Full characterization of quantum states and processes is a fundamental requirement for verification and benchmarking of quantum devices. It has been realized in systems with few components, but for larger systems it becomes unfeasible because of the exponential growing with the system size of the number of measurements and the amount of computational power required to process them. A new approach for quantum state tomography and quantum process tomography, requiring a limited number of measurements, has been recently introduced by Maciel et al. [ Quantum Inf. Comput. 12 0442 (2012) Int. J. Mod. Phys. C 22 1361 (2011)], namely variational quantum-process tomography (VQT). Here we adopt the VQT approach for the experimental characterization of two-qubit quantum processes and compare the reconstructed maps with those obtained by standard tomographic methods. The results demonstrate the high performance of this approach and propose VQT as a powerful alternative to the standard quantum process tomography.
R.A. Vianna, A. Crespi, R. Osellame, R. Ramponi, L. Sansoni, P. Mataloni, and F. Sciarrino, Variatonal quantum process tomography of two-qubit maps, Physical Review A 87, 032304 (2013).