Mechanism of Molecular Polariton Decoherence in the\nCollective Light–Matter Couplings Regime

Molecular polaritons,\nthe hybridization of electronic states in\nmolecules with photonic excitation inside a cavity, play an important\nrole in fundamental quantum science and technology. Understanding\nthe decoherence mechanism of molecular polaritons is among the most\nsignificant fundamental questions. We theoretically demonstrate that\nhybridizing many molecular excitons in a cavity protects the overall\nquantum coherence from phonon-induced decoherence. The polariton coherence\ntime can be prolonged up to 100 fs with a realistic collective Rabi\nsplitting and quality factor at room temperature, compared to the\ntypical electronic coherence time which is around 15 fs. Our numerically\nexact simulations and analytic theory suggest that the dominant decoherence\nmechanism is the population transfer from the upper polariton state\nto the dark state manifold. Increasing the collective coupling strength\nwill increase the energy gap between these two sets of states and\nthus prolong the coherence lifetime. We further derived valuable scaling\nrelations that directly indicate how polariton coherence depends on\nthe number of molecules, Rabi splittings, and light–matter\ndetunings.