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We present an ab initio method for computing vibro-polariton and phonon-polariton spectra of molecules and solids coupled to the photon modes of optical cavities. We demonstrate that if interactions of cavity photon modes with both nuclear and electronic degrees of freedom are treated on the level of the cavity Born–Oppenheimer approximation, spectra can be expressed in terms of the matter response to electric fields and nuclear displacements, which are readily available in standard density functional perturbation theory implementations. In this framework, results over a range of cavity parameters can be obtained without the need for additional electronic structure calculations, enabling efficient calculations on a wide range of parameters. Furthermore, this approach enables results to be more readily interpreted in terms of the more familiar cavity-independent molecular electric field response properties, such as polarizability and Born effective charges, which enter into the vibro-polariton calculation. Using corresponding electric field response properties of bulk insulating systems, we are also able to obtain the Γ point phonon-polariton spectra of two dimensional (2D) insulators. Results for a selection of cavity-coupled molecular and 2D crystal systems are presented to demonstrate the method. [ABSTRACT FROM AUTHOR]

Free molecules undergo processes with photons; in particular, they can undergo photoionization and photodissociation, which are relevant processes in nature and laboratory. Recently, it has been shown that in a cavity, the reverse process of photoionization, namely, electron capture becomes highly probable. The underlying mechanism is the formation of a hybrid resonance state. In this work, we demonstrate that the idea of enhanced reverse processes is more general. We discuss the case of the reverse process of photodissociation, namely, making a molecule out of separate atoms in a cavity. For bound electronic states, the interaction of atoms and molecules with quantum light as realized in cavities is known to give rise to the formation of hybrid light–matter states (usually called polaritons). In the scenarios discussed here, the hybrid light–matter states are resonance (metastable) states, which decay into the continuum of either electrons or of the fragments of a molecule. Resonances can substantially enhance the outcome of processes. In addition to the new resonant mechanism of molecule formation, the impact of the hybrid resonances on the scattering cross section of the atoms can be dramatic. [ABSTRACT FROM AUTHOR]

Gas-phase molecules are a promising platform to elucidate the mechanisms of action and scope of polaritons for optical control of chemistry. Polaritons arise from the strong coupling of a dipole-allowed molecular transition with the photonic mode of an optical cavity. There is mounting evidence of modified reactivity under polaritonic conditions; however, the complex condensed-phase environment of most experimental demonstrations impedes mechanistic understanding of this phenomenon. While the gas phase was the playground of early efforts in atomic cavity quantum electrodynamics, we have only recently demonstrated the formation of molecular polaritons under these conditions. Studying the reactivity of isolated gas-phase molecules under strong coupling would eliminate solvent interactions and enable quantum state resolution of reaction progress. In this Perspective, we contextualize recent gas-phase efforts in the field of polariton chemistry and offer a practical guide for experimental design moving forward. [ABSTRACT FROM AUTHOR]

The motional narrowing effect has been extensively studied for cavity exciton–polariton systems in recent decades both experimentally and theoretically, which is featured by (1) the subaverage behavior and (2) the asymmetric linewidths for the upper polariton and the lower polariton. However, a minimal theoretical model that is clear and adequate to address all these effects as well as the linewidth scaling relations remains missing. In this work, based on the single mode 1D Holstein–Tavis–Cummings (HTC) model, we studied the motional narrowing effect of the polariton linear absorption spectra via both semi-analytic derivations and numerically exact quantum dynamics simulations using the hierarchical equations of motion approach. The results reveal that under collective light–matter coupling between a cavity mode and N molecules, the polariton linewidth scales as 1 / N under the slow limit, while scales as 1/N under the fast limit, due to the polaron decoupling effect. Furthermore, by varying the detunings, the polariton linewidths exhibit significant motional narrowing, covering both characters mentioned above. Our analytic linewidth expressions [Eqs. (34) and (35)] agree well with the numerical exact simulations in all the parameter regimes we explored. These results indicate that the physics of motional narrowing is adequately accounted for by the single-mode 1D HTC model. We envision that both the numerical results and the analytic polariton linewidths expression presented in this work will offer great theoretical value for providing a better understanding of the exciton–polariton motional narrowing based on the HTC model. [ABSTRACT FROM AUTHOR]

The decisive experimental evidence of enhanced heat conduction driven by surface phonon polaritons (SPhPs) has been recently demonstrated along polar nanofilms. However, a proper quantitative interpretation remains to be fully established. In this work, we provide a consistent theoretical explanation of the measured thermal conductivities of polar nanofilms, based on a coupled Boltzmann transport equation and heat diffusion equation for describing the dynamics of SPhPs and phonons, respectively. This formalism enables to separately quantify the SPhP and phonon contributions to the in-plane heat transport and shows the overestimation of the SPhP thermal conductivity predicted by previous empirical model for predominant boundary scattering. This study, thus, promotes the understanding of the observed thermal conductivity enhancement driven by SPhPs, as a novel heat conduction channel for heat dissipation applications in nanoelectronics and optoelectronics. [ABSTRACT FROM AUTHOR]

We have used surface plasmon resonant metal gratings to induce and probe the dielectric response (i.e., electro-optic modulation) of ionic liquids (ILs) at electrode interfaces. Here, the cross-plane electric field at the electrode surface modulates the refractive index of the IL due to the Pockels effect. This is observed as a shift in the resonant angle of the grating (i.e., Δϕ), which can be related to the change in the local index of refraction of the electrolyte (i.e., Δnlocal). The reflection modulation of the IL is compared against a polar (D2O) and a non-polar solvent (benzene) to confirm the electro-optic origin of resonance shift. The electrostatic accumulation of ions from the IL induces local index changes to the gratings over the extent of electrical double layer (EDL) thickness. Finite difference time domain simulations are used to relate the observed shifts in the plasmon resonance and change in reflection to the change in the local index of refraction of the electrolyte and the thickness of the EDL. Simultaneously using the wavelength and intensity shift of the resonance enables us to determine both the effective thickness and Δn of the double layer. We believe that this technique can be used more broadly, allowing the dynamics associated with the potential-induced ordering and rearrangement of ionic species in electrode–solution interfaces. [ABSTRACT FROM AUTHOR]

