Return the adjoint quantum channel.
참고
This is equivalent to the matrix Hermitian conjugate in the
SuperOp representation
ie. for a channel \(\mathcal{E}\), the SuperOp of
the adjoint channel \(\mathcal{{E}}^\dagger\) is
\(S_{\mathcal{E}^\dagger} = S_{\mathcal{E}}^\dagger\).