Quantum dot molecules with control of two-electron orbital configuration

Spin-photon interfaces based on III-V semiconductor quantum dots (QDs) are a promising platform for quantum technologies, combining strong light-matter interactions, robust spin-photon selection rules, and ease of integration into optoelectronic devices. It has been demonstrated that a QD hosting a single spin can be used to generate a string of entnagled photons, a linear cluster state. Tunnel-coupled pairs of QDs, known as QD molecules (QDMs), can host two electron spins, which may be used to generate multi-dimensional photonic cluster states, an important resource for quantum information applications. In our experiments, we study a single QDM embedded in a p-i-n diode structure. Using an optical charging protocol, we can deterministically prepare our QDM with two electrons and subsequently tune their orbtial configuration into resonance with both QDs. Under optical excitation, the two-electron state exhibits intriguing features, such as spin pumping from singlet to triplet states and spin relaxation times that strongly depend on the applied electric field.