  We report on the spatial coherence of interlayer exciton ensembles as formed
in MoSe$_2$/WSe$_2$ heterostructures and characterized by point-inversion
Michelson-Morley interferometry. Below 10 K, the measured spatial coherence
length of the interlayer excitons reaches values equivalent to the lateral
expansion of the exciton ensembles. In this regime, the light emission of the
excitons turns out to be homogeneously broadened in energy with a high temporal
coherence. At higher temperatures, both the spatial coherence length and the
temporal coherence time decrease, most likely because of thermal processes. The
presented findings point towards a spatially extended, coherent many-body state
of interlayer excitons at low temperature.
