Minimal double quantum dot in ZnO*

Minimal double quantum dots (DQDs) are prepared in ZnO, a wide band-gap semiconductor matrix. The QDQs are of the atomic scale that is difficult to achieve for for conventional microfabrication techniques. It is comprised of a pair of strongly coupled donor atoms that can each be doubly charged. Using scanning tunneling microscopy and spectroscopy, we mapped out the donor excitation diagram of this system which mimicks the charge stability diagram observed in transport measurements of DQDs. The charge and spin degrees of freedom of the minimal DQDs may also be used as quantum bits. The DQDs can be prepared in the quantum entangled state, e.g., in a Bell state. The results open an intriguing perspective for quantum electronics with atomic-scale structures.