  Interface disorder and its effect on the valley degeneracy of the conduction
band edge remains among the greatest theoretical challenges for understanding
the operation of spin qubits in silicon. Here, we investigate a
counterintuitive effect occurring at Si/SiO2 interfaces. By applying tight
binding methods, we show that intrinsic interface states can hybridize with
conventional valley states, leading to a large ground state energy gap. The
effects of hybridization have not previously been explored in details for
valley splitting. We find that valley splitting is enhanced in the presence of
disordered chemical bonds, in agreement with recent experiments.
