  Doped Si is a promising candidate for quantum computing due to its
scalability properties, long spin coherence times, and the astonishing progress
on Si technology and miniaturization in the last few decades. This proposal for
a quantum computer ultimately relies on the quantum control of electrons bound
to donors near a Si/barrier (e.g. SiO2) interface. We address here several
important issues and define critical parameters that establish the conditions
that allow the manipulation of donor electrons in Si by means of external
electric and magnetic fields.
