About writing a unitary matrix in another way

[aalma]

It is easy to see that a matrix of the given form is actually an unitary matrix i,e, satisfying AA^*=I with determinant 1. But, how to see that an unitary matrix can be represented in the given way?

 

[DrClaude]

Take the most general matrix,
$$
A =
\begin{bmatrix}
a + bi & c + di \\
e+ fi & g+hi
\end{bmatrix}
$$
and show that imposing $AA^\dagger = I$ requires $e = -c$, $f=d$, and so on.

 

[aalma]

Yes, thanks. Tried to do this however got somehow long equations with these eight real numbers. guessing how it should be solved!
I also wrote the condition that the det of this matrix=1.

 

[malawi_glenn]

Can't you just find the inverse of the matrix using the standard formula, and then you do the hermitian of the matrix and thus figure out what the relationsships of a, b, c, ... must be?

$A^\dagger = A^{-1}$