Unrestricted generation of pure two-qubit states and entanglement diagnosis by single-qubit tomography

We present an experimental proof-of-principle for the generation and detection of pure two-qubit states that have been encoded in degrees of freedom that are common to both classical-light beams and single photons. Our protocol requires performing polarization tomography on a single qubit from a qubit pair. The degree of entanglement in the qubit pair is measured by concurrence, which can be directly extracted from intensity measurements—or photon counting—entering single-qubit polarization tomography.