Abstract
Strong light-matter interactions in both the single-emitter and collective strong coupling regimes attract significant attention due to emerging applications in quantum and nonlinear optics as well as opportunities for modifying material-related properties. Exploration of these phenomena is theoretically demanding, as polaritons exist at the intersection between quantum optics, solid state physics, and quantum chemistry. Fortunately, nanoscale polaritons can be realized in small plasmon-molecule systems, enabling treatment with ab initio methods. Here, we show that time-dependent density-functional theory calculations access the physics of nanoscale plasmon-molecule hybrids and predict vacuum Rabi splitting. By considering a system comprising a few-hundred-atom aluminum nanoparticle interacting with benzene molecules, we show that cavity quantum electrodynamics holds down to resonators of a few cubic nanometers in size, yielding a single-molecule coupling strength exceeding 200 meV due to a massive vacuum field of 4.5 V · nm−1. In a broader perspective, ab initio methods enable parameter-free in-depth studies of polaritonic systems for emerging applications.
Highlights
Strong light-matter interactions in both the single-emitter and collective strong coupling regimes attract significant attention due to emerging applications in quantum and nonlinear optics as well as opportunities for modifying material-related properties
We model the entire plasmon-exciton system by time-dependent density-functional theory (TDDFT), which allows the whole system to be treated on the same footing, enabling one to track effects related to modification of the matter subpart, which are inaccessible by purely quantum optical or classical electromagnetism methods
While the commonly-used TDDFT approaches with classical description of electric fields may not be able to describe the full range of quantum optical phenomena that QED-density-functional theory (DFT) aims at, we demonstrate in this paper that the cavity mode created by a localized surface plasmon resonance as well as its strong coupling with excitons can be described already within the standard TDDFT
Summary
Strong light-matter interactions in both the single-emitter and collective strong coupling regimes attract significant attention due to emerging applications in quantum and nonlinear optics as well as opportunities for modifying material-related properties. Polaritonic behavior associated with “dressing” of the emitter by a cavity field is usually captured by traditional quantum optical approaches such as Jaynes–Cummings or Dicke models[2,3,4,16,17] These quantum optical formalisms treat matter in an extremely simplified manner, that is, as a two-level system, leading to oversimplifications and inconsistencies in the description of the material subpart. Advanced theoretical techniques developed recently allow for more sophisticated effects including, for example, multiple electronic resonances, accounting for atomic vibrations, and light-matter interactions beyond the point-dipole approximation Significant progress along these lines has been achieved by several groups using various quantum optical and quantum chemistry methods[9,10,11,18,19,20,21]. Many recent experimental observations cannot be explained with current theories[34,35,36]
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