Quantum strong coupling between emitters and cavities generates hybrid modes which provide a platform for quantum devices. The atom based systems require precise control over the position of atoms within the cavity and are difficult to be integrated on a chip. The quantum dots-photonic crystal system is limited to the cryogenic temperature. On the contrary, the molecule-plasmonic cavity is a good candidate for chip scale, room temperature operating strong coupling units due to the extremely small mode volume of plasmonic nanocavities.
However, to precisely position a single or a few molecules into a plasmonic nanocavity is challenging. In this work, a few molecules are integrated into the nanocavity through oligonucleotides. The clear Rabi splitting is observed and the anti-crossing curve shows a clear verification of coupling. The number of fluorophore integrated into the nanocavity is estimated to be one. The deterministic strong coupling may be realized based on this configuration.