Dipolar excitonic quantum wires at atomically sharp lateral interfaces

One-dimensional (1D) quantum systems are a cornerstone of many-body physics. However, their realization in solids has traditionally relied on top-down methods, which are limited by structural disorder and coarse confinement. Here, we demonstrate a fundamentally distinct route: the emergence of 1D quantum matter at the atomically sharp interface between monolayer semiconductors. Using lateral $MoSe_2-WSe_2$ heterostructures, we identify interfacial excitonic quasiparticles that are bound to the crystal junction. Photoluminescence spectroscopy resolves these excitons into a ladder of discrete states, establishing nanoscopic 1D confinement at length scales of 3 nm. These excitons possess exceptional large permanent in-plane electric dipole moments exceeding e x 2 nm, and exhibit micron-scale, highly anisotropic diffusion confined to the interface. Crucially, the lateral geometry enables dynamic, in-situ reconfiguration of the exciton's internal structure. By introducing electrostatic doping, we demonstrate a collapse of the dipole moment and a 20-fold reduction in radiative lifetime. This structural tunability establishes lateral interfaces as a uniquely powerful platform for the 'bottom-up' engineering of 1D quantum matter. By enabling the dynamic tuning of wavefunctions within a single atomic monolayer, this work opens a scalable route toward 1D excitonic circuits and strongly correlated 1D bosonic phases.