Upper Bound on Singlet Fraction of Two Qubit Mixed Entangled States

We demonstrate the possibility of achieving the maximum possible singlet fraction using a entangled mixed two-qubit state as a resource. For this, we establish a tight upper bound on singlet fraction and show that the maximal singlet fraction obtained in \cite{Verstraete} does not attain the obtained upper bound on the singlet fraction. Interestingly, we found that the required upper bound can in fact be achieved using local filtering operations.