  The bandstructure of bulk silicon has a six-fold valley degeneracy. Strain in
the Si/SiGe quantum well system partially lifts the valley degeneracy, but the
materials factors that set the splitting of the two lowest lying valleys are
still under intense investigation. We propose a method for accurately
determining the valley splitting in Si/SiGe double quantum dots embedded into a
superconducting microwave resonator. We show that low lying valley states in
the double quantum dot energy level spectrum lead to readily observable
features in the cavity transmission. These features generate a "fingerprint" of
the microscopic energy level structure of a semiconductor double quantum dot,
providing useful information on valley splittings and intervalley coupling
rates.
