Ultrafast hole spin qubit with spin-orbit switch*

Hole spins in Ge/Si core/shell nanowires hold great promise as spin qubits with all-electrical control, taking advantage of the very strong direct Rashba spin-orbit interaction (SOI) for ultrafast electric dipole spin resonance. This SOI arises from the strong 1D confinement in the nanowire and provides full electrical control over its strength, thus making possible the implementation of a spin-orbit switch. Such switch allows to toggle the SOI-strength between a 'Control' state, with strong SOI for fast qubit operations, and an 'Idle' state, with weaker SOI for increased qubit lifetime.
Here [1], we demonstrate the basics of this qubit operation scheme and find the Rabi oscillation frequency as well as the g-factor to be highly tunable with small changes in gate voltages. A 7-fold variability of the Rabi frequency and a corresponding increase of qubit coherence at slower Rabi frequencies establish the feasibility of a spin-orbit switch in this material system. Furthermore, tuning to an optimal gate configuration allows us to drive ultrafast Rabi oscillations above 400 MHz at a Larmor frequency of 3.4 GHz, thus approaching the strong driving regime.
[1] arXiv:2006.11175