Feist Group
MMUSCLES
MMUSCLES: Modification of Molecular structure Under Strong Coupling to confined Light modES
MMUSCLES, which ran from April 2017 to March 2023, was funded by an ERC Starting Grant from the European Research Council.
Principal Investigator: Johannes Feist
Introduction
MMUSCLES is an ERC-funded research project that focuses on polaritonic chemistry, i.e., the manipulation of chemical structure that can be achieved through strong coupling between confined light modes and organic molecules. Understanding and controlling the properties of matter is one of the overarching goals of modern science. A powerful way to achieve is this by using light, usually in the form of intense laser beams. However, modern advances in nanophotonics allow us to confine light modes so strongly that their effect on matter is felt even when no external fields are present. In this regime of “strong coupling” or “vacuum Rabi splitting”, the fundamental excitations of the coupled system are hybrid light-matter states which combine the properties of both constituents, so-called polaritons. This has recently been shown to significantly alter the chemical structure of the coupled molecules, which opens the possibility to manipulate and control reactions. We developed theoretical methods that can treat these modifications of molecular structure. These methods combine well-known techniques from quantum chemistry and quantum optics.
Publications
Publications financially supported by MMUSCLES:
2024
58.
Coherent multidimensional spectroscopy in polariton systems (PDF)
Abstract: ...The fast dynamics of molecular polaritonics is scrutinized theoretically through the implementation of two-dimensional spectroscopy protocols. We derive conceptually simple and computationally efficient formulas to calculate two-dimensional spectra for molecules, each of them modeled as a system of two electronic states including vibrational relaxation, immersed in an optical cavity, thus coupled to quantized radiation. Cavity photon losses and molecular relaxation are incorporated into the Hamiltonian dynamics to form an open quantum system that is solved through a master equation. In the collective case, the relaxation dynamics into dark states is revealed to be the crucial factor to explain the asymmetries in both the diagonal and cross peaks of two-dimensional spectra for long waiting times between excitation and detection, a feature shown by recent experiments. Our theoretical method provides a deeper insight in those processes that yield relevant signals in multidimensional molecular spectroscopy.
57.
Electrostatic nature of cavity-mediated interactions between low-energy matter excitations (PDF)
Abstract: ...The use of cavity quantum electrodynamical effects, i.e., of vacuum electromagnetic fields, to modify material properties in cavities has rapidly gained popularity and interest in the last few years. However, there is still a scarcity of general results that provide guidelines for an intuitive understanding and limitations of what kind of effects can be achieved. We provide such a result for the effective interactions between low-energy matter excitations induced either directly by their mutual coupling to the cavity electromagnetic (EM) field or indirectly through coupling to mediator modes that couple to the EM field. We demonstrate that the induced interactions are purely electrostatic in nature and are thus fully described by the EM Green's function evaluated at zero frequency. Our findings imply that reduced models with one or a few cavity modes can easily give misleading results.
56.
Unconventional magnetism mediated by spin-phonon-photon coupling (PDF)
Abstract: ...Magnetic order typically emerges due to the short-range exchange interaction between the constituent electronic spins. Recent discoveries have found a crucial role for spin-phonon coupling in various phenomena from optical ultrafast magnetization switching to dynamical control of the magnetic state. Here, we demonstrate theoretically the emergence of a biquadratic long-range interaction between spins mediated by their coupling to phonons hybridized with vacuum photons into polaritons. The resulting ordered state enabled by the exchange of virtual polaritons between spins is reminiscent of superconductivity mediated by the exchange of virtual phonons. The biquadratic nature of the spin-spin interaction promotes ordering without favoring ferro- or antiferromagnetism. It further makes the phase transition to magnetic order a first-order transition, unlike in conventional magnets. Consequently, a large magnetization develops abruptly on lowering the temperature which could enable magnetic memories admitting ultralow-power thermally-assisted writing while maintaining a high data stability. The role of photons in the phenomenon further enables an in-situ static control over the magnetism. These unique features make our predicted spin-spin interaction and magnetism highly unconventional paving the way for novel scientific and technological opportunities.
55.
Lindblad Master Equation Capable of Describing Hybrid Quantum Systems in the Ultrastrong Coupling Regime (PDF)
Abstract: ...Despite significant theoretical efforts devoted to studying the interaction between quantized light modes and matter, the so-called ultrastrong coupling regime still presents significant challenges for theoretical treatments and prevents the use of many common approximations. Here we demonstrate an approach that can describe the dynamics of hybrid quantum systems in any regime of interaction for an arbitrary electromagnetic (EM) environment. We extend a previous method developed for few-mode quantization of arbitrary systems to the case of ultrastrong light-matter coupling, and show that even such systems can be treated using a Lindblad master equation where decay operators act only on the photonic modes by ensuring that the effective spectral density of the EM environment is sufficiently suppressed at negative frequencies. We demonstrate the validity of our framework and show that it outperforms current state-of-the-art master equations for a simple model system, and then study a realistic nanoplasmonic setup where existing approaches cannot be applied.
54.
Classical approaches to chiral polaritonics (PDF)
Abstract: ...We provide a theoretical framework based on classical electromagnetism to describe optical properties of Fabry-Pérot cavities filled with multilayered and linear chiral materials. We find a formal link between transfer-matrix, scattering-matrix, and Green-function approaches to compute the polarization-dependent optical transmission, and cavity-modified circular dichroism signals. We show how general symmetries like Lorentz's reciprocity and time-reversal symmetry constrain the modeling of such cavities. We apply this approach to investigate numerically and analytically the properties of various Fabry-Pérot cavities, made of either metallic or helicity-preserving dielectric photonic crystal mirrors. In the latter case, we analyze the onset of chiral cavity polaritons in terms of partial helicity preservation of electromagnetic waves reflected at the mirror interfaces. Our approach is relevant for designing innovative Fabry-Pérot cavities for chiral sensing and for probing cavity-modified stereochemistry.
53.
The Effect of the Relative Size of the Exciton Reservoir on Polariton Photophysics (PDF)
Abstract: ...Strong interactions between excitons and photons lead to the formation of exciton-polaritons, which possess different properties compared to their constituents. Polaritons are created by incorporating a dye in an optical cavity where the electromagnetic field is tightly confined. The interest in the subject has exploded in recent years due to the ability to change (photo)chemistry, but still as simple a variable as the yield of emission varies between studies. For the field to progress, linking observables to system parameters is a dire need. Here, the study pairs emission yield to the size of the so-called exciton reservoir, which dictates polariton relaxation dynamics. To do this, a method is devised to experimentally control the relative size of the exciton reservoir and link it to the yield of emission. Thus, the results enable comparison of the photophysics of previous studies within the field and provide the tools to study the effect of the exciton reservoir on polariton photochemistry.
52.
