Mechanism of the unexplained measurement background

Determine the physical origin of the fluctuating, drive-independent background that limits the visibility of singlet-triplet readout in the Si/SiGe double quantum dot and contributes to state-preparation-and-measurement errors.

Background

The readout procedure yields a visibility of approximately 20–30% together with a fluctuating background that is independent of the microwave drive. The authors compensate for slow contrast fluctuations by separately thresholding adequately chunked data, but the underlying mechanism remains undetermined.

Intervalley tunneling and a weak Zeeman gradient are proposed as possible contributors, but these are explicitly presented as speculation rather than an established explanation.

References

The exact origin of this background remains unclear. We speculate that intervalley tunneling and a weak Zeeman gradient contribute to overall state-preparation-and-measurement errors.

— Enhanced intrinsic spin-orbit driving of a Loss-DiVincenzo qubit near the spin-valley hotspot in Si/SiGe  (2608.23246 - Willmes et al., 24 Aug 2026) in Section 2, “Experiment”