单个等离激元纳米颗粒和纳米间隙结构与量子发光体的强耦合

Strong coupling of single plasmonic nanoparticles and nanogaps with quantum emitters

在腔量子电动力学中,如果量子发光体与腔模式的耦合强度超过二者的平均损耗,就进入了强耦合区域,此时会形成部分光部分物质的新量子态——极化激元态.强耦合在室温玻色-爱因斯坦凝聚、极化激元激光、单光子非线性、量子信息等领域有重要的应用价值.基于单个金属纳米颗粒的结构可以支持局域表面等离激元共振,拥有极小的模式体积,非常有利于强耦合现象的发生.本文主要介绍了强耦合的理论背景、单个金属纳米颗粒和纳米间隙结构与量子发光体的强耦合、以及强耦合的动态调控,并展望了该领域的研究前景.

In cavity quantum electrodynamics,when the interaction between quantum emitter and cavity mode is strong enough to overcome the mean decay rate of the system,it will enter into a strong coupling regime,thereby forming part-light part-matter polariton states.Strong coupling can serve as a promising platform for room temperature Bose-Einstein condensation,polariton lasing,single photon nonlinearity,quantum information,etc.Localized surface plasmons supported by single metal nanostructures possess extremely small mode volume,which is favorable for realizing strong coupling.Moreover,the nanoscale dimensions of plasmonic structures can facilitate the miniaturization of strong coupling systems.Here,the research progress of strong plasmon-exciton coupling between single metal nanoparticles/nanogaps and quantum emitters is reviewed.The theory background of strong coupling is first introduced,including quantum treatment,classical coupled oscillator model,as well as the analytical expressions for scattering and photoluminescence spectra.Then,strong coupling between different kinds of plasmonic nanostructures and quantum emitters is reviewed.Single metal nanoparticles,nanoparticle dimers,and nanoparticle-on-mirror structures constitute the most typical plasmonic nanostructures.The nanogaps in the latter two systems can highly concentrate electromagnetic field,providing optical nanocavities with smaller mode volume than single nanoparticles.Therefore,the larger coupling strength can be achieved in the nanogap systems,which is conducive to strong coupling at the single-exciton level.In addition,the active tuning of strong coupling based separately on thermal,electrical and optical means are reviewed.The energy and oscillator strength of the excitons in transition metal dichalcogenide(TMDC)monolayers are dependent on temperature.Therefore,the strong coupling can be tuned by heating or cooling the system.The excitons in TMDC monolayers can also be tuned by electrical gating,enabling electrical control of strong coupling.Optically tuning the quantum emitters provides another way to actively control the strong coupling.Overall,the research on active tuning of strong plasmon-exciton coupling is still very limited,and more investigations are needed.Finally,this review is concluded with a short summary and the prospect of this field.