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.
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.