Spatial Triangulation and Characterization of Two-Level Fluctuators in Si/SiGe Quantum Dot Devices

Charge noise limits the fidelities of gate operations in silicon spin qubits and is often modeled as arising due to an ensemble of Two-Level Fluctuators (TLFs). To mitigate this noise, it is important to identify the microscopic origins and spatial locations of these TLFs. In this study, we simulate recent experimental data [F. Ye, et. al., arXiv:2401.14541], which measures the chemical potential shift of a charge sensing dot caused by a fluctuating TLF and this TLF’s state as a function of gate voltages, to determine the TLF’s location.

By varying the TLF’s position, orientation and dipole moment in the simulated device, we can identify TLF locations and configurations that agree with measurements of the gate-referred voltage dipole and the different gates’ lever arms of the TLF detuning. These potential locations and configurations can be further narrowed down using experimentally determined constraints on the electric dipole moments of defects in the device materials.

Additionally, our simulations help elucidate the TLF’s origin. A TLF resulting from a defect acting as a charge trap differs from one resulting from a bistable defect switching between different configurations, while maintaining the same charge state. Our simulations help eliminate certain models for this TLF, thereby helping narrow down both the defect identity and its location.