A team of researchers achieved single-molecule strong coupling at room temperature using plasmonic nanocavities. By reducing the cavity volume below 40 nm³ and aligning isolated methylene-blue molecules via host-guest chemistry, they observed strong coupling in ambient conditions. Dispersion curves from over 50 plasmonic nanocavities showed characteristic anticrossings, with Rabi frequencies of 300 meV for 10 molecules decreasing to 90 meV for single molecules, matching theoretical models. Statistical analysis of vibrational spectroscopy and dark-field scattering spectra confirmed single-molecule strong coupling. This coupling can modify photochemistry, enabling studies of complex natural processes like photosynthesis and chemical bond manipulation. The study overcame challenges in achieving strong coupling by using high-quality plasmonic nanocavities with sub-nanometer gaps between nanoparticles and a mirror. They used a nanoparticle-on-mirror (NPoM) geometry to precisely position single molecules within the gap. The intense interaction between each nanoparticle and its image created a dimer-like structure with high field enhancement. The resonant wavelength was tunable from 600-1200 nm, allowing precise control over the plasmonic mode. To prevent molecular aggregation and align the transition dipole with the gap plasmon, they used cucurbit[n]uril molecules to encapsulate methylene-blue dye. This allowed precise orientation of the dye molecules within the nanocavity. The resulting plasmonic nanocavities supported strong coupling with Rabi frequencies up to 380 meV, far exceeding cavity loss and emitter scattering rates. The researchers mapped the dispersion curve by analyzing scattering spectra from different-sized nanoparticles. A coupled-oscillator model matched the quantum mechanical Jaynes-Cummings picture, showing anticrossing behavior with strong coupling. The Purcell factor, a key figure of merit for cavity systems, was found to be 3.5×10⁶ for their plasmonic nanocavities, much higher than state-of-the-art photonic crystal cavities. By systematically reducing the number of MB molecules, they observed distinct systematic jumps in coupling strength, confirming single-molecule strong coupling. The results showed that single MB molecules in their nanocavities produced Rabi splittings of 80-95 meV. The study also demonstrated the potential for applications in single-photon emitters, quantum chemistry, nonlinear optics, and molecular reactions. The findings highlight the importance of controlled molecular orientation and precise cavity design in achieving strong coupling at room temperature.A team of researchers achieved single-molecule strong coupling at room temperature using plasmonic nanocavities. By reducing the cavity volume below 40 nm³ and aligning isolated methylene-blue molecules via host-guest chemistry, they observed strong coupling in ambient conditions. Dispersion curves from over 50 plasmonic nanocavities showed characteristic anticrossings, with Rabi frequencies of 300 meV for 10 molecules decreasing to 90 meV for single molecules, matching theoretical models. Statistical analysis of vibrational spectroscopy and dark-field scattering spectra confirmed single-molecule strong coupling. This coupling can modify photochemistry, enabling studies of complex natural processes like photosynthesis and chemical bond manipulation. The study overcame challenges in achieving strong coupling by using high-quality plasmonic nanocavities with sub-nanometer gaps between nanoparticles and a mirror. They used a nanoparticle-on-mirror (NPoM) geometry to precisely position single molecules within the gap. The intense interaction between each nanoparticle and its image created a dimer-like structure with high field enhancement. The resonant wavelength was tunable from 600-1200 nm, allowing precise control over the plasmonic mode. To prevent molecular aggregation and align the transition dipole with the gap plasmon, they used cucurbit[n]uril molecules to encapsulate methylene-blue dye. This allowed precise orientation of the dye molecules within the nanocavity. The resulting plasmonic nanocavities supported strong coupling with Rabi frequencies up to 380 meV, far exceeding cavity loss and emitter scattering rates. The researchers mapped the dispersion curve by analyzing scattering spectra from different-sized nanoparticles. A coupled-oscillator model matched the quantum mechanical Jaynes-Cummings picture, showing anticrossing behavior with strong coupling. The Purcell factor, a key figure of merit for cavity systems, was found to be 3.5×10⁶ for their plasmonic nanocavities, much higher than state-of-the-art photonic crystal cavities. By systematically reducing the number of MB molecules, they observed distinct systematic jumps in coupling strength, confirming single-molecule strong coupling. The results showed that single MB molecules in their nanocavities produced Rabi splittings of 80-95 meV. The study also demonstrated the potential for applications in single-photon emitters, quantum chemistry, nonlinear optics, and molecular reactions. The findings highlight the importance of controlled molecular orientation and precise cavity design in achieving strong coupling at room temperature.