Quantum process tomography of a controlled-NOT gate

The complete characterization of a two-quibit entangling process such as a linear optics controlled NOT gate, operating with coincident detection was demonstrated using quantum process tomography. Maximum likelihood estimation process was used for converting the experimental data into a physical process matrix. It was found that the matrix allowed for an accurate prediction of the operation of the gate for arbitrary input states. The matrix was also shown to allow calculation of gate performance measures, such as the average gate fidelity, average purity, and entangling capability of the gate.