  We explore a solid state qubit defined on valley isospin of an electron
confined in a gate-defined quantum dot created in an area of monolayer
MoS$_2$/WS$_2$ lateral junction, where a steep dipolar potential emerges. We
show that the junction oriented along an armchair direction can induce
intervalley transitions of the electron confined in the neighboring quantum dot
when the (gate-controllable) overlapping with the junction is significant and
pumping frequency tuned. The pumping scheme that induces transitions is
all-electrical: obtained by applying oscillating voltages to control gates and
thus enables for scalable qubit architectures. We also report another
possibility of valley-qubit manipulation by accumulating non-Abelian valley
Berry phase. To model nanodevice we solve the time-dependent
Schr\"odinger-Poisson equations in a tight-binding approach and obtain exact
time-evolution of the valley-qubit system.