In this paper, design and fabrication of a dual-band near-zero index metamaterial (MTM) structure using copper on an epoxy resin fiber (FR-4) dielectric substrate is reported for refractive index sensing applications. The primary objective is to achieve dual-band operation spanning a 1–15 GHz frequency range, with a specific focus on achieving a broad bandwidth in the C-band. The resonance of the MTM structure was ascribed to the coupling of plane electromagnetic waves with surface plasmon polaritons on the structure, resulting in a quadrupole plasmon resonance mode. Furthermore, transmission characteristics of the fabricated MTM structure were experimentally measured and found to align closely with the simulated results obtained through the finite element method in COMSOL Multiphysics. The designed MTM structure demonstrates negative and near-zero permittivity at resonance frequencies, enabling left-handed and near-zero index behavior in dual microwave frequency bands. Under room temperature conditions, the MTM sensor exhibited sensitivities of 1 GHz/RIU and 3 GHz/RIU at resonance frequencies of 2.7 and 7.3 GHz, respectively. Consequently, the MTM structure exhibits significant potential for diverse applications, serving as a valuable component in sensors, detectors, and optoelectronic devices operating in the GHz region. [ABSTRACT FROM AUTHOR]

The generation of exciton–polaritons through strong light–matter interactions represents an emerging platform for exploring quantum phenomena. A significant challenge in colloidal nanocrystal-based polaritonic systems is the ability to operate at room temperature with high fidelity. Here, we demonstrate the generation of room-temperature exciton–polaritons through the coupling of CdSe nanoplatelets (NPLs) with a Fabry–Pérot optical cavity, leading to a Rabi splitting of 74.6 meV. Quantum–classical calculations accurately predict the complex dynamics between the many dark state excitons and the optically allowed polariton states, including the experimentally observed lower polariton photoluminescence emission, and the concentration of photoluminescence intensities at higher in-plane momenta as the cavity becomes more negatively detuned. The Rabi splitting measured at 5 K is similar to that at 300 K, validating the feasibility of the temperature-independent operation of this polaritonic system. Overall, these results show that CdSe NPLs are an excellent material to facilitate the development of room-temperature quantum technologies. [ABSTRACT FROM AUTHOR]

Hyperbolic metasurfaces exhibit unique dispersion and polarization properties, making them a promising platform for a plethora of photonic applications. At the same time, the ability to engineer the hyperbolicity via the predefined spectral positions of the metasurface resonances remains a notable challenge. Here, we analyze the dependencies of the spectral positions of the resonances corresponding to the limits of the hyperbolic regime for the metasurfaces based on square arrays of the rectangular nanopatches. We show that the spectral difference between the resonances increases linearly with stretching of the nanopatch, but this dependence becomes quadratic when the length of the stretched nanopatch exceeds 85% of the lattice constant, indicating the regime of extreme anisotropy. Finally, we demonstrate the characteristic feature of the engineered resonances by showing the canalization (divergenceless propagation) of the surface plasmon-polariton along the anisotropic nanopatch-based metasurface in the vicinity of the resonance. The results obtained may be used for the engineering of the anisotropic nanoparticle-based metasurfaces for a plethora of photonic applications. [ABSTRACT FROM AUTHOR]

The use of cavities to impact molecular structure and dynamics has become popular. As cavities, in particular plasmonic nanocavities, are lossy and the lifetime of their modes can be very short, their lossy nature must be incorporated into the calculations. The Lindblad master equation is commonly considered an appropriate tool to describe this lossy nature. This approach requires the dynamics of the density operator and is thus substantially more costly than approaches employing the Schrödinger equation for the quantum wave function when several or many nuclear degrees of freedom are involved. In this work, we compare numerically the Lindblad and Schrödinger descriptions discussed in the literature for a molecular example where the cavity is pumped by a laser. The laser and cavity properties are varied over a range of parameters. It is found that the Schrödinger description adequately describes the dynamics of the polaritons and emission signal as long as the laser intensity is moderate and the pump time is not much longer than the lifetime of the cavity mode. Otherwise, it is demonstrated that the Schrödinger description gradually fails. We also show that the failure of the Schrödinger description can often be remedied by renormalizing the wave function at every step of time propagation. The results are discussed and analyzed. [ABSTRACT FROM AUTHOR]

Metasurface has the ability to flexibly modulate the wavefront and detect the polarization states, thus receiving widespread research attention. The combination of polarization multiplexing techniques and focused beams with polarization information provides a new approach to compact polarization detection behavior. Here, an all-dielectric metasurface based on polarization multiplexing encoding technique is demonstrated and assigns the independent phase distributions to x- and y-polarized channels to separate different polarized components. Combining Stokes parameters and visualized polarization ellipses, realizing one-to-one mapping of the incident polarization states with far-field images. We obtain the Poincaré sphere and visualized polarization ellipses based on Stokes parameters to verify the polarization detection ability of the designed metasurface. The proposed scheme is expected to provide potential applications in fields such as full-Stokes polarization detection, high-resolution imaging, and terahertz communication. [ABSTRACT FROM AUTHOR]

In this article, we show that the collective light–matter strong coupling regime where N molecular emitters couple to the photon mode of an optical cavity can be mapped to a quantum impurity model where the photon is the impurity that is coupled to a bath of anharmonic transitions. In the thermodynamic limit where N ≫ 1, we argue that the bath can be replaced with an effective harmonic bath, leading to a dramatic simplification of the problem into one of the coupled harmonic oscillators. We derive simple analytical expressions for linear optical spectra (transmission, reflection, and absorption) where the only molecular input required is the molecular linear susceptibility. This formalism is applied to a series of illustrative examples, showing the role of temperature, disorder, vibronic coupling, and optical saturation of the molecular ensemble, explaining that it is useful even when describing an important class of nonlinear optical experiments. For completeness, we provide Appendixes A–C that include a self-contained derivation of the relevant spectroscopic observables for arbitrary anharmonic systems (for both large and small N) within the rotating-wave approximation. While some of the presented results herein have already been reported in the literature, we provide a unified presentation of the results as well as new interpretations that connect powerful concepts in open quantum systems and linear response theory with molecular polaritonics. [ABSTRACT FROM AUTHOR]

