Valley and Qubit States in a Si/SiGe Quantum Dot with a Spatially-Modulated Ge Concentration

Gate-defined quantum dots in silicon/silicon-germanium are widely regarded as a promising platform for scalable quantum computing. They also have particularly rich materials physics, because of the silicon band structure, which in bulk has six equivalent conduction band minima, or valleys. In strained-silicon quantum dots, two of these valleys are lower in energy than the other four. The energy difference between these two low-lying states is known as the valley splitting, and it plays an essential role in readout of many quantum dot spin qubits. I will discuss new types of structures that incorporate germanium with a spatially oscillating concentration directly in the quantum well, leading to an increased splitting between these two low-lying valleys in silicon. This physics has important consequences for the development of qubits in silicon/silicon-germanium quantum dots.