Silicon-quantum-dot qubits must contend with low-lying valley excited states that are sensitive functions of the quantum-well heterostructure and disorder; quantifying and maximizing the energies of these states are critical to improving device performance. We describe a spectroscopic method for probing excited states in isolated $\mathrm{Si}$/$\mathrm{Si}$-$\mathrm{Ge}$ double quantum dots using standard baseband pulsing techniques, easing the extraction of energy spectra in multiple-dot devices. We use this method to measure dozens of valley excited-state energies spanning multiple wafers, quantum dots, and orbital states, which are crucial for evaluating the dependence of valley splitting on quantum well width and other epitaxial conditions. Our results suggest that narrower wells can be beneficial for increasing valley splittings, but this effect can be confounded by variations in growth and fabrication conditions. These results underscore the importance of valley-splitting measurements for guiding the development of $\mathrm{Si}$ qubits.

中文翻译：

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Si / Si-GeQuantum点中谷轨道状态的失谐轴脉冲光谱

硅量子点量子位必须与低洼谷激发态竞争，低谷激发态是量子阱异质结构和无序的敏感功能。量化和最大化这些状态的能量对于提高设备性能至关重要。我们描述了一种光谱方法，用于探测孤立状态下的激发态$硅$/$硅$--$\mathrm{通用电器}$使用标准基带脉冲技术的双量子点，简化了多点设备中能量谱的提取。我们使用这种方法来测量跨越多个晶片，量子点和轨道状态的数十个谷激发态能量，这对于评估谷分裂对量子阱宽度和其他外延条件的依赖性至关重要。我们的结果表明，较窄的井可能有利于增加山谷裂谷，但这种影响可能会因生长和制造条件的变化而混淆。这些结果强调了谷值分流测量对于指导水文地质勘探发展的重要性。$硅$ 量子比特。