  Solid-state quantum computer architectures with qubits encoded using single
atoms are now feasible given recent advances in atomic doping of
semiconductors. Here we present a charge qubit consisting of two dopant atoms
in a semiconductor crystal, one of which is singly ionised. Surface electrodes
control the qubit and a radio-frequency single electron transistor provides
fast readout. The calculated single gate times, of order 50ps or less, are much
shorter than the expected decoherence time. We propose universal one- and
two-qubit gate operations for this system and discuss prospects for fabrication
and scale up.
