  We develop a microscopic and atomistic theory of electron spin-based qubits
in gated quantum dots in a single layer of transition metal dichalcogenides.
The qubits are identified with two degenerate locked spin and valley states in
a gated quantum dot. The two-qubit states are accurately described using a
multi-million atom tight-binding model solved in wavevector space. The
spin-valley locking and strong spin-orbit coupling result in two degenerate
states, one of the qubit states being spin-down located at the $+K$ valley of
the Brillouin zone, and the other state located at the $-K$ valley with spin
up. We describe the qubit operations necessary to rotate the spin-valley qubit
as a combination of the applied vertical electric field, enabling spin-orbit
coupling in a single valley, with a lateral strongly localized valley-mixing
gate.
