  Let $U_d$ be a unitary operator representing an arbitrary $d$-dimensional
unitary quantum operation. This work presents optimal quantum circuits for
transforming a number $k$ of calls of $U_d$ into its complex conjugate
$\bar{U_d}$. Our circuits admit a parallel implementation and are proven to be
optimal for any $k$ and $d$ with an average fidelity of
$\left\langle{F}\right\rangle =\frac{k+1}{d(d-k)}$. Optimality is shown for
average fidelity, robustness to noise, and other standard figures of merit.
This extends previous works which considered the scenario of a single call
($k=1$) of the operation $U_d$, and the special case of $k=d-1$ calls. We then
show that our results encompass optimal transformations from $k$ calls of $U_d$
to $f(U_d)$ for any arbitrary homomorphism $f$ from the group of
$d$-dimensional unitary operators to itself, since complex conjugation is the
only non-trivial automorphisms on the group of unitary operators. Finally, we
apply our optimal complex conjugation implementation to design a probabilistic
circuit for reversing arbitrary quantum evolutions.
