Fast EDSR in a disordered Si/SiGe Wiggle Well with strong spin-orbit coupling

Silicon-based spin qubits commonly use micromagnets to create an artificial spin-orbit coupling (SOC) for Electric Dipole Spin Resonance (EDSR); however, this approach faces scalability challenges. Previously, it has been shown that the Wiggle Well may sufficiently enhance the otherwise weak SOC in the conduction band of Si, allowing for implementation of a strong micromagnet-free EDSR protocol; preliminary calculations indicate that Rabi frequencies exceeding 500 MHz/T may be possible [1]. However, SiGe random-alloy disorder causes spatial variations that have not been fully accounted for in these calculations.

In this work, we show that alloy disorder gives rise to two main effects relevant for EDSR: the generation of a strong valley dipole (providing an additional EDSR mechanism), and randomization of valley parameters (providing a position-dependent Rabi frequency). Specifically, we show that the Rabi frequency depends on the phase differences between the valley-coupling and SOC matrix elements. We also show that the valley-dipole-assisted EDSR is enhanced in regions where the valley splitting is low. Finally, we evaluate the dephasing rates due to charge noise and identify ‘sweet spots’ for single-qubit gate operations, where dephasing rates are suppressed.

[1] Woods, B. D., Eriksson, M. A., Joynt, R., & Friesen, M. (2023). Spin-orbit enhancement in Si/SiGe heterostructures with oscillating Ge concentration. Physical Review B, 107(3), 035418. https://doi.org/10.1103/PhysRevB.107.035418