  Coherent Tunneling Adiabatic Passage (CTAP) has been proposed as a long-range
physical qubit transport mechanism in solid-state quantum computing
architectures. Although the mechanism can be implemented in either a chain of
quantum dots or donors, a 1D chain of donors in Si is of particular interest
due to the natural confining potential of donors that can in principle help
reduce the gate densities in solid-state quantum computing architectures. Using
detailed atomistic modeling, we investigate CTAP in a more realistic triple
donor system in the presence of inevitable fabrication imperfections. In
particular, we investigate how an adiabatic pathway for CTAP is affected by
donor misplacements, and propose schemes to correct for such errors. We also
investigate the sensitivity of the adiabatic path to gate voltage fluctuations.
The tight-binding based atomistic treatment of straggle used here may benefit
understanding of other donor nanostructures, such as donor-based charge and
spin qubits. Finally, we derive an effective 3 \times 3 model of CTAP that
accurately resembles the voltage tuned lowest energy states of the
multi-million atom tight-binding simulations, and provides a translation
between intensive atomistic Hamiltonians and simplified effective Hamiltonians
while retaining the relevant atomic-scale information. This method can help
characterize multi-donor experimental structures quickly and accurately even in
the presence of imperfections, overcoming some of the numeric intractabilities
of finding optimal eigenstates for non-ideal donor placements.
