Quantum dots in silicon are a promising architecture for semiconductor quantum computing due to a high degree of electric control and compatibility with existing silicon fabrication processes. Although electron charge and spin are prominent methods for encoding the qubit state, valley states in silicon can also store quantum information via valley-orbit coupling with protection against charge noise. By observing coherent oscillations between valley states in a Si/SiGe double quantum dot device tuned to the two-electron charge configuration, we measure the valley energy splitting in both quantum dots individually. We further demonstrate two-axis quantum control of the valley qubit using gated pulse sequences with X and Z rotations occurring within a fast operation time of 300 ps. This control is used to completely map out the surface of the Bloch sphere in a single phase-space plot that is subsequently used for state and process tomography.

由于高度的电控制以及与现有硅制造工艺的兼容性，硅中的量子点是半导体量子计算的有前途的体系结构。尽管电子电荷和自旋是编码量子位态的重要方法，但是硅中的谷态也可以通过谷-轨耦合存储量子信息，并具有防止电荷噪声的作用。通过观察调谐到双电子电荷配置的Si / SiGe双量子点器件中谷状态之间的相干振荡，我们分别测量了两个量子点中的谷能量分裂。我们进一步演示了使用在300 ps的快速操作时间内发生X和Z旋转的门控脉冲序列对谷底量子位的两轴量子控制。