Cavity-assisted ultrafast long-range periodic energy transfer between plasmonic nanoantennas

Radiationless energy transfer is at the core of diverse phenomena, such as light harvesting in photosynthesis1, energy-transfer-based microspectroscopies2, nanoscale quantum entanglement3 and photonic-mode hybridization4. Typically, the transfer is efficient only for separations that are much shorter than the diffraction limit. This hampers its application in optical communication and quantum information processing, which require spatially selective addressing. Here, we demonstrate highly efficient radiationless coherent energy transfer over a distance of twice the excitation wavelength by combining localized and delocalized5 plasmonic modes. Analogous to the Tavis–Cummings model, two whispering-gallery-mode antennas6 placed in the foci of an elliptical plasmonic cavity7 fabricated from single-crystal gold plates act as a pair of oscillators coupled to a common cavity mode. Time-resolved two-photon photoemission electron microscopy (TR 2P-PEEM) reveals an ultrafast long-range periodic energy transfer in accordance with the simulations. Our observations open perspectives for the optimization and tailoring of mesoscopic energy transfer and long-range quantum emitter coupling.