Manipulating optical nonlinearities of molecular polaritons by delocalization

Abstract

Optical nonlinearities are key resources in the contemporary photonics toolbox, relevant to quantum gate operations and all-optical switches. Chemical modification is often employed to control the nonlinear response of materials at the microscopic level, but on-the-fly manipulation of such response is challenging. Tunability of optical nonlinearities in the mid-IR is even less developed, hindering its applications in chemical sensing or IR photonic circuitry. Here, we report control of vibrational polariton coherent nonlinearities by manipulation of macroscopic parameters such as cavity longitudinal length or molecular concentration. Further 2D IR investigations reveal that nonlinear dephasing provides the dominant source of the observed ultrafast polariton nonlinearities. The reported phenomena originate from the nonlinear macroscopic polarization stemming from strong coupling between microscopic molecular excitations and a macroscopic photonic cavity mode. RESULTS. Polariton bleach dependence on cavity longitudinal length.To investigate the optical nonlinearities of vibrational polaritons, we measure their third-order nonlinear susceptibilities by femtosecond IR pumpprobe spectroscopy. The hybrid light-matter system consists of a FP microcavity filled with an ensemble of asymmetric carbonyl stretch modes originating from W(CO)6 molecules in a hexane solution (14). At zero waiting time, when IR pump and probe pulses overlap, we see a notable reduction in the intensity of the polariton transmission (Figs. 1b). This reduction gives rise to absorptive features in the differential transmission spectra (Figs. 1c). Qualitatively, the observed behavior resembles the well-known "photon blockade effect" in the single-emitter quantum regime of the Jaynes-Cummings model (18)(19)(20): when a photon excites the emitter-cavity system, the latter is blocked from further interactions with incoming photons of the same frequency. Here, we observe a similar effect, although it is in the ensemble regime and the mechanism for reduced transmission is quite different from the single oscillator case. We hereafter term this phenomenon "polariton bleach". Note this effect is not a trivial coherent artifact from the overlap between the pump and probe pulses. The IR pulse duration is ~100 fs, while the bleach lasts for less than 5 ps (which is also the approximate lifetime of the cavity photon), indicating the effect is intrinsic to the lifetime of the cavity polaritons. The polariton bleach concept provides a foundation for developing mid-IR photonic devices in the ensemble regime of light-matter strong coupling. Chen for his help on designing Figure 1 and Jiaxi Wang for her help on the experiments.

Molecular polaritons for controlling chemistry with quantum optics

“…Fabry-Perot cavities [43,55,153], and also cavity-controlled steady-state [38-40, 42, 44, 46, 47, 49, 53, 152, 190] and ultrafast [51,52,54,56,191,192] vibrational spectroscopy.…”

Recent Progress in Vibropolaritonic Chemistry

“…The mechanism by which VSC influences chemical reactivity remains a question under vigorous debate. To gain some mechanistic insight into the effect of VSC on chemical reactions, the dynamics of vibro‐polaritonic states have begun to be investigated . In addition, a number of theoretical studies have been developed since the first observation of the VSC‐modified reaction kinetics.…”

Polariton panorama

“…Progress with nanostructures enabled a demonstration of the strong-light matter coupling with a single molecule embedded in a plasmonic cavity [316]. Molecular molaritons enable control of optical nonlinarities via manipulations of cavity characteristics [317]. Molecular polaritons can form hybrid polaritons by coupling to surface plasmons [318], for example.…”