Atomic fluctuations lifting the energy degeneracy in Si/SiGe quantum dots
Abstract
Electron spins in Si/SiGe quantum wells suffer from nearly degenerate conduction band valleys, which compete with the spin degree of freedom in the formation of qubits. Despite attempts to enhance the valley energy splitting deterministically, by engineering a sharp interface, valley splitting fluctuations remain a serious problem for qubit uniformity, needed to scale up to large quantum processors. Here, we elucidate and statistically predict the valley splitting by the holistic integration of 3D atomic-level properties, theory and transport. We find that the concentration fluctuations of Si and Ge atoms within the 3D landscape of Si/SiGe interfaces can explain the observed large spread of valley splitting from measurements on many quantum dot devices. Against the prevailing belief, we propose to boost these random alloy composition fluctuations by incorporating Ge atoms in the Si quantum well to statistically enhance valley splitting. Spin qubits in Si/SiGe quantum dots suffer from variability in the valley splitting which will hinder device scalability. Here, by using 3D atomic characterization, the authors explain this variability by random Si and Ge atomic fluctuations and propose a strategy to statistically enhance the valley splitting
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