External field control of donor electron exchange at the Si/SiO2 interface

We analyze several important issues for the single- and two-qubit operations in Si quantum computer architectures involving P donors close to a SiO2 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 similar to 10 nm below the interface and similar to 40 nm apart, J similar to 10(-4) meV), opening the perspective for similar experiments to be performed in Si.