C) which are trapped in magnetic fields.

1. B and C are entangled.
2. C is moved away.
3. B and A are entangled.
4. The state of A and B are read, which affected C at a distance.
5. When a pulse of laser light was aimed at C, then C was turned into an A (but which destroyed the A,B state, by the no-cloning theorem)

Here's the links, to newspaper: [1], to abstracts: [2] [3]. I think this should be included in the article, which does not say a word about existing implementations. Conscious 07:20, 27 June 2007 (UTC)

New teleportation experiments are conducted on a regular basis. So far none have made it into the article. On the process you outlined: A and B are destroyed as soon as they are read. Contrary to what your link #1 seems to be suggesting no atoms are teleported, only quantum information that happens to be encoded in the atoms is teleported. Skippydo 15:02, 27 June 2007 (UTC)

I'm only arguing for the inclusion of information about existing experiments in the article. It's not me who wrote the passage above, but the links I have found may be helpful. If there are any newer (and more successful) implementations of quantum teleportation, they should be mentioned in the article. Conscious 20:16, 27 June 2007 (UTC)

It's a good idea. But there have been many steps along the way. There would be a lot of information to collect. I come across a few every month. Skippydo 11:56, 28 June 2007 (UTC)

External links

• Information on Quantum teleportation including a link to an electronic version of the article
• Quantum teleportation DMOZ category
• Quantum teleportation team at Innsbruck, Austria
• Deterministic quantum teleportation of atomic qubits, Nature 429
• Teleportation goes long distance

Yet Another Question from a Layperson

A question for those more knowledgeable than me: why must a classical information channel - i.e. something at the speed of light - be involved in quantum teleportation? I understand that this is because information cannot be transmitted faster than the speed of light; what I don't understand is *why*. Thank you very much for your time. - Brasswatchman August 20, 2005. 12:55 PM EST.

Hah! I've been working in this field for quite a while, and I can tell you we'd all like to know *why*. Dave Kielpinski 07:06, 15 December 2005 (UTC)

Quantum channels can not transport information in the classical sense. They just designate the transformation process of the quantum information. If you ever need to transport that information elsewhere, you must use classical means of transportation, whose speed is limited by speed of light according to the special relativity. So, you have two measured bits in your hand in place A, and you need to send them to place B somehow. The speed of that kind of transportation of information is always limited by the speed of light. There are no other alternatives. SYS64738 23:33, 1 February 2006 (UTC)

Cleanup Tone

There has to be a formal discussion of the topic before we get into Alice and Bob. Superm401 | Talk 09:28, 13 November 2005 (UTC)

As it stands now Alice and Bob have no introduction at all - 128.243.220.42 removed the intro which discusses indistinguishability, saying it had nothing to do with teleportation. As I understand it, indistinguishability is in fact intimately related to the idea, because it sets up the problem of how we tell one thing from another, which is related to how we can tell something has "moved". At any rate, I don't think Alice and Bob are necessary for a clear and relatively accurate description of the concept. Pjrich 04:49, 1 March 2006 (UTC)

Why is this non-formal?

May i suggest this thing be taken off the non-formal list? As far as I can see, it is fairly formally written.

Nazgjunk||(talk) 20:56, 18 November 2005 (UTC)

I don't agree. I write and review academic papers and this text is very informal according to those standards. The text is filled with subjective adjectives and adverbs, and the manner of explanation is very informal. SYS64738 23:44, 1 February 2006 (UTC)

Replicators

I was wondering: Would it be fair to say that Replicators would use a system much like this? Let's say I wanted a cup of coffee and I went over to the replicator and told it I wanted a cup of coffee, inside the replicators database is a large file on pre-programmed foods (or other objects) that the replicator has examined and stored. The Replicator has an ability to recycle as well, by "dis-assembling" un-needed objects such as garden rocks or dirt, then converting that energy into raw energy which would be used to assemble/produce your coffee (or whatever object). If this were possible, wouldn't it be basically the end of currency? If one could simply replicate their produce or product by using recycled energy what need would there be to go to the store? Davethewave 13:33, 15 February 2006 (UTC)

Landroo 08:19, 9 June 2006 (UTC) I think this type of "teleportation" needs to be reassigned to a science fiction discussion article. Quantum teleportation and Star Trek teleportation really don't belong in the same article.

Amen to that. If you just want a cup of coffee, it doesn't matter if it's in the same quantum state as some other cup of coffee used to be. —Keenan Pepper 14:43, 9 June 2006 (UTC)

No-communication vs. no-broadcast

This article mentions both a no-communication theorem and a no-broadcast theorem. I don't know enough about quantum teleportation to decide, but it sounds like these might be the same theorems. Are they? --Manscher 07:55, 9 August 2006 (UTC)

no, not quite the same. no-communication says communication can not be achieved via shared entanglement alone. on the other hand, no-broadcasting is a corollary of the no-cloning theorem, (quantum states can not be copied in general, therefore can not be broadcasted). Mct mht 08:12, 9 August 2006 (UTC)

I started no-broadcast theorem based on your answer. Feel free to expand it :-) --Manscher 07:27, 11 August 2006 (UTC)

Writing 3 particle state with new basis?

