Design and Simulation of a Back-Gated Si/SiGe Double Quantum Well for Valley Splitting Mapping

Spatial variations in valley splitting present a challenge for realizing high-fidelity Si/SiGe quantum dot qubits, as low-lying valley states can lead to leakage outside the logical qubit subspace. Operating qubits in regions of large valley splitting mitigates this problem, but the spatial variability across a device makes pre-characterization desirable. We present simulation results for a proposed back-gated Si/SiGe Double Quantum Well (DQW) device designed for spatial mapping of valley splitting using a Scanning Gate Microscope (SGM). In this scheme, the lower quantum well serves as an electron reservoir, while the upper well hosts an SGM-induced quantum dot. The SGM tip integrates a resonator that couples to quantum dot transitions, enabling pulsed-gate spectroscopy of the valley splitting. We systematically optimize device parameters—including inter-well spacing, well depth, and well width—to ensure sufficient tunnel coupling between the dot and the reservoir. This DQW–SGM platform provides a new pathway for spatially resolved mapping of valley splitting in Si/SiGe heterostructures prior to gate deposition, enabling deterministic placement of quantum dots in regions with large valley splitting.