Quantum process tomography of a controlled-NOT gate

Phys Rev Lett. 2004 Aug 20;93(8):080502. doi: 10.1103/PhysRevLett.93.080502. Epub 2004 Aug 20.


We demonstrate complete characterization of a two-qubit entangling process--a linear optics controlled-NOT gate operating with coincident detection--by quantum process tomography. We use a maximum-likelihood estimation to convert the experimental data into a physical process matrix. The process matrix allows an accurate prediction of the operation of the gate for arbitrary input states and a calculation of gate performance measures such as the average gate fidelity, average purity, and entangling capability of our gate, which are 0.90, 0.83, and 0.73, respectively.