Process verification of two-qubit quantum gates by randomized benchmarking

TL;DR

This paper demonstrates a complete randomized benchmarking protocol on two superconducting qubits, achieving precise error estimates for two-qubit gates, which are crucial for quantum computing fidelity improvements.

Contribution

It introduces an improved two-qubit gate implementation and applies a comprehensive randomized benchmarking protocol to accurately assess gate errors.

Findings

Optimal average error per Clifford: 0.0936

Two-qubit gate error from interleaved benchmarking: 0.0653

Quantum process tomography error estimate: ~0.12

Abstract

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.