  We devise a platform for noise-resistant quantum computing using the valley
degree of freedom of Si quantum dots. The qubit is encoded in two polarized
(1,1) spin-triplet states with different valley compositions in a double
quantum dot, with a Zeeman field enabling unambiguous initialization. A top
gate gives a difference in the valley splitting between the dots, allowing
controllable interdot tunneling between opposite valley eigenstates, which
enables one-qubit rotations. Two-qubit operations rely on a stripline
resonator, and readout on charge sensing. Sensitivity to charge and spin
fluctuations is determined by intervalley processes and is greatly reduced as
compared to conventional spin and charge qubits. We describe a valley echo for
further noise suppression.
