Strong coupling between quantum emitters and cavities is of particular interest because of the potential application in quantum devices such as quantum gates and single photon sources. The quantum gate based on the strong coupling between a single atom and a cavity has been realized. The atoms based systems require precise control of the atoms which are difficult to be integrated and scaled up on a single chip. For the solid state system, strong coupling between a photonic crystal cavity and a single quantum dot has been demonstrated at cryogenic temperature. Recently, the plasmonic nanocavity provides a platform for strong coupling at the ambient temperature due to its extremely small mode volume. However, to precisely position a single emitter into a high field region of a plasmonic nanocavity is still challenging.
In this work, a few fluorophores are embedded into a plasmonic nanocavity through the oligonucleotides. A plasmonic nanocavity consists of a functionalized nanoparticle and a metal film. Among 45 fluorophore-embedded nanocavities we measured, 20% of them show clear mode splitting. On the contrary, for the controls, none of the nanocavities shows mode splitting. We believe that some of the molecules have been strongly coupled to the plasmonic nanocavity. The EM simulation shows the mode volume is extremely small, which means only a few molecules can be located in the high field region. With the improvement of the molecule design, the deterministic strong coupling can be realized based on this configuration for quantum devices.