Ja. Smolin et Dp. Divincenzo, 5 2-BIT QUANTUM GATES ARE SUFFICIENT TO IMPLEMENT THE QUANTUM FREDKINGATE, Physical review. A, 53(4), 1996, pp. 2855-2856
We present an analytic construction of the three-bit quantum condition
al swap (Fredkin) gate that uses only five quantum gates, each acting
on only two qubits. Our implementation is based on previous work on th
e three-bit quantum conditional-NOT (Toffoli) gate. Numerical evidence
suggests that this is a minimal implementation.