| Summary: | We demonstrate rapid high-fidelity state preparation and measurement in exchange-only Si/SiGe triple-quantum-dot qubits. Fast measurement integration (980-ns) and initialization (approximately 300-ns) operations are performed with all-electrical baseband control. We emphasize a leakage-sensitive joint initialization and measurement metric, developed in the context of exchange-only qubits but applicable more broadly, and report an infidelity of 2.5±0.5×10^{−3}. This result is enabled by a high-valley-splitting heterostructure, initialization at the two- to three-electron charge boundary, and careful assessment and mitigation of T_{1} during spin-to-charge conversion. The ultimate fidelity is limited by a number of comparably important factors and we identify clear paths toward further improved fidelity and speed. Along with an observed single-qubit randomized benchmarking error rate of 1.7×10^{−3}, this work demonstrates initialization, control, and measurement of Si/SiGe triple-dot qubits at fidelities and durations that are promising for scalable quantum information processing.
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