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. 
Satyabrata Adhikari, Atul Kumar
quant-ph cs.IT math.IT