Demonstration of high-fidelity gates in a strongly anharmonic with long-coherence C-shunt flux qubit

We demonstrate high-fidelity single-qubit gates on a C-shunt flux qubit that simultaneously combines a large anharmonicity (A/2π=848 MHz) with long relaxation time (T1=23 μs). The large anharmonicity significantly suppresses leakage to higher energy levels, enabling fast and precise microwave control. Using derivative removal by adiabatic gate pulses and randomized benchmarking, the qubit achieves gate fidelities exceeding 99.9%, highlighting the capability of C-shunt flux qubits for robust and high-performance quantum operations. These results establish them as a promising platform for scalable quantum information processing.