Could someone give a few lines of derivation of how this is done, or give a link to explain how this transformation is done? Thanks

try substituting according to the identities provided and check that the claim is true. it's straightforward. in linear algebra terms, this is a change of basis unitary transformation. Mct mht 06:24, 5 October 2006 (UTC)

Danes

http://www.sciam.com/article.cfm?chanID=sa003&articleID=000E9691-0261-1524-826183414B7F0000

vague statement

the following statement was recently added to article:

"teleportation...will allow quantum computing to be more secure and also function more quickly."

could the precise justifications for this claim to given (be it theoretical or experimenal)? Mct mht 01:39, 21 January 2007 (UTC)

Partial measurement

The idea of partial measurement needs to be explained more. It took me a while to understand that partial measurement is actually a technical term, and I had to look up elsewhere what it really meant. I feel that I am not qualified to explain it though. Could someone who is give it a shot?

130.126.39.182 04:53, 24 April 2007 (UTC)

i assume by "partial measurement" you mean that the measurement apparatus only interacts with part of the system. in the formalism, it means only certain factors in the tensor product are involved. it's stated in the article, including the section on general teleportation schemes (see the statements on the tensor factors). feel free to make the language more explicit. Mct mht 05:42, 24 April 2007 (UTC)

Undefined term

The term "Bell basis" is essential to the understanding of the article, yet defined nowhere. How have people who have gotten their understanding of teleportation from this article gotten past that hurdle? Has anyone actually tried to follow the article's math? --Vaughan Pratt 05:07, 1 August 2007 (UTC)

hello, Prof. Pratt. "Bell basis" refers to the four Bell states. they span $C^{2}\otimes C^{2}=C^{4}$; you get them by basically shuffling around +/- 1's and 0's between the four components in the obvious way. the article should probably point this out more explicitly. Mct mht 05:23, 1 August 2007 (UTC)

I've listed the four bell states. Thanks for the advice! Skippydo 05:40, 1 August 2007 (UTC)

Copying the four Bell states over from the Bell state article helps a little, but still leaves the term "Bell basis" itself undefined in both articles which was the main problem. Also the reader who actually tries verifying the identities for the rewrite of Alice's two qubits will come up with equations that seem to equate Alice's two qubits with the two qubits shared between Alice and Bob. Following "thus becomes", Bell states subscripted by A make their first appearance, without definition. In general there's a lot of moving around of subscripts that is neither adequately explained nor formally derivable from the present formulas---a lot of creativity is being asked of the reader. --Vaughan Pratt 06:42, 1 August 2007 (UTC)

In general, I think the article is a little 'too much' like a formal derivation, while it shouldn't be. This is an encyclopedia, not a quantum information manual. Maybe we should rewrite this article to include less formal equations and more wishy-washy hand-waving kind of explanations. Also, there should be more emphasis on the history of the discovery and what is does/might mean to science in general. UnHoly 07:03, 1 August 2007 (UTC)

As a metacomment, it's really too bad the quantum computing crowd has stuck with a notation better suited to analogue experiments than the digital world of qubits. The explanation would be so much easier to read if the Bell states were written ab + a'b' where a denotes ${\frac {1}{\sqrt[{4}]{2}}}(|1\rangle )_{A}$ and a' denotes ${\frac {1}{\sqrt[{4}]{2}}}(|0\rangle )_{A}$. Having distinct variables for distinct qubits and treating them like literals in propositional calculus allows you to use ordinary high school algebra instead of having to invent a whole new set of rules for sound manipulation of subscripts. The need for Greek variables goes away if we use t and r for transmit and receive instead a and b for Alice and Bob (imagine what you'd think if a handbook of digital electronics named all its ports after people as a pedagogical technique to get people to think of ports as people sending and receiving bits). The data qubit to be teleported becomes d. Rather than primes for the negative literals I'll follow the convention De Morgan used in his 1858 paper introducing relation algebra of upper and lower case for positive and negative literals (but by all means use whatever you prefer for literals). The account would then read as follows.

The qubit to be teleported is in the superposition aD + bd while the teleportation channel is in the superposition TR + tr. The collective superposition is then (aD + bd)(TR + tr) = aDTR + aDtr + bdTR + bdtr. Teleportation is accomplished by rotating a measurement apparatus suitably in the four-dimensional space corresponding to qubits t and r, measuring the two qubits at that angle to produce two (classical) bits, transmitting the bits to the receiver, and using them to choose one of four unitary transformations chosen to transform the receive qubit to the superposition aR + br, the definition of teleportation of aD + bd.

