Talk:No cloning theorem

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[edit] Clarification of implications?

This is generally a very clear article, but the principle raises some questions for newcomers. The second paragraph deals with quantum entanglement, but what about Bose–Einstein condensates and lasers? In the case of a condensate, I guess the same quantum state is reached because it is a known and definite state forced by cooling, rather then a superposition. But does a photon in a laser not stimulate emission of another identically-polarised photon, even if that polarisation is not known? --Cedderstk 08:25, 16 May 2006 (UTC)

I think that would be an example of entanglement. E.g., if |0> and |1> are the two possible polarization states of the inital photon, then the final state can be |0>|0> or |1>|1>. So, if we start with a superposition of |0> and |1> (with coefficients a and b), we have:
a|0> + b|1> --> a|0>|0> + b|1>|1>
Whereas, for cloning we would need:
a|0> + b|1> --> (a|0> + b|1>)x(a|0> + b|1>) = aa|0>|0> + ab|0>|1> + ba|1>|0> + bb|0>|0>
In other words, cloning refers to the creation of two separable states, and that's what the theorem forbids. -- Tim314 00:37, 19 February 2007 (UTC)

[edit] No-cloning prevents superluminal communication?

The article states, "The no cloning theorem prevents superluminal communication via quantum entanglement, as cloning is a sufficient condition for such communication." Logically, this makes no sense: to prevent superluminal communication, cloning would have to be a _necessary_ condition. As stated, there is nothing to say that some condition other than cloning might also imply superluminal communication. Indeed, if cloning implies superluminal communication, then a proof of no superluminal communication would imply no-cloning as a corollary.

yes, you're right. feel free to modify the article. Mct mht 02:31, 26 June 2007 (UTC)
In your contrapositive the consequent is missing a negation. You are correct in stating that the no-cloning theorem is a corollary of no superliminal communication. Skippydo 05:24, 26 July 2007 (UTC)

[edit] Telecloning demonstrated.

There are several articles about telecloning as a fact already made in a laboratory. In arXiv you can find too a lot of topics talking about telecloning. Please, consult this article.

http://www.physorg.com/news10924.html

I'm wondering if could be appropriated, expand the article, talking about telecloning as being also demonstrated in laboratory. I think the article need urgent attention. Is a fact that the no cloning theorem is a topic of phsyics, but is also a fact, that telecloning is being demonstrated, so this article can bring the people to wrong conclussions. It should be expanded, talking about recents experiments in telecloning and quantum mechanics. Thanks.

telecloning and cloning are not the same. telecloning is a teleportation-type protocol where shared multipartite entanglement is essential, yet another example of entanglement being the crucial enabler in quantum communication. without shared entanglement: no cloning. the comparison deserves to be mentioned here and some remarks can be added to the teleportation article. but i'd suggest that telecloning be given its own article also. Mct mht 00:23, 26 July 2007 (UTC)
To clearify, even with shared entanglement there is no cloning. You may of course teleport an arbitrary state but this will destroy the source leaving only the target qubit. Any article you find about telecloning will no dobt mention the no cloning theorem and state that they will be accepting some error to preform so a called optimal cloning. As always, after reading your link, I must mention that people will never be cloned or teleported using this technique as we are talking about information and not matter. Skippydo 05:17, 26 July 2007 (UTC)
Wow, I never expected the article could expand so fast with a part explaining imperfect cloning, I think that it should be expanded a bit more, is very very short. That part added to the article, clarify a lot the things, because cloning telecloning... are similar terms and you get confussed. One thing that have been forgotten is an IMPORTANT POINT, that is the "ACCURACY LEVEL" or... theoretical accuracy level, for imperfect telecloning, which have been demonstrated in a 58%, and is allegedly able to reach a 66%. The accuracy gives us an idea about how well we are doing the copies, I find it interesting to be mentioned
Watch this please
http://www.nkj.ru/en/news/3775/
Someone could add this?

[edit] Edit by143.239.130.221, reverted by Mct mht

Is it possible to get an actual reason for the revert as opposed to the "..." that was given? With the exception of a minor typo at one point and some general formatting errors the proof was correct and would be much easier for a layman to "get" since there's no advanced QM formulation like the adjoint present. Hell, my lecturer gave me full credit for using this method in a problem set earlier this year. Also would it kill you to provide actual summaries if you're going to bother to type something in the summary box? Eccentricned (talk) 03:18, 13 May 2008 (UTC)

It's certainly as good as the current proof but I oppose it's addition. We only need one version of the proof.
I would also, like to point out that the current proof is not sufficiently general. Either axillary qubits need to be added or more general quantum operations need to be allowed. Skippydo (talk) 01:34, 14 May 2008 (UTC)