Strong Light-matter Coupling Research Articles

Chiral discrimination in helicity-preserving Fabry-Pérot cavities

We theoretically study circular dichroism of chiral molecules embedded inside a helicity-preserving Fabry-P\'erot cavity. We find an increase of the intrinsic chiroptical response of the molecules by 2 orders of magnitude and report the first clear signature of chiral cavity polaritons upon entering the regime of strong light-matter coupling. We study a cavity design based on two dielectric photonic crystal mirrors acting, in a narrow frequency range, as efficient polarization cross-converters in transmission for one polarization and almost perfect reflectors for the other polarization. We show that a Pasteur medium hosted inside such a cavity can couple efficiently to both the outside of the cavity and to the helicity-preserving mode, inheriting an enhanced chiral character. We expect such a device to be useful in the future to design ultrasensitive chiral sensors for optics and stereochemistry.

Boosting Light–Matter Interaction in a Longitudinal Bonding Dipole Plasmon Hybrid Anapole System

Achieving strong electromagnetic enhancement is critical for realizing strong light–matter coupling at the nanoscale. In this study, we constructed a hybrid anapole system composed of a nanohole silicon disk and a longitudinal bonding dipole plasmon mode-supported plasmonic dimer. Compared with the bare dimer plasmon, the hybrid system shows strong plasmonic resonance tuning ability, and its resonance peak can be tuned to the near-infrared region only by adjusting the radius of the silicon disk. Meanwhile, the E-field enhancement in the gap region can exceed four orders of magnitude without sacrificing the quality factor of the system. Furthermore, it is demonstrated that the emitter’s radiative decay rate enhancement in the hybrid system is much higher than that of a similar LBDP mode-supported plasmonic dimer nanodisk and the reported plasmonic nanocavity. In summary, our hybrid anapole systems combine the advantages of metal plasmonic nanodimers and conventional anapole mode-supported systems and avoid their disadvantages. This study provides a useful reference for the further exploration of single-photon emission sources, light harvesting, and other quantum nanophotonic applications.

Hartree method for molecular polaritons

The formation of the composite photonic-excitonic particle, known as a polariton, is a phenomenon emerging in materials possessing strong coupling to light. The organic-based materials besides the strong light-matter coupling also demonstrate strong interaction of electronic and vibrational degrees of freedom. We study the vibration-assisted polariton wave-function evolution treating both types of interactions as equally strong. Using the multiconfiguration Hartree approach we derive the equations of motion for the polariton wave function, where the vibration degrees of freedom interact with the polariton quantum field through the mean-field Hartree term. For the conventional quadratic polariton Hamiltonian and the Holstein-type vibration Hamiltonian (Tavis-Cummings-Holstein model), the obtained equations are in one-to-one correspondence with the original Schr\"odinger equation. In the second part of the paper, we show that our theory reproduces the physical properties of the polariton light emission spectrum. In particular, the theory explains experimental observations of the molecular Stokes shift in the polariton fluorescence spectra in the systems with strong light-matter coupling. We also investigate the behavior of the polariton wave function in the vicinity of the anticrossing point and demonstrate that the Hartree term can produce an infinite potential barrier of a dynamical origin, which is responsible for the formation of the mixed upper-lower polariton states. The nonlinear nature of the polariton theory reflects their collective behavior. We expect that the multiconfiguration Hartree approach being applied to polaritons and similar systems will result in a manifestation of new physical phenomena.

A Mean-Field Treatment of Vacuum Fluctuations in Strong Light-Matter Coupling.

Mean-field mixed quantum-classical dynamics could provide a much-needed means to inexpensively model quantum electrodynamical phenomena by describing the optical field and its vacuum fluctuations classically. However, this approach is known to suffer from an unphysical transfer of energy out of the vacuum fluctuations when the light-matter coupling becomes strong. We highlight this issue for the case of an atom in an optical cavity and resolve it by introducing an additional set of classical coordinates to specifically represent vacuum fluctuations whose light-matter interaction is scaled by the instantaneous ground-state population of the atom. This not only rigorously prevents the aforementioned unphysical energy transfer but is also shown to yield a radically improved accuracy in terms of the atomic population and the optical field dynamics, generating results in excellent agreement with full quantum calculations. As such, the resulting method emerges as an attractive solution for the affordable modeling of strong light-matter coupling phenomena involving macroscopic numbers of optical modes.

