  A gate electric field has a small but non-negligible effect on the phase of
the valley-orbit coupling in Si quantum dots. Finite interdot tunneling between
valley eigenstates in a double quantum dot is enabled by a small difference in
the phase of the valley-orbit coupling between the two dots, and it in turn
allows controllable rotations of two-dot valley eigenstates at a level
anticrossing. We present a comprehensive analytical discussion of this process,
with estimates for realistic structures.
