Valley splitting is a key feature of silicon-based spin qubits. Quantum dots in $\mathrm{Si}$/${\mathrm{Si}}_x{\mathrm{Ge}}_{1-x}$ heterostructures reportedly suffer from a relatively low valley splitting, limiting the operation temperature and the scalability of such qubit devices. Here, we demonstrate a robust and large valley splitting exceeding 200 $\mu \mathrm{eV}$ in a gate-defined single quantum dot, hosted in molecular-beam-epitaxy-grown ${}^{68}\mathrm{Si}/{\mathrm{Si}}_x{\mathrm{Ge}}_{1-x}$. The valley splitting is monotonically and reproducibly tunable up to 15% by gate voltages, originating from a 6-nm lateral displacement of the quantum dot. We observe static spin relaxation times $T_1>1$ s at low magnetic fields in our device containing an integrated nanomagnet. At higher magnetic fields, $T_1$ is limited by the valley hotspot and by phonon noise coupling to intrinsic and artificial spin-orbit coupling, including phonon bottlenecking.

中文翻译：

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aSi / SixGe1-xQuantum点中的大可调谷劈裂和单旋弛豫机制

谷值分裂是硅基自旋量子位的关键特征。量子点$硅$/${硅}_X{\mathrm{通用电器}}_{\mathrm{1个}-X}$据报道，异质结构具有相对较低的谷裂，从而限制了这种量子位器件的工作温度和可扩展性。在这里，我们展示了超过200的稳健且大的山谷裂谷$\mu \mathrm{电子伏特}$ 在门定义的单个量子点中，存在于分子束外延生长中 ${}^{68}硅/{硅}_X{\mathrm{通用电器}}_{\mathrm{1个}-X}$。谷值分裂可通过栅极电压单调且可复制地调整至15％，该电压源自量子点的6 nm横向位移。我们观察到静态自旋弛豫时间${Ť}_{\mathrm{1个}}>\mathrm{1个}$在包含集成纳米磁铁的设备中处于低磁场的情况下。在更高的磁场下${Ť}_{\mathrm{1个}}$ 受山谷热点和声子噪声耦合到固有和人工自旋轨道耦合（包括声子瓶颈）的限制。