Active control of polariton-enabled long-range energy transfer (PDF)
Abstract: ...Optical control is achieved on the excited state energy transfer between spatially separated donor and acceptor molecules, both coupled to the same optical mode of a cavity. The energy transfer occurs through the formed hybrid polaritons and can be switched on and off by means of ultraviolet and visible light. The control mechanism relies on a photochromic component used as donor, whose absorption and emission properties can be varied reversibly through light irradiation, whereas in-cavity hybridization with acceptors through polariton states enables a 6-fold enhancement of acceptor/donor contribution to the emission intensity with respect to a reference multilayer. These results pave the way for synthesizing effective gating systems for the transport of energy by light, relevant for light-harvesting and light-emitting devices, and for photovoltaic cells.
2023
51.
Vacuum-field-induced state mixing (PDF)
Abstract: ...By engineering the electromagnetic vacuum field, the induced Casimir-Polder shift (also known as Lamb shift) and spontaneous emission rates of individual atomic levels can be controlled. When the strength of these effects becomes comparable to the energy difference between two previously uncoupled atomic states, an environment-induced interaction between these states appears after tracing over the environment. This interaction has been previously studied for degenerate levels and simple geometries involving infinite, perfectly conducting half-spaces or free space. Here, we generalize these studies by developing a convenient description that permits the analysis of these non-diagonal perturbations to the atomic Hamiltonian in terms of an accurate non-Hermitian Hamiltonian. Applying this theory to a hydrogen atom close to a dielectric nanoparticle, we show strong vacuum-field-induced state mixing that leads to drastic modifications in both the energies and decay rates compared to conventional diagonal perturbation theory. In particular, contrary to the expected Purcell enhancement, we find a surprising decrease of decay rates within a considerable range of atom-nanoparticle separations. Furthermore, we quantify the large degree of mixing of the unperturbed eigenstates due to the nondiagonal perturbation. Our work opens new quantum state manipulation possibilities in emitters with closely spaced energy levels.
50.
Multi-scale molecular dynamics simulations of enhanced energy transfer in organic molecules under strong coupling (PDF)
Abstract: ...Exciton transport can be enhanced in the strong coupling regime where excitons hybridize with confined light modes to form polaritons. Because polaritons have group velocity, their propagation should be ballistic and long-ranged. However, experiments indicate that organic polaritons propagate in a diffusive manner and more slowly than their group velocity. Here, we resolve this controversy by means of molecular dynamics simulations of Rhodamine molecules in a Fabry-Pérot cavity. Our results suggest that polariton propagation is limited by the cavity lifetime and appears diffusive due to reversible population transfers between polaritonic states that propagate ballistically at their group velocity, and dark states that are stationary. Furthermore, because long-lived dark states transiently trap the excitation, propagation is observed on timescales beyond the intrinsic polariton lifetime. These insights not only help to better understand and interpret experimental observations, but also pave the way towards rational design of molecule-cavity systems for coherent exciton transport.
49.
Can We Observe Nonperturbative Vacuum Shifts in Cavity QED? (PDF)
Abstract: ...We address the fundamental question of whether or not it is possible to achieve conditions under which the coupling of a single dipole to a strongly confined electromagnetic vacuum can result in nonperturbative corrections to the dipole’s ground state. To do so we consider two simplified, but otherwise rather generic cavity QED setups, which allow us to derive analytic expressions for the total ground-state energy and to distinguish explicitly between purely electrostatic and genuine vacuum-induced contributions. Importantly, this derivation takes the full electromagnetic spectrum into account while avoiding any ambiguities arising from an ad hoc mode truncation. Our findings show that while the effect of confinement per se is not enough to result in substantial vacuum-induced corrections, the presence of high-impedance modes, such as plasmons or engineered LC resonances, can drastically increase these effects. Therefore, we conclude that with appropriately designed experiments it is at least in principle possible to access a regime where light-matter interactions become nonperturbative.
48.
Non-Hermitian Anharmonicity Induces Single-Photon Emission (PDF)
Abstract: ...Single-photon sources are in high demand for quantum information applications. A paradigmatic way to achieve single-photon emission is through anharmonicity in the energy levels, such that the absorption of a single photon from a coherent drive shifts the system out of resonance and prevents absorption of a second one. We identify a novel mechanism for single-photon emission through non-Hermitian anharmonicity, i.e., anharmonicity in the losses instead of in the energy levels. We demonstrate the mechanism in two types of systems, including a feasible setup consisting of a hybrid metallodielectric cavity weakly coupled to a two-level emitter, and show that it induces high-purity single-photon emission at high repetition rates.
47.
Quantitative Investigation of the Rate of Intersystem Crossing in the Strong Exciton–Photon Coupling Regime (PDF)
Abstract: ...Strong interactions between excitons and photons lead to the formation of exciton-polaritons, which possess completely different properties compared to their constituents. The polaritons are created by incorporating a material in an optical cavity where the electromagnetic field is tightly confined. Over the last few years, the relaxation of polaritonic states has been shown to enable a new kind of energy transfer event, which is efficient at length scales substantially larger than the typical Förster radius. However, the importance of such energy transfer depends on the ability of the short-lived polaritonic states to efficiently decay to molecular localized states that can perform a photochemical process, such as charge transfer or triplet states. Here, we investigate quantitatively the interaction between polaritons and triplet states of erythrosine B in the strong coupling regime. We analyze the experimental data, collected mainly employing angle-resolved reflectivity and excitation measurements, using a rate equation model. We show that the rate of intersystem crossing from the polariton to the triplet states depends on the energy alignment of the excited polaritonic states. Furthermore, it is demonstrated that the rate of intersystem crossing can be substantially enhanced in the strong coupling regime to the point where it approaches the rate of the radiative decay of the polariton. In light of the opportunities that transitions from polaritonic to molecular localized states offer within molecular photophysics/chemistry and organic electronics, we hope that the quantitative understanding of such interactions gained from this study will aid in the development of polariton-empowered devices.
46.
Chiral discrimination in helicity-preserving Fabry-Pérot cavities (PDF)
Abstract: ...We theoretically study circular dichroism of chiral molecules embedded inside a helicity-preserving Fabry-Pérot 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.
Erratum: Phys. Rev. A 108, 069902 (2023) (PDF)
2022
45.
Few-mode field quantization for multiple emitters (PDF)
Abstract: ...The control of the interaction between quantum emitters using nanophotonic structures holds great promise for quantum technology applications, while its theoretical description for complex nanostructures is a highly demanding task as the electromagnetic (EM) modes form a high-dimensional continuum. We here introduce an approach that permits a quantized description of the full EM field through a small number of discrete modes. This extends the previous work in ref. (I. Medina, F. J. García-Vidal, A. I. Fernández-Domínguez, and J. Feist, “Few-mode field quantization of arbitrary electromagnetic spectral densities,” Phys. Rev. Lett. , vol. 126, p. 093601, 2021) to the case of an arbitrary number of emitters, without any restrictions on the emitter level structure or dipole operators. The low computational demand of this method makes it suitable for studying dynamics for a wide range of parameters. We illustrate the power of our approach for a system of three emitters placed within a hybrid metallodielectric photonic structure and show that excitation transfer is highly sensitive to the properties of the hybrid photonic–plasmonic modes.
