An electron spin qubit in silicon quantum dots holds promise for quantum information processing due to the scalability and long coherence. An essential ingredient to recent progress is the employment of micromagnets. They generate a synthetic spin–orbit coupling (SOC), which allows high-fidelity spin manipulation and strong interaction between an electron spin and cavity photons. To scaled-up quantum computing, multiple technical challenges remain to be overcome, including controlling the valley degree of freedom, which is usually considered detrimental to a spin qubit. Here, we show that it is possible to significantly enhance the electrical manipulation of a spin qubit through the effect of constructive interference and the large spin-valley mixing. To characterize the quality of spin control, we also studied spin dephasing due to charge noise through spin-valley mixing. The competition between the increased control strength and spin dephasing produces two sweet-spots, where the quality factor of the spin qubit can be high. Finally, we reveal that the synthetic SOC leads to distinctive spin relaxation in silicon, which explains recent experiments.

由于可扩展性和长相干性，硅量子点中的电子自旋量子位有望用于量子信息处理。近期进展的一个重要组成部分是使用微磁体。它们产生合成的自旋轨道耦合 (SOC)，允许高保真自旋操纵以及电子自旋和腔光子之间的强相互作用。为了扩大量子计算，仍有许多技术挑战有待克服，包括控制谷自由度，这通常被认为对自旋量子位不利。在这里，我们表明可以通过相长干涉和大自旋谷混合的效应显着增强自旋量子位的电操纵。为了表征自旋控制的质量，我们还通过自旋谷混合研究了由于电荷噪声引起的自旋移相。增加的控制强度和自旋移相之间的竞争产生了两个最佳点，其中自旋量子位的品质因数可能很高。最后，我们揭示了合成 SOC 导致硅中独特的自旋弛豫，这解释了最近的实验。