Fredkin gates
This gate is mainly worth mention as one of the first gate that formed a universal set (see below) by itself. The idea is that the first input (A) controls whether there is a transformation on the other two inputs (what the value of BÕ and CÕ are in the diagram below): If A = |1>, B = B and C = C but, if A = |0>, B = C and C = B [7]. As you can easily verify, this gate shares with the NOT gates that, when you run the output of the gate through another gate of the same type, the original qubits are returned.
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Created by Brian Patterson
Last Modified 11/22/00