44.
A Theoretical Perspective on Molecular Polaritonics (PDF)
Abstract: ...In the past decade, much theoretical research has focused on studying the strong coupling between organic molecules (or quantum emitters, in general) and light modes. The description and prediction of polaritonic phenomena emerging in this light–matter interaction regime have proven to be difficult tasks. The challenge originates from the enormous number of degrees of freedom that need to be taken into account, both in the organic molecules and in their photonic environment. On one hand, the accurate treatment of the vibrational spectrum of the former is key, and simplified quantum models are not valid in many cases. On the other hand, most photonic setups have complex geometric and material characteristics, with the result that photon fields corresponding to more than just a single electromagnetic mode contribute to the light–matter interaction in these platforms. Moreover, loss and dissipation, in the form of absorption or radiation, must also be included in the theoretical description of polaritons. Here, we review and offer our own perspective on some of the work recently done in the modeling of interacting molecular and optical states with increasing complexity.
43.
Not dark yet for strong light-matter coupling to accelerate singlet fission dynamics (PDF)
Abstract: ...Polaritons are unique hybrid light-matter states that offer an alternative way to manipulate chemical processes. In this work, we show that singlet fission dynamics can be accelerated under strong light-matter coupling. For superexchange-mediated singlet fission, state mixing speeds up the dynamics in cavities when the lower polariton is close in energy to the multiexcitonic state. This effect is more pronounced in non-conventional singlet fission materials in which the energy gap between the bright singlet exciton and the multiexcitonic state is large (>0.1 eV). In this case, the dynamics is dominated by the polaritonic modes and not by the bare-molecule-like dark states, and, additionally, the resonant enhancement due to strong coupling is robust even for energetically broad molecular states. The present results provide a new strategy to expand the range of suitable materials for efficient singlet fission by making use of strong light-matter coupling.
42.
Permutational symmetry for identical multilevel systems: A second-quantized approach (PDF)
Abstract: ...We develop a framework that provides a straightforward approach to fully exploit the permutational symmetry of identical multilevel systems. By taking into account the permutational symmetry, we outline a simple scheme that allows us to map the dynamics of N identical d-level systems to the dynamics of d bosonic modes with N particles, achieving an exponential reduction on the dimensionality of the problem in a simple and straightforward way. In particular, we consider the Lindblad dynamics of several identical multilevel systems interacting with a common subsystem under the action of collective dissipation terms.
41.
Plexcitonic Quantum Light Emission from Nanoparticle-on-Mirror Cavities (PDF)
Abstract: ...We investigate the quantum-optical properties of the light emitted by a nanoparticle-on-mirror cavity filled with a single quantum emitter. Inspired by recent experiments, we model a dark-field setup and explore the photon statistics of the scattered light under grazing laser illumination. Exploiting analytical solutions to Maxwell’s equations, we quantize the nanophotonic cavity fields and describe the formation of plasmon–exciton polaritons (or plexcitons) in the system. This way, we reveal that the rich plasmonic spectrum of the nanocavity offers unexplored mechanisms for nonclassical light generation that are more efficient than the resonant interaction between the emitter natural transition and the brightest optical mode. Specifically, we find three different sample configurations in which strongly antibunched light is produced. Finally, we illustrate the power of our approach by showing that the introduction of a second emitter in the platform can enhance photon correlations further.
40.
Theoretical Challenges in Polaritonic Chemistry (PDF)
Abstract: ...Polaritonic chemistry exploits strong light–matter coupling between molecules and confined electromagnetic field modes to enable new chemical reactivities. In systems displaying this functionality, the choice of the cavity determines both the confinement of the electromagnetic field and the number of molecules that are involved in the process. While in wavelength-scale optical cavities the light–matter interaction is ruled by collective effects, plasmonic subwavelength nanocavities allow even single molecules to reach strong coupling. Due to these very distinct situations, a multiscale theoretical toolbox is then required to explore the rich phenomenology of polaritonic chemistry. Within this framework, each component of the system (molecules and electromagnetic modes) needs to be treated in sufficient detail to obtain reliable results. Starting from the very general aspects of light–molecule interactions in typical experimental setups, we underline the basic concepts that should be taken into account when operating in this new area of research. Building on these considerations, we then provide a map of the theoretical tools already available to tackle chemical applications of molecular polaritons at different scales. Throughout the discussion, we draw attention to both the successes and the challenges still ahead in the theoretical description of polaritonic chemistry.
2021
39.
Selective isomer emission via funneling of exciton polaritons (PDF)
Abstract: ...Polaritons in organic systems have shown the potential to modify chemical properties and to mediate long-range energy transfer between individual chromophores, among other capabilities. Here, we demonstrate that strong coupling and formation of organic exciton-polaritons can be used to selectively tune the isomer emission of organic molecules. By taking advantage of their delocalized and hybrid character, polaritons emerging in the strong
coupling regime open a new relaxation pathway that allows for an efficient funneling of the excitation between
the molecular isomers. We implement this by strong coupling to trans-DCS (E-4-dimethylamino-4′cyanostilbene) molecules, which present two isomers in different amounts when immersed in a polymer matrix. Thanks to this new relaxation pathway, the photoexcitation that is first shared by the common polaritonic mode is then selectively funneled to the excited states of one of the isomers, recognizing pure emission from the isomeric states that
do not contribute to emission under normal conditions.
38.
Ultrastrong Exciton–Photon Coupling in Broadband Solar Absorbers (PDF)
Abstract: ...The recent development of organic polaritonic solar cells, in which sunlight absorbers and photon modes of a resonator are hybridized as a result of their strong coupling, has revealed the potential this interaction offers to control and enhance the performance of these devices. In this approach, the photovoltaic cell is built in such a way that it also behaves as an optical cavity supporting spectrally well-defined resonances, which match the broad absorption bands of the dyes employed. Herein we focus on the experimental and theoretical analysis of the specific spectral and angular optical absorption characteristics of a broadband light harvester, namely a subphthalocyanine, when operating in the ultrastrong coupling regime. We discuss the implications of having a broad distribution of oscillator strengths and demonstrate that rational design of the layered structure is needed to optimize both the spectral and the angular response of the sunlight harvester dye.
37.
Exact time-dependent density-functional theory for nonperturbative dynamics of the helium atom (PDF)
Abstract: ...By inverting the time-dependent Kohn-Sham equation for a numerically exact dynamics of the helium atom, we show that the dynamical step and peak features of the exact correlation potential found previously in one-dimensional models persist for real three-dimensional systems. We demonstrate that the Kohn-Sham and true current densities differ by a rotational component. The results have direct implications for approximate time-dependent density functional theory calculations of atoms and molecules in strong fields, emphasizing the need to go beyond the adiabatic approximation, and highlighting caution in the quantitative use of the Kohn-Sham current.
