Characterizing universal gate sets via dihedral benchmarking

We describe a practical experimental protocol for robustly characterizing the error rates of non-Clifford gates associated with dihedral groups, including small single-qubit rotations. Our dihedral benchmarking protocol is a generalization of randomized benchmarking that relaxes the usual unitary 2-design condition. Combining this protocol with existing randomized benchmarking schemes enables practical universal gate sets for quantum information processing to be characterized in a way that is robust against state-preparation and measurement errors. In particular, our protocol enables direct benchmarking of the /8 gate even under the gate-dependent error model that is expected in leading approaches to fault-tolerant quantum computation.