Coherent Energy Exchange Research Articles

Real-Time Simulation of Ultrafast Electronic Dynamics of Nanoscale Systems Involving an Organic Molecule and a Nanoparticle Dimer.

Understanding and predicting the behavior of nanomaterials composed of plasmons interacting with quantum emitters at ultrafast timescales is crucial for the better manipulation of light at the nanoscale and advancing technologies like ultrafast communication and computing. Here we perform a simulation of the "real-time" electronic dynamics of a coupled molecule-metal nanoparticle dimer interacting with an ultrashort resonant laser pulse by combining the real-time time-dependent density functional theory (RT-TDDFT) approach with the time-domain frequency-dependent fluctuating charge (TD-ωFQ) model, an atomistic electromagnetic (AEM) model for the dynamic plasmonic response of nanoparticles. It is shown that the induced dipoles evolve from an exponential decay pattern to a beat pattern with an increase in coupling strength, which is altered by changing the molecular orientation relative to the dimer axis. It is further shown that in the strong coupling regime, both the excited molecule and the plasmon relax rapidly due to the molecule-plasmon interaction, and the efficient coherent energy exchange between the interacting molecule and plasmon modes occurs on a femtosecond (fs) timescale. This work provides guidance on manipulating light-matter interaction and studying molecular plasmonics at extremely fast timescales.

Strong coupling between plasmonic nanocavity gold nanorods and quantum dots emitter

The discovery of hybrid states in strong coupling interaction has gained growing attention in cavity-quantum electrodynamics research owing to its fundamental directives and potential in advanced optical applications. The ultra-confined mode volume of plasmonic cavity gold nanorods (AuNRs), particularly at the nanorod tip “hotspot” provides a large coupling strength, a prerequisite for a coherent energy exchange in the strong coupling regime. Here, we reported a remarkable Rabi splitting of ∼231 meV between gold nanorods longitudinal localized surface plasmon resonance (LLSPR) mode and quantum dots (QDs) at ambient conditions, monitored by dielectric medium tuning. Numerical simulations confirmed the result, displaying absorption spectral splitting.

Energy Transport and Conversion Within Earth's Supercritical Bow Shock: The Role of Intense Lower‐Hybrid Whistler Waves

AbstractDetailed analysis of a high Mach number quasiperpendicular Earth bow shock crossing by the Magnetospheric Multiscale (MMS) spacecraft fleet reveal that lower‐hybrid (LH) whistler waves generated in the shock foot region transport energy predominately along the shock surface and slightly toward the shock ramp in the shock normal incidence frame, where wave energy accumulates and is dissipated into the plasma. This suggests the LH whistlers play an integral role in energy reconfiguration at high Mach number collisionless shocks with ramifications to plasma heating. The multipoint observations are used to quantify the wave characteristic parameters (via interferometry), Poynting fluxes, and energy conversion rates D, and to assess their scale dependencies and spatial and temporal properties. The whistler associated energy transport and conversion are found to depend on scale and location within the layer. High‐frequency electrostatic waves yield largest values of D. However, the dominant net energy exchange contribution is from the LH whistlers. In the foot spatially temporally coherent net energy exchange from the plasma to whistlers is observed, whereas deeper in the ramp net wave energy dissipation to the plasma is observed exhibiting significant space‐time variability. These results are consistent with the modified two stream instability driven by the relative drift between reflected ions and electrons as the mechanism for wave growth in the foot. Owing to strong electron heating, whistler energy dissipation in the ramp is attributed to Landau damping, which out‐competes the destabilizing effect of the reflected ion and electron drift.

Ultrafast Spectroscopy under Vibrational Strong Coupling in Diphenylphosphoryl Azide.

Strong coupling of cavity photons and molecular vibrations creates vibrational polaritons that have been shown to modify chemical reactivity and alter material properties. While ultrafast spectroscopy of vibrational polaritons has been performed intensively in metal complexes, ultrafast dynamics in vibrationally strongly coupled organic molecules remain unexplored. Here, we report ultrafast pump-probe measurement and two-dimensional infrared spectroscopy in diphenylphosphoryl azide under vibrational strong coupling. Early time oscillatory structures indicate coherent energy exchange between the two polariton modes, which decays in ∼2 ps. We observe a large transient absorptive feature around the lower polariton, which can be explained by the overlapped excited-state absorption and derivative-shaped structures around the lower and upper polaritons. The latter feature is explained by the Rabi splitting contraction, which is ascribed to a reduced population in the ground state. These results reassure the previously reported spectroscopic theory to describe nonlinear spectroscopy of vibrational polaritons. We have also noticed the influence of the complicated layer structure of the cavity mirrors. The penetration of the electric field distribution into the layered structure of the dielectric-mirror cavities can significantly affect the Rabi splitting and the decay time constant of polaritonic systems.

