  Electrons confined in Si quantum dots possess orbital, spin, and valley
degrees of freedom (d.o.f.). We perform Landau-Zener-Stuckelberg-Majorana
(LZSM) interferometry on a Si double quantum dot that is strongly coupled to a
microwave cavity to probe the valley d.o.f. The resulting LZSM interference
pattern is asymmetric as a function of level detuning and persists for drive
periods that are much longer than typical charge decoherence times. By
correlating the LZSM interference pattern with charge noise measurements, we
show that valley-orbit hybridization provides some protection from the
deleterious effects of charge noise. Our work opens the possibility of
harnessing the valley d.o.f. to engineer charge-noise-insensitive qubits in Si.
