Calibration of drive non-linearity for arbitrary-angle single-qubit gates using error amplification

The ability to execute high-fidelity operations is crucial to scaling up quantum devices to large numbers of qubits. However, signal distortions originating from non-linear components in the control lines can limit the performance of single-qubit gates. In this work, we use a measurement based on error amplification to characterize and correct the small single-qubit rotation errors produced by the non-linear scaling of the qubit drive rate with the amplitude of the programmed pulse. With our hardware, and for a 15-ns pulse, the rotation angles deviate by up to 3.4° from a linear model. Using purity benchmarking, we find that control errors reach 2 × 10^-4, which accounts for half of the total gate error. Using cross-entropy benchmarking, we demonstrate arbitrary-angle single-qubit gates with coherence-limited errors of 2 × 10^-4 and leakage below 6 × 10^-5. While the exact magnitude of these errors is specific to our setup, our method is applicable to most sources of non-linearity. Our work shows that the non-linearity of qubit drive lines imposes an upper limit on the fidelity of single-qubit gates, independent of improvements in coherence times, circuit design, or leakage mitigation.