Strain engineering hole state g-factors in parabolic Ge/SiGe quantum dots

Hole spins in Ge quantum dots have emerged as a promising platform for semiconductor spin qubits. Among many positive attributes is a strong spin-orbit coupling allowing for an all-electrical spin control. Through the spin-orbit interaction, the hole state's spin behavior is coupled to the strain sensitive orbital structure. In quantum wells with a parabolic alloy profile along the growth axis, there exists a region of the well with transverse compressive strain. This is opposed to the tensile strain in square wells. Using a valence force field and tight-binding model, we demonstrate the effect of strain on spin-orbit dependent properties of the hole state, such as g-factor. We show that by moving the wavefunction with an electrical bias, we can select the desired strain and actively tune the hole states. We further discus other aspects of parabolic quantum wells, such as the significantly larger well width, and the benefits thereof for scalable qubit platforms.