The energy landscape of a single electron in a triple quantum dot can be tuned such that the energy separation between ground and excited states becomes a flat function of the relevant gate voltages. These so-called sweet spots are beneficial for charge coherence since the decoherence effects caused by small fluctuations of gate voltages or surrounding charge fluctuators are minimized. We propose a new operation point for a triple quantum dot charge qubit, a so-called $C{Q}_3$-qubit, having a third-order sweet spot. We show strong coupling of the qubit to single photons in a frequency tunable high-impedance SQUID-array resonator. In the dispersive regime, we investigate the qubit linewidth in the vicinity of the proposed operating point. In contrast to the expectation for a higher-order sweet spot, we there find a local maximum of the linewidth. We find that this is due to a non-negligible contribution of noise on the quadrupolar detuning axis not being in a sweet spot at the proposed operating point. While the original motivation to realize a low-decoherence charge qubit was not fulfilled, our analysis provides insights into charge decoherence mechanisms relevant also for other qubits.

中文翻译：

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具有可调相干的三重量子点中的电荷量子位

可以调整三重量子点中单个电子的能量分布，以使基态和激发态之间的能量分离成为相关栅极电压的平坦函数。这些所谓的最佳点对于电荷相干性是有益的，因为由栅极电压或周围电荷起伏器的小波动引起的去相干效应被最小化。我们为三重量子点电荷量子比特提出了一个新的工作点，即所谓的$C{问}_3$-qubit，具有三阶最佳点。我们显示了在频率可调高阻抗SQUID阵列谐振器中量子位与单光子的强耦合。在色散状态下，我们研究拟议工作点附近的量子位线宽。与对更高阶最佳点的期望相反，我们找到了线宽的局部最大值。我们发现这是由于在建议的工作点处四极失谐轴上的噪声的贡献不可忽略而导致的。尽管没有实现低退相干电荷量子位的最初动机，但我们的分析提供了与其他量子位相关的电荷退相干机制的见识。