  We study the entangling power and perfect entangler nature of (SWAP)1/m, for
m>=1, and controlled unitary (CU) gates. It is shown that (SWAP)1/2 is the only
perfect entangler in the family. On the other hand, a subset of CU which is
locally equivalent to CNOT is identified. It is shown that the subset, which is
a perfect entangler, must necessarily possess the maximum entangling power.
