Strong Coupling Conditions Research Articles

Analytical Evaluation of Ground State Gradients in Quantum Electrodynamics Coupled Cluster Theory.

Analytical gradients of potential energy surfaces play a central role in quantum chemistry, allowing for molecular geometry optimizations and molecular dynamics simulations. In strong coupling conditions, potential energy surfaces can account for strong interactions between matter and the quantized electromagnetic field. In this paper, we derive expressions for the ground state analytical gradients in quantum electrodynamics coupled cluster theory. We also present a Cholesky-based implementation for the coupled cluster singles and doubles model. We report timings to show the performance of the implementation and present optimized geometries to highlight cavity-induced molecular orientation effects in strong coupling conditions.

Quantum nature of reactivity modification in vibrational polariton chemistry.

In this work, we present a mixed quantum-classