In multivalley semiconductors, the valley degree of freedom can be potentially used to store, manipulate, and read quantum information, but its control remains challenging. The valleys in bilayer graphene can be addressed by a perpendicular magnetic field which couples by the valley $g$ factor $g_v$. However, control over $g_v$ has not been demonstrated yet. We experimentally determine the energy spectrum of a quantum point contact realized by a suitable gate geometry in bilayer graphene. Using finite bias spectroscopy, we measure the energy scales arising from the lateral confinement as well as the Zeeman splitting and find a spin $g$ factor $g_s\sim 2$. $g_v$ can be tuned by a factor of 3 using vertical electric fields, $g_v\sim 40–120$. The results are quantitatively explained by a calculation considering topological magnetic moment and its dependence on confinement and the vertical displacement field.

中文翻译：

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双层石墨烯量子点接触中的拓扑轨道磁矩可调谐谷裂。

在多谷半导体中，谷自由度可以潜在地用于存储，操纵和读取量子信息，但是其控制仍然具有挑战性。双层石墨烯中的谷可以通过与谷耦合的垂直磁场来寻址$G$ 因子 $G_v$。但是，控制$G_v$尚未被证明。我们实验确定由双层石墨烯中合适的栅极几何结构实现的量子点接触的能谱。使用有限偏差光谱法，我们测量了由横向约束以及塞曼分裂产生的能级，并找到了一个自旋$G$ 因子 $G_s〜2$。 $G_v$ 可以使用垂直电场将其调谐3倍， $G_v〜40–120$。通过考虑拓扑磁矩及其对约束和垂直位移场的依赖关系的计算来定量解释结果。