Tunnel coupling measurement of Si quantum dots based on charge sensing

Tunnel coupling in a double quantum dot (DQD) is one of the most important parameters. It determines the charge and spin dynamics, and is essential to many applications in quantum information processing. The most widely used approach to detect tunnel coupling of a GaAs DQDs is based on the charge sensing technique proposed by DiCarlo et. al. [PRL 92, 226801 (2004)]. However, this method can result in significant errors when it is applied directly to a Si DQD since the Si DQD has an extra valley degree of freedom. Here we propose an updated theory to account for the valley dynamics and provide a more accurate description of the tunnel coupling measurement in Si QDs.

We develop a fitting procedure based on a 4-level model, which allows not only measurement of the ground state tunnel splitting, but also that for excited valley states. When applied to measurements on a Si/SiGe triple-dot sample, we observe an average of 46% difference in the fitting results compared to the previous 2-level model. We analyze the fitting performance and robustness of both models in various conditions and identify situations when the 4-level theory is required to obtain accurate results.