Controlled-swap gate

There is another gate which can be used to prove reversible computation. It is the Fredkin gate it performs a controlled swap operation between two bits [6]. 

Controlled-SWAP (CSWAP), with spin X as a control if X2 = 1) (F was cooled), transfer the improved state of F (doubled bias) to a chosen location by alternate SWAP and CSWAP gates. 

Figure 2.11 Sample fragment of a quantum circuit illustrating the effect of some typical quantum gates a SWAP operation between the upper and centre qubits is effected through three consecutive controlled-NOT ...

The logic gate called SWAP is built from a circuit containing only cnot gates, as shown on Figure 3.3. The first CNOT is the controlled by the first qubit (CNOTa), and second one is controlled by the second qubit (CNOT ). 

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