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

TL;DR

This paper demonstrates rapid, high-fidelity initialization and measurement of triple-quantum-dot spin qubits in silicon, achieving fidelities suitable for scalable quantum computing through all-electrical control and careful mitigation of error sources.

Contribution

It introduces a high-fidelity, fast state preparation and measurement protocol for silicon triple-quantum-dot qubits, with a novel leakage-sensitive metric and detailed analysis of fidelity limitations.

Findings

Measurement integration time of 980 ns

Initialization time of approximately 300 ns

Single-qubit randomized benchmarking error rate of 1.7×10⁻³

Abstract

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.