  Recent experiments on silicon nanostructures have seen breakthroughs toward
scalable, long-lived quantum information processing. The valley degree of
freedom plays a fundamental role in these devices, and the two lowest-energy
electronic states of a silicon quantum dot can form a valley qubit. In this
work, we show that a single-atom high step at the silicon/barrier interface
induces a strong interaction of the qubit and in-plane electric fields, and
analyze the consequences of this enhanced interaction on the dynamics of the
qubit. The charge densities of the qubit states are deformed differently by the
interface step, allowing non-demolition qubit readout via valley-to-charge
conversion. A gate-induced in-plane electric field together with the interface
step enables fast control of the valley qubit via electrically driven valley
resonance. We calculate single- and two-qubit gate times, as well as relaxation
and dephasing times, and present predictions for the parameter range where the
gate times can be much shorter than the relaxation time and dephasing is
reduced.