Writing w, x, y, z for the coordinates of the frame of the apparatus, the appropriate orientation for the apparatus is 2w = DT + dt, 2x = DT - dt, 2y = Dt + dT, 2z = Dt - dT, the so-called Bell states. Expressed in this new framework our old framework had axes DT = w + x, dt = w - x, Dt = y + z, and dT = y - z. Our system state in apparatus coordinates then becomes w(aR + br) + x(aR - br) + y(ar + bR) + z(ar - bR). Measurement of the data and transmit qubits nondeterministically projects the whole three-qubit state onto one of these four axes, leaving the component of the axes associated with r unchanged. This puts the three entangled qubits in one of the states w(aR + br), x(aR - br), y(ar + bR), or z(ar - bR), up to a constant factor. The knowledge of which state the system collapses to permits the appropriate unitary transformation to be applied to the receive qubit to put it in the superposition aR + br.

Classically speaking, a and b (more precisely, a/b) express infinitely many bits, all but two of which were transmitted instantaneously at the moment of measurement. Thus already the receiver possesses most of the state of the teleported data long before the last two bits arrive (delayed by the speed of light) to complete the process. In the process the two qubits at the transmitter end have been put in a Bell state, thereby overwriting the original data and the transmit qubit with the two ends of a reusable but zero-length teleportation channel. Teleportation of a stream of qubits can be accomplished by keeping all four of the data, transmit, receive, and classical streams synchronized, bearing in mind that the transmit and receive streams must be prepared, and the receive stream physically transported, on an earlier schedule than the data and classical streams. --Vaughan Pratt 18:30, 1 August 2007 (UTC)

The types in the above should be declared as scalar for a and b, C² for D, d, T, t, R, and r, C²ⁿ for terms of degree n (e.g. C⁴ for TR, aDT, w, etc. and C⁸ for DTR, wR, bdtr etc.), and (for completeness) Boolean for the two classical bits. Also it might be worth mentioning that since rotation of a rigid body has only three degrees of freedom (pitch, roll, yaw), any physical measuring apparatus needs to be articulated in order to have the requisite four degrees of freedom (the meaning of rotation in four dimensions). --Vaughan Pratt 20:26, 1 August 2007 (UTC)

You are confusing physical rotation and qubit rotation on the Bloch sphere. The Bloch sphere is an abstract space. Operations on qubits act like rotations, but they are not actual rotations. For example, if you use polarized photons as qubits, "rotations" are performed using fixed half-wave-plates and quarter-wave-plates. UnHoly 06:00, 2 August 2007 (UTC)

(Sorry for the delayed response, I was away for a while.) Oops, you're right, I screwed up badly on that detail. Hopefully the rest was ok? --Vaughan Pratt 00:17, 21 September 2007 (UTC)

You make some good points. I just looked at the bell state article for the first time and it could use some cleanup. It should be pointed out, at the very least, that the bell states form a basis. But about the subscripts, perhaps they should be removed? Skippydo 01:07, 2 August 2007 (UTC)

obscure entry

This article is obscure. I came here to ascertain something tangible. It does not do this. as per wikipedia objective, it is contextually unfulfilled. Wikipedia articles should deal with real facts. The article tells the reader what quantum teleportation does not do or what it might be useful to do. This is not an encyclopaedic submission. Tell the reader what it does do. Who wrote this stuff ? Why would anybody 'suppose Alice' did anything? Supposition is not stated. Start again and keep it real please or I propose {afd}. Discuss. PalX 00:29, 19 August 2007 (UTC)

Quantum Mechanics is obscure and untangible. We state what teleportation is not because there are a lot of misconceptions which are propagated by most mainstream news articles. Using the word suppose is typical in mathematics. Skippydo 08:02, 19 August 2007 (UTC)

Thank you for the reply. I'm sure you mean intangible and your point on suppose is fair. In so far as the subject matter is obscure then this ought to be stated.PalX 20:59, 19 August 2007 (UTC)

More mechanics, less mathematics

The page is a bit of a nightmare to those who aren't mathematically inclined. A simple look at some of the comments here tells me the article needs cleanup, possibly the mathematics reduced or moved into another section so it isn't as entangled (no pun intended) with the layman's information. Because of this I've added the "{{cleanup-jargon}}" tag to the page.
Also, the article currently says almost nothing about the mechanics of how it can be done. I seemed to recall that in one experiment they used fiber optic cable to transmit the entangled state, and I wanted to check that here, but there was no information about the mechanics of how it could be done. Some information on this part of the topic would be appreciated. -- HiEv 17:48, 2 December 2007 (UTC)

The page is a nightmare for those who aren't mathematically inclined because it is meaningless to those who aren't. At the very least we need to assume the reader knows something about quantum information and quantum computation. How it can be done is a topic for quantum communication, not for this article. I suggest we remove the jargon tag. Skippydo 02:05, 3 December 2007 (UTC)

