Fast and high-fidelity state preparation and measurement in triple-quantum-dot spin qubits

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 (\(\approx 300\) 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 \(2.5\pm0.5\times 10^{-3}\). This result is enabled by a high-valley-splitting heterostructure, initialization at the 2-to-3 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 towards further improved fidelity and speed. Along with an observed single-qubit randomized benchmarking error rate of \(1.7\times 10^{-3}\), this work demonstrates initialization, control, and measurement of Si/SiGe triple-dot qubits at fidelities and durations which are promising for scalable quantum information processing.