title: Exchange in silicon-based quantum computer architecture.
abstract: The silicon-based quantum computer proposal has been one of the actively pursued ideas during the past three years. Here we calculate the donor electron exchange in silicon and germanium, and demonstrate an atomic-scale challenge for quantum computing in Si (and Ge), as the six (four) conduction-band minima in Si (Ge) lead to intervalley electronic interference, generating strong oscillations in the exchange splitting of two-donor two-electron states. Donor positioning with atomic-scale precision within the unit cell thus becomes a decisive factor in determining the strength of the exchange coupling-a fundamental ingredient for two-qubit operations in a silicon-based quantum computer.
authors.affiliation: Department of Physics, University of Maryland, College Park, Maryland 20742-4111 and Instituto de Física, Universidade Federal do Rio de Janeiro, 21945 Rio de Janeiro, Brazil.
authors.forename: Belita
authors.initials: B
authors.lastname: Koiller
authors.forename: Xuedong
authors.initials: X
authors.lastname: Hu
authors.forename: S
authors.initials: S
authors.lastname: Das Sarma