  The excitonic fine structure plays a key role for the quantum light generated
by semiconductor quantum dots, both for entangled photon pairs and single
photons. Controlling the excitonic fine structure has been demonstrated using
electric, magnetic, or strain fields, but not for quantum dots in optical
cavities, a key requirement to obtain high source efficiency and near-unity
photon indistinguishability. Here, we demonstrate the control of the fine
structure splitting for quantum dots embedded in micropillar cavities. We
propose a scheme based on remote electrical contacts connected to the pillar
cavity through narrow ridges. Numerical simulations show that such a geometry
allows for a three-dimensional control of the electrical field. We
experimentally demonstrate tuning and reproducible canceling of the fine
structure, a crucial step for the reproducibility of quantum light source
technology.
