Ultrafast single-qubit gates through multi-photon transition removal.

Fast qubit control is essential for scalable quantum computing. However, the strong driving that is required can induce significant leakage from the computational subspace, particularly in weakly anharmonic qubits. We demonstrate single qubit gates with a total leakage error consistently below 2.0 × 10-5 on a transmon qubit, and obtain fidelities above 99.98% at 6.8 ns pulse duration in both X and X/2 gates. This is achieved by removing direct transitions beyond nearest-neighbor levels using double recursive applications of Derivative Removal by Adiabatic Gate pulse shape. We also introduce the amplified leakage error sequence which can directly measure the leakage error down to 10-6. We test single qubit gates across a range of pulse durations using multiple benchmarking methods to reveal the error channels. The presented approach can be straightforwardly adapted by other platforms.