Probing disorder in semiconductor qubit devices with device simulations

Gate-defined quantum dots in silicon and germanium have shown great potential as a platform for scalable quantum computing systems and recent progress in the field suggests that demonstrations of large numbers of qubits will come in the near future. Fundamental limitations on qubit gate fidelities are still likely to be at the materials and device level, however, and charge noise and variations in valley splitting are important examples of temporal and spatial disorder that need better understanding and characterization. In this talk, I will show how high precision simulations of realistic devices can be used in conjunction with experimental data to probe the spatial location of charge fluctuators and design new devices that probe the variation of valley splitting in semiconductor heterostructures. In the first part of the talk, I will describe how experimental data can be used in conjunction with device simulations to triangulate the location of individual charge fluctuators. The procedure we develop is quite general and could be applied to data from any spin qubit device. In the second part of the talk, I will describe how device simulations can be used to aid in the design of a scanning gate microscope for probing material properties such as valley splitting [1]. We have been able to identify the parameters for such a microscope that indicate feasibility of the design and have taken preliminary steps to understand how subsequent simulations could be used in conjunction with experimental data to understand the connection between material structure and measured valley splitting. Finally, we speculate on how the scanning gate microscope could also be used as a charge noise sensor and allow for exquisite triangulation of charge fluctuators in spin qubit devices.