Phonon-induced modification of polaritonic Rabi oscillations in the presence of the dark excitonic condensate

Optically inactive (dark) excitons are characterized by relatively long life time, and therefore are desirable candidates for realizing collective excitonic phases. However, a detection of their coherence by light is problematic. Here we propose a method for detecting a dark excitonic condensate. It relies on the interaction between excitons and phonons responsible for the interconversion between bright and dark excitons. As long as the dark condensate forms, the Rabi oscillations between photons and bright excitons can become strongly modified. The analysis is conducted in the limit of weak interaction, and the perspective for the case of the strong interaction leading to the polaronic effect is discussed.