36.
Hybrid light–matter states formed in self-assembling cavities
Abstract: ...Tiny flakes of metal suspended in a solution have been observed to self-assemble into pairs separated by a narrow gap — offering a tunable system for studying combinations of light and matter known as polaritons.
35.
Accurate Truncations of Chain Mapping Models for Open Quantum Systems (PDF)
Abstract: ...The dynamics of open quantum systems are of great interest in many research fields, such as for the interaction of a quantum emitter with the electromagnetic modes of a nanophotonic structure. A powerful approach for treating such setups in the non-Markovian limit is given by the chain mapping where an arbitrary environment can be transformed to a chain of modes with only nearest-neighbor coupling. However, when long propagation times are desired, the required long chain lengths limit the utility of this approach. We study various approaches for truncating the chains at manageable lengths while still preserving an accurate description of the dynamics. We achieve this by introducing losses to the chain modes in such a way that the effective environment acting on the system remains unchanged, using a number of different strategies. Furthermore, we demonstrate that extending the chain mapping to allow next-nearest neighbor coupling permits the reproduction of an arbitrary environment, and adding longer-range interactions does not further increase the effective number of degrees of freedom in the environment.
34.
Light-Harvesting Properties of a Subphthalocyanine Solar Absorber Coupled to an Optical Cavity (PDF)
Abstract: ...Herein, both from the experimental and theoretical point of view, the optical absorption properties of a subphthalocyanine (SubPc), an organic macrocycle commonly used as a sunlight harvester, coupled to metallic optical cavities are analyzed. How different electronic transitions characteristic of this compound and specifically those that give rise to excitonic (Q band) and charge transfer (CT band) transitions couple to optical cavity modes is investigated. It is observed that whereas the CT band couples weakly to the cavity, the Q band transitions show evidence of hybridization with the photon eigenstates of the resonator, a distinctive trait of the strong coupling regime. As a result of the different coupling regimes of the two electronic transitions, very different spectral and directional light-harvesting features are observed, which for the weakly coupled CT transitions are mainly determined by the highly dispersive cavity modes and for the strongly coupled Q band by the less angle-dependent exciton-polariton bands. Modeling also allows discriminating parasitic from productive absorption in each case, enabling the estimation of the expected losses in a solar cell acting as an optical resonator.
33.
Reply to the Comment on “On the SN2 Reactions Modified in Vibrational Strong Coupling Experiments: Reaction Mechanisms and Vibrational Mode Assignments”
32.
Cavity-modified Chemistry: Towards Vacuum-field Catalysis
Abstract: ...In the preceding chapters, electric field effects on chemical reactivity have been extensively discussed, focusing on STM setups and enzyme catalysis among many others. Here we will focus on a rather different and only recently explored approach to manipulate chemical reactions with electric fields. With the use of resonant cavity modes hosted in Fabry–Pérot cavities for instance, as well as plasmonic modes, very recent investigations have shown modifications of chemical reactivity and dynamics, including thermal reactions and photochemistry, as well as manipulation of materials properties and non-adiabatic processes. All these works have given birth to a new field termed polaritonic chemistry due to the fact that in the so-called strong-coupling regime, polaritons become the new eigenstates of the system. These are hybrid states of light and matter that inherit properties from both constituents, providing new means to modify chemical phenomena. The aim of this chapter is two-fold: on one side, we aim to provide a general background on confined light modes and strong coupling for the non-specialised reader, and on the other, we aim to review the recent achievements of the field, paying special attention to modifications in ground-state reactivity. To this end, the chapter is organised as follows. After an introduction to settle basic concepts, we review the most relevant experimental and theoretical work in which modified chemical reactivity has been reported and conclude with the challenges faced by the field.
31.
Photoisomerization Efficiency of a Solar Thermal Fuel in the Strong Coupling Regime (PDF)
Abstract: ...Strong exciton-photon coupling is achieved when the interaction between molecules and an electromagnetic field is increased to a level where they cannot be treated as separate systems. This leads to the formation of polaritonic states and an effective rearrangement of the potential energy surfaces, which opens the possibility to modify photochemical reactions. This work investigates how the strong coupling regime is affecting the photoisomerization efficiency and thermal backconversion of a norbornadiene–quadricyclane molecular photoswitch. The quantum yield of photoisomerization shows both an excitation wavelength and exciton/photon constitution dependence. The polariton-induced decay and energy transfer processes are discussed to be the reason for this finding. Furthermore, the thermal back conversion of the system is unperturbed and the lower polariton effectively shifts the absorption onset to lower energies. The reason for the unperturbed thermal backconversion is that it occurs on the ground state, which is unaffected. This work demonstrates how strong coupling can change material properties towards higher efficiencies in applications. Importantly, the experiments illustrate that strong coupling can be used to optimize the absorption onset of the molecular photoswitch norbonadiene without affecting the back reaction from the uncoupled quadricyclane.
30.
Multi-scale dynamics simulations of molecular polaritons: The effect of multiple cavity modes on polariton relaxation (PDF)
Abstract: ...Coupling molecules to the confined light modes of an optical cavity is showing great promise for manipulating chemical reactions. However, to fully exploit this principle and use cavities as a new tool for controlling chemistry, a complete understanding of the effects of strong light–matter coupling on molecular dynamics and reactivity is required. While quantum chemistry can provide atomistic insight into the reactivity of uncoupled molecules, the possibilities to also explore strongly coupled systems are still rather limited due to the challenges associated with an accurate description of the cavity in such calculations. Despite recent progress in introducing strong coupling effects into quantum chemistry calculations, applications are mostly restricted to single or simplified molecules in ideal lossless cavities that support a single light mode only. However, even if commonly used planar mirror micro-cavities are characterized by a fundamental mode with a frequency determined by the distance between the mirrors, the cavity energy also depends on the wave vector of the incident light rays. To account for this dependency, called cavity dispersion, in atomistic simulations of molecules in optical cavities, we have extended our multi-scale molecular dynamics model for strongly coupled molecular ensembles to include multiple confined light modes. To validate the new model, we have performed simulations of up to 512 Rhodamine molecules in red-detuned Fabry–Pérot cavities. The results of our simulations suggest that after resonant excitation into the upper polariton at a fixed wave vector, or incidence angle, the coupled cavity-molecule system rapidly decays into dark states that lack dispersion. Slower relaxation from the dark state manifold into both the upper and lower bright polaritons causes observable photo-luminescence from the molecule–cavity system along the two polariton dispersion branches that ultimately evolves toward the bottom of the lower polariton branch, in line with experimental observations. We anticipate that the more realistic cavity description in our approach will help to better understand and predict how cavities can modify molecular properties.
