  Using angle-resolved photoemission spectroscopy, combined with first
principle and coupled self-consistent Poisson-Schr\"odinger calculations, we
demonstrate that potassium (K) atoms adsorbed on the low-temperature phase of
1$T$-TiSe$_2$ induce the creation of a two-dimensional electron gas (2DEG) and
quantum confinement of its charge-density-wave (CDW) at the surface. By further
changing the K coverage, we tune the carrier-density within the 2DEG that
allows us to nullify, at the surface, the electronic energy gain due to exciton
condensation in the CDW phase while preserving a long-range structural order.
Our study constitutes a prime example of a controlled exciton-related many-body
quantum state in reduced dimensionality by alkali-metal dosing.
