Hole Spins in Ge/Si Nanowires*

Ge/Si core/shell nanowires form a promising platform to implement a unique kind of spin qubit that is highly controllable and highly coherent. Both silicon and germanium can be isotopically purified to contain virtually no non-zero nuclear spins. Moreover, hole spins have due to their p-wave character zero contact-hyperfine interaction with any nuclear spins. These factors promise high coherence times of qubits defined by single holes in Ge/Si nanowires.
Furthermore, spin-orbit interaction is predicted to be especially large and electrically tunable for hole spins in Ge/Si nanowires. However, so far a thorough characterization of this spin-orbit interaction has not been made. We electrostatically tune hole quantum dots of variable length to very low hole occupation numbers and study their excited state spectrum, allowing us to make comparisons to theoretical predictions on the nature and strength of the spin-orbit interaction. In a next step, we intend to implement spin manipulation via the spin-orbit interaction.