  Long lifetimes of spatially indirect excitons (IXs), also known as interlayer
excitons, make possible long-range IX propagation. Van der Waals
heterostructures composed of atomically thin layers of transition-metal
dichalcogenides (TMDs) give an opportunity to realize excitons with high
binding energies and provide a materials platform for the realization of both
excitonic quantum phenomena and excitonic devices. Propagation of IXs in TMD
heterostructures is intensively studied. However, in spite of long IX
lifetimes, orders of magnitude longer than lifetimes of spatially direct
excitons (DXs), a relatively short-range IX propagation with the $1/e$ decay
distances $d_{1/e}$ up to few $\mu$m was reported in the studies of TMD
heterostructures. The short-range of IX propagation originates from in-plane
potentials, which localize excitons and suppress exciton transport. In
particular, significant in-plane moir\'e potentials predicted in TMD
heterostructures can cause an obstacle for IX propagation. In this work, we
realize in a MoSe$_2$/WSe$_2$ heterostructure a macroscopically long-range IX
propagation with $d_{1/e}$ reaching $\sim 100$ $\mu$m. The strong enhancement
of IX propagation is realized using an optical excitation resonant to DXs in
the heterostructure. The strong enhancement of IX propagation originates from
the suppression of IX localization and scattering and is observed in the
quantum regime.