Born–Huang expansion is the cornerstone for studying potential energy surfaces and non-adiabatic couplings (NACs) in molecular systems. However, the traditional approach is insufficient to describe the molecular system, which strongly interacts with quantum light. Inspired by the work by Schäfer et al., we develop the generalized Born–Huang expansion theory within a macroscopic quantum electrodynamics (QED) framework. The theory we present allows us to describe electromagnetic vacuum fluctuations in dielectric media and incorporate the effects of dressed photons (or polaritons) into NACs. With the help of the generalized Born–Huang expansion, we clearly classify electronic nuclear NACs, polaritonic nuclear NACs, and polaritonic electronic NACs. Furthermore, to demonstrate the advantage of the macroscopic QED framework, we estimate polaritonic electronic NACs without any free parameter, such as the effective mode volume, and demonstrate the distance dependence of the polaritonic electronic NACs in a silver planar system. In addition, we take a hydrogen atom in free space as an example and derive spontaneous emission rates from photonic electronic NACs (polaritonic electronic NACs are reduced to photonic electronic NACs). We believe that this work not only provides an avenue for the theoretical exploration of NACs in a nucleus–electron–polariton coupled system but also offers a more comprehensive understanding for molecules coupled with quantum light. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) transition metal dichalcogenides have emerged as promising quantum functional blocks benefitting from their unique combination of spin, valley, and layer degrees of freedom, particularly for the tremendous flexibility of moiré superlattices formed by van der Waals stacking. These degrees of freedom coupled with the enhanced Coulomb interaction in 2D structures allow excitons to serve as on-chip information carriers. However, excitons are spatially circumscribed due to their low mobility and limited lifetime. One way to overcome these limitations is through the coupling of excitons with surface plasmon polaritons (SPPs), which facilitates an interaction between remote quantum states. Here, we showcase the successful coupling of SPPs with interlayer excitons in molybdenum diselenide/tungsten diselenide heterobilayers. Our results indicate that the valley polarization can be efficiently transferred to SPPs, enabling preservation of polarization information even after propagating tens of micrometers. [ABSTRACT FROM AUTHOR]

We theoretically study the magnetic phase transition of condensed exciton-polariton microcavities in an applied magnetic field. When the magnetic field is strong, all polariton spins are polarized parallel to the magnetic field as usual. On the contrary, in the weak magnetic-field region, the polariton polarization degree is negative, namely, anti-parallel to the magnetic field. For a strong magnetic field, the magnetic phase of the polaritons arises and leads to a paramagnetic, while around a weak magnetic field, with zero exciton–photon detunings, and weak Rabi splitting the spin polarization of the polaritons leads to a diamagnetic. Thus, magneto-polariton phase transition polarization originates from the competition between the polariton Zeeman effect and polariton–polariton interactions. Moreover, the polariton polarization strongly depends on the exciton–photon detuning and Rabi splitting and has a large negative value as they are both small. At last, we compare our theoretical results with the experiments and find they match each other very well. [ABSTRACT FROM AUTHOR]

The observation that materials can change their properties when placed inside or near an optical resonator has sparked a fervid interest in understanding the effects of strong light–matter coupling on molecular dynamics, and several approaches have been proposed to extend the methods of computational chemistry into this regime. Whereas the majority of these approaches have focused on modeling a single molecule coupled to a single cavity mode, changes to chemistry have so far only been observed experimentally when very many molecules are coupled collectively to multiple modes with short lifetimes. While atomistic simulations of many molecules coupled to multiple cavity modes have been performed with semi-classical molecular dynamics, an explicit description of cavity losses has so far been restricted to simulations in which only a very few molecular degrees of freedom were considered. Here, we have implemented an effective non-Hermitian Hamiltonian to explicitly treat cavity losses in large-scale semi-classical molecular dynamics simulations of organic polaritons and used it to perform both mean-field and surface hopping simulations of polariton relaxation, propagation, and energy transfer. [ABSTRACT FROM AUTHOR]

Magnetically ordering media support spin waves or magnons, which can couple with electromagnetic waves to form magnon polaritons. Based on insulating antiferromagnets, magnon polaritons are situated in the far-infrared or THz frequency range. We investigated Dyakonov surface magnon polaritons (DSMPs) at the antiferromagnetic surface in an external magnetic field, where the external field and antiferromagnetic easy axis lie in the surface plane and are normal to each other. Our numerical results are based on the MnF2 crystal, but the conclusions and qualitative results are also available to other insulating antiferromagnets. We predicted two field-tunable DSMPs and one tunable Dyakonov surface magnon. We discerned the main effects of the external magnetic field on the DSMPs; either DSMPs are sensitively modulated by the external field or there is a cutoff magnetic field. Their individual Poynting vector seriously deviates the propagation direction and is sensitively controlled by the external field. The spin angular momentum contains two components normal to each other, unlike conventional surface magnon polaritons. One of the DSMPs can carry a huge Poynting vector and spin angular momentum in the external magnetic field. These results are interesting for micromechanics and spintronics and relevant technologies in the far-infrared or THz domain. [ABSTRACT FROM AUTHOR]

Acoustic metamaterial concepts, such as metalenses and hyperlenses, have been studied with much interest for super-resolution imaging. However, the physics of wave scattering by sub-wavelength sized defects is still not very well understood. Here, we present studies on acoustic wave interactions with circular defects of sizes varying from over a wavelength to sub-wavelength scale. Near- and far-field scattering patterns of single circular defects are presented, connecting them to analytical frameworks. Scattering field signatures produced by two identical circular defects of different sizes placed side by side are then discussed. The separation distance between the defects is among the parameters varied to understand the effects of geometric features in successful imaging. Experimental results are presented to support the predictions reported in the paper. The insights have important implications for sub-wavelength imaging using acoustic metamaterials. [ABSTRACT FROM AUTHOR]

Plasmon-mechanical resonators are frequently employed in sensor development. Here, I report the coupling of plasmon and mechanical modes in a multilayer architecture. In the experiment, the multilayer comprised indium tin oxide (ITO) and silver (Ag) mirrors placed on the top and bottom of a SiO2 substrate. By activating a Fabry–Pérot hybrid mode and surface plasmon polariton in a Kretschmann configuration, I demonstrated the generation of a hybrid plasmon-mechanical mode by plasmonic dispersion and through strong coupling, which resulted in mechanical distortion at multiple frequencies. Adsorption of rhodamine G6 on Ag modifies the optomechanical spectrum; it causes eigenmodes to split, resulting in a coupling rate greater than the optical decay rate (κ ∗ < g). Besides, the excitonic modes were observed to interact with plasmon-mechanical modes, especially on-resonance, where the plasmon-mechanical modes exhibited the higher intensity. For example, the out-of-phase flexural mode (iii, g 0 = 427 × 2 π kHz) became active because of the coupling of the dye. Meanwhile, after dye absorption, the strong in-phase compressional mode (iv, g 0 = 560 × 2 π kHz) exhibited the widest splitting and an increase in the side peaks, which merged when the pump power was raised. The system was then analyzed to determine the ideal experimental settings for detecting mass by the oscillator in a controlled experiment. The mass sensor responsivity was evaluated to be F = 10 17 Hz g − 1 . Advantages and disadvantages of this approach are presented. [ABSTRACT FROM AUTHOR]

