Measurement of Tunnel Coupling in a Si Double Quantum dot Based on Charge Sensing

In Si quantum dots, the valley degree of freedom, in particular the generally small valley splitting and the dot-dependent valley-orbit phase, adds complexities to the low-energy electron dynamics. In particular, tunnel coupling, a key knob in charge and spin qubit manipulations, is strongly dependent on the valley-orbit coupling in a Si double dot. Here we propose a four-level model that incorporates excited valley states to extract ground-state tunnel coupling information for a Si double quantum dot. This scheme is based on a charge-sensing measurement on a double dot in equilibrium, as proposed in the widely used protocol for a GaAs double dot [DiCarlo et al., Phys. Rev. Lett. 92, 226801 (2004)]. Our theory helps determine both intra- and intervalley tunnel coupling with high accuracy, and is robust against uncertainties in system parameters such as valley splittings in the individual quantum dots.