Origins and enhancement of hole spin-mixing in InAs quantum dot molecules

Hole spins in self-assembled InAs quantum dots molecules (QDMs) are a strong candidate for qubit architecture due to their all-optical operation and enhanced tunability via voltage bias across the two dots. In order to capitalize on the all-optical operation and the enhanced tunability, we exploit the spin-mixing provided by the “molecule-like” coupled hole states. Through an atomistic tight-binding model and perturbative field analysis, we discuss the origin of spin-mixing and compare it with previous models using effective Hamiltonians. We then apply our understanding to the case where the GaAs inter-dot region is alloyed with a dilute amount of Bi. Replacing As atoms with the heavier Bi atoms enhances spin-orbit effects and, in turn, increases spin-mixing. However, it complicates the model, as atomistic alloying effects have to be considered, something not explored by prior models. Finally, we briefly discuss the practical operation of InAs/GaBiAs QDM qubits with the enhanced spin-mixing.