Heavy Hole vs. Light Hole Spin Qubits: A Strain-Driven Study of SiGe/Ge and GeSn/Ge

Abstract: This work investigates and compares the impact of strain on heavy hole (HH) spin qubits in SiGe/Ge and light hole (LH) spin qubits in GeSn/Ge heterostructures, focusing on energy states, g-factor, Rabi frequency, spin relaxation, and dephasing times. By exploring the distinct properties of HH and LH spin qubits under strain, we demonstrate how strain serves as a tunable parameter to optimize qubit performance. The study highlights that LH spin qubits in Ge quantum dots exhibit lower relaxation rates and higher Rabi frequencies, offering significant advantages for addressing current challenges in gate-defined spin qubits. A significant difference is observed in the g-factor anisotropy, where for HHs the out-of-plane g-factor is larger than the in-plane g-factor, whereas for LHs, the in-plane g-factor dominates both in GeSn/Ge and SiGe/Ge quantum dots. This comparative analysis provides a deeper understanding of HH and LH spin dynamics, advancing the development of scalable quantum technologies based on strained Ge systems.