  Monolayer transition metal dichalcogenides (TMDs) offer new opportunities for
realizing quantum dots (QDs) in the ultimate two-dimensional (2D) limit. Given
the rich control possibilities of electron valley pseudospin discovered in the
monolayers, this quantum degree of freedom can be a promising carrier of
information for potential quantum spintronics exploiting single electrons in
TMD QDs. An outstanding issue is to identify the degree of valley
hybridization, due to the QD confinement, which may significantly change the
valley physics in QDs from its form in the 2D bulk. Here we perform a
systematic study of the intervalley coupling by QD confinement potentials on
extended TMD monolayers. We find that the intervalley coupling in such geometry
is generically weak due to the vanishing amplitude of the electron wavefunction
at the QD boundary, and hence valley hybridization shall be well quenched by
the much stronger spin-valley coupling in monolayer TMDs and the QDs can well
inherit the valley physics of the 2D bulk. We also discover sensitive
dependence of intervalley coupling strength on the central position and the
lateral length scales of the confinement potentials, which may possibly allow
tuning of intervalley coupling by external controls