Gauge-invariant theory of truncated quantum light-matter interactions in arbitrary media

The loss of gauge invariance in models of light-matter interaction which arises from material and photonic space truncation can pose significant challenges to conventional quantum optical models when matter and light strongly hybridize. In structured photonic environments, necessary in practice to achieve strong light-matter coupling, a rigorous model of field quantization within the medium is also needed. Here we use the framework of macroscopic QED by quantizing the fields in an arbitrary material system, with a spatially dependent dispersive and absorptive dielectric, starting from a fundamental light-matter action. We truncate the material and mode degrees of freedom while respecting the gauge principle by imposing a partial gauge-fixing constraint during canonical quantization, which admits a large number of gauges including the Coulomb and multipolar gauges commonly used in quantum optics. We also consider gauge conditions with explicit time dependence, enabling us to unambiguously introduce additional phenomenologically time-dependent light-matter interactions in any gauge. Our results allow one to derive rigorous nonrelativistic models of ultrastrong light-matter interactions in structured photonic environments with no gauge ambiguity. Results for two-level systems and the dipole approximation are discussed, as well as how to go beyond the dipole approximation for effective single-particle models. By comparing with the limiting case of an inhomogeneous dielectric, where dispersion and absorption can be neglected and the fields can be expanded in terms of the generalized transverse eigenfunctions of the dielectric, we show how lossy systems can introduce an additional gauge ambiguity, which we resolve and predict to have fundamental implications for open quantum system models. Finally, we show how observables in mode-truncated systems can be calculated without ambiguity by using a simple gauge-invariant model of photodetection.

Tunable Nonlinearity and Efficient Harmonic Generation from a Strongly Coupled Light–Matter System

Strong light–matter coupling within electromagnetic environments provides a promising path to modify and control chemical and physical processes. The origin of the enhancement of nonlinear optical processes such as second-harmonic and third-harmonic generation (SHG and THG) due to strong light–matter coupling is attributed to distinct physical effects, which questions the relevance of strong coupling in these processes. In this work, we leverage a first-principles approach to investigate the origins of the experimentally observed enhancement of resonant SHG and THG under strong light–matter coupling. For the proposed system under consideration, we find that the enhancement of the nonlinear conversion efficiency has its origins in a modification of the associated nonlinear optical susceptibilities as polaritonic resonances emerge in the nonlinear spectrum. Further, we find that the nonlinear conversion efficiency can be tuned by increasing the light–matter coupling strength. Finally, we provide an alternative framework to compute the harmonic generation spectra from the displacement field as opposed to the standard approach, which computes the harmonic spectrum from the matter-only induced polarization. Our results provide useful insights that shed light on this key debate in the field and pave the way for predicting and understanding quantum nonlinear optical phenomena in strongly coupled light–matter systems.

Programmable Polariton Topological Insulators All-Optically Controlled by the Stark Effect.

Efficiently and flexibly manipulating unidirectional edge states is key to developing topological insulators as functional devices. In this work, we propose an all-optical method that utilizes the valley-selective optical Stark effect to realize programmable topological insulators. We pattern a two-dimensional honeycomb structure in an exciton-polariton platform resulting from a strong light-matter coupling in a monolayer transition metal dichalcogenide. The optical Stark effect is induced to generate a pseudo magnetic field, combined with spin-orbit coupling to form the topological one-way edge states of the polariton. On account of the ultrafast switching speed and precisely spatial controllability of the optical Stark effect, two applications, i.e., ports ratio tunable polariton splitter and programmable polariton router, were demonstrated, showing designable and rewritable functionality of all-optically controllable polariton topological insulators. This study paves the way to robustly and intelligently control/form polaritonic and spintronic devices for future classical and quantum information processing and application.

Room-Temperature Electrical Field-Enhanced Ultrafast Switch in Organic Microcavity Polariton Condensates.