J-aggregates and two-dimensional materials indirect-coupling with polariton-assisted resonance energy transfer

Researching resonance energy transfer (RET) from one quantum emitter to another in the strong coupling regime can provide a new route to empower ultrafast quantum manipulations and possess fascinating technological frontiers. However, most of the reports only discussed the weak electronic coupling limit and incoherent energy transfer. Here, we establish a universal theory to investigate RET between two emitters weakly/strongly coupled to a plasmonic mode and analyze the dynamics of RET by utilizing a full-quantum method. Combining with our theory, we investigate the RET rate of a multilayer system in which J-aggregates/monolayer WS2 acts as the donor/acceptor. The calculated results verify that RET rates in the strong coupling regime increase two orders of magnitude compared to the weak coupling regime. Moreover, the coherent energy exchange between two detuned emitters is realized in the strong coupling regime by the time-dependent population calculations. The double Rabi splitting appears in the photoluminescence (PL) spectrum with sufficient RET rates (103ns−1) and coupling strength (g=60 meV). Our work demonstrates a quantitative calculation of RET rates and PL spectrum for the plasmon-biexciton coupled systems, providing a promising way for precise photochemical control, integrated optical device design and quantum information processing.

Fine-tuning biexcitons-plasmon coherent states in a single nanocavity

Abstract A tunable plexcitonic material that sustains multimode hybridization is highly desirable, which is vital for advanced quantum devices. However, the research about regulations of biexcitons-plasmon coherent states has rarely been reported. Here we apply single-nanoparticle scattering spectroscopy correlative with SEM imaging to identify biexcitons-plasmon interaction in a metal-semiconductor hybrid structure composed of a single Au@Ag nanoparticle, J-aggregates molecules and tungsten disulfide (WS2) monolayer. The mode competition within the localized plasmonic hotspots (∼240 nm3) is revealed by continuously regulating the J-aggregates spacer. Two distinct anticrossings are observed at both excitons resonances, and large double Rabi splittings (137 meV and 124 meV) are obtained successfully. We establish experimentally that J-aggregates and WS2 monolayer are responsible for the middle polariton states, while plasmon rarely contributes. Further calculations show that plasmonic nanocavity enables coherent energy exchange with different excitons by providing a highly enhanced localized E-field. In addition, we find that the multimode coupling strengths can be efficiently tuned by changing the cavity morphology and environment temperature, where the tuning spectral accuracy can reach up to 1 nm. Our findings uncover the distinctive properties of biexcitons-plasmon polaritons, suggest an easily obtainable multiqubit states platform, and open up a new way to construct nanoscale photonic devices.

Molecular Chemistry in Cavity Strong Coupling.

The coherent exchange of energy between materials and optical fields leads to strong light-matter interactions and so-called polaritonic states with intriguing properties, halfway between light and matter. Two decades ago, research on these strong light-matter interactions, using optical cavity (vacuum) fields, remained for the most part the province of the physicist, with a focus on inorganic materials requiring cryogenic temperatures and carefully fabricated, high-quality optical cavities for their study. This review explores the history and recent acceleration of interest in the application of polaritonic states to molecular properties and processes. The enormous collective oscillator strength of dense films of organic molecules, aggregates, and materials allows cavity vacuum field strong coupling to be achieved at room temperature, even in rapidly fabricated, highly lossy metallic optical cavities. This has put polaritonic states and their associated coherent phenomena at the fingertips of laboratory chemists, materials scientists, and even biochemists as a potentially new tool to control molecular chemistry. The exciting phenomena that have emerged suggest that polaritonic states are of genuine relevance within the molecular and material energy landscape.

Persistent dynamics in coupled non-degenerate parametric oscillators: pump saturation prevents mode competition.

