= Binary Schmidt filter
{title2=$M_1=\operatorname{diag}(\sin\theta,\cos\theta),\quad M_2=\operatorname{diag}(\cos\theta,\sin\theta)$}
For a pure state with two descending squared <Schmidt coefficients> $\lambda_0\ge\lambda_1$, this <quantum instrument> acts in one party's <Schmidt basis>. The first outcome balances the two Schmidt amplitudes when $\tan\theta=\sqrt{\lambda_1/\lambda_0}$, with probability $2\lambda_0\lambda_1$. This is not the optimal unrestricted success probability $2\lambda_1$ in <single-copy entanglement concentration>. An embedding in a larger subsystem requires a <POVM on the occupied support> or a full-space completion.
Back to article page