Strong coupling of a confined optical field to the excitonic or vibronic transitions of a molecular material results in the formation of new hybrid states called polaritons. Such effects have been extensively studied in Fabry–Pèrot microcavity structures where an organic material is placed between two highly reflective mirrors. Recently, theoretical and experimental evidence has suggested that strong coupling can be used to modify chemical reactivity as well as molecular photophysical functionalities. However, the geometry of conventional microcavity structures limits the ability of molecules "encapsulated" in a cavity to interact with their local environment. Here, we fabricate mirrorless organic membranes that utilize the refractive index contrast between the organic active material and its surrounding medium to confine an optical field with Q-factor values up to 33. Using angle-resolved white light reflectivity measurements, we confirm that our structures operate in the strong coupling regime, with Rabi-splitting energies between 60 and 80 meV in the different structures studied. The experimental results are matched by transfer matrix and coupled oscillator models that simulate the various polariton states of the free standing membranes. Our work demonstrates that mechanically flexible and easy-to-fabricate free standing membranes can support strong light–matter coupling, making such simple and versatile structures highly promising for a range of polariton applications. [ABSTRACT FROM AUTHOR]

Photonic spin–orbit (SO) coupling is an important physical mechanism leading to numerous interesting phenomena in the systems of microcavity photons and exciton-polaritons. We report the effect of SO coupling in a tunable open-access microcavity embedded with anisotropic active media. The SO coupling associated with the TE–TM splitting results in an emergent anisotropy, which further leads to fine energy splittings allowing clear observation of the full set of eigenstates, in sharp contrast with the isotropic situation which leads to the isotropic eigenstates of spin vortices. We show that the photonic potential can be engineered by playing with the relation between the emergent anisotropy and the cavity ellipticity. All the experimental results are well reproduced by the degenerate perturbation theory. Our results constitute a significant extension to the research field of microcavity spinoptronics, with potential applications in polarization control and optical property measurement of photonic devices and materials. [ABSTRACT FROM AUTHOR]

Cavity coupling of gas-phase molecules will enable studies of benchmark chemical processes under strong light–matter interactions with a high level of experimental control and no solvent effects. We recently demonstrated the formation of gas-phase molecular polaritons by strongly coupling bright ν3, J = 3 → 4 rovibrational transitions of methane (CH4) to a Fabry–Pérot optical cavity mode inside a cryogenic buffer gas cell. Here, we further explore the flexible capabilities of this infrastructure. We show that we can greatly increase the collective coupling strength of the molecular ensemble to the cavity by increasing the intracavity CH4 number density. In doing so, we can tune from the single-mode coupling regime to a multimode coupling regime in which many nested polaritonic states arise as the Rabi splitting approaches the cavity mode spacing. We explore polariton formation for cavity geometries of varying length, finesse, and mirror radius of curvature. We also report a proof-of-principle demonstration of rovibrational gas-phase polariton formation at room temperature. This experimental flexibility affords a great degree of control over the properties of molecular polaritons and opens up a wider range of simple molecular processes to future interrogation under strong cavity-coupling. We anticipate that ongoing work in gas-phase polaritonics will facilitate convergence between experimental results and theoretical models of cavity-altered chemistry and physics. [ABSTRACT FROM AUTHOR]

The material dependence of phonon-polariton-based in-plane thermal conductance is investigated by examining systems composed of air and several wurtzite and zinc-blende crystals. Phonon-polariton-based thermal conductance varies by over an order of magnitude (∼ 0.5 – 60 nW/K), which is similar to the variation observed in the materials corresponding to bulk thermal conductivity. Regardless of the material, phonon-polaritons exhibit similar thermal conductance to that of phonons when layers become ultrathin (∼ 10 nm), suggesting the generality of the effect at these length-scales. A figure of merit is proposed to explain the large variation of in-plane polariton thermal conductance that is composed entirely of easily predicted and measured optical phonon energies and lifetimes. Using this figure of merit, in-plane phonon-polariton thermal conductance enlarges with increases in (1) optical phonon energies, (2) splitting between transverse and longitudinal mode pairs, and (3) phonon lifetimes. [ABSTRACT FROM AUTHOR]

We investigate the potential of surface plasmon polaritons at noble metal interfaces for surface-enhanced chiroptical sensing of dilute chiral drug solutions with nl volume. The high quality factor of surface plasmon resonances in both Otto and Kretschmann configurations enables the enhancement of circular dichroism differenatial absorption thanks to the large near-field intensity of such plasmonic excitations. Furthermore, the subwavelength confinement of surface plasmon polaritons is key to attain chiroptical sensitivity to small amounts of drug volumes placed around ≃100 nm by the metal surface. Our calculations focus on reparixin, a pharmaceutical molecule currently used in clinical studies for patients with community-acquired pneumonia, including COVID-19 and acute respiratory distress syndrome. Considering realistic dilute solutions of reparixin dissolved in water with concentration ≤ 5 mg/ml and nl volume, we find a circular-dichroism differential absorption enhancement factor of the order ≃20 and chirality-induced polarization distortion upon surface plasmon polariton excitation. Our results are relevant for the development of innovative chiroptical sensors capable of measuring the enantiomeric imbalance of chiral drug solutions with nl volume. [ABSTRACT FROM AUTHOR]

