  As an ensemble scheme of solid-state NMR quantum computers the extension of
Kane's many-qubits silicon scheme based on the array of 31 P donor atoms are
spaced lengthwise of the strip gates is considered. The possible planar
topology of such ensemble quantum computer is suggested. The estimation of the
output NMR signal was performed and it was shown that for the number N>=10^5 of
ensemble elements involving L~10^3 qubits each, the standard NMR methods are
usable.
  As main mechanisms of decoherence for low temperature (<0.1K), the adiabatic
processes of random modulation of qubit resonance frequency determined by
secular part of nuclear spin hyperfine interaction with electron magnetic
moment of basic atom and dipole-dipole interaction with nuclear moments of
neighboring impurity atoms was considered, It was made estimations of allowed
concentrations of magnetic impurities and of spin temperature whereby the
required decoherence suppression is obtained. Semiclassical decoherence model
of two qubit entangled states is also presented.
  As another variant of the solid-state ensemble quantum computer, the gateless
architecture of cellular-automaton with antiferromagnetically ordered electron
spins is also discussed here.
