We examine the quantum dynamics of surface plasmons weakly coupled to optical soliton photons in a metal-dielectric-nonlinear Kerr medium interface. We consider a photon-number-dependent coupling model which is a heuristic extension of the classical soliton excitation of surface plasmons in the quantum limit. The coupling coefficient additionally depends on the distance between the dielectric and the metal. We propose a practical scheme to control the number of surface plasmons using a Gaussian variation of the metal-dielectric spatial separation. Our numerical simulations show that the curvature of the Gaussian distance profile can be used for controlling the number of surface plasmons.
We examine the quantum dynamics of surface plasmons weakly coupled to optical soliton photons in a metal-dielectric-nonlinear Kerr medium interface. We consider a photon-number-dependent coupling model which is a heuristic extension of the classical soliton excitation of surface plasmons in the quantum limit. The coupling coefficient additionally depends on the distance between the dielectric and the metal. We propose a practical scheme to control the number of surface plasmons using a Gaussian variation of the metal-dielectric spatial separation. Our numerical simulations show that the curvature of the Gaussian distance profile can be used for controlling the number of surface plasmons.
Surface plasmon polaritons are charge density waves of electrons in a metal, which are coupled to an electromagnetic field at a metal-dielectric interface. The electro- magnetic field associated with surface plasmons is confined, resulting in increased field intensities near the interface. Optical emitters placed near a metal film interact strongly with the surface plasmon modes present, not only modifying the radiation rates, but also the radiation profile. These emitters may be used to store and process information, and understanding their behaviour in the presence of a lossy metal film is important in determining the advantages and limitations of using surface plasmons. In this thesis, we wish to understand how we can optically control atoms by exploring two physical phenomena: first, the influence of surface plasmons on collective effects in an ensemble of emitters. Secondly, the single photon excitation of an emitter near a metal film. In the first case, we analyze the collective radiative behaviour of multiple classical emitters near a metal film that radiatively couple to the far-field through surface plasmon modes. We demonstrate that the contributions of dipolar image charges within the metal film significantly affect the cooperative emission of nearby sources, generating sub- and super-radiant emission that can be controlled with a suitably detuned external driving field. In the second case, we determine the excitation probability of an atom near a metal film by a single photon pulse that is time reversed. Using a quantum electro- dynamic description of absorbing dielectrics, we show that non-radiative decay will limit the excitation probability to about half of the maximum that could be achieved in the absence of losses.
We develop a microscopic quantum theory of surface plasmon polaritons valid for arbitrary metal-dielectric geometries. Our framework is based on the Power-Zienau-Woolley representation of quantum electrodynamics, which provides an optimal separation between electronic and photonic degrees of freedom and is therefore particularly well suited for constructing quantum descriptions of polaritonic excitations in strongly dispersive media. Within this formulation, the fundamental electronic oscillator is identified as the bulk plasmon mode, which is nonperturbatively coupled to the radiative continuum of free photon modes. This coupling induces a geometry-dependent renormalization of the bulk plasma frequency, giving rise to confined plasmonic resonances. As specific applications, we recover the localized surface plasmon modes of metallic nanoparticles, including radiative frequency shifts and decay, as well as the exact dispersion relation of propagating surface plasmon polaritons at planar interfaces. Our quantum treatment further reveals that light-matter interactions at metal-dielectric interfaces are inherently in the ultrastrong coupling regime. As a result, in the quasistatic limit, the system exhibits unconventional ground-state quantum fluctuations that can be controlled through the refractive index. These results open new intriguing perspectives in the field of quantum plasmonics.