Exciton transport in extended molecular systems and how to manipulate such transport in a complex environment are essential to many energy and optical-related applications. We investigate the mechanism of plasmon-coupled exciton transport by using the Pauli master equation approach, combined with kinetic rates derived from macroscopic quantum electrodynamics. Through our theoretical framework, we demonstrate that the presence of a silver nanorod induces significant frequency dependence in the ability of transporting exciton through a molecule chain, indicated by the exciton diffusion coefficient, due to the dispersive nature of the silver dielectric response. Compared with the same system in vacuum, great enhancement (up to a factor of 103) in the diffusion coefficient can be achieved by coupling the resonance energy transfer process to localized surface plasmon polariton modes of the nanorod. Furthermore, our analysis reveals that the diffusion coefficients with the nearest-neighbor coupling approximation are ∼10 times smaller than the results obtained beyond this approximation, emphasizing the significance of long-range coupling in exciton transport influenced by plasmonic nanostructures. This study not only paves the way for exploring practical approaches to study plasmon-coupled exciton transport but also provides crucial insights for the design of innovative plasmon-assisted photovoltaic applications. [ABSTRACT FROM AUTHOR]

Recently, we predicted theoretically that in cavities that support several longitudinal modes, strong coupling can occur in very different manners, depending on the system parameters. Distinct longitudinal cavity modes are either entangled with each other via the material or independently coupled to the exciton mode. Here, we experimentally demonstrate the transition between those two regimes as the cavity thickness is gradually increased while maintaining fixed coupling strength. We study the properties of the system using reflection and emission spectroscopy and show that even though the coupling strength is constant, different behavior in the spectral response is observed along the coupling–decoupling transition. In addition, we find that in such multimode cavities, pronounced upper polariton emission is observed, in contrast to the usual case of a single-mode cavity. Furthermore, we address the ultrafast dynamics of the multimode cavities by pump–probe spectroscopic measurements and observe that the transient spectra significantly change through the transition. [ABSTRACT FROM AUTHOR]

This work is a numerical description of the interaction between optical pulses and plasmonic oscillations in nanoparticle composites. We present a numerical demonstration of enhanced second-harmonic generation (SHG) in plasmonic nanoparticles caused by collective resonances. The SHG and dispersion associated with core–shell nanoparticles are studied based on the Drude model. The shape of nanoparticles and the SHG enhancement factor are closely intertwined. It is shown that shape effects can be applied to enhance the SHG from plasmonic nanoshells and also the absorption and dispersion of a nonlinear dielectric function of the recommended structure are evaluated. At metal–dielectric interfaces, it has been demonstrated that the association of plasmonic nanostructures with nonlinear dielectric systems provides useful platforms for boosting frequency conversion processes. In addition, examining the effect of various geometrical parameters on the slow-light factor reveals a reduction in the slow-light spectrum, laying the groundwork for optical pulse storage and retrieval in optical communication applications in the future. This core–shell nanoparticle structure is attractive for a wide range of applications, including optical communication devices, due to the mentioned unique optical properties. [ABSTRACT FROM AUTHOR]

Vibrational strong coupling results from the interaction between optically allowed molecular vibrational excitations and the resonant mode of an infrared cavity. Strong coupling leads to the formation of hybrid states, known as vibrational polaritons, which are readily observed in transmission measurements and a manifold of the reservoir states. In contrast, Raman spectroscopy of vibrational polaritons is elusive and has recently been the focus of both theoretical and experimental investigations. Because Raman measurements are frequently performed with high-numerical aperture excitation/collection optics, the angular dispersion of the strongly coupled system must be carefully considered. Herein, we experimentally investigated vibrational polaritons involving dispersive collective lattice resonances of infrared antenna arrays. Despite clear indications of the strong coupling to vibrational excitations in the transmission spectrum; we found that Raman spectra do not bear signatures of the polaritonic transitions. Detailed measurements indicate that the disappearance of the Raman signal is not due to the polariton dispersion in our samples. On the other hand, the Tavis–Cummings–Holstein model that we employed to interpret our results suggests that the ratio of the Raman transition strengths between the reservoir and the polariton states scales according to the number of strongly coupled molecules. Because the vibrational transitions are relatively weak, the number of molecules required to achieve strong coupling conditions is about 109 per unit cell of the array of infrared antennas. Therefore, the scaling predicted by the Tavis–Cummings–Holstein model can explain the absence of the polariton signatures in spontaneous Raman scattering experiments. [ABSTRACT FROM AUTHOR]

We develop an accurate and numerically efficient non-adiabatic path-integral approach to simulate the non-linear spectroscopy of exciton–polariton systems. This approach is based on the partial linearized density matrix approach to model the exciton dynamics with explicit propagation of the phonon bath environment, combined with a stochastic Lindblad dynamics approach to model the cavity loss dynamics. Through simulating both linear and polariton two-dimensional electronic spectra, we systematically investigate how light–matter coupling strength and cavity loss rate influence the optical response signal. Our results confirm the polaron decoupling effect, which is the reduced exciton–phonon coupling among polariton states due to the strong light–matter interactions. We further demonstrate that the polariton coherence time can be significantly prolonged compared to the electronic coherence outside the cavity. [ABSTRACT FROM AUTHOR]

The interaction between condensed matter excitations and electromagnetic cavity fields serves as a rich playground for fundamental research and lies at the core of photonic and quantum technologies. Herein, the intriguing concept of composite states formed by distinct quasiparticles strongly coupled to the same optical cavity modes is experimentally and theoretically demonstrated. Specifically, magnons excited in a slab of an antiferromagnetic crystal and phonons excited in a distinct specimen of an insulating material are explored. The crystal slabs form an optical cavity with Fabry–Pérot oscillations in the terahertz range. Hybridized phonon–magnon polariton modes and their tunability by adjusting the distance between the slabs, showing that hybridization persists even at separations of up to several millimeters is demonstrated. The experimental results are interpreted using both classical and quantum electrodynamical models. The quantum description allows us to quantify the degree of hybridization linked to a topological behavior of the electric field phasor, in agreement with the classical electrodynamics expectations. The presented results are obtained at room temperature and cavities of millimeter size, paving the way for the engineering of realistic, frequency‐tunable THz devices through the hybridization of electric (phononics) and magnetic (spintronics) elementary excitations of matter. [ABSTRACT FROM AUTHOR]

A significant (up to 4 times) photoluminescence enhancement of single InP/InAsP/InP nanowires transferred onto a silicon oxide‐covered silver layer on silicon substrate with a metal surface roughness level of less than 1 nm and a dielectric thickness of 5 nm has been demonstrated. This phenomenon is explained by the interaction of electron–hole pairs in the semiconductor with surface plasmon polaritons. The photoluminescence kinetics and results of modeling confirm the indicated enhancement mechanism. [ABSTRACT FROM AUTHOR]