29.
Few-Mode Field Quantization of Arbitrary Electromagnetic Spectral Densities (PDF)
Abstract: ...We develop a framework that provides a few-mode master equation description of the interaction between a single quantum emitter and an arbitrary electromagnetic environment. The field quantization requires only the fitting of the spectral density, obtained through classical electromagnetic simulations, to a model system involving a small number of lossy and interacting modes. We illustrate the power and validity of our approach by describing the population and electric field spatial dynamics in the spontaneous decay of an emitter placed in a complex hybrid plasmonic-photonic structure.
28.
Macroscopic QED for quantum nanophotonics: emitter-centered modes as a minimal basis for multiemitter problems (PDF)
Abstract: ...We present an overview of the framework of macroscopic quantum electrodynamics from a quantum nanophotonics perspective. Particularly, we focus our attention on three aspects of the theory that are crucial for the description of quantum optical phenomena in nanophotonic structures. First, we review the light–matter interaction Hamiltonian itself, with special emphasis on its gauge independence and the minimal and multipolar coupling schemes. Second, we discuss the treatment of the external pumping of quantum optical systems by classical electromagnetic fields. Third, we introduce an exact, complete, and minimal basis for the field quantization in multiemitter configurations, which is based on the so-called emitter-centered modes. Finally, we illustrate this quantization approach in a particular hybrid metallodielectric geometry: two quantum emitters placed in the vicinity of a dimer of Ag nanospheres embedded in a SiN microdisk.
27.
Molecular photodissociation enabled by ultrafast plasmon decay (PDF)
Abstract: ...We propose a strategy for enabling photodissociation of a normally photostable molecule through coupling to a nanoparticle plasmon. The large possible coupling on the single-molecule level combined with the highly lossy nature of plasmonic modes, with lifetimes on the order of femtoseconds, opens an ultrafast decay channel for the molecule. For plasmon mode frequencies below the vertical photoexcitation energy of the molecule, the difference between the excitation and emission energies is converted into vibrational energy on the molecular ground state in a Raman-like process. Under the correct conditions, this energy can be high enough to enable efficient photodissociation on the electronic ground state. We demonstrate the concept using numerical simulations of the Lindblad master equation for the hydrogen molecule in the vicinity of an aluminum nanoparticle and explore the photodissociation efficiency as a function of various system parameters.
2020
26.
Long-distance heat transfer between molecular systems through a hybrid plasmonic-photonic nanoresonator (PDF)
Abstract: ...We theoretically study a hybrid plasmonic-photonic cavity setup that can be used to induce and control long-distance heat transfer between molecular systems through optomechanical interactions. The structure we propose consists of two separated plasmonic nanoantennas coupled to a dielectric cavity. The hybrid modes of this resonator can combine the large optomechanical coupling of the sub-wavelength plasmonic modes with the large quality factor and delocalized character of the cavity mode that extends over a large distance (∼µm). We show that this can lead to effective long-range heat transport between molecular vibrations that can be actively controlled through an external driving laser.
25.
Impact of Vibrational Modes in the Plasmonic Purcell Effect of Organic Molecules (PDF)
Abstract: ...By means of quantum tensor network calculations, we investigate the large Purcell effect experienced by an organic molecule placed in the vicinity of a plasmonic nanostructure. In particular, we consider a donor-π bridge-acceptor dye at the gap of two Ag nanospheres. Our theoretical approach allows for a realistic description of the continua of both molecular vibrations and optical nanocavity modes. We analyze both the ultrafast exciton dynamics in the large Purcell enhancement regime and the corresponding emission spectrum, showing that these magnitudes are not accurately represented by the simplified models used up to date. Specifically, both the two-level system model and the single vibrational mode model can only reproduce the dynamics over short time scales, whereas the Fermi’s golden rule approach accounts only for the behavior at very long times. We demonstrate that including the whole set of vibrational modes is necessary to capture most of the dynamics and the corresponding spectrum. Moreover, by disentangling the coupling of the molecule to radiative and nonradiative plasmonic modes, we also shed light into the quenching phenomenology taking place in the system.
24.
On the SN2 reactions modified in vibrational strong coupling experiments: reaction mechanisms and vibrational mode assignments (PDF)
Abstract: ...Recent experiments have reported modified chemical reactivity under vibrational strong coupling (VSC) in microfluidic Fabry–Pérot cavities. In particular, the reaction rate of nucleophilic substitution reactions at silicon centers (SN2@Si) has been altered when a vibrational mode of the reactant was coupled to a confined light mode in the strong coupling regime. In this situation, hybrid light–matter states known as polaritons are formed and seem to be responsible for the modified chemical kinetics. These results are very encouraging for future applications of polaritonic chemistry to catalyze chemical reactions, with the ability to manipulate chemical phenomena without any external excitation of the system. Still, there is no theory capable of explaining the mechanism behind these results. In this work we address two points that are crucial for the interpretation of these experiments. Firstly, by means of electronic structure calculations we report the reaction mechanism in normal conditions of the two recently modified SN2@Si reactions, obtaining in both cases a triple-well PES where the rate-determining step is due to the Si–C and Si–O bond cleavage. Secondly, we characterize in detail the normal modes of vibration of the reactants. In the VSC experiments, reaction rates were modified only when specific vibrations of the reactants were coupled to a cavity mode. We find that these vibrations are highly mixed among the different fragments of the reactants leading to a completely new assignment of the IR peaks coupled to cavity modes in the original experimental works. Our results are fundamental for the interpretation of the VSC experiments given that in the absence of a theory explaining these results, the current phenomenological understanding relies on the assignment of the character of the vibrational IR peaks.
23.
Theory of Energy Transfer in Organic Nanocrystals (PDF)
Abstract: ...Recent experiments have shown that highly efficient energy transfer can take place in organic nanocrystals at extremely low acceptor densities. This striking phenomenon has been ascribed to the formation of exciton polaritons thanks to the photon confinement provided by the crystal itself. An alternative theoretical model that accurately reproduces fluorescence lifetime and spectrum measurements in these systems without such an assumption is proposed. The approach treats molecule–photon interactions in the weak-coupling regime, and describes the donor and acceptor population dynamics by means of rate equations with parameters extracted from electromagnetic simulations. The physical insight and predictive value of this model also enables the authors to propose nanocrystal configurations in which acceptor emission dominates the fluorescence spectrum at densities orders of magnitude lower than the experimental ones.
22.
