Dark-State Coherent Control of Excitons in TMD Monolayers: A Reduced Intravalley Lindblad Framework for WSe$_2$

Abstract

Dark-state coherence in driven three-level systems underlies electromagnetically induced transparency (EIT) and stimulated Raman adiabatic passage (STIRAP). Their performance depends on the coupling topology: in a ladder ($Ξ$) scheme the coherence can bypass a lossy intermediate state, whereas in a $V$ scheme it is carried by two excited states that both decay. We develop a topology-resolved Lindblad framework for driven three-level excitonic manifolds at fixed center-of-mass momentum, in which a single exciton couples to phonons, the radiation field and a dilute exciton gas. The $Ξ$ and $V$ manifolds are selected from the exciton spectrum by systematically screening optical brightness, intra-excitonic dipole strength and state compactness, making the selection reproducible and transferable to other materials. Within this framework, in the $Ξ$ manifold of hBN-encapsulated WSe$_2$, a weak optical pulse, preceded by a terahertz pulse in the counterintuitive STIRAP order, converts the excitation it creates into an optically dark exciton by dark-state following, while the lossy bright intermediate exciton stays nearly empty. The conversion is limited by emission from that intermediate state rather than by non-adiabatic coupling, and is controlled by a single adiabaticity parameter of the terahertz leg. The exchange mean field of the exciton gas shifts the two-photon resonance by more than the conversion tolerates at moderate densities; the center of the cascade transparency window provides an in situ calibration, and we identify the control strengths at which it is true EIT rather than Autler--Townes splitting. The $V$ manifold loses its coherence on the radiative timescale and serves as the unprotected reference. These results provide a minimal, material-specific baseline for dark-state coherent control of excitons in two-dimensional semiconductors in the radiative limit.