  The energies of valley-orbit states in silicon quantum dots are determined by
an as yet poorly understood interplay between interface roughness, orbital
confinement, and electron interactions. Here, we report measurements of one-
and two-electron valley-orbit state energies as the dot potential is modified
by changing gate voltages, and we calculate these same energies using full
configuration interaction calculations. The results enable an understanding of
the interplay between the physical contributions and enable a new probe of the
quantum well interface.