Photoprotecting Uracil by Coupling with Lossy Nanocavities (PDF)
Abstract: ...We analyze how the photorelaxation dynamics of a molecule can be controlled by modifying its electromagnetic environment using a nanocavity mode. In particular, we consider the photorelaxation of the RNA nucleobase uracil, which is the natural mechanism to prevent photodamage. In our theoretical work, we identify the operative conditions in which strong coupling with the cavity mode can open an efficient photoprotective channel, resulting in a relaxation dynamics twice as fast as the natural one. We rely on a state-of-the-art chemically detailed molecular model and a non-Hermitian Hamiltonian propagation approach to perform full-quantum simulations of the system dissipative dynamics. By focusing on the photon decay, our analysis unveils the active role played by cavity-induced dissipative processes in modifying chemical reaction rates, in the context of molecular polaritonics. Remarkably, we find that the photorelaxation efficiency is maximized when an optimal trade-off between light–matter coupling strength and photon decay rate is satisfied. This result is in contrast with the common intuition that increasing the quality factor of nanocavities and plasmonic devices improves their performance. Finally, we use a detailed model of a metal nanoparticle to show that the speedup of the uracil relaxation could be observed via coupling with a nanosphere pseudomode, without requiring the implementation of complex nanophotonic structures.
21.
Polaritonic molecular clock for all-optical ultrafast imaging of wavepacket dynamics without probe pulses (PDF)
Abstract: ...Conventional approaches to probing ultrafast molecular dynamics rely on the use of synchronized laser pulses with a well-defined time delay. Typically, a pump pulse excites a molecular wavepacket. A subsequent probe pulse can then dissociate or ionize the molecule, and measurement of the molecular fragments provides information about where the wavepacket was for each time delay. Here, we propose to exploit the ultrafast nuclear-position-dependent emission obtained due to large light–matter coupling in plasmonic nanocavities to image wavepacket dynamics using only a single pump pulse. We show that the time-resolved emission from the cavity provides information about when the wavepacket passes a given region in nuclear configuration space. This approach can image both cavity-modified dynamics on polaritonic (hybrid light–matter) potentials in the strong light–matter coupling regime and bare-molecule dynamics in the intermediate coupling regime of large Purcell enhancements, and provides a route towards ultrafast molecular spectroscopy with plasmonic nanocavities.
20.
Cumulant expansion for the treatment of light-matter interactions in arbitrary material structures (PDF)
Abstract: ...Strong coupling of quantum emitters with confined electromagnetic modes of nanophotonic structures may be used to change optical, chemical, and transport properties of materials, with significant theoretical effort invested toward a better understanding of this phenomenon. However, a full theoretical description of both matter and light is an extremely challenging task. Typical theoretical approaches simplify the description of the photonic environment by describing it as a single mode or few modes. While this approximation is accurate in some cases, it breaks down strongly in complex environments, such as within plasmonic nanocavities, and the electromagnetic environment must be fully taken into account. This requires the quantum description of a continuum of bosonic modes, a problem that is computationally hard. We here investigate a compromise where the quantum character of light is taken into account at modest computational cost. To do so, we focus on a quantum emitter that interacts with an arbitrary photonic spectral density and employ the cumulant, or cluster, expansion method to the Heisenberg equations of motion up to first, second, and third order. We benchmark the method by comparing it with exact solutions for specific situations and show that it can accurately represent dynamics for many parameter ranges.
2019
19.
Tracking Polariton Relaxation with Multiscale Molecular Dynamics Simulations (PDF)
Abstract: ...When photoactive molecules interact strongly with confined light modes in optical cavities, new hybrid light–matter states form. They are known as polaritons and correspond to coherent superpositions of excitations of the molecules and of the cavity photon. The polariton energies and thus potential energy surfaces are changed with respect to the bare molecules, such that polariton formation is considered a promising paradigm for controlling photochemical reactions. To effectively manipulate photochemistry with confined light, the molecules need to remain in the polaritonic state long enough for the reaction on the modified potential energy surface to take place. To understand what determines this lifetime, we have performed atomistic molecular dynamics simulations of room-temperature ensembles of rhodamine chromophores strongly coupled to a single confined light mode with a 15 fs lifetime. We investigated three popular experimental scenarios and followed the relaxation after optically pumping (i) the lower polariton, (ii) the upper polariton, or (iii) uncoupled molecular states. The results of the simulations suggest that the lifetimes of the optically accessible lower and upper polaritons are limited by (i) ultrafast photoemission due to the low cavity lifetime and (ii) reversible population transfer into the “dark” state manifold. Dark states are superpositions of molecular excitations but with much smaller contributions from the cavity photon, decreasing their emission rates and hence increasing their lifetimes. We find that population transfer between polaritonic modes and dark states is determined by the overlap between the polaritonic and molecular absorption spectra. Importantly, excitation can also be transferred ”upward” from the lower polariton into the dark-state reservoir due to the broad absorption spectra of the chromophores, contrary to the common conception of these processes as a ”one-way” relaxation from the dark states down to the lower polariton. Our results thus suggest that polaritonic chemistry relying on modified dynamics taking place within the lower polariton manifold requires cavities with sufficiently long lifetimes and, at the same time, strong light–matter coupling strengths to prevent the back-transfer of excitation into the dark states.
18.
Optomechanical heat transfer between molecules in a nanoplasmonic cavity (PDF)
Abstract: ...We explore whether localized surface plasmon polariton modes can transfer heat between molecules placed in the hot spot of a nanoplasmonic cavity through optomechanical interaction with the molecular vibrations. We demonstrate that external driving of the plasmon resonance indeed induces an effective molecule-molecule interaction corresponding to a heat transfer mechanism that can even be more effective in cooling the hotter molecule than its heating due to the vibrational pumping by the plasmon. This mechanism allows us to actively control the rate of heat flow between molecules through the intensity and frequency of the driving laser.
17.
Cavity-Modified Exciton Dynamics in Photosynthetic Units (PDF)
Abstract: ...Recently, exciton-photon strong coupling has been proposed as a means to control and enhance energy transfer in ensembles of organic molecules. Here, we demonstrate that the exciton dynamics in an archetypal purple bacterial photosynthetic unit, composed of six LH2 antennas surrounding a single LH1 complex, is greatly modified by its interaction with an optical cavity. We develop a Bloch-Redfield master equation approach that accounts for the interplay between the B800 and B850 bacteriochlorophyll molecules within each LH2 antenna, as well as their interactions with the central LH1 complex. Using a realistic parametrization of both the photosynthetic unit and optical cavity, we investigate the formation of polaritons in the system, revealing that these can be tuned to accelerate its exciton dynamics by 3 orders of magnitude. This yields a significant occupation of the LH1 complex, the stage immediately prior to the reaction center, with only a few-femtosecond delay after the initial excitation of the LH2 B800 pigments. Our theoretical findings unveil polaritonic phenomena as a promising route for the characterization, tailoring, and optimization of light-harvesting mechanisms in natural and artificial photosynthetic processes.
16.
