Monitoring polariton dynamics in the LHCII photosynthetic antenna in a microcavity by two-photon coincidence counting

The relaxation dynamics of light-harvesting complex II in an optical cavity is explored theoretically by multidimensional photon coincidence counting spectroscopy. This technique reveals the dynamics in both single (e) and double (f) excitation bands. We study how the polariton dynamics are affected by coupling to photon modes and molecular vibrations described by a realistic spectral density at 77 K. Without the cavity, the e- and f-band energy transfer pathways are not clearly resolved due to the line broadening caused by fast exciton dephasing. The strong coupling to cavity photons results in well-resolved polariton modes. The hybrid nature of polaritons slows down their energy transfer rates.