The coherent dynamics in networks of coupled oscillators is of great interest in wave-physics since the coupling produces various dynamical effects, such as coherent energy exchange (beats) between the oscillators. However, it is common wisdom that these coherent dynamics are transients that quickly decay in active oscillators (e.g. lasers) since pump saturation causes mode competition that results, for homogeneous gain, in the prevalence of the single winning mode. We observe that pump saturation in coupled parametric oscillators counter-intuitively encourages the multi-mode dynamics of beating and indefinitely preserves it, despite the existence of mode competition. We explore in detail the coherent dynamics of a pair of coupled parametric oscillators with a shared pump and arbitrary coupling in a radio frequency (RF) experiment, as well as in simulation. Specifically, we realize two parametric oscillators as different frequency-modes of a single RF cavity and couple them arbitrarily using a digital high-bandwidth FPGA. We observe persistent coherent beats that are maintained at any pump level, even high above the threshold. The simulation highlights how the interplay of pump depletion between the two oscillators prevents them from synchronizing, even when the oscillation is deeply saturated.

Resonance coupling between chiral quasi-BICs and achiral molecular excitons in dielectric metasurface J-aggregate heterostructures.

The realization of flexible tuning and enhanced chiral responses is vital for many applications in nanophotonics. This study proposes to manipulate the collective optical responses with heterostructures consisting of chiral dielectric metasurfaces and achiral J-aggregates. Owing to the resonance coupling between the chiral quasi-bound states in the continuum (QBICs) and the achiral exciton mode, large mode splitting and anticrossing are observed in both the transmission and circular dichroism (CD) spectra, which indicates the formation of hybrid chiral eigenmodes and the realization of the strong coupling regime. Considering that the radiative and dissipative damping of the hybrid eigenmodes depends on the coherent energy exchange, the chiral resonances can be flexibly tuned by adjusting the geometry and optical constants for the heterostructure, and the CD of the three hybrid eigenmodes approach the maximum (∼1) simultaneously when the critical coupling conditions are satisfied, which can be promising for enhanced chiral light-matter interactions.

Plasmon-induced thermal tuning of few-exciton strong coupling in 2D atomic crystals

Strong light–matter interaction in 2D materials at the few-exciton level is important for both fundamental studies and quantum optical applications. Characterized by a fast coherent energy exchange between photons and excitons, strongly coupled plasmon–exciton systems in 2D materials have been reported with large Rabi splitting. However, large Rabi splitting at the few-exciton level generally requires large optical fields in a highly confined mode volume, which are difficult to achieve for in-plane excitons in 2D materials. In this work, we present a study of a strongly coupled gold dimer antenna with a sub-10 nm gap on a monolayer tungsten disulphide ( W S 2 ), with an estimated number of excitons of 4.67 ± 0.99 . We demonstrate that varying the spatial mode overlap between the plasmonic field and the 2D material can result in up to a ∼ t e n f o l d increase in the number of excitons, a value that can be further actively tuned via plasmon-induced heating effects. The demonstrated results would represent a key step toward quantum optical applications operating at room temperatures.

Coherent energy exchange between carriers and phonons in Peierls-distorted bismuth unveiled by broadband XUV pulses

In Peierls-distorted materials, photoexcitation leads to a strongly coupled transient response between structural and electronic degrees of freedom, always measured independently of each other. Here we use transient reflectivity in the extreme ultraviolet to quantify both responses in photoexcited bismuth in a single measurement. With the help of first-principles calculations based on density-functional theory (DFT) and time-dependent DFT, the real-space atomic motion and the temperature of both electrons and holes as a function of time are captured simultaneously, retrieving an anticorrelation between the ${A}_{1g}$ phonon dynamics and carrier temperature. The results reveal a coherent, bidirectional energy exchange between carriers and phonons, which is a dynamical counterpart of the static Peierls-Jones distortion, providing validation of previous theoretical predictions.

Plexcitonic Quasi-Bound States in the Continuum.

Enhancing light-matter interactions is fundamental to the advancement of nanophotonics and optoelectronics. Yet, light diffraction on dielectric platforms and energy loss on plasmonic metallic systems present an undesirable trade-off between coherent energy exchange and incoherent energy damping. Through judicious structural design, both light confinement and energy loss issues could be potentially and simultaneously addressed by creating bound states in the continuum (BICs) where light is ideally decoupled from the radiative continuum. Herein, the authors present a general framework based on the two-coupled resonances to first conceptualize and then numerically demonstrate a type of quasi-BICs that can be achieved through the interference between two bare resonance modes and is characterized by the considerably narrowed spectral line shape even on lossy metallic nanostructures. The ubiquity of the proposed framework further allows the paradigm to be extended for the realization of plexcitonic quasi-BICs on the same metallic systems. Owing to the topological nature, both plasmonic and plexcitonic quasi-BICs display strong mode robustness against parameters variation, thereby providing an attractive platform to unlock the potential of the coupled plasmon-exciton systems for manipulation of the photophysical properties of condensed phases.

