Process verification of two-qubit quantum gates by randomized   benchmarking
  We implement a complete randomized benchmarking protocol on a system of two superconducting qubits. The protocol consists of randomizing over gates in the Clifford group, which experimentally are generated via an improved two-qubit cross-resonance gate implementation and single-qubit unitaries. From this we extract an optimal average error per Clifford of 0.0936. We also perform an interleaved experiment, alternating our optimal two-qubit gate with random two-qubit Clifford gates, to obtain a two-qubit gate error of 0.0653. We compare these values with a two-qubit gate error of ~0.12 obtained from quantum process tomography, which is likely limited by state preparation and measurement errors. 
A. D. C\'orcoles, Jay M. Gambetta, Jerry M. Chow, John A. Smolin,   Matthew Ware, J. D. Strand, B. L. T. Plourde and M. Steffen
quant-ph cond-mat.mes-hall