There is absolutely no reason why the article must be laden with mathematics or can't be meaningful to those who aren't mathematically inclined. Compare these other articles on quantum teleportation: [4] [5] [6] [7]. None of them rely on mathematics and they explain the subject to the layperson, which is just what this article should do. If you want to keep the mathematics, that's fine, but you should allow people to get a good basic understanding of the subject without forcing them to read around mathematical notations (which is what I meant by "jargon.") Please, don't forget the Wikipedia:Explain jargon guideline, especially the mathematics section. -- HiEv 03:10, 3 December 2007 (UTC)

All of these articles suggest that some physical object is being teleported. Quantum teleportation is the transfer of quantum information from one location to another. It is more like the teleportation of these binary bits I'm typing now than than it is teleportation as seen on star trek. To speak of quantum teleportation on any relevant level one must describe what a quantum state is. To describe quantum states one must describe the Hilbert space otherwise we end up with silly statements such as binary bits can store 0 or 1 but quantum bits can store both!, further propagating the disinformation surrounding quantum computation/information.

Quantum mechanics cannot be made meaningful to those not mathematically inclined because those who are don't claim to understand it. We simply verify the mathematics, briefly ponder the philosophical implications and get on with our lives. Skippydo (talk) 04:24, 5 February 2008 (UTC)

i don't see excessive jargon either, but adding some details from the experimentalist's perspective wouldn't hurt. Mct mht 02:17, 3 December 2007 (UTC)

Yes, it's communication, not teleportation.Turtleguy1134 (talk) 21:05, 21 August 2012 (UTC)

Perhaps this article could be amended and added to the Simplified English Wikipedia? Rebelyell2006 (talk) 04:37, 2 February 2008 (UTC)

Who the hell is this article written for? Is it just supposed to serve as some sort of monument to scientific knowledge in this area? This is supposed to be an encyclopedia. I don't think that anybody that understands all of these equations and such would be going to wikipedia for this sort of information. Is some physics professor somewhere going to say "hey, I think I wanna get into this whole quantum teleportation business. I think I'll go see how it's done on wikipedia." —Preceding unsigned comment added by 74.167.239.139 (talk) 05:30, 18 May 2009 (UTC)

Some examples

I'll chime on the jargon issue and say that this article is definitely too gear-headed. IMHO Wikipedia should set as a goal that for most articles (if not all) the majority of the article should be understandable by an average educated person with little or no prior knowledge of the subject without having to follow the links. Certainly it is reasonable that there may be sections of the article that have technical details only a person more versed in the fundamentals would understand but this should not be the majority of the article.

The following are a few sample links that illustrate how the concepts can be presented in a way that is accessible to the layman.

• What is Teleportation?
• IBM: Quantum Teleportation

The arguments that science cannot be made accessible to non-mathematicians or non-scientists is arrogant and untrue. Certainly Einstein and Hawking would disagree with this as they specifically made efforts to share their understanding of science with the general public through their writings. Obviously there are details that cannot be explained but the general principles and practical applications can be.

--Mcorazao (talk) 18:34, 13 February 2008 (UTC)

Both of those articles are completely irrelevant to the actual topic of quantum teleportation. Quantum teleportion is about the transference of data using qubits via entanglement, and does not relate to the actual transportation of matter via "teleporting". And sorry, not meaning to be/seem arrogant, but certain topics are quite hard to simplify to point of allowing the average educated individual to understand the topic, without simplifying to the point of misrepresenting the actual idea. Sure it could be simplified to not include mathematics, but it would be meaningless. One cannot discuss a topic inherently derived from mathematics without mathematics. The math really isn't even that complex, an undergrad Electrical Engineer should have enough mathematics background to understand it. 24.33.135.250 (talk) 23:50, 4 April 2012 (UTC)

Another request to reduce jargon

I concur with the 'jargon' tag and sentiment of the other 'lay people' who like myself cannot derive any value from this article due to its technical nature.

To give relative comparison, through Wikipedia I have gained a firm high level understanding of quantum mechanics and am able to articulate the Copenhagen and other interepretations through Bell's inequalities to the variations on the double slit experiments such as the delayed choice quantum eraser. I am now able to debate the mind boggling philisophical implications of quantum mechanics around the nature of reality, space/time, and causality. I have accomplished this understanding without being able to understand a single equation.

