Some context: I am a “quantum autodidact”, and I am currently reading a book Q is for Quantum, which is a very gentle, beginner-friendly introduction to quantum computing. I was thinking how it relates to the things I have read before, and then I noticed that I was confused. I looked at Wikipedia, which said that CNOT does not violate the no-cloning theorem… but I didn’t understand the explanation why.
I think I get it now. |00> + |11> is not a copy (looking at one qubit collapses the other), |00> + |01> + |10> + |11> would be a copy (looking at one qubit would still leave the other as |0> + |1>).
Thank you!
Some context: I am a “quantum autodidact”, and I am currently reading a book Q is for Quantum, which is a very gentle, beginner-friendly introduction to quantum computing. I was thinking how it relates to the things I have read before, and then I noticed that I was confused. I looked at Wikipedia, which said that CNOT does not violate the no-cloning theorem… but I didn’t understand the explanation why.
I think I get it now. |00> + |11> is not a copy (looking at one qubit collapses the other), |00> + |01> + |10> + |11> would be a copy (looking at one qubit would still leave the other as |0> + |1>).
I recommend this article by the discoverers of the no-cloning theorem for a popular science magazine over the Wikipedia page for anyone trying to understand it.