Three-electron bonding and entanglement in single and molecular quantum dots

The study of three-electron quantum dots (QDs) is interesting in several ways. First, it was demonstrated\footnote{C. Ellenberger, T. Ihn, C. Yannouleas, U. Landman, K. Ensslin, D. Driscoll, and A.C. Gossard, Phys. Rev. Lett. {\bf 96}, 126806 (2006).} recently that detailed ground-state and excited spectra of few-electron elliptic QDs can be measured as a function of the externally applied magnetic field. Second, three-qubit electron spin devices are expected to exhibit enhanced efficiency for quantum computing purposes compared to single-qubit and two-qubit gates. We carry out exact diagonalization (EXD) studies for a three-electron single QD and for a wide range of anisotropies. We analyze the properties of the EXD many-body wave functions with respect to electron localization in a linear geometry, as well as to generation of model quantum entangled states that are often employed in the theory of quantum computing. We further examine three-electron bonding and entanglement in the case of a double quantum dot.