However, I have drawn a complete blank with this article, apart from the vague concept that quantum communication is constrained by the use of classical physics. I would very much appreciate if this article could be re-written to enable lay people to gain the same level of understanding that I have achieved with every other quantum mechanics related article on Wikipedia 82.44.221.140 (talk) 19:52, 3 April 2008 (UTC)

Has the new section I added improved your understanding? Your insight is much appreciated. Skippydo (talk) 02:05, 5 April 2008 (UTC)

That's great - got it! Your application of pure logic makes this summary easier to understand. The key is the (classical) transmission of the information from Alice's measurement that will enable Bob to replicate the 'spin' (or specific state) of his 'c' cubit. Of course a nice diagram would be fantastic, but I won't push my luck :-) 82.44.221.140 (talk) 20:22, 5 April 2008 (UTC)

New intro

Skippydo, I guess I'd like an explanation of why you deleted the bulk of my rewritten introduction. I think there are a lot of important points about quantum teleportation which ought to be made in the article and currently aren't.

1. It might be useful but it's never necessary. A lot of people seem to have the idea that without quantum teleportation it's impossible to get a quantum state from point A to point B. It needs to be made clear that you don't need quantum teleportation for this, you just need a coaxfiber-optic cable. The Motivation section also feeds this misconception when it says that "Alice seems to face an impossible problem"; this needs to be rewritten or deleted.
2. It doesn't avoid the need for a quantum channel, since you still need one to transport the Bell pairs. All that it does is shift the economics around—e.g. it lets you move the quantum channel earlier in time, or make it slower, or make it unidirectional, all of which might be beneficial in some cases.
3. It's not teleportation. A lot of journalists have reported on quantum teleportation experiments as though they represent a step toward Star Trek transporters. None of the engineering difficulties of building a Star Trek transporter are solved by quantum teleportation, and the article needs to say so; otherwise people will (like the reporters) jump to the wrong conclusion based on the name.
4. The fact that the transmitted bits are uncorrelated with the teleported state is not mere trivia, it's the essence of the thing: that's why you can measure them without destroying the state. The analogy to the classical one-time pad is very close, and I think it ought to be played up in the article because it gives real insight into why quantum teleportation works, something which I think is currently lacking in the forest of state vectors.

On the other hand I don't think I should have written that quantum teleportation isn't very useful in practice, since I don't know that that's true. It was a guess based on the economics of generating Bell pairs, sending them over a quantum channel, storing them, and then using them for teleportation versus just sending the qubits of interest over the same channel. I thought that the latter would always be cheaper where it's possible, but I just noticed that Nielsen and Chuang mention that a teleportation-based protocol might be the cheapest way of sending qubits over a noisy channel, so I guess I was wrong about that. -- BenRG (talk) 14:15, 26 April 2008 (UTC)

i'd second skippydo's removal. teleportation should be viewed in the context where a quantum channel is not feasible. this is alluded to in the article. as G. Brassard told it once, one could assume alice and bob are physically close at one point but is now not. the point of the protocol is that entanglement allows one to bypass no-go theorems, in this case no-teleportation and no-broadcast theorems. i'd buy the one-time pad analogy with the shared Bell state, although it would be misleading to read too much into it. pt #4 above is just wrong. Mct mht (talk) 19:20, 26 April 2008 (UTC)

Thank you for your comments. I appreciate your commitment to improvement through discussion, it's really the best way.

1) As the article states on the matter of transmitting information: She can attempt to physically transport the qubit to Bob. Perhaps this should be stressed that by physically move, we mean that that the photon may travel through, for instance, a fiber-optic cable. To believe, as suggested in the article, that a Bell pair can be shared but a qubit cannot be physically moved, is dubious (as you alluded to in point 2). This should be changed, as I believe you are suggesting. It may be that one may transmit part of a bell pair with less degradation than an arbitrary qubit through a noisy channel. I don't know enough about implementations to comment. This may be what the Nielsen and Chuang text has stated. I don't have my copy on hand.

2) I have thought of presenting teleportation as trading the use of a quantum channel now (in either direction) for the transmission of quantum information later without the use of a quantum channel. Perhaps this view would illustrate the relevant nuances. Let me know if I have presented my idea clearly, and if you agree.

3) One of my main reasons for desiring a small concise introduction is to make it clear that this is not science fiction teleportation. It needs to be made painfully clear that this has nothing to do with matter and everything to do with information.

4) Transmission of a quantum state is the topic of this article. Secure transmission, is a different issue all together. I don't know if it's discussed in any literature. Certainly, if an attacker intercepts the bell pair and the classical bits, the scheme is broken. I don't believe that it's remarkable that the classical transmitted bits are chosen uniformly at random. I don't see any connection with the one-time pad. Skippydo (talk) 19:51, 26 April 2008 (UTC)

confusing

this article is confusing if you don't know anything about quantum physics and the like. —Preceding unsigned comment added by 86.166.49.0 (talk) 15:08, 30 May 2008 (UTC)

________________ dear ones.) i'm neither a mathematician nor physician. i understood almost nothing. the vague idea about quantum physics and related issues doesn't help a lot.

