  The use of buried dopants to construct quantum-dot cellular automata is
investigated as an alternative to conventional electronic devices for
information transport and elementary computation. This provides a limit in
terms of miniaturisation for this type of system as each potential well is
formed by a single dopant atom. As an example, phosphorous donors in silicon
are found to have good energy level separation with incoherent switching times
of the order of microseconds. However, we also illustrate the possibility of
ultra-fast quantum coherent switching via adiabatic evolution. The switching
speeds are numerically calculated and found to be 10's of picoseconds or less
for a single cell. The effect of decoherence is also simulated in the form of a
dephasing process and limits are estimated for operation with finite dephasing.
The advantages and limitations of this scheme over the more conventional
quantum-dot based scheme are discussed. The use of a buried donor cellular
automata system is also discussed as an architecture for testing several
aspects of buried donor based quantum computing schemes.
