An important requirement for spin-based quantum information processing is reliable and fast readout of electron spin states, allowing for feedback and error correction. However, common readout techniques often require additional gate structures, hindering device scaling, or impose stringent constraints on the tuning configuration of the sensed quantum dots. Here, we operate an in-line charge sensor within a triple quantum dot, where one of the dots is coupled to a microwave cavity and used to readout the charge states of the other two dots. Owing to the proximity of the charge sensor, we observe a near-digital sensor response with a power signal-to-noise ratio greater than $450$ at an integration time of $t_{\mathrm{int}}=1\mu \mathrm{s}$. Despite small singlet-triplet splittings of approximately 40 $\mu \mathrm{eV}$, we further utilize the sensor to measure the spin relaxation time of a singlet-triplet qubit, achieving an average single-shot spin readout fidelity greater than 99%. Our approach enables high-fidelity spin readout, combining minimal device overhead with flexible qubit operation in semiconductor quantum devices.

中文翻译：

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自旋数字化仪，用于腔耦合硅三重量子点的高保真读出

基于自旋的量子信息处理的一项重要要求是可靠且快速地读出电子自旋态，以实现反馈和纠错。然而，普通的读出技术通常需要附加的栅极结构，阻碍了器件的缩放，或者对所感测的量子点的调谐配置施加了严格的约束。在这里，我们在三重量子点内操作一个在线电荷传感器，其中一个点耦合到微波腔，并用于读出其他两个点的电荷状态。由于电荷传感器的接近性，我们观察到近数字传感器的响应，其功率信噪比大于$450$ 在整合时间 ${Ť}_{\mathrm{整型}}=\mathrm{1个}\mu \mathrm{s}$。尽管单重态-三重态分裂约有40个$\mu \mathrm{电子伏特}$，我们进一步利用传感器测量单重态-三重态量子位的自旋弛豫时间，实现了平均单次自旋读出保真度大于99％。我们的方法实现了高保真自旋读出，将最小的器件开销与半导体量子器件中灵活的qubit操作相结合。