Integrated electro-optical switches are essential as one of the fundamental elements in the development of modern optoelectronics. As an architecture for photonic systems exciton polaritons, hybrid bosonic quasiparticles that possess unique properties derived from both excitons and photons, have shown much promise. For this system, we demonstrate a significant improvement of emitted intensity and condensation threshold by applying an electric field to a microcavity filled with an organic microbelt. Our theoretical investigations indicate that the electric field makes the excitons dipolar and induces an enhancement of the exciton-polariton interaction and of the polariton lifetime. Based on these electric field-induced changes, a sub-nanosecond electrical field-enhanced polariton condensate switch is realized at room temperature, providing the basis for developing an on-chip integrated photonic device in the strong light-matter coupling regime.

Controlling the strong light-matter coupling in metal-dielectric optical resonators using spin-crossover molecules

We report the observation of (ultra)strong light-matter coupling, in the UV spectral region, between optical modes of a metal/dielectric bilayer nanocavity and the electronic excitations of spin-crossover (SCO) molecules. By thermally switching the SCO molecules between their low-spin and high-spin states, we demonstrate the possibility of fine-tuning the light-molecule hybridization strength, allowing a reversible switching between strong- (with Rabi splitting values of up to 550 meV) and weak-coupling regimes within a single photonic resonator. As a result, we show that spin-crossover molecular compounds constitute a novel, promising class of active nanomaterials in the context of tuneable and reconfigurable polaritonic devices.

Versatile Tunable Microresonator for the Light-Matter Interaction Studying in the Strong-Coupling Mode

The interaction between an ensemble of molecules and an electromagnetic field in a highly limited volume makes it possible to control the properties of a substance and, therefore, is an exceptionally promising area of research. The most common way to achieve weak or strong light-matter coupling is to place an ensemble of molecules in a micron-sized resonator. In such a system,the interaction of light with matter appears in the form of a change in the spectral response of the system, which depends on the strength of the coupling between the ensemble of molecules and the modes of the resonator. Currently, there is no general and user-friendly approach that allows studying a lot of different samples in a wide optical range using the same resonator setup. The present paper describes the design of a device that makes it possible to overcome this disadvantage, speed up and facilitate the study of the light-matter interaction, and also obtain weak and strong light-matter coupling modes for a large number of samples in the UV, visible, and IR regions of the optical spectrum. The device developed here is based on the tunable unstable λ/2 Fabry-Perot microresonator, consisting of flat and convex mirrors, which satisfy the condition of plane-parallelism at least at one point of the curved mirror and can significantly reduce the mode volume. The device was used to study the effect of the strong-coupling regime on the fluorescent properties of the Rhodamine 6G (R6G) dye embedded in a boron nitride nanoparticles matrix. It was found that the use of boron nitride (h-BN) as a carrier matrix has an orienting effect on the dye molecules, that results in an increase of the light-matter coupling strength at a lower resonator mode energy required. Keywords: microspectroscopy, optical microresonator, strong coupling, boron nitride.

Strong light-matter coupling in pentacene thin films on plasmonic arrays.

Utilizing strong light-matter coupling is an elegant and powerful way to modify the energy landscapes of excited states of organic semiconductors. Consequently, the chemical and photophysical properties of these organic semiconductors can be influenced without the need of chemical modification but simply by implementing them in optical microcavities. This has so far mostly been shown in Fabry-Pérot cavities and with organic single crystals or diluted molecules in a host matrix. Here, we demonstrate strong, simultaneous coupling of the two Davydov transitions in polycrystalline pentacene thin films to surface lattice resonances supported by open cavities made of silver nanoparticle arrays. Such thin films are more easily fabricated and, together with the open architecture, more suitable for device applications.

Multi-resonance TADF in optical cavities: suppressing excimer emission through efficient energy transfer to the lower polariton states

Strong light-matter coupling is exploited as a way to reduce aggregation-induced excimer losses in multi-resonance thermally activated delayed fluorescence emitters.

Light-responsive organic polaritons from first principles.

