Simultaneous High-Fidelity Single-Qubit Gates in a Spin Qubit Array
Silicon spin qubits offer a promising path to scalable quantum computing due to their compatibility with industrial semiconductor manufacturing and recent advances in multi-qubit integration. A key requirement for scaling quantum processors is the ability to perform high-fidelity operations in parallel across many qubits. In silicon spin systems, however, simultaneous control remains a major challenge, as fidelities typically degrade under parallel operation. In a five-qubit silicon spin array, we identify microwave-drive-induced AC Stark shifts as the dominant source of this degradation. We address this by introducing a scalable mitigation protocol based solely on pairwise phase calibrations. Using tailored control pulses on a shared control line, we achieve primitive $π/2$ gate fidelities well above 99.99% for each qubit individually, with some approaching 99.999%, surpassing previously reported fidelities in silicon spin qubits. Crucially, these fidelities are preserved above 99.99% during simultaneous operation of up to three qubits. During parallel five-qubit operation, fidelities remain at the practical fault-tolerant threshold of 99.9%, with the loss attributed to drive-induced decoherence resulting from increased microwave power. This effect can be mitigated through device-level improvements. By demonstrating that high-fidelity control is maintained during simultaneous operation, we overcome a central challenge in silicon spin qubits and highlight the potential of shared qubit-control lines for scaling.