Resonant and non-resonant driving of linearly-polarized excitons in Cd3P2 magic-size clusters.

Coherent driving of optical transitions in matter using laser fields has been established as an important paradigm in quantum optics, quantum information processing and Floquet engineering. Recent studies extended coherent driving to solution-processed materials such as lead halide perovskites and colloidal semiconductor nanocrystals. Such systems, however, often feature broad and continuous absorption profiles that limit the studies mostly to below-bandgap driving, while a comprehensive understanding of coherent light-matter interaction requires both nonresonant and resonant driving. Here we utilize magic-size clusters of Cd3P2 in the limit of extreme quantum confinement to solve these issues. Their sharp, well-isolated and linearly-polarized band-edge exciton transition allows to coherently drive it at resonance, producing a Mollow-like lineshape using cross-polarized transient absorption measurements, which is also captured by our quantum simulation using the density matrix method. Analyzing the spectral responses under both nonresonant and resonant driving consistently yields a transition dipole moment exceeding 20 Debye.