Cavity Casimir-Polder Forces and Their Effects in Ground-State Chemical Reactivity (PDF)
Abstract: ...Here, we present a fundamental study on how the ground-state chemical reactivity of a single molecule can be modified in a QED scenario, i.e., when it is placed inside a nanoscale cavity and there is strong coupling between the cavity field and vibrational modes within the molecule. We work with a model system for the molecule (Shin-Metiu model) in which nuclear, electronic, and photonic degrees of freedom are treated on the same footing. This simplified model allows the comparison of exact quantum reaction rate calculations with predictions emerging from transition state theory based on the cavity Born-Oppenheimer approach. We demonstrate that QED effects are indeed able to significantly modify activation barriers in chemical reactions and, as a consequence, reaction rates. The critical physical parameter controlling this effect is the permanent dipole of the molecule and how this magnitude changes along the reaction coordinate. We show that the effective coupling can lead to significant single-molecule energy shifts in an experimentally available nanoparticle-on-mirror cavity. We then apply the validated theory to a realistic case (internal rotation in the 1,2-dichloroethane molecule), showing how reactions can be inhibited or catalyzed depending on the profile of the molecular dipole. Furthermore, we discuss the absence of resonance effects in the present scenario, which can be understood through its connection to Casimir-Polder forces. Finally, we treat the case of many-molecule strong coupling and find collective modifications of reaction rates if the molecular permanent dipole moments are oriented with respect to the cavity field.
15.
Strong coupling between weakly guided semiconductor nanowire modes and an organic dye (PDF)
Abstract: ...The light-matter coupling between electromagnetic modes guided by a semiconductor nanowire and excitonic states of molecules localized in its surrounding media is studied from both classical and quantum perspectives, with the aim of describing the strong-coupling regime. Weakly guided modes (bare photonic modes) are found through a classical analysis, identifying those lowest-order modes presenting large electromagnetic fields spreading outside the nanowire while preserving their robust guided behavior. Experimental fits of the dielectric permittivity of an organic dye that exhibits excitonic states are used for realistic scenarios. A quantum model properly confirms through an avoided mode crossing that the strong-coupling regime can be achieved for this configuration, leading to Rabi splitting values above 100 meV. In addition, it is shown that the coupling strength depends on the fraction of energy spread outside the nanowire, rather than on the mode field localization. These results open up a new avenue towards strong-coupling phenomenology involving propagating modes in nonabsorbing media.
Erratum: Phys. Rev. B 102, 239901 (2020) (PDF)
14.
Plasmonic Nanocavities Enable Self-Induced Electrostatic Catalysis (PDF)
Abstract: ...The potential of strong interactions between light and matter remains to be further explored within a chemical context. Towards this end herein we study the electromagnetic interaction between molecules and plasmonic nanocavities. By means of electronic structure calculations, we show that self-induced catalysis emerges without any external stimuli through the interaction of the molecular permanent and fluctuating dipole moments with the plasmonic cavity modes. We also exploit this scheme to modify the transition temperature T1/2 of spin-crossover complexes as an example of how strong light–matter interactions can ultimately be used to control a materials responses.
2018
13.
Tensor Network Simulation of Non-Markovian Dynamics in Organic Polaritons (PDF)
Abstract: ...We calculate the exact many-body time dynamics of polaritonic states supported by an optical cavity filled with organic molecules. Optical, vibrational, and radiative processes are treated on an equal footing employing the time-dependent variational matrix product states algorithm. We demonstrate signatures of non-Markovian vibronic dynamics and its fingerprints in the far-field photon emission spectrum at arbitrary light-matter interaction scales, ranging from the weak to the strong coupling regimes. We analyze both the single- and many-molecule cases, showing the crucial role played by the collective motion of molecular nuclei and dark states in determining the polariton dynamics and the subsequent photon emission.
Erratum: Phys. Rev. Lett. 122, 159902 (2019) (PDF)
12.
A pump–probe scheme with a single chirped pulse to image electron and nuclear dynamics in molecules (PDF)
Abstract: ...A single chirped few-femtosecond pulse can be used to control and image coupled electron-nuclear dynamics. Using full ab initio simulations of the simplest molecule, H2+, as a prototype target, we show that for intermediate values of the chirp, interference between sequential and direct contributions enables significant control over ionization yields, even when taking into account the effective decoherence introduced by nuclear motion and the presence of an electronic continuum. For larger values of the chirp, the single chirped pulse reproduces a classical pump-probe setup, with the chirp parameter mapping an effective time delay between the pumping and probing frequencies of the pulse. After demonstrating this numerically, we present a full analytical solution for the two-photon ionization amplitudes that provides an intuitive analogy between the molecular dynamics induced by a single chirped pulse and a traditional pump-probe setup.
11.
Tensor network simulation of polaron-polaritons in organic microcavities (PDF)
Abstract: ...In the regime of strong coupling between molecular excitons and confined optical modes, the intramolecular degrees of freedom are profoundly affected, leading to a reduced vibrational dressing of polaritons compared to bare electronically excited states. However, existing models only describe a single vibrational mode in each molecule, while actual molecules possess a large number of vibrational degrees of freedom and additionally interact with a continuous bath of phononic modes in the host medium in typical experiments. In this work, we investigate a small ensemble of molecules with an arbitrary number of vibrational degrees of freedom under strong coupling to a microcavity mode. We demonstrate that reduced vibrational dressing is still present in this case, and show that the influence of the phononic environment on most electronic and photonic observables in the lowest excited state can be predicted from just two collective parameters of the vibrational modes. Besides, we explore vibrational features that can be addressed exclusively by our extended model and could be experimentally tested. Our findings indicate that vibronic coupling is more efficiently suppressed for environments characterized by low-frequency (sub-Ohmic) modes.
10.
Exploring the Limits of Super-Planckian Far-Field Radiative Heat Transfer Using 2D Materials (PDF)
Abstract: ...Very recently it has been predicted that the far-field radiative heat transfer between two macroscopic systems can largely overcome the limit set by Planck’s law if one of their dimensions becomes much smaller than the thermal wavelength (λTh ≈ 10 μm at room temperature). To explore the ultimate limit of the far-field violation of Planck’s law, here we present a theoretical study of the radiative heat transfer between two-dimensional (2D) materials. We show that the far-field thermal radiation exchanged by two coplanar systems with a one-atom-thick geometrical cross section can be more than 7 orders of magnitude larger than the theoretical limit set by Planck’s law for blackbodies and can be comparable to the heat transfer of two parallel sheets at the same distance. In particular, we illustrate this phenomenon with different materials such as graphene, where the radiation can also be tuned by a external gate, and single-layer black phosphorus. In both cases the far-field radiative heat transfer is dominated by TE-polarized guiding modes, and surface plasmons play no role. Our predictions provide a new insight into the thermal radiation exchange mechanisms between 2D materials.
9.
