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arXiv:2603.17269

Engineering strong coupling with molecular coatings in optical nanocavities

Athul S. Rema, Adrián E. Rubio López, Felipe Herrera

quant-phcond-mat.mes-hallphysics.chem-phSubmitted Mar 18, 2026• Announced Mar 19, 2026
v1 · Mar 18, 2026v2 · Sep 20, 2026
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Abstract

Quantum emitters near the surface of silver nanoparticles undergo Rabi oscillations in electronic population dynamics due to strong coupling with near-field multipole modes that are not radiative. Low-frequency nanoparticle dipole modes are radiative but do not couple strong enough to quantum emitters. These features limit the observation of strong coupling. Using macroscopic quantum electrodynamics theory within a Lorentzian pseudo-mode approximation for the non-Markovian interaction kernel, we demonstrate that by coating spherical silver nanoparticles with a thin molecular J-aggregate layer, the resulting core-shell plexciton resonance restructures the local electromagnetic vacuum at dipole-mode frequencies to enable Rabi oscillations for quantum emitters that otherwise would only undergo exponential population decay. Specifically, we show for quantum dot emitters in the near field of silver nanospheres of 20 nm radius, that weak-to-strong coupling crossovers can be induced using 2 nm J-aggregate shells. Our work demonstrates the potential of molecular aggregates to enable deep sub-wavelength structuring of the vacuum field for the observation of coherent quantum dynamics in optical nanocavities.