Controlling light at subwavelength scales is crucial in nanophotonics. Hyperbolic polaritons, supporting arbitrarily large wavevectors, enable extreme light confinement beyond the diffraction limit. Traditional hyperbolic metamaterials suffer from high losses due to metallic components, while natural low-loss hyperbolic phonon polaritons are limited to the mid-infrared range. Some hyperbolic materials at visible frequencies have been studied, but they are either very lossy or only feature out-of-plane hyperbolicity. Here, we demonstrate the presence of low-loss, in-plane hyperbolic plasmon polaritons in the visible and near-infrared in thin-films of MoOCl2, a natural van der Waals crystal. The polariton dispersion is predicted based on the framework of light propagation in biaxial media and experimentally confirmed by real space nano imaging on exfoliated flakes. MoOCl2 constitutes an ideal material platform for visible range applications leveraging the unboundedness of hyperbolic modes, such as hyperlensing, Purcell factor enhancement, and super-resolution imaging, without the drawbacks of metamaterials. Hyperbolic polaritons in van der Waals materials are light-matter excitations holding potential for nanophotonics applications, but they are mostly observed in the mid-infrared range. Here, the authors report the observation of low-loss in-plane hyperbolic plasmon polaritons in MoOCl2 thin-films at visible and near-infrared frequencies. [ABSTRACT FROM AUTHOR]

1D models with topological non‐trivial band structures are a simple and effective way to study novel and exciting concepts in topological photonics. In this work, the propagation of light‐matter quasi‐particles, so‐called exciton‐polaritons, is studied in waveguide arrays. Specifically, topological states are being investigated at the interface between dimer chains, characterized by a non‐zero winding number. In order to exercise precise control over the polariton propagation, non‐resonant laser excitation, as well as resonant excitation, are studied in transmission geometry. The results highlight a new platform for the study of quantum fluids of light and non‐linear optical propagation effects in coupled semiconductor waveguides. [ABSTRACT FROM AUTHOR]

Within this manuscript, we provide a novel Fano resonance-driven micro-nanosensor. Its primary structural components are a metal-insulator-metal (MIM) waveguide, a shield with three disks, and a T-shaped cavity (STDTC). The finite element approach was used to study the gadget in theory. It is found that the adjustment of the structure and the change of the dimensions are closely related to the sensitivity (S) and the quality factor (FOM). Different model structural parameters affect the Fano resonance, which in turn changes the transmission characteristics of the resonator. Through in-depth experimental analysis and selection of appropriate parameters, the sensor sensitivity finally reaches 3020 nm/RIU and the quality factor reaches 51.89. Furthermore, the installation of this microrefractive index sensor allows for the quick and sensitive measurement of glucose levels. It is a positive contribution to the field of optical devices and micro-nano sensors and meets the demand for efficient detection when applied in medical and environmental scenarios. [ABSTRACT FROM AUTHOR]

In non-Hermitian open quantum systems, such as polariton condensates, the local tailoring of gains and losses opens up an interesting possibility to realize functional optical elements. Here, we demonstrate that deliberately introducing losses via a photonic defect, realized by reducing the quality factor of a DBR mirror locally within an ultrahigh-quality microcavity, may be utilized to create directed polariton currents towards the defect. We discuss the role of polariton–polariton interactions in the process and how to tailor the effective decay time of a polariton condensate by coupling it to the defect. Our results highlight the far-reaching potential of non-Hermitian physics in polaritonics. [ABSTRACT FROM AUTHOR]

Polaritons, arising from the strong coupling between excitons and photons within microcavities, hold promise for optoelectronic and all-optical devices. They have found applications in various domains, including low-threshold lasers and quantum information processing. To realize complex functionalities, non-intuitive designs for polaritonic devices are required. In this contribution, we use finite-difference time-domain simulations of the dissipative Gross–Pitaevskii equation, written in a differentiable manner, and combine it with an adjoint formulation. Such a method allows us to use topology optimization to engineer the potential landscape experienced by polariton condensates to tailor its characteristics on demand. The potential directly translates to a blueprint for a functional device, and various fabrication and optical control techniques can experimentally realize it. We inverse-design a selection of polaritonic devices, i.e., a structure that spatially shapes the polaritons into a flat-top distribution, a metalens that focuses a polariton, and a nonlinearly activated isolator. The functionalities are preserved when employing realistic fabrication constraints such as minimum feature size and discretization of the potential. Our results demonstrate the utility of inverse design techniques for polaritonic devices, providing a stepping stone toward future research in optimizing systems with complex light–matter interactions. [ABSTRACT FROM AUTHOR]

Controlling the nonlinear relationship between surface plasmon polariton (SPP) mode index and chemical potential of graphene can be used in the field of active transformation optics. Here, we propose an electrically tunable 2D Graded Photonic Crystal (GPC) lens based on graphene SPP platform. Our platform comprises a graphene monolayer integrated into a back-gated structure with nano-patterned gate insulators. When the chemical potential of the graphene surface is designed to operate in the nonlinear region, the designed GPC lens can be continuously transformed between a Maxwell's fish-eye lens and a Luneburg lens by tuning the gate voltage. The range of the lens background chemical potential for allowing this transformation is systematically studied. To compensate for the significant errors inherent in the conventional effective medium theory (EMT) during the homogenization of photonic crystals (PCs), we propose a generalized effective medium theory (GEMT). The validity and accuracy of this approach are verified through comparisons with true values (based on rigorous eigenvalue solutions) and EMT values. Due to its advantages of on-site controls and easy fabrication characteristics, the proposed graphene GPC provides a new way for practical on-chip light manipulation. [ABSTRACT FROM AUTHOR]

Phonon-polaritons are known to emerge at the surface of solids under infrared (IR) irradiation at frequencies close to the optical phonon resonance. Metal, patterned on the top of the polariton-active surface, locally blocks the excitation of surface waves due to plasmonic screening and can be used for the design of wave patterns. We excite polaritonic waves at the surface of SiC under the irradiation of a CO2 laser (λ ∼ 10 μ m) and visualize them using apertureless near-field interference scanning probe microscopy. From the near-field scans in the vicinity of gold film periodical strip structures, we identify the Bragg scattering (diffraction) outside the grating with the contribution from separate strips coherently summed up, provided that the wavelength matching condition is fulfilled. The observed phenomena agree with wavefield calculations. Our observations demonstrate the potential of metal-patterned silicon carbide for the fabrication of on-chip polaritonic IR circuits. [ABSTRACT FROM AUTHOR]

