Quantum Process Tomography of a Controlled-NOT Gate
Jeremy L. O’Brien, Geoff J. Pryde, Alexei Gilchrist, Daniel F. V. James, Nathan K. Langford, Timothy C. Ralph, Andrew G. White · Physical Review Letters · 2004
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.