  Silicon quantum dots are a leading approach for solid-state quantum bits.
However, developing this technology is complicated by the multi-valley nature
of silicon. Here we observe transport of individual electrons in a silicon
CMOS-based double quantum dot under electron spin resonance. An anticrossing of
the driven dot energy levels is observed when the Zeeman and valley splittings
coincide. A detected anticrossing splitting of 60 MHz is interpreted as a
direct measure of spin and valley mixing, facilitated by spin-orbit interaction
in the presence of non-ideal interfaces. A lower bound of spin dephasing time
of 63 ns is extracted. We also describe a possible experimental evidence of an
unconventional spin-valley blockade, despite the assumption of non-ideal
interfaces. This understanding of silicon spin-valley physics should enable
better control and read-out techniques for the spin qubits in an all CMOS
silicon approach.