A novel spoof surface plasmon polaritons (SSPP) structure is applied to the design of radio frequency (RF) power amplifiers (PAs) in this work. Both standard SSPP and the proposed SSPP structures are used as input and output matching networks of a multioctave PA design. An analysis and discussion of the electromagnetic characteristics of the proposed SSPP structures is presented. Further optimization of PA performance is achieved by utilizing the gradient algorithm of the Advanced Design System tool. According to the test results, the newly developed SSPP‐based PA achieves output power ranging from 40.5 to 42.6 dBm, while the power additional efficiency varies between 60% and 66.55%, with a total layout size of 59.8 mm × 14.6 mm in the frequency band of 0.8–3.2 GHz. In comparison with recent published work, the PA designed in this work expands the bandwidth while maintaining high output power and efficiency while being smaller in size. [ABSTRACT FROM AUTHOR]

The vast repository of van der Waals (vdW) materials supporting polaritons offers numerous possibilities to tailor electromagnetic waves at the nanoscale. The development of twistoptics—the modulation of the optical properties by twisting stacks of vdW materials—enables directional propagation of phonon polaritons (PhPs) along a single spatial direction, known as canalization. Here we demonstrate a complementary type of directional propagation of polaritons by reporting the visualization of unidirectional ray polaritons (URPs). They arise naturally in twisted hyperbolic stacks with very different thicknesses of their constituents, demonstrated for homostructures of α -MoO3 and heterostructures of α -MoO3 and β -Ga2O3. Importantly, their ray-like propagation, characterized by large momenta and constant phase, is tunable by both the twist angle and the illumination frequency. Apart from their fundamental importance, our findings introduce twisted asymmetric stacks as efficient platforms for nanoscale directional polariton propagation, opening the door for applications in nanoimaging, (bio)-sensing, or polaritonic thermal management. The directional propagation of phonon polaritons has been demonstrated in various twisted van der Waals materials. Here, the authors report a complementary type of directional polariton propagation by visualizing unidirectional ray polaritons in twisted asymmetric stacks of α-MoO3 and/or β-Ga2O3. [ABSTRACT FROM AUTHOR]

We demonstrate scalable ultra-strong light–matter coupling with intersubband polaritons in a truly harmonic confining potential. The harmonicity grants immunity from electron–electron interactions, a protection guaranteed by the Kohn theorem, allowing the intersubband transition frequency to be lowered while keeping the light–matter interaction strength constant. In principle, this procedure permits increasing the relative coupling strength (η = ΩRabi/ω12) at will. We measure a record low intersubband transition at 1.24 THz and a lower polaritonic mode at 920 GHz, below the barrier of 1 THz. The system exhibits a η ratio of 0.24, fully in the ultra-strong coupling regime, and remains stable up to 78 K. This approach is valuable for future non-adiabatic quantum electrodynamic experiments at long wavelengths. [ABSTRACT FROM AUTHOR]

In‐plane Hyperbolic Phonon polaritons (HPhPs) are quasiparticles formed via coupling of photons and optical phonons in in‐plane hyperbolic materials and offer unique applications in sensing, thermal emitters and high‐resolution imaging. However, the large momentum mismatch between photons and these in‐plane HPhPs has restricted their technological potential as most experimental demonstrations rely on sophisticated and expensive near‐field detection schemes. In this work, using the example of α‐MoO3, it is demonstrated that by constructing photonic hypercrystals of this material, one can not only excite these in‐plane HPhPs in the far field but also tune the far field response via twisting the hypercrystal lattice with respect the lattice of α‐MoO3. The findings will pave the way for the development of practical in‐plane HPhP devices as well as provide access to new fundamental physics of such materials via conventional and well developed far‐field measurement techniques. [ABSTRACT FROM AUTHOR]

A broadband hollow-core single-polarization 3dB coupler based on a dual-hollow-core anti-resonant fiber (DHC-ARF) embellished with semicircular silver nanowires is proposed. Semicircular silver nanowires are attached to the outer walls of two cladding tubes along the y-direction in the DHC-ARF to excite the localized surface plasmon resonance. By utilizing the mode coupling between y-polarized (y-pol) fundamental mode (FM) and surface plasmon polariton mode to increase the loss of y-pol FM, single-polarization operation can be implemented by filtering the y-pol FM and allowing only x-polarized (x-pol) FM to propagate with low loss between two cores. Finite element method combined with perfectly matched layer as a boundary condition is employed to optimize the properties of the DHC-ARF. Numerical results demonstrate that a hollow-core single-polarization 3dB coupler is constructed by only using a 1.82 cm long DHC-ARF within a wide bandwidth of 140 nm covering the wavelength range from 1480 nm to 1620 nm, in which the polarization extinction ratio (PER) is lower than − 20 dB and the coupling ratio is within 50 ± 2%. At the wavelength of 1550 nm, the PER reaches − 49.3 dB and the loss of the coupler are as low as 0.22 dB. To the best of our knowledge, this hollow-core single-polarization 3dB coupler exhibits the widest bandwidth so far, which is at least 12.7 times that of the current reports. This broadband hollow-core single-polarization 3dB coupler has great potential in polarization-sensitive fiber systems. [ABSTRACT FROM AUTHOR]

In this study, we present a novel design for a photonic crystal fiber (PCF) biosensor utilizing a quadruple silica channel configuration, specifically engineered for highly sensitive external sensing through surface plasmon resonance (SPR). In order to take advantage of the interaction between the surface plasmon polariton (SPP) and core-guided modes within the fiber, the silica channels are carefully positioned to generate an H-shaped PCF. The suggested sensor is designed and completely characterized by the finite element method-based COMSOL Multiphysics program, taking into account the refractive index (RI) variation in the analyte channels. A noticeably performance is achieved with a maximum wavelength sensitivity (WS) of 20,000 nm/RIU and amplitude sensitivity (AS) of - 1367.62 R I U - 1 in the wide RI range of 1.33 to 1.41. The proposed research aids in the early identification of certain cancer cells. Due to the variation in RI between cancer-affected and normal cell samples, the resonance wavelength of cancer-affected cell samples differs from their normal cell samples. The study demonstrates the sensor's specific sensitivities, AS of - 792.8853, - 422.7596, and - 985.2674 R I U - 1 and WS of 5000, 4000, and 7857.14 nm/RIU for HeLa, Basal, and MDA-MB-231 cell lines, respectively. The proposed SPR sensor is a strong contender in a variety of refractive index detection applications due to its high sensing performance and fabrication viability that is evident in this study. [ABSTRACT FROM AUTHOR]

