  Room-temperature Bose--Einstein condensates (BECs) of exciton polaritons have
been realized in organic molecular systems owing to the strong light--matter
interaction, strong exciton binding energy, and low effective mass of a
polaritonic particle. These molecular-exciton-polariton BECs have demonstrated
their potential in nonlinear optics and optoelectronic applications. In this
study, we demonstrate that molecular-polariton BECs can be utilized for Bose
enhancement of excitation-energy transfer (EET) in a molecular system with an
exciton donor coupled to a group of exciton acceptors that are further strongly
coupled to a single mode of an optical cavity. Similar to the stimulated
emission of light in which photons are bosonic particles, a greater rate of EET
is observed if the group of acceptors is prepared in the exciton-polariton BEC
state than if the acceptors are initially either in their electronic ground
states or in a normal excited state with an equal average number of molecular
excitations. The Bose enhancement also manifests itself as the growth of the
EET rate with an increasing number of exciton polaritons in the BEC. Finally, a
permutation-symmetry-based approach to suppress the EET to the huge manifold of
dark states in the acceptor group is proposed to facilitate the Bose-enhanced
EET to the polariton BEC.
