We calculate the electron exchange coupling for a phosphorus donor pair insilicon perturbed by a J-gate potential and the boundary effects of the siliconhost geometry. In addition to the electron-electron exchange interaction wealso calculate the contact hyperfine interaction between the donor nucleus andelectron as a function of the varying experimental conditions. Donorseparation, depth of the P nuclei below the silicon oxide layer and J-gatevoltage become decisive factors in determining the strength of both theexchange coupling and the hyperfine interaction - both crucial components forqubit operations in the Kane quantum computer. These calculations wereperformed using an anisotropic effective-mass Hamiltonian approach. Thebehaviour of the donor exchange coupling as a function of the device parametersvaried provides relevant information for the experimental design of thesedevices.
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