Photon statistics in collective strong coupling: Nanocavities and microcavities (PDF)
Abstract: ...There exists a growing interest in the properties of the light generated by hybrid systems involving a mesoscopic number of emitters as a means of providing macroscopic quantum light sources. In this work, the quantum correlations of the light emitted by a collection of emitters coupled to a generic optical cavity are studied theoretically using an effective Hamiltonian approach. Starting from the single-emitter level, we analyze the persistence of photon antibunching as the ensemble size increases. Not only is the photon blockade effect identifiable, but photon antibunching originated from destructive interference processes, the so-called unconventional antibunching, is also present. We study the dependence of these two types of negative correlations on the spectral detuning between cavity and emitters, as well as its evolution as the time delay between photon detections increases. Throughout this work, the performance of plasmonic nanocavities and dielectric microcavities is compared: despite the distinct energy scales and the differences introduced by their respectively open and closed character, the bunching and antibunching phenomenology presents remarkable similarities in both types of cavities.
8.
Electron correlations in the antiproton energy-loss distribution in He (PDF)
Abstract: ...We present ab initio calculations of the electronic differential energy-transfer cross sections for antiprotons with energies between 3 keV and 1 MeV interacting with helium. By comparison with simulations employing the mean-field description based on the single-active electron approximation we are able to identify electron correlation effects in the stopping and straggling cross sections. Most remarkably, we find that straggling exceeds the celebrated Bohr straggling limit when correlated shake-up processes are included.
7.
Organic polaritons enable local vibrations to drive long-range energy transfer (PDF)
Abstract: ...Long-range energy transfer in organic molecules has been experimentally obtained by strongly coupling their electronic excitations to a confined electromagnetic cavity mode. Here, we shed light into the polariton-mediated mechanism behind this process for different configurations: donor and acceptor molecules either intermixed or physically separated.We numerically address the phenomenon by means of Bloch-Redfield theory, which allows us to reproduce the effect of complex vibrational reservoirs characteristic of organic molecules. Our findings reveal the key role played by the middle polariton as the nonlocal intermediary in the transmission of excitations from donor to acceptor molecules.We also provide analytical insights on the key physical magnitudes that help to optimize the efficiency of the long-range energy transfer.
6.
Polaritonic Chemistry with Organic Molecules (PDF)
Abstract: ...We present an overview of the general concepts of polaritonic chemistry with organic molecules, i.e., the manipulation of chemical structure that can be achieved through strong coupling between confined light modes and organic molecules. Strong coupling and the associated formation of polaritons, hybrid light-matter excitations, leads to energy shifts in such systems that can amount to a large fraction of the uncoupled transition energy. This has recently been shown to significantly alter the chemical structure of the coupled molecules, which opens the possibility to manipulate and control reactions. We discuss the current state of theory for describing these changes and present several applications, with a particular focus on the collective effects observed when many molecules are involved in strong coupling.
5.
Dispersion Anisotropy of Plasmon–Exciton–Polaritons in Lattices of Metallic Nanoparticles (PDF)
Abstract: ...When the electromagnetic modes supported by plasmonic-based cavities interact strongly with molecules located within the cavity, new hybrid states known as plasmon-exciton-polaritons (PEPs) are formed. The properties of PEPs, such as group velocity, effective mass and lifetime, depend on the dispersive and spectral characteristics of the optical modes underlying the strong coupling. In this work, we focus on lattice modes supported by rectangular arrays of plasmonic nanoparticles known as surface lattice resonances (SLRs). We show that SLRs arising from different in-plane diffraction orders in the lattice can couple with the molecular excitons leading to PEPs with distinct dispersions, and thus different group velocities. These results illustrate the possibility of tailoring the transport of PEPs through the design of lattices of plasmonic particles.
4.
Super-Planckian far-field radiative heat transfer (PDF)
Abstract: ...We present here a theoretical analysis that demonstrates that the far-field radiative heat transfer between objects with dimensions smaller than the thermal wavelength can overcome the Planckian limit by orders of magnitude. To guide the search for super-Planckian far-field radiative heat transfer, we make use of the theory of fluctuational electrodynamics and derive a relation between the far-field radiative heat transfer and the directional absorption efficiency of the objects involved. Guided by this relation, and making use of state-of-the-art numerical simulations, we show that the far-field radiative heat transfer between highly anisotropic objects can largely overcome the black-body limit when some of their dimensions are smaller than the thermal wavelength. In particular, we illustrate this phenomenon in the case of suspended pads made of polar dielectrics like SiN or SiO2 . These structures are widely used to measure the thermal transport through nanowires and low-dimensional systems and can be employed to test our predictions. Our work illustrates the dramatic failure of the classical theory to predict the far-field radiative heat transfer between micro- and nanodevices.
2017
3.
Enhancing photon correlations through plasmonic strong coupling (PDF)
Abstract: ...There is an increasing scientific and technological interest in the design and implementation of nanoscale sources of quantum light. Here, we investigate the quantum statistics of the light scattered from a plasmonic nanocavity coupled to a mesoscopic ensemble of emitters under low coherent pumping. We present an analytical description of the intensity correlations taking place in these systems and unveil the fingerprint of plasmon-exciton-polaritons in them. Our findings reveal that plasmonic cavities are able to retain and enhance excitonic nonlinearities, even when the number of emitters is large. This makes plasmonic strong coupling a promising route for generating nonclassical light beyond the single-emitter level.
2.
Long-distance operator for energy transfer (PDF)
Abstract: ...Nonradiative energy transfer is a ubiquitous phenomenon in nature. Photosynthesis begins with light harvesting, where pigment-protein complexes transform sunlight into excitations, usually called excitons, within the molecules. Excitons are formed by an excited electron and the positively charged hole that is left in the ground state. In photosynthesis, the energy of this exciton is finally transferred to the reaction center, where a charge separation process provides chemical energy for plants, algae, and bacteria. Human-made organic photovoltaic cells try to mimic this natural process, and it is the transport of the excitons after light absorption that determines the efficiency of the cell. In organic materials, energy transfer is governed by short-range dipole-dipole interactions through the process of Förster resonance energy transfer (FRET), whose spatial range is limited to distances less than 10 nm. Recent work by Zhong et al. shows how this range can be extended to distances larger than 100 nm by taking advantage of a quantum electrodynamics (QED) phenomenon called strong coupling.
1.
Many-Molecule Reaction Triggered by a Single Photon in Polaritonic Chemistry (PDF)
Abstract: ...The second law of photochemistry states that in most cases, no more than one molecule is activated for an excited-state reaction for each photon absorbed by a collection of molecules. In this work, we demonstrate that it is possible to trigger a many-molecule reaction using only one photon by strongly coupling the molecular ensemble to a confined light mode. The collective nature of the resulting hybrid states of the system (the so-called polaritons) leads to the formation of a polaritonic "supermolecule" involving the degrees of freedom of all molecules, opening a reaction path on which all involved molecules undergo a chemical transformation. We theoretically investigate the system conditions for this effect to take place and be enhanced.