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.
@article{arxiv.1210.7011,
title = {Process verification of two-qubit quantum gates by randomized benchmarking},
author = {A. D. Córcoles and Jay M. Gambetta and Jerry M. Chow and John A. Smolin and Matthew Ware and J. D. Strand and B. L. T. Plourde and M. Steffen},
journal= {arXiv preprint arXiv:1210.7011},
year = {2013}
}