Strong Coupling State on Plasmonic Lattice Structures Under Electrochemical Potential Control

The collective oscillation of free electrons in the metal nanostructures induced by the visible light illumination is recognized as the localized surface plasmon (LSP). The coherent light energy exchange between excitons of molecules and LSP can modulate not only the absorption characteristic but also the individual energy decay. This reversible light energy exchange process between LSP and molecular exciton is called as the strong coupling regime. Although the strong coupling can allow use the light energy efficiently, the relative short lifetime of LSP due to the energy dissipation via the radiative damping limits the application. On the other hand, the surface lattice plasmon (SLR) mode which is excited on the two dimensionally arranged metal nanoparticles shows the longer excited lifetime because the diffractive light scattered from each particle is used for the excitation of the LSP at neighboring nanoparticle, resulting in the suppression of the scattering loss. As we demonstrated in our previous study, we have successfully achieved the fine electrochemical structure control method for obtaining the longest lifetime of the SLR mode. From these backgrounds, in this study, we have fabricated the Au lattice structure on a conductive glass and to support organic dye molecules on it to achieve the strong coupling regime. Through the extinction and fluorescence measurements, we have successfully observed the peak splitting which was originated from the formation of the strong coupling. In addition, by the combination of electrochemical method, we have confirmed our successful results for the reversible tuning of the coupling strength. From all experiments, we have successfully estimated the number of the molecules contributing to the strong coupling state.[1] H. Minamimoto et al., Phys. Chem. C 2018, 122, 14162.

Surpassing the thermal Cramér-Rao bound with collisional thermometry

In collisional thermometry, a system in contact with the thermal bath is probed by a stream of ancillas. Coherences and collective measurements were shown to improve the Fisher information in some parameter regimes, for a stream of independent and identically prepared (i.i.d.) ancillas in some specific states [Seah et al., Phys. Rev. Lett. 123, 180602 (2019)]. Here we refine the analysis of this metrological advantage by optimizing over the possible input ancilla states, also for block-i.i.d. states of block size $b=2$. For both an indirect measurement interaction and a coherent energy exchange channel, we show when the thermal Cram\'er-Rao bound can be beaten, and when a collective measurement of $N>1$ ancilla may return advantages over single-copy measurements.

Thermodynamics of optical Bloch equations

Optical Bloch equations (OBE) describe the coherent exchange of energy between a quantum bit (qubit) and a quasi-resonant driving field in the presence of a thermal bath. Despite it being an ubiquitous process in quantum technologies, a sound thermodynamic analysis is still missing. We hereby provide such an analysis, by deriving the relevant framework from first principles. We start from a complete microscopic description of the qubit-bath system where definitions of heat, work and entropy production are unambiguous. We trace out the bath and coarse-grain the resulting expressions in time, using a methodology similar to the derivation of the dynamical master equation, to derive closed expressions for the first and second law in terms of system properties. Long coarse graining times yield the Floquet Master equation and its already known thermodynamic description. Short coarse-graining times yield instead the OBE and a novel thermodynamic framework which explicitly depends on quantum coherences in the qubit’s energy basis which produce quantum signatures in the heat and entropy production flows. This allows us to characterize a genuinely quantum non-equilibrium situation, where the coherences created by the driving field are continuously erased by the bath. Our findings can be readily extended to larger open quantum systems. They carry the seeds for future thermodynamic analyses of quantum gates and the design of quantum engines in the strong coherent driving regime.

