  We apply the full power of modern electronic band structure engineering and
epitaxial heterostructures to design a transistor that can sense and control a
single donor electron spin. Spin resonance transistors may form the
technological basis for quantum information processing. One and two qubit
operations are performed by applying a gate bias. The bias electric field pulls
the electron wave function away from the dopant ion into layers of different
alloy composition. Owing to the variation of the g-factor (Si:g=1.995,
Ge:g=1.563), this displacement changes the spin Zeeman energy, allowing
single-qubit operations. By displacing the electron even further, the overlap
with neighboring qubits is affected, which allows two-qubit operations. Certain
Silicon-Germanium alloys allow a qubit spacing as large as 200 nm, which is
well within the capabilities of current lithographic techniques. We discuss
manufacturing limitations and issues regarding scaling up to a large size
computer.
