Two-photon spontaneous emission (TPSE) is a second-order quantum course of with promising functions in quantum optics that is still largely unexplored in molecular programs, that are normally very inefficient emitters. On this work, we mannequin the primary molecular two-photon emitters and set up the design guidelines, highlighting their variations from these governing two-photon absorbers. Utilizing each time-dependent density purposeful principle and Pariser-Parr-Pople calculations, we calculate TPSE in three π-conjugated molecules and establish a dominant pathway. To beat the inherently low TPSE charges in vacuum, we suggest plasmonic nanoparticle-on-mirror cavities, engineered for degenerate TPSE. Our simulations reveal over 10 orders of magnitude enhancement and radiative efficiencies exceeding 50 %. Notably, for nitro-substituted phenylene vinylene in an optimized nanocone-on-mirror construction, the two-photon emission price surpasses that of vacuum one-photon emission from a unit dipole. These findings open new avenues for environment friendly and molecular-based on-demand sources of entangled photon pairs.