The transition dynamics of photons between an optical soliton in a nonlinear dielectric waveguide and a spatially coupled surface-plasmon excitation on a parallel flat metal surface can be formulated in analogy to that of a Josephson junction of two-level (double-well) Bose-Einstein condensates, albeit with a nonlinear coupling that inherently depends on the population imbalance of the levels. The present work demonstrates that asymmetric Rosen-Zener--like transitions can be obtained through this optical Josephson junction, by turning on and off the coupling across a hyperbolically varying separation between the soliton and the surface-plasmon. The transitions can generate full population transfer, population splitting, or merging between the quasistationary initial and final states, which are defined by a fixed population imbalance in the decoupled limit. Transitions from a pure soliton or pure surface-plasmon initial state are found to be robust against the relative phase, whereas the transitions from an initial state with mixed population depend strongly on the relative phase. The soliton--surface-plasmon system also bears similarities to the spatially coupled optical waveguides which are introduced further as the classical analogs of the spatial adiabatic passage and stimulated Raman adiabatic passage mechanisms in quantum and atom optics.
We propose a scheme for the coupler-free excitation of surface polaritonic solitons and breathers in a planar plasmonic waveguide structure comprising a transparent layer, a metal layer, and a layer of a three-level lambda-type atomic medium. In the proposed system, an enhanced Kerr nonlinearity is achieved via electromagnetically induced transparency (EIT) in the bottom atomic medium, which can be controlled through proper modulation of the frequency detunings and Rabi frequencies of the driving laser fields. This nonlinearity balances the dispersion in the system, thus providing the necessary condition for the excitation of polaritonic solitons in the proposed system. As a result, the system yields laterally self-trapped bright and dark surface polaritonic solitons that are tightly guided at the interface of the metal and the EIT medium. Furthermore, we investigate the excitation of surface polaritonic Akhmediev breathers at the metal-EIT medium interface in the proposed system. A stable propagation of the surface polaritonic Akhmediev breathers is achieved with the proper choice of parameters in the proposed planar plasmonic waveguide structure. This experimentally feasible scheme could be significant in the development of highly compact nanophotonic devices in the optical regime.
Tunable surface plasmons on the interface of a multilevel atomic medium with a cross coupling of the electric and magnetic components of a plasmonic field are investigated. The strong chirality resulting from the quantum coherence leads to some exciting properties of the surface plasmons. Compared to the traditional chiral-metal interface, surface plasmonic mode can still be found at the interface between such atomic media and a dielectric even when both the permittivity and the permeability of the medium are positive. This is in contrast to the conventional plasmonic systems where the signs of the permittivities or permeabilities on the two sides of the interface are opposite. We call this phenomenon an electromagnetically induced plasmon. Additionally, as the chirality and effective refractive index of the atomic medium are dependent on the intensity and phase of the controlling field, we can conveniently manipulate the properties of the surface plasmons.
Quantum coherence controlled by the resonant condition of electromagnetically induced transparency (EIT) has attracted considerable attention for the excitation of surface plasmon polaritons (SPPs) in various metal–dielectric hybrid structures. However, for all coherent fields operating resonantly in the system, the exact extent to which perfect EIT is effective in establishing coupler-free SPP excitation has not yet been well examined. Here, we investigate the excitation of SPPs in an air–metal–atom composite structure incorporating a three-level Λ-type atomic model that operates in the strong ground-state coherence-dephasing regime. Such decoherence limits the establishment of true EIT under the condition of two-photon Raman resonance. It is found that, although the characteristic narrow resonant field enhancement associated with EIT mediated by the resonant fields disappears, significant SPP-assisted field enhancement survives over a broad off-resonant spectral region. This behavior originates from the preservation of the momentum-matching condition together with the fulfillment of the dielectric requirements for surface plasmon resonance (SPR) in the normal-dispersion regime. If the coupling field is tuned to the SPR condition, the detuned two-photon Raman resonance plays a vital role in structuring a doublet in the spectral response of an initially single-peaked broadband SPP excitation. This observation demonstrates that, although true EIT does not occur in the system, an EIT-like plasmonic spectral signature appears through the off-resonant SPP excitation mechanism. All-optical switching can be realized by turning the detuned condition of the coupling field on and off, thereby exhibiting this coherence feature. Furthermore, we show that the present model remains robust in the Doppler-broadened regime, providing a realistic route toward coherence-controlled coupler-free SPP excitation beyond the conventional ideal-EIT framework.