Electric-Dipole Spin Resonance for Light-Holes in Germanium Quantum Well

Holes in Germanium (Ge) have recently attracted a great deal of attention due to their numerous attractive properties for the realization of quantum processors. Notably, they have proven to be extremely effective for encoding and manipulating quantum information. In contrast to electrons, holes in Ge are significantly less affected by hyperfine interactions with the surrounding crystal nuclei, which allows for longer relaxation and dephasing times. Moreover, holes are more affected than electrons by the large spin-orbit coupling in Ge, enabling fast all-electrical spin-manipulation schemes such as electric-dipole spin resonance (EDSR).<br/>EDSR has been demonstrated in Ge quantum wells, nanowires, and hut wires, and is especially convenient in gate-defined quantum dots because the driving field can be applied through the same gates that define the dots. Previous studies of EDSR on holes in two-dimensional quantum dots focused mainly on heavy holes, because their large out-of-plane effective mass usually favors them as the ground state. However, a novel type of two-dimensional hole gas consisting of light holes can be achieved by applying a significant amount of tensile train (&gt;1%) to the quantum well. A light-hole based quantum device also benefits of a more efficient transfer of quantum information from a photon to a spin.<br/>This work discusses the properties of light-hole spins in highly tensile strained Ge quantum wells, whose strain is caused by coherent growth onto highly relaxed germanium-tin buffer layers. A perturbative framework describing Rabi-flopping of a light hole spin in a parabolic isotropic gate-defined quantum dot is derived from 8-band k.p theory. A quantitative analysis of the Rabi frequency versus physical parameters shows that light-holes can be manipulated 2 to 3 orders of magnitude faster than heavy-holes. The framework explicitly takes in account the spread of the envelope wavefunctions into the barriers and is suitable for any out-of-plane confining potential. Ongoing work focuses on describing rabi-flopping in different magnetic field configurations, while incorporating the effects of spin-relaxation to the Rabi frequencies.