Concurrence in the magic basis
= Concurrence in the magic basis
{title2=$\mathcal C=|\sum_jb_j^2|$}
For a normalized pure two-qubit state written in a <magic basis>, <concurrence> is $\mathcal C=|\sum_jb_j^2|$, while $\det\rho_A=\mathcal C^2/4$. This bilinear sum uses no <complex conjugation> inside its square; replacing it by $\sum_j|b_j|^2$ would incorrectly give maximal <concurrence> for every state.