Could somebody tell me whether or not a CNOT gate has actually been built or not?
I believe there are several CNOT physical realisation up to today. One of them:
Yes, Controlled-NOT gates have been made, even teleported, and several quantum circuits implementing them studied. Here's one proposed quantum circuit, a variation of the "quantum multiplexor circuit", using CNOT gates
Another quantum circuit using CNOT gates is the Brassard teleportation circuit
The Japanese invented them.
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