Common entanglement witnesses and their characteristics
  We investigate the issue of finding common entanglement witness for certain class of states and extend this study to the case of Schmidt number witnesses. We also introduce the notion of common decomposable and non-decomposable witness operators which is specially useful for constructing a common witness where one of the entangled states is with a positive partial transpose. Our approach is illustrated with the help of suitable examples of qutrit systems. 
Nirman Ganguly, Satyabrata Adhikari, A.S.Majumdar
quant-ph