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This question already has an answer here:

Please consider commenting on this basic quantum entanglement question or point me to articles that may enhance my knowledge.

Does quantum entanglement only occur in pairs, or can three or more particles become entangled?

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marked as duplicate by fibonatic, Jim, ACuriousMind, Kyle Kanos, JamalS Jan 28 '15 at 21:45

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ Welcome to Physics.SE. It is much preferred to ask one question per post. This will actually help you get better answers. I would strongly recommend that you edit this question so that it asks just your first point, and then post the other two separately. $\endgroup$ – DanielSank Jan 28 '15 at 17:33
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    $\begingroup$ Suggestion: it is much better if you ask one time one question. This packaged questions are bad. Reformulate this to 3 different, and independent questions, and ask them again. If you ask multiple questions, it is not a problem here. $\endgroup$ – user259412 Jan 28 '15 at 17:33
  • $\begingroup$ If you google for "three particles entangled", the second hit is physics.stackexchange.com/q/54366 $\endgroup$ – Norbert Schuch Jan 28 '15 at 18:33
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Entanglement with more than two particles is allowed. Mathematically, you could write, for example, $$|\psi\rangle = a|111\rangle + b|000\rangle.$$ Here, if you measure particle 1 to be in the "0" state, then you know immediately what the entire wave function is after measurement.

One applications is quantum error correction.

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    $\begingroup$ Just to add a somewhat canonic reference: arxiv.org/abs/quant-ph/0005115 "Three qubits can be entangled in two inequivalent ways. Multipartite entanglement is very rich! $\endgroup$ – Martin Jan 28 '15 at 17:58
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Yes, it is possible for even more particles. A such experiment was done to prove entanglement, which was done using three entangled photons. You can Google about that, if you are interested in more detail.

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    $\begingroup$ Please note that an answer to the question should completely answer it. The main point of writing full answers is that we want this to be useful moreso to all of the readers coming in from google than to the OP. While the OP can ask you for further clarification, other readers can not. So an answer should contain all of the details and fully answer the question. As it is, this should be made as a comment on the question $\endgroup$ – Jim Jan 28 '15 at 18:29

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