Maximally entangled mixed states: Creation and concentration

The extension of the boundaries of experimentally accessible two-qubit Hilbert space using correlated photons from parametric down-conversion was investigated. Maximally entangled mixed states that lie above the Werner boundary in the linear entropy-tangle plane were created and characterized. A sensitivity imbalance in common state measures such as the tangle, linear entropy and fidelity was also investigated. It was demonstrated that the mixed states can be efficiently concentrated, simultaneously increasing both the purity and the degree of entanglement.