Statistical characterization of valley coupling in Si/SiGe quantum dots via g-factor measurements

The presence of low-energy valley excitations in Si/SiGe heterostructures often leads to failed spin qubits. Therefore, it is necessary to both engineer enhanced valley coupling and develop protocols for characterizing the valley coupling. Here, we show that a naive fitting of valley splitting data often leads to a dramatic overestimation of the deterministic component of the valley coupling. We find that knowledge of the valley phase in addition to the valley splitting avoids this issue. Motivated by this finding, we propose a novel method for probing the valley phase landscape across the quantum well through g-factor measurements. A key calibration step in this method is measuring the g-factor in a loop enclosing a valley vortex, where the valley splitting vanishes, to establish the relationship between the g-factor and valley phase. Our scheme provides a robust new tool for characterizing spatially varying valley coupling distributions in Si/SiGe.