Mapping of Valley Splitting Variations in Si/SiGe via Coherent Shuttling of Electron Spin Qubits

Valley splitting depends on the atomistic details of the Si/SiGe heterostructure [1]. Lateral variations and in particular low valley splittings lead to spin dephasing and qubit decoherence. This is problematic for large arrays of static qubits and for long-range spin qubit shuttling [2]. For progression in scaling qubit chips, the local valley splitting of Si/SiGe heterostructures needs to be enhanced and their lateral distribution benchmarked.

Building upon our previous work [3], we explored a state-of-art ²⁸Si/SiGe heterostructure [4] using conveyor-mode coherent electron shuttling [5]. We have extended the mapping of valley splitting to a large area of 400 nm by 40 nm. Compared to [3], our measurements reveal larger valley splittings up to 200 µeV, but also significant lateral variations. 2800 recorded and partly correlated valley splitting values support the theory of alloy disorder at the Si/SiGe interface governing the valley splitting [1]. In particular, we find several spots with valley splittings smaller than 5 µeV.

These results underline the reproducibility of this method [3]. Our findings support strategies to mitigate valley-induced decoherence in scalable quantum computing architectures [6].

[1] Klos ea., Adv. Sci. 2407442 (2024)

[2] Langrock ea., PRX Quantum 4 (2023)

[3] Volmer ea., npj Quantum Inf. 10, 61 (2024)

[4] Wuetz ea., Nat. Commun. 14, 1385 (2023)

[5] Struck ea., Nat. Commun. 15, 1325 (2024)

[6] Losert ea., arXiv 2405.01832 (2024)