  We present measurements of single-qubit gate errors for a superconducting
qubit. Results from quantum process tomography and randomized benchmarking are
compared with gate errors obtained from a double pi pulse experiment.
Randomized benchmarking reveals a minimum average gate error of 1.1+/-0.3% and
a simple exponential dependence of fidelity on the number of gates. It shows
that the limits on gate fidelity are primarily imposed by qubit decoherence, in
agreement with theory.
