Origin of enhanced frequency noise and distorted Chevron patterns

Identify the physical origin of the enhanced resonance-frequency noise, shortened inhomogeneous dephasing time, and distorted Rabi-Chevron patterns observed near the spin-valley hotspot in the intrinsic-spin-orbit-coupling-driven Si/SiGe qubit.

Background

The measured T_2* depends more weakly on hotspot detuning than expected from a model in which gate-equivalent charge noise is the sole source of dephasing. An additional fitted frequency-noise contribution is needed, but its magnitude is much larger than expected from the measured gate-voltage susceptibility.

Near the hotspot, Rabi-Chevron patterns become irregular and can exhibit abrupt jumps, discontinuities, and loss of the characteristic Chevron structure. The authors discuss nuclear-spin-mediated feedback, dynamic nuclear polarization, and electron-mediated nuclear flip-flops as possible explanations, while noting that charge noise may also contribute. The available measurements do not determine the responsible mechanism.

References

In addition, the measured $T_2*$ is shorter than expected for isotopically purified silicon, and the observed deformed Chevron patterns point to a significant noise source whose origin ultimately remains unresolved.

— 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 4.2, “Qubit coherence”; Section 5, “Conclusion”