  Moir\'e superlattices of semiconducting transition metal dichalcogenides
(TMDCs) enable unprecedented spatial control of electron wavefunctions in an
artificial lattice with periodicities more than ten times larger than that of
atomic crystals, leading to emerging quantum states with fascinating electronic
and optical properties. The breaking of translational symmetry further
introduces a new degree of freedom inside each moir\'e unit cell: high symmetry
points of energy minima called moir\'e sites, behaving as spatially separated
quantum dots. The superposition of a quasiparticle wavefunction between
different moir\'e sites will enable a new platform for quantum information
processing but is hindered by the suppressed electron tunneling between moir\'e
sites. Here we demonstrate the superposition between two moir\'e sites by
constructing an angle-aligned trilayer WSe2/monolayer WS2 moir\'e
heterojunction. The two moir\'e sites with energy minimum allow the formation
of two different interlayer excitons, with the hole residing in either moir\'e
site of the first WSe2 layer interfacing the WS2 layer and the electron in the
third WSe2 layer. An external electric field can drive the hybridization of
either of the interlayer excitons with the intralayer excitons in the third
WSe2 layer, realizing the continuous tuning of interlayer exciton hopping
between two moir\'e sites. Therefore, a superposition of the two interlayer
excitons localized at different moir\'e sites can be realized, which can be
resolved in the electric-field-dependent optical reflectance spectra,
distinctly different from that of the natural trilayer WSe2 in which the
moir\'e modulation is absent. Our study illustrates a strategy of harnessing
the new moir\'e site degree of freedom for quantum information science, a new
direction of twistronics.
