  Moir\'e potential acts as periodic quantum confinement for optically
generated exciton, generating spatially ordered zero-dimensional quantum
system. However, broad emission spectrum arising from inhomogeneity among
moir\'e potential hinders the exploration of the intrinsic properties of
moir\'e exciton. In this study, we have demonstrated a new method to realize
the optical observation of quantum coherence and interference of a single
moir\'e exciton in twisted semiconducting heterobilayer beyond the diffraction
limit of light. A significant single and sharp photoluminescence peak from a
single moir\'e exciton has been demonstrated after nano-fabrication. We present
the longer duration of quantum coherence of a single moir\'e exciton, which
reaches beyond 10 ps and the accelerated decoherence process with elevating
temperature and excitation power density. Moreover, the quantum interference
has revealed the coupling between moir\'e excitons in different moir\'e
potential minima. The observed quantum coherence and interference of moir\'e
exciton will facilitate potential application toward quantum technologies based
on moir\'e quantum systems.
