The physical realization of the strong coupling at room-temperature is of great interest and significance in quantum technologies. Plasmonic system is ideal for achieving strong light-matter interaction. This thesis mainly investigates the optical properties of plasmonic nanostructure dimers and their ability to interact with quantum emitters. In addition to plasmonic dimers, we also proposed a long-desired phonon laser model driven by the temperature gradient.
The background theory of plasmons, emitters, plexcitons, and the numerical method will be presented in Chapter 2. In Chapter 3, we first investigate the plasmonic gap resonance of bowtie-shaped gold plasmonic nanocavity on substrates. By varying the substrate materials, the elevation of the hotspot is discovered, which is ideal for interacting with 2D emitters on the upper surface of the nanocavity. Then the interaction and coupling dynamics with the single cell and 2D emitter are revealed.
Next, we integrate the plasmonic dimer resonances with the concept of coherent perfect absorption (CPA) via driving the plasmonic dimer by a plasmonic guided mode of a semi-infinite metal nanowire in Chapter 4. We demonstrated that the CPA condition can be predicted and CPA for both the bonding and anti-bonding modes can be achieved. When a single cell emitter is added to the dimer, the reflectance spectrum demonstrates a dual-peak lineshape and anti-crossing behaviour. The plexcitonic dressed states can be sustained under the corresponding CPA states.
Finally, an innovative four-level phonon laser driven by plasmonics near-field transducer generating temperature gradient is proposed in Chapter 5. By coupling the gain medium with the thermal reservoirs, we demonstrated that population inversion can be achieved and the amplification of phonon modes is realized. We discovered that the incoherent transitions of the gain medium are deleterious for lasing process, resulting in a significant decrease in the phonon amplitude.