Direct measurement of concurrence for atomic two-qubit pure states
  We propose a general scheme to measure the concurrence of an arbitrary two-qubit pure state in atomic systems. The protocol is based on one- and two-qubit operations acting on two available copies of the bipartite system, and followed by a global qubit readout. We show that it is possible to encode the concurrence in the probability of finding all atomic qubits in the ground state. Two possible scenarios are considered: atoms crossing 3D microwave cavities and trapped ion systems. 
G. Romero, C.E. Lopez, F. Lastra, E. Solano, and J.C. Retamal