Fully tunable strong spin orbit interactions in light hole germanium quantum channels

Spin-orbit interaction is a fundamental component for electrically driven spin qubits and hybrid superconducting-semiconducting systems. In particular, Rashba spin-orbit interaction is a key mechanism enabling all-electrical spin manipulation schemes. However, in common planar systems, Rashba interaction is weak because of the small mixing between heavy-holes and light-holes, and instead relies on complex strain and interface phenomena that are hard to reliably harness in experiment. Here, MOS-like epitaxial germanium on relaxed germanium-tin is introduced and shown to exhibit an inherently large, highly gate-tunable Rashba interaction that is compatible with both spin qubits and hybrid devices. This large Rashba interaction is a consequence of the light-hole-like ground state in germanium. Notably, the built-in asymmetry of the device causes the Rashba interaction to completely vanish at specific gate fields, effectively acting as an on/off spin-orbit interaction switch. The light-hole g-tensor is less anisotropic than that of state-of-the-art heavy-hole qubits, alleviating precise magnetic field orientation requirements. The large in-plane g-factor also facilitates the integration of superconductors. Moreover, the out-of-plane g-factor is strongly gate-tunable and completely vanishes at specific gate fields. Thus, this material system combines the large Rashba interaction with the scalability of planar devices, paving the way towards robust spin qubit applications and enabling access to regimes of complex spin physics.