Entanglement Measurement in a Two-photon Generalized Werner State with Single-photon Detection

Traditional entanglement measurement techniques require the detection of all entangled particles if the quantum state is not pure. Recently, it has been shown theoretically and experimentally that if one employs quantum interferometry, one can measure entanglement in a certain kind of two-photon mixed states without detecting one of the photons. These mixed states have three free parameters and can be obtained by generalizing Bell states. Here, we extend the method to cover an important case, in which a mixed state is created by adding white noise to the above-mentioned mixed states. Such states can also be viewed as two-photon generalized Werner states. We show how to determine the concurrence of these mixed states without detecting one of the photons.