Controlling the optical properties of light-responsive organic molecules is essential for their application in photonics. We demonstrate how light-responsive organic polaritons formed inside an optical cavity can be used to modify these properties based on first principles. Specifically, we study the excited state properties of the trans-azobenzene molecule and the free base tetraphenyl porphyrin (H2TPP) molecule under weak to strong light-matter coupling. Our results show that the cavity can modulate the dispersion and absorption properties of organic molecules. Compared to the case outside the cavity, the anomalous dispersion of the trans-azobenzene molecule inside the cavity is suppressed and this suppression decreases with increasing coupling strength, showing the potential of strong light-matter coupling in manipulating the optical dipole trap of organic molecules. Moreover, by adjusting the cavity parameters to tune the strength of the light-matter coupling, we achieve free switching between symmetric Lorentz and asymmetric Fano line shapes for H2TPP polaritonic excitations. During the switching between these spectral features, we also find that the cavity can be used to control the spontaneous radiation of organic molecules via the Purcell effect. These findings provide a new pathway to manipulate the optical properties of light-responsive organic molecules.

Универсальный перестраиваемый микрорезонатор для исследования взаимодействия света с веществом в ржиме сильной связи

The interaction between an ensemble of molecules and an electromagnetic field in a highly limited volume makes it possible to control the properties of a substance and, therefore, is an exceptionally promising area of research. The most common way to achieve weak or strong light-matter coupling is to place an ensemble of molecules in a micron-sized resonator. In such a system,the interaction of light with matter appears in the form of a change in the spectral response of the system, which depends on the strength of the coupling between the ensemble of molecules and the modes of the resonator. Currently, there is no general and user-friendly approach that allows studying a lot of different samples in a wide optical range using the same resonator setup. The present paper describes the design of a device that makes it possible to overcome this disadvantage, speed up and facilitate the study of the light-matter interaction, and also obtain weak and strong light-matter coupling modes for a large number of samples in the UV, visible, and IR regions of the optical spectrum. The device developed here is based on the tunable unstable λ/2 Fabry-Perot microresonator, consisting of flat and convex mirrors, which satisfy the condition of plane-parallelism at least at one point of the curved mirror and can significantly reduce the mode volume. The device was used to study the effect of the strong-coupling regime on the fluorescent properties of the Rhodamine 6G (R6G) dye embedded in a boron nitride nanoparticles matrix. It was found that the use of boron nitride (h-BN) as a carrier matrix has an orienting effect on the dye molecules, that results in an increase of the light-matter coupling strength at a lower resonator mode energy required.

Molecular polariton electroabsorption

We investigate electroabsorption (EA) in organic semiconductor microcavities to understand whether strong light-matter coupling non-trivially alters their nonlinear optical [{chi }^{(3)}left(omega,{{{{mathrm{0,0}}}}}right)] response. Focusing on strongly-absorbing squaraine (SQ) molecules dispersed in a wide-gap host matrix, we find that classical transfer matrix modeling accurately captures the EA response of low concentration SQ microcavities with a vacuum Rabi splitting of hslash Omega approx 200 meV, but fails for high concentration cavities with hslash Omega approx 420 meV. Rather than new physics in the ultrastrong coupling regime, however, we attribute the discrepancy at high SQ concentration to a nearly dark H-aggregate state below the SQ exciton transition, which goes undetected in the optical constant dispersion on which the transfer matrix model is based, but nonetheless interacts with and enhances the EA response of the lower polariton mode. These results indicate that strong coupling can be used to manipulate EA (and presumably other optical nonlinearities) from organic microcavities by controlling the energy of polariton modes relative to other states in the system, but it does not alter the intrinsic optical nonlinearity of the organic semiconductor inside the cavity.

Strong coupling of excitons in monolayer WS2 with guided-mode resonance

Strong photon-exciton coupling has garnered considerable interest due to its potential applications in quantum information processing, quantum light sources, and even quantum metrology. Here, we designed an “open cavity” consisting of monolayer WS2 and a square perforated SiN structure. By taking advantage of the guided-mode resonance with high quality factor excited in perforated SiN structure, the strong photon-exciton coupling with the Rabi splitting energies of about 40 meV can be obtained. Furthermore, the Rabi splitting can be engineered by varying the hole filling factor. Our findings provide a new way to achieve the TMD-based light-matter strong coupling.

