Fast and tunable Rabi oscillations of hole spins in Ge/Si nanowires

The strong confinement of holes to one dimension in Ge/Si core/shell nanowires gives rise to direct Rashba spin-orbit interaction which is predicted to be both very strong and electric field tunable. The full electrical control promises to switch the spin-orbit interaction either on, enabling fast qubit operations, or off, protecting the spin state in order to achieve an increased qubit lifetime. These properties make Ge/Si nanowires a very promising system for the implementation of hole spin qubits. Recent experiments have found a spin-orbit interaction length on the order of only 30 nm, paving the way to very fast spin manipulation by electric dipole spin resonance. This mechanism allows us to drive very fast Rabi oscillations above 400 MHz at a Larmor frequency of 3.4 GHz, thus entering the strong driving regime. Furthermore, we find the Rabi oscillation frequency as well as the g-factor to be highly tunable with small changes in gate voltages, indicating the feasibility to electrically control the spin-orbit interaction strength.