High-quality lattice resonances in arrays of infrared antennas operating in an open-cavity regime form polariton states by means of strong coupling to molecular vibrations. We studied polaritons formed by carbonyl stretching modes of (poly)methyl methacrylate on resonant antenna arrays using femtosecond 2DIR spectroscopy. At a normal incidence of excitation light, doubly-degenerate antenna-lattice resonances (ALR) form two polariton states: a lower polariton and an upper polariton. At an off-normal incidence geometry of the 2DIR experiments, the ALR degeneracy is lifted and, consequently, the polariton energies are split. We spectrally resolved and tracked the time-dependent evolution of a cross-peak signal associated with the excitation of reservoir states and the unidirectional transfer of the excess energy to lower polaritons. Bi-exponential decay of the cross-peak suggests that a reversible energy exchange between the bright and dark lower polaritons occurs with a characteristic transfer time of ~200 fs. The cross-peak signal further decays within ~800 fs, which is consistent with the relaxation time of the carbonyl stretching vibration and with the dephasing time of the ALR. An increase in the excitation pulse intensity leads to saturation of the cross-peak amplitude and to a modification of the relaxation dynamics. Using quantum-mechanical modelling, we found that kinetic scheme that captures all the experimental observations implies that only the bright lower polariton accepts the energy from the reservoir, suggesting that transfer occurs via a mechanism involving dipole-dipole interaction. Efficient reservoir-to-polariton transfer can play an important role in developing novel room-temperature quantum optical devices in the mid-infrared wavelength region.

2D- semiconductors with strong light-matter interaction are attractive materials for integrated and tunable optical devices. Here, we demonstrate room-temperature wavelength multiplexing of the two-primary bright excitonic channels (Ab-, Bb-) in...

Disorder is an intrinsic attribute of any realistic molecular system. It is known to lead to localization, which hampers efficient transport. It was recently proposed that in molecular ensembles strongly coupled to photonic cavities, moderate disorder leads to delocalization and increases of the transport and chemical reaction rates. Vibrational polaritons involve molecular vibrations hybridized with an infrared cavity. When the coupling strength largely exceeds the molecular inhomogeneity, polaritons are unaffected by disorder. However, in many experiments, such a homogeneous limit does not apply. We investigated vibrational polaritons involving molecular ensembles with systematically modified disorder. Counterintuitively, moderate disorder leads to an increase in Rabi splitting and the modification of the polariton bandwidths. Experimental spectroscopic data agree with a Tavis–Cummings-like model that suggests enhanced delocalization of the reservoir states occurs via the admixture of the cavity mode. Our results provide new insights into the paradigm of disorder-induced cavity-assisted delocalization in molecular polaritons.