Comments
15 pages, 6 figures, 4 appendices

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Quantum emitters near the surface of silver nanoparticles undergo Rabi oscillations in electronic population dynamics due to strong coupling with near-field multipole modes that are not radiative. Low-frequency nanoparticle dipole modes are radiative but do not couple strong enough to quantum emitters. These features limit the observation of strong coupling. Using macroscopic quantum electrodynamics theory within a Lorentzian pseudo-mode approximation for the non-Markovian interaction kernel, we demonstrate that by coating spherical silver nanoparticles with a thin molecular J-aggregate layer, the resulting core-shell plexciton resonance restructures the local electromagnetic vacuum at dipole-mode frequencies to enable Rabi oscillations for quantum emitters that otherwise would only undergo exponential population decay. Specifically, we show for quantum dot emitters in the near field of silver nanospheres of 20 nm radius, that weak-to-strong coupling crossovers can be induced using 2 nm J-aggregate shells. Our work demonstrates the potential of molecular aggregates to enable deep sub-wavelength structuring of the vacuum field for the observation of coherent quantum dynamics in optical nanocavities.
We study a molecular emitter above a silver surface in the framework of macroscopic quantum electrodynamics and explore the population dynamics including non-Markovian effects. The theory we present is general for molecular fluorescence in the presence of dielectrics with any space-dependent, frequency-dependent, or complex dielectric functions. Furthermore, the proposed theory allows us to calculate the memory kernel of polaritons using computational electrodynamics packages. In the limit of a high vibration frequency, the different strengths of exciton-polariton couplings lead to distinct characteristics in the population dynamics, e.g., Franck-Condon-Rabi oscillation. (The frequency of Rabi oscillation is dependent on the Franck-Condon factor.) Additionally, in a specific condition, we derive a parameter-free formula that can be used to estimate the exciton-polariton coupling between a molecular emitter and a nanocavity, and the coupling estimated by our theory is in good agreement with the reported experimental results [Chikkaraddy et al., Nature 535, 127-130 (2016)].
The stationary spectrum of individual dipole emitters in plasmonic nanocavities has been studied for a range of cavity geometries and dipole configurations. Less is known about the coherent dynamics of single photon creation in the nanocavity near field by an excited dipole. We address this gap by developing a Lorentzian kernel approximation that solves the time-dependent Schrödinger equation that describes the coupled dipole-photon dynamics in the single-excitation manifold. Our approach encodes the broadband nature of the nanocavity field through a non-Markovian memory kernel, derived from macroscopic QED theory. For a two-level dipole near a metallic nanosphere, we show that the single photon probability density in frequency space evolves in strong coupling from an initially localized source at the qubit frequency into a Rabi doublet over a timescale governed by the kernel spectrum. This dynamical crossover is accompanied by the formation of single-photon interference patterns in frequency and time, propagating coherently over a timescale limited by the shape of kernel spectrum to ∼100−150\sim 100-150∼100−150 fs, which is accessible to ultrafast spectroscopy. We also show that the stationary spectrum of the coupled system can be manipulated by driving the nanocavity field using coherent pulses with variable spectral bandwidth. Using single-photon pulses narrower than the kernel spectrum, the Rabi splitting in a system that supports strong coupling can be effectively removed. The applicability of our results to other dipole-nanocavity configurations is discussed and a general strong coupling criterion for nanocavities is formulated.
Strong coupling-like phenomenon between plasmonic cavities and emitters provides a new way to realize the quantum-like effect controlling at microscale/nanoscale. We investigate the strong coupling-like phenomenon in the structure of single metallic nanoparticle embedded in molecular J-aggregates by the classical simulation method and show that the size of the metallic nanoparticle and the oscillator strength of molecular J-aggregates impact the strong coupling-like phenomenon. The strong coupling-like phenomenon is induced by the interactions between two dipoles formed by the metallic nanoparticle and molecular J-aggregates or the interactions between the dipole generated from molecular J-aggregates and the quadrupole generated from the metallic nanoparticle. The strong coupling-like phenomenon appears evidently with the increase in oscillator strength of molecular J-aggregates. The detuning energy linearly decreases with the increase in radius of the metallic nanoparticle. Our structure has potential applications in quantum networks, quantum key distributions and so on.
Abstract In the light–matter strong coupling regime, the excited state of quantum emitters is inextricably linked to a photonic mode, leading to hybrid states that are part light and part matter. Recently, there has been a huge effort to realize strong coupling with nanoplasmonics, since it provides a versatile environment to study and control molecules in ambient conditions. Among the most promising designs are plasmonic nanocavities that confine light to unprecedentedly small volumes. Such nanocavities, though, support multiple types of modes, with different field profiles and radiative decay rates (bright and dark modes). Here, we show theoretically that the different nature of these modes leads to mode beating within the nanocavity and the Rabi oscillations, which alters the spatiotemporal dynamics of the hybrid system. By specifically designing the illumination setup, we decompose and control the dark and bright plasmon mode excitation and therefore their coupling with quantum emitters. Hence, this work opens new routes for dynamically dressing emitters, to tailor their hybrid states with external radiation.
We investigate excitation dynamics in the system of a quantum dipole emitter (QDE) coupled to a located nearby metal nanoparticle (MNP), which exhibits a dipolar localized surface plasmon (LSP) resonance at the frequency of the QDE radiative transition, in the presence of a strong external resonant electromagnetic field. Considering the QDE-field interactions in the regime of strong QDE-field coupling, we show that the feedback provided by the MNP on the QDE (due to the LSP excitation with the field generated by the dipole moment of the QDE transition) influences significantly the coherent process of Rabi oscillations, resulting in the occurrence of additional satellite frequencies in the radiation spectrum scattered by the QDE-MNP configuration. The relative ratio of high harmonics depends strongly on the QDE-MNP separation, an important characteristic feature that can be used for observing this effect and can be exploited, for example, for controlling distances at the nanoscale.
Abstract Strong radiative coupling realizes coherent exchange of single excitation between two quantum emitters, while their dipole orientation influences the coupling strength in anisotropic environments. We propose a silver nano-arc with arbitrary radian which can support two hot spots of electric field with radian-independent resonant wavelength. Two quantum emitters resonant with the cavity mode, embedded inside the two hot spots and oriented along the nano-arc axis, can realize strong radiative coupling, verified by the large splitting and anti-crossing behavior in the spectrum and the population oscillation in the time domain. All these signatures of strong radiative coupling are robust against the nano-arc’s curvature. Our work provides a flexible approach to realize strong radiative coupling between two quantum emitters with arbitrary mutual orientation and facilitates quantum information processing.