Spontaneous Emission of Plasmon‐Exciton Polaritons Revealed by Ultrafast Nonradiative Decays

AbstractSpontaneous emission can be altered by external electromagnetic environment with the bridge of local density of optical states. Microcavities have been widely integrated to accelerate the irreversible spontaneous decay, known as the Purcell effect. However, the Purcell effect breaks down in the strong coupling regime, where the light‐matter interaction is not a perturbation to Fermi's golden rule. Here, it is found that the emission intensity of plasmon–exciton polaritons is asymmetrically dependent on the spectral detuning, confirming the collapse of Purcell effect in strongly coupled systems. Ultrafast nonradiative decays of polaritons play a significant role in revealing the polariton emission intensity. The nonradiative effect is not affected by the coherent energy exchange since final states of nonradiative decays are optically dark and decoupled from Rabi oscillations. Moreover, the nonradiative effect is still valid under intermediate coupling and agrees with the Purcell effect, which suggests its universality at a variety of coupling regimes. This study opens up a successful approach to investigate spontaneous emission in cavity quantum electrodynamics, which is insightful to photonic and opto‐electronic applications based on exciton‐polaritons.

Identification and time-resolved study of ferrimagnetic spin-wave modes in a microwave cavity in the strong-coupling regime

Recently, the hybridization of microwave-frequency cavity modes with collective spin excitations attracted large interest for the implementation of quantum computation protocols, which exploit the transfer of information among these two physical systems. Here, we investigate the interaction among the magnetization precession modes of a small YIG sphere and the MW electromagnetic modes, resonating in a tridimensional aluminum cavity. In the strong coupling regime, anti-crossing features were observed in correspondence of various magnetostatic modes, which were excited in a magnetically saturated sample. Time-resolved studies show evidence of Rabi oscillations, demonstrating coherent exchange of energy among photons and magnons modes. To facilitate the analysis of the standing spin-wave patterns, we propose here a new procedure, based on the introduction of a novel functional variable. The resulting easier identification of magnetostatic modes can be exploited to investigate, control and compare many-levels hybrid systems in cavity- and opto-magnonics research.

Transient response of the cavity magnon-polariton

The Rabi oscillations of a coupled spin-photon system are experimentally studied using time domain microwave transmission measurements. An external magnetic bias field is applied to control the amplitude and frequency of Rabi oscillations, which are a measure of the coherent spin-photon energy exchange and coupling strength respectively. The amplitude and frequency control is described in the time domain as the transient response of a two-level spin-photon system. This approach reveals the link between steady state and transient behaviour of the cavity-magnon-polariton, which is necessary to interpret time domain cavity-spintronic experiments. This transient model also allows us to understand and quantify the polariton mode composition, which can be controlled by the bias field.

Strong interaction of quantum emitters with a WS2 layer enhanced by a gold substrate.

We investigate the spontaneous emission (SE) effects of a two-level quantum emitter (QE) near a WS2 layer. The QE is placed above the WS2 layer in a host medium with constant dielectric permittivity. The material below the WS2 layer is either the same as the host medium or Au. We find that the Purcell factor of the QE near the dielectric/WS2 takes values up to 104. When the value of the dielectric permittivity of the host medium is increased, the enhancement of the Purcell factor diminishes. For a dielectric/WS2/dielectric structure, we obtain a Rabi splitting in the SE spectrum of the QE up to 75meV at room temperature. This splitting is more pronounced for a WS2 layer of improved material quality which can be achieved by improved fabrication methods or operating at lower temperatures. When the WS2 layer is placed on top of an Au substrate, the hybrid exciton-surface plasmon polariton modes strongly interact with the QE, inducing coherent energy exchange between the two, as manifested by a pronounced Rabi splitting in the emission spectrum which is increased to 100meV.

Real-Time Tunable Strong Coupling: From Individual Nanocavities to Metasurfaces

Strong light–matter coupling, characterized by a coherent exchange of energy between an emitter and cavity, plays an important role in, for example, quantum information science and thresholdless lasing. To achieve strong coupling, precise spatial and spectral overlap between the emitter and cavity is required, presenting a significant challenge to move from individually strongly coupled cavities to a large number of cavity-coupled systems, as required for future practical applications. Here we demonstrate a versatile platform for realizing strong coupling that scales uniformly from individual nanocavities up to millimeter-scale metasurfaces, while the coupling strength can be tuned dynamically. Fluorescent dye molecules are sandwiched between silver nanocubes and a metallic film creating a plasmonic cavity with a mode volume of only ∼0.002 (λ/n)3. A prominent anticrossing behavior is observed which corresponds to a large Rabi splitting energy of 152 meV. The plasmon resonance can be tuned up to 45 nm (∼21...