In this article, we introduce a novel H-shaped plasmonic refractive index (RI) sensor coupled with a bus waveguide. The sensor is designed to interact with a straight metal-insulator-metal (MIM) waveguide configuration. To analyze the proposed structure, the finite element method (FEM) is employed, allowing for a comprehensive numerical investigation. The primary function of this sensor is to detect changes in RI by monitoring alterations in the resonant wavelength. The sensing mechanism involves the interaction of light with the plasmonic structure, and any variations in the RI of the surrounding medium induce changes in the resonant wavelength of the sensor. This phenomenon is crucial for applications such as biosensing and chemical analysis. To optimize the sensor's performance, the authors conducted a thorough process of geometric parameter optimization. Consequently, the recorded maximum sensitivity of the sensor, reported as 1960 nm/RIU for mode 2 and 1420 nm/RIU for mode 1, underscores its exceptional capability to discern minute quantities of molecules, showcasing a heightened sensitivity that sets it apart in molecular detection applications. Furthermore, we extend the applicability of their proposed sensor by numerically analyzing its performance in measuring the glucose content of blood. This highlights the versatility of the sensor, showcasing its potential for biomedical applications. [ABSTRACT FROM AUTHOR]

In this article, a wearable full-textile spoof surface plasmon polariton transmission line (SSPP TL) with improved communication data security has been presented. Equivalent circuit analyses reveal that the new proposed SSPP TL based on the patch-loading technique achieves flexible dispersion control by changing the patch dimension. As compared to conventional SSPP TL with periodical corrugations, the proposed wearable SSPP TL has similar transmission performance, but with a 43% reduction in transversal width. Such results are beneficial to the size reduction of the wearable wireless body area network (WBAN) system. Besides, the proposed SSPP TL achieves stricter field confinement, which helps to improve communication data security. The proposed wearable SSPP TL is pattered by hand-cutting the conductive E-textile. The feasibility of the wearable SSPP TL has been verified through the S-parameter simulation, specific absorption rate (SAR) simulation, the measurement in the free space, and measurements on different mounting positions of the human body. [ABSTRACT FROM AUTHOR]

This paper presents a photonic crystal fiber (PCF)-based surface plasmon resonance (SPR) sensor designed to achieve precise malaria detection in blood samples. The sensor's innovative architecture incorporates carefully optimized layers of plasmonic materials, including gold and TiO2, to attain sensitivity and specificity. Extensive assessment of this sensor's performance has been carried out through rigorous finite element analysis using COMSOL Multiphysics v5.6. The sensor's configuration features a gold-coated PCF with a thin analyte layer, enabling the external detection of malaria parasites within blood samples. The air-hole configuration of the PCF sensor resembles the shape of a "barred spiral galaxy". It has undergone comprehensive testing across various stages of infected blood cells (ring, trophozoite, schizont), as well as normal red blood cells, each with their distinct refractive indices (RI). Through meticulous adjustments to the sensor's geometric parameters, remarkable wavelength sensitivity of 17,857.14 nm/RIU and amplitude sensitivity of 442.92 RIU−1 have been achieved for the ring phase, 10,210.53 nm/RIU and 392.72 RIU−1 for the trophozoite phase, and 8758.62 nm/RIU and 352.86 RIU−1 for the schizont phase. The numerical investigation also shows that the sensor possesses a low confinement loss of 50.25 dB/cm, 34.97 dB/cm, 28.74 dB/cm, and 25.47 dB/cm for normal RBC, ring phase RBC, trophozoite phase RBC, and schizont phase RBC, respectively. The results confirm the potential of the proposed sensor to detect malaria compared to existing methods. Hence, this sensor holds significant promise for advancing malaria detection and monitoring in blood samples, potentially leading to improved diagnostic and management strategies for this disease. [ABSTRACT FROM AUTHOR]

Graphene has garnered significant interest since its discovery. In graphene, surface plasmon polaritons (SPPs) are excited at frequencies ranging from mid-infrared to terahertz, which is not possible with traditional plasmonic materials. In this manuscript, numerical analysis of SPPs at uniaxial chiral-graphene planar structure is delineated. The surface conductivity of monolayer graphene is modeled by Kubo formulism. The dispersion relation is obtained analytically by applying impedance boundary conditions on the tangential field components. Extended electromagnetic theory is utilized to solve the analytical problem. The variation in effective mode index under the different values of chirality and graphene features (chemical potential, relaxation time, and number of layers) for three types of uniaxial chiral media, i.e., ε t > 0, ε z > 0, ε t < 0, ε z < 0 and ε t > 0, ε z < 0 are analyzed in the THz frequency regime. It is found that the effective mode index is very sensitive when both longitudinal and transverse components of permittivity exhibit opposite signs as compared to other two cases. To confirm the presence of SPPs for the suggested structure, the normalized field distribution for uniaxial chiral medium is also studied. The present work holds promising potential for the fabrication of high-density nanophotonic chips at THz frequency regime. [ABSTRACT FROM AUTHOR]

In this paper, we propose a cavity-coupled perfect absorber (CCPA) consisting of a bottom gold layer, a SiO2 layer, and multilayer MIM (metal–insulator-metal) nanowires. By coupling the Fabry-Pérot (F-P) cavity mode with the magnetic plasmons (MPs) resonance mode in multilayer MIM structure, the MPs resonance in the multilayer MIM structure is enhanced and leads to increased absorption of the structure. By designing and optimizing the parameters, near-perfect absorption in the mid-infrared wavelengths can be achieved. The positions of the two absorption peaks can be adjusted by changing the width of the nanowires and the thickness of the SiO2 layer, resulting in the formant excitation at any position in the mid-infrared. The full-width at half-maximum (FWHM) of the short-wave peak is only 0.076 µm, and the FWHM of the long-wave peak is only 0.46 µm. The long-wave absorption peak maintains high efficiency and stability even at large incident angles, exhibiting "omnidirectional" characteristics. The tunable mid-infrared emission peak can be matched to the characteristic spectra of gases, making it suitable for infrared radiation sources in gas detection. [ABSTRACT FROM AUTHOR]