Strong plasmon-molecule coupling at the nanoscale revealed by first-principles modeling

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.

Relevance of the Quadratic Diamagnetic and Self-Polarization Terms in Cavity Quantum Electrodynamics

“…More closely connected to our current situation is the coupling to modes of a plasmonic environment. In principle, if we describe the plasmonic environment as part of the full system [113,114], the density oscillations of the plasmonic environment are captured in an ab initio description by the Coulomb interaction and the induced transversal photon field and hence Eq. (5) is directly applicable.…”

Plasmon excitations in chemically heterogeneous nanoarrays

“…2(a)] with an intensity proportional to the normalized photoabsorption decomposition weight of the KS electron-hole transition (S ia /S) [see Eqs. (17) and (21) in Ref. [10]].…”

“…TCMs are increasingly practical for the analysis of plasmonic systems [10,11,[14][15][16][17]. TCMs of the intense photoabsorption excitations have provided fundamental insight into how the individual electron-hole contributions are pieced together from the nodal structure of the delocalized sp states within homogeneous metallic arrays of varying width [16].…”

Strong coupling as an interplay of quantum emitter hybridization with plasmonic dark and bright modes

“…We used a local-response approximation for a silver nanosphere for simplicity, but this scheme could apply to nonlocal-corrected models where the dark pseudomode is replaced by the quadrupolar mode [53]. Also, nonlocal effects were recently shown to have negligible effect on vacuum Rabi splittings [41,54], and modeling of strongly coupled Al-benzene systems showed an equally strong hybrid modes [29]. For the bright-and dark-mode linewidths, we use γ rad B = γ non−rad D = 0.1 eV.…”

“…The high oscillator strength of these transitions could potentially be used to enhance the magnitude of Rabi splitting if the dipolar plasmon resonance can be tuned to the appropriate frequency range to overlap with those transitions. However, such an approach would require tuning dipolar plasmon resonances to the ultraviolet (UV) range, which has a number of disadvantages, including the complexity of optical measurements in this spectral range and the necessity of utilizing metals with significantly high plasma frequency, such as aluminium [27][28][29].…”