Disorder-enhanced transport in a chain of lossy dipoles strongly coupled to cavity photons

We study the interplay between disorder and light-matter coupling by considering a disordered one-dimensional chain of lossy dipoles coupled to a multimode optical cavity, through a microscopically derived Hamiltonian. Such a system, hosting polaritonic excitations, may be realized experimentally in a wide range of platforms under strong light-matter coupling. By analyzing both the eigenspectrum and the driven-dissipative transport properties of our system, we find that in the strong-coupling regime, increasing disorder leads almost uncoupled dark states to acquire a photonic part, allowing them to inherit polaritonic long-range transport characteristics. Crucially, we show that this disorder-enhanced transport mechanism is increasingly noticeable when the considered dipoles are lossier.

Shining light on the microscopic resonant mechanism responsible for cavity-mediated chemical reactivity

Strong light–matter interaction in cavity environments is emerging as a promising approach to control chemical reactions in a non-intrusive and efficient manner. The underlying mechanism that distinguishes between steering, accelerating, or decelerating a chemical reaction has, however, remained unclear, hampering progress in this frontier area of research. We leverage quantum-electrodynamical density-functional theory to unveil the microscopic mechanism behind the experimentally observed reduced reaction rate under cavity induced resonant vibrational strong light-matter coupling. We observe multiple resonances and obtain the thus far theoretically elusive but experimentally critical resonant feature for a single strongly coupled molecule undergoing the reaction. While we describe only a single mode and do not explicitly account for collective coupling or intermolecular interactions, the qualitative agreement with experimental measurements suggests that our conclusions can be largely abstracted towards the experimental realization. Specifically, we find that the cavity mode acts as mediator between different vibrational modes. In effect, vibrational energy localized in single bonds that are critical for the reaction is redistributed differently which ultimately inhibits the reaction.

Tamm‐Plasmon Exciton‐Polaritons in Single‐Monolayered CsPbBr3 Quantum Dots at Room Temperature

AbstractConstructing polaritonic devices in monolithic, ultra‐compact photonic architectures with monolayer‐featured exciton‐emitters is decisive to exploit the coherent superposition between entangled photonic and excitonic eigenstates for potential realizations of optical nonlinearities, macroscopic condensations, and superfluidity. Here, a feasible strategy for exciton‐polariton formations is demonstrated by implementing a Tamm‐plasmon (TP) polaritonic device with the active material composed of single‐monolayered perovskite (CsPbBr3) quantum dots (QDs). The metallic character of the TP configuration is able to concentrate its resonance mode into a confined region beyond the diffraction limit, which highly overlaps, both spatially and spectrally, with the single‐monolayered CsPbBr3 QDs embedded inside. The mode volume of the device is hence reduced dramatically, leading to an enhanced light–matter coupling strength for the polaritonic emission at room temperature. In particular, it is found that the dispersion relation of the TP polaritonic device is tunable by detuning the excitonic and photonic eigenmodes and that the polariton–polariton interaction energy is strongly dependent on the polariton's spin state. The presented strategy is a determinant step toward the realization of strong light–matter coupling and polariton spintronics in the CsPbBr3 QDs with a single‐monolayered feature.

Quantum Electrodynamic Behavior of Chlorophyll in a Plasmonic Nanocavity.

Plasmonic nanocavities have been used as a novel platform for studying strong light-matter coupling, opening access to quantum chemistry, material science, and enhanced sensing. However, the biomolecular study of cavity quantum electrodynamics (QED) is lacking. Here, we report the quantum electrodynamic behavior of chlorophyll-a in a plasmonic nanocavity. We construct an extreme plasmonic nanocavity using Au nanocages with various linker molecules and Au mirrors to obtain a strong coupling regime. Plasmon resonance energy transfer (PRET)-based hyperspectral imaging is applied to study the electrodynamic behaviors of chlorophyll-a in the nanocavity. Furthermore, we observe the energy level splitting of chlorophyll-a, similar to the cavity QED effects due to the light-matter interactions in the cavity. Our study will provide insight for further studies in quantum biological electron or energy transfer, electrodynamics, the electron transport chain of mitochondria, and energy harvesting, sensing, and conversion in both biological and biophysical systems.