# Tag Info

$\left(\begin{array}{c} \alpha \\ \beta \end{array}\right)$
where $\alpha$ and $\beta$ are two complex numbers subject to $|\alpha|^2+|\beta|^2 =1$. An alternative is the corresponding "bra", which has the same information content:
$\left(\begin{array}{cc} \alpha^* & \beta^* \end{array}\right)$
$\left(\begin{array}{cc} |\alpha|^2 & \alpha\beta^* \\ \alpha^*\beta & |\beta|^2 \end{array} \right)$,
in which the extraneous complex phase information has been removed. From this we see that there are only two real informational degrees of freedom in a qubit, for example, $|\alpha|^2$ and the complex phase of $\alpha\beta^*$. Another way of representing these two degrees of freedom is with the Bloch sphere.