therefore, i repeat the question - who is the target group for the article - professionals who do not need wiki for reference or research in the field of concern? or ppl like me who want to understand - but lack the necessary math basis.

so, yes - i agree that such articles should be arranged and separated into several levels of proficiency (?), when the first would be for profanes like me. without formulae. - in the first paragraph. 132.69.228.204 (talk) 18:10, 17 March 2010 (UTC)

too much maths and ego

wikipedia is not a scientific journal. All these equations are pointless. Anyone who is actually going to use them would not be going to wikipedia for the source. I studied maths and physics at varsity, but can't grasp very much from this article. Just a bunch of equations. I'd like to see an example, the implications etc. —Preceding unsigned comment added by 41.241.58.245 (talk) 00:36, 2 June 2008 (UTC)

Discussion of experiments

I think that there should be some mention in this article of the past and current experiments into quantum teleportation. Whilst I don't want to dumb down the science or maths, I think that we can appease both the physicists and the laypeople. By adding an Experimentation section and Practical Application section we can explain some of the basics and direct the laypeople to other articles that may be more relevant. For example I searched this article looking for a reference to the experiment done in Australia in 2002 that (as I understood it) teleported light from one end of the lab to the other. However I couldn't find a reference and did some of my own searching on google and discovered that they only transferred the quantum state of a series of photons to another set of photons. It's not that hard to understand, so I'm going to add this sort of info to the article. Master z0b (talk) 23:58, 9 July 2008 (UTC)

Actually I also think the intro sentence needs to be addressed, I don't see why we can't have a single sentence at the beginning of the article that states what Quantum Teleportation is without referring to q-bits or other technical jargon. I understand what it's saying but I can also understand why people find it confusing.Master z0b (talk) 00:14, 10 July 2008 (UTC)

Possible problem with the example given

There's an example where Alice wants to send Bob a qubit. It goes on to give three options, dismissing one because transferring the qubit is really hard because it's fragile. It then goes on to say that Bob and Alice can use an entangled qubit to transmit the information. But for Bob and Alice to posses entangled qubits, qubits must be physically transported, which is the very reason solution 1 was not acceptable, no? —Preceding unsigned comment added by 74.202.89.125 (talk) 17:59, 27 January 2009 (UTC)

No energy transported

The article mentions that there is no transfer of energy. From the description of teleportation, I can't see this part to be obvious. Can some one please add the appropriate reference or show mathematically that no energy has bee teleported?

61.95.189.147 (talk) 08:51, 30 June 2009 (UTC)sid

Energy is transferred. Energy and information are the same thing. So if information is transferred (as it must) then so too is energy. In the transfer of what would have been, say a "yellow photon", at A, to where it is subsequently observered (at B) the energy of the yellow light is no different from what it would have been, had it been observed at A. Indeed it can't be observed at A, or B, if it has no energy. A subtle point is perhaps the fact that the photon is not fully observed at A. However the byproduct of entanglement at A, is information, and that is transmitted between A and B. And that information has at least half the energy of the final result. The other half is entangled between A and B, and is not transmitted per se, but is certainly manifested at B - converted into an observation. —Preceding unsigned comment added by 210.84.46.224 (talk) 01:36, 31 October 2009 (UTC)

Removed reference

I removed this reference, added by User:Yoonho72:

• • Y.-H. Kim, S.P. Kulik, and Y. Shih, Quantum teleportation of a polarization state with a complete bell state measurement, Phys. Rev. Lett. 86, 1370 (2001).

The user has made only 1 edit, and only to this article. Moreover, the first name of the first author is indeed Yoonho, thus it might be self-promotion. I don't know how notable this reference is, thus I've removed it. If the other editors feel this reference is notable enough to be put back in, feel free to put it back. --Robin (talk) 12:41, 19 August 2009 (UTC)

The paper looks okay. I don't know how important it is, but I'm inclined to give it the benefit of the doubt since it's in PRL. I added it back in, but anyone who disagrees is welcome to remove it again... -- BenRG (talk) 22:05, 19 August 2009 (UTC)

True, but PRL+PRA have 250+ papers on quantum teleportation. Not all of them are notable enough to be included. PRL alone has 29 papers with the words "quantum" and "teleportation" in the title. --Robin (talk) 22:38, 19 August 2009 (UTC)

Quantum Teleportation is a trick. Real teleportation is impossible (ie. magic)

The word "teleportation" existed a long time before quantum teleportation appropriated the word. There are major differences between teleportation as depicted in works of fiction and quantum "teleportation". For one thing, fictional teleportation is typically about impossible scenarios (magic).

Quantum teleportation, at least, is not impossible.

But it is a trick, although a clever one. It exploits a feature of particles that, prior to observation, a particle can not be defined in terms of where it is. If I told you that in one hand I have a coin, and in the other I don't, but then produced a coin from the hand that wasn't supposed to have a coin - is that teleportation? No. It's a trick. The coin was never in the first hand in the first place.

In quantum teleportation the trick is slightly complicated by the fact that the coin is not in the second hand either.

An act of observation (opening the hand) brings the coin into existence (or less metaphorically: converts it into an observation).

So what is transferred, from one hand to the other? It is effectively an observation. Or at least half of one. In the metaphorical version it is the story being told (that the coin is one hand). The other half is provided by the observer who completes the act - observing the coin in the other hand.

Now quantum teleportaion is a little more complicated than the above suggests but it's still a trick. It is a trick because it is playing with expectations and vague assunptions about how the world works in order to create the impression that something magical has transpired. --210.84.46.224 (talk) 02:05, 31 October 2009 (UTC)

This misuse of the term "teleportation" probably originated as the gimmic of a journalist of publicist wanting to boost ratings. This may have begun with the BBC announcement from Australia in 2002. EDIT: 22:00, 11 September 2010 (UTC)Okay; I see that the term is used at least as early as 1993. Can anyone trace it earlier?

Sensationalism is the journalists' steroid; if the competition is on steroids, everyone else must do the same to survive. I think Wikipedia should rise about all that. This article should be renamed, eliminating the word "teleportation". Under the present title, teleportation should be in quotes, with only be a brief statement redirecting the user to the corrected title.--Onerock (talk) 21:41, 11 September 2010 (UTC)

Bullshit. Real teleportation is possible. That's what this is all about. Up till now, we've only ever suceeded in teleporting a few electrons, that's all; not even an entire atom, much less a molecule, a bacterium, or a grain of dust. But, given what we now know, real teleportation is possible, in principle. User:Linas (talk) 17:10, 20 November 2013 (UTC)

Introduction is incorrect

"Quantum teleportation, or entanglement-assisted teleportation, is a technique used to transfer information on a quantum level, usually from one particle (or series of particles) to another particle (or series of particles) in another location via quantum entanglement. It does not transport energy or matter, nor does it allow communication of information at superluminal (faster than light) speed. Neither does it concern rearranging the particles of a macroscopic object to copy the form of another object. Its distinguishing feature is that it can transmit the information present in a quantum superposition, useful for quantum communication and computation."

First of all, the information transferred is not done at a "quantum level". You can transfer the information by any menas you like, eg. writing numbers down on a peice of paper, and walking over to the destination device.

Secondly, the particle(s) involved in QT are entangled so they do not possess a definite location.

Entanglement means that at the same time, particle A is at location X (A@X) AND particle B is at location Y (B@Y), OR just as likely, particle B is at location X (B@X) AND particle A is at location Y A@Y). Both these possibilitys (A@X,B@Y) and (B@X,A@Y) have equal probability and neither can be said to be definitely the case, until AFTER the teleportation experiment is completed (and even then there is some question as to whether it ever is universally one and not the other). In the theoretical domain it always resolves to A | B. For example: (A & (!B)) | (B & (!A)) equals A | B

During "teleportation" the information being transferred from X to Y, is simply a representation of the entanglement: (A@X | B@X). The representation of this entanglement (eg. a note on paper) is transferred to location Y, so the information, by virtue of the transport becomes (A@Y | B@Y). Depending on what is then observered at Y (eg. A@Y) means that what was "observed" at X must have been B.

Thirdly, energy IS transported insofar as information == energy. So if information is transported (as it is) then energy is transported. The ammount of energy transported is, at minimum, exactly half the energy of the completed observation.

--210.84.46.224 (talk) 22:49, 31 October 2009 (UTC)

On your second point I think you're confusing the Bell state used in quantum teleportation with particle indistinguishability. For quantum teleportation it doesn't matter whether the systems are bosons or fermions. They needn't even be the same—you can teleport an electron spin state to a photon spin state, for example.

Yes, my second point is a little confusing. Only particles (ie. plural) are said to be "entangled". Whereas the lack of definition (regarding location) is applicable to any particle, ie. even those not entangled. If we limit location to X and Y, then a single particle can be said to be at X | Y (where the pipe operator means exclusive OR). But this is not, of course, entanglement. It is only when we introduce a second particle (or more), that we can speak of entanglement (if we arrange for such of course). Entanglement is not possible without the former - so it "means" the former by implication. But, of course, the former doesn't need entanglement to be the case.

I agree with that, but I still don't understand what you meant in your original post. "[T]he particle(s) involved in QT are entangled so they do not possess a definite location" is a non sequitur.

Yes, I see what you mean. I should have written: "The particles involved are quantum mechanical particles ..."

Two particles can be entangled but have definite locations (such as an electron here and a proton there with entangled spins).

Well yes, 'definite' with respect to each other. They will have, for example, opposite spin. But at which location is the spin left?

In quantum teleportation, Bob's qubit is definitely at Bob's location, not Alice's.

Yes by definition that is so. Likewise my cat is, by definition, my cat, irregardless of whether she is found to be male or female.

If Alice's and Bob's qubits are physically identical bosons/fermions then technically you should symmetrize/antisymmetrize the state, but it's not necessary because indistinguishability is only physically relevant when particles might occupy the same state, and that's impossible here (they're always spatially separated by assumption).

Fair enough.

-- BenRG (talk) 16:54, 8 November 2009 (UTC)

The paragraph now says "quantum information" in place of "information on a quantum level", which I think is an improvement. I suppose that energy is transferred in quantum teleportation—the energy in the classical signal, for starters—but I don't think that's related to the point that the paragraph is attempting to make. I removed the reference to energy, but I think the paragraph still needs work. -- BenRG (talk) 21:18, 2 November 2009 (UTC)

I'd agree that "quantum information" is probably the best choice of words. It's not ideal but I haven't come across any better alternative (when speaking in an introductory paragraph).

--Klaussfreire (talk) 23:19, 28 May 2010 (UTC)

The paragraph, related to a later paragraph, seems to contradict the very same cited article (the no communication theorem), which clearly says:

Of course Zeilinger and Dopfer's experiment does not prove superluminal communication, but neither does the no-communication prohibit all forms of communication. If superluminal communication is prohibited, it is not because of the no-communication theorem. Thus, the question of superluminal communication remains open.

...which also makes sense. The no-communication theorem (let me say, though, I'm no expert in quantum-mechanics) says simply that, under some circumstances, instantaneous communication is impossible. But superluminal isn't necessarily instantaneous, and the theorem doesn't even apply under relativistic conditions (whatever that means, it seems to be a big if), so the conclusion drawn in this article's paragraph is dubious at best, and needs a citation at least.

Considering that, I'm adding a "needs citation" note, reviewers feel free to remove it if you think it's inappropriate. I really think it is.

Conceptual artefact?

Isn't "Quantum teleportation" just a conceptual artefact created by the flawed idea that the wave function collapses at observation? If instead there is no collapse, and particle pairs have a definite state at sending position, then the concept of "Quantum teleportation" isn't needed. I.e. from a linguist and computer science perspective, the emergence of the idea of "Quantum teleportation" is just the "Quantum theory" bugging out and generating erroneous answers. ... said: Rursus (^mbork³) 09:37, 13 November 2009 (UTC)

I forgot: "Bouahahahaa!". ... said: Rursus (^mbork³) 09:41, 13 November 2009 (UTC)

Well, no, quantum teleportation isn't just a conceptual artefact, though I'm not completely sure what you mean by that. You should think of the teleportation protocol as part of some larger computation involving qubits, and the empirical meaning of it is that the "teleported" qubit can be substituted for the original qubit in any context without altering the result. The nature of measurement doesn't play any important role in quantum teleportation. The two bits sent from Alice to Bob don't even have to be measured; they can be sent as qubits over a quantum channel and used as qubits by Bob and the protocol will still work, though it becomes rather pointless. -- BenRG (talk) 13:21, 13 November 2009 (UTC)

Let me put the question another way, so that you might understand what I mean with "conceptual artefact": is "Quantum teleportation" a "teleportation" even when using the de Broglie–Bohm interpretation, or the Ensemble Interpretation instead of the Copenhagen interpretation? And the nature of measurement play a very major role for the phenomenon described as "quantum teleportation" being named a "teleportation". There is certainly a phenomenon in the bottom of this, but it is a "teleportation" only if one is using certain interpretations, and in others it is not. My question is entirely about the description and logic models (physics interpretations) we peruse, not about the physics. ... said: Rursus (^mbork³) 10:02, 27 November 2009 (UTC)

The de Broglie–Bohm interpretation includes an inherently non-local pilot wave. So yes, as all quantum mechanics, the non-locality of the teleportation protocol can be conceptually located in the pilot wave or in the particle states themselves, with no experimental discrimination possible. In the de Broglie–Bohm interpretation, one would say that as soon as the Bell state measurement occurs, a pilot wave instantaneously and outside space-time rushes to the other particle to modify its state. We call this teleportation, it could be called by another name. UnHoly (talk) 14:46, 28 November 2009 (UTC)

Thanks for correction

User Skippydo: Thank you for reverting my edit (so sorry I forgot to log in). Yet I hope you don't mind that I have done some new editing so as to prevent other readers from making the same mistake I made. After consulting the paper by Bennett et al. I discovered that it would be advisable to be somewhat more specific about which particles the different expressions refer to.WMdeMuynck (talk) 21:45, 20 January 2010 (UTC)

I thought I was clarifying things but I think I had introduced an error. I think your style is superior. However, I believe we can further edit it so that bits appear in order. At the moment, I'm not feeling up to the task. Skippydo (talk) 03:37, 21 January 2010 (UTC)

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