  The electrical control of single spin qubits based on semiconductor quantum
dots is of great interest for scalable quantum computing since electric fields
provide an alternative mechanism for qubit control compared with magnetic
fields and can also be easier to produce. Here we outline the mechanism for a
drastic enhancement in the electrically-driven spin rotation frequency for
silicon quantum dot qubits in the presence of a step at a hetero-interface. The
enhancement is due to the strong coupling between the ground and excited states
which occurs when the electron wave-function overcomes the potential barrier
induced by the interface step. We theoretically calculate single qubit gate
times of 170ns for a quantum dot confined at a silicon/silicon-dioxide
interface. The engineering of such steps could be used to achieve fast
electrical rotation and entanglement of spin qubits despite the weak spin-orbit
coupling in silicon.
