Biological\nCavity Quantum Electrodynamics via Self-Aligned\nNanoring Doublets: QED-SANDs

Quantum\nmechanics is applied to create numerous electronic devices,\nincluding lasers, electron microscopes, magnetic resonance imaging,\nand quantum information technology. However, the practical realization\nof cavity quantum electrodynamics (QED) in various applications is\nlimited due to the demanding conditions required for achieving strong\ncoupling between an optical cavity and excitonic matter. Here, we\npresent biological cavity QED with self-aligned nanoring doublets:\nQED-SANDs, which exhibit robust room-temperature strong coupling with\na biomolecular emitter, chlorophyll-<i>a</i>. We observe\nthe emergence of plasmon-exciton polaritons, which manifest as a bifurcation\nof the plasmonic scattering peak of biological QED-SANDs into two\ndistinct polariton states with Rabi splitting up to ∼200 meV.\nWe elucidate the mechanistic origin of strong coupling using finite-element\nmodeling and quantify the coupling strength by employing temporal\ncoupled-mode theory to obtain the coupling strength up to approximately\n3.6 times the magnitude of the intrinsic decay rate of QED-SANDs.\nFurthermore, the robust presence of the polaritons is verified through\nphotoluminescence measurements at room temperature, from which strong\nlight emission from the lower polariton state is observed, while emission\nfrom the upper polariton state is quenched. QED-SANDs present significant\npotential for groundbreaking insights into biomolecular behavior in\nnanocavities, especially in the context of quantum biology.