Sources of Dephasing in Si/SiGe Quantum Dots

We utilize a sensor dot positioned near the Si/SiGe quantum dot (QD) to probe the Hz range of the power spectral density (PSD) of electrostatic charge noise. We use data from Ramsey and CPMG experiments to probe sub-mHz and sub-KHz PSD of frequency detuning noise, allowing us to estimate the dominance of charge noise. Discrepancies between charge noise characterizations and frequency detuning noise measurements indicate that other noise sources such as hyperfine interactions could play a considerable role in qubit dephasing. To remove the effect of spatial-separation of the sensor dot from the QD, we measure the QD chemical potential after each Ramsey shot. We see little time-correlation between the chemical potential and frequency detuning, indicating that charge noise may not be the dominant source of dephasing in this device, and we may need better techniques for budgeting noise considerations.