We analyze several important issues for the single- and two-qubit operations in Si quantum computer architectures involving P donors close to a $\mathrm{Si}{\mathrm{O}}_2$ interface. For a single donor, we investigate the donor-bound electron manipulation (i.e., one-qubit operation) between the donor and the interface by electric and magnetic fields. We establish conditions to keep a donor-bound state at the interface in the absence of local surface gates and estimate the maximum planar density of donors allowed to avoid the formation of a two-dimensional electron gas at the interface. We also calculate the times involved in single electron shuttling between the donor and the interface. For a donor pair we find that, under certain conditions, the exchange coupling (i.e., two-qubit operation) between the respective electron pair at the interface may be of the same order of magnitude as the coupling in GaAs-based two-electron double quantum dots, where coherent spin manipulation and control have recently been demonstrated (for example, for donors $\sim 10\mathrm{nm}$ below the interface and $\sim 40\mathrm{nm}$ apart, $J\sim {10}^{-4}\mathrm{meV}$), opening the perspective for similar experiments to be performed in Si.

• Received 3 December 2006

DOI:https://doi.org/10.1103/PhysRevB.75.125311