Valley-splitting mapping by conveyor-mode spin-coherent single electron shuttling

In Si/SiGe heterostructures, the low-lying excited valley state causes spin-dephasing for spin qubits. Coherent electron shuttling [1,2] may serve as a cornerstone for scaling spin qubits [3], offering spatial control over electrons, but is in itself prone to information loss at points of low valley splitting [4]. Hence, for characterizing and understanding the local variations in valley splitting across a Si/SiGe wafer, the valley splitting needs to be measured efficiently with high spatial and energy resolution.

Leveraging the spatial control granted by conveyor-mode spin-coherent electron shuttling [1], we map valley splittings at various positions in the shuttling path by detecting magnetic anticrossings of ground and excited valley states. Our new method has sub μeV energy accuracy and a lateral resolution limited by quantum dot size and potential disorder. In addition to shuttling, we orthogonally displace the shuttle path by 6 nm steps in order to gain a 2D valley splitting map of 210 nm by 18 nm size. Its correlation length is given by the dot size and its energy spectrum agrees well with magneto-spectroscopy data for the same wafer, which, however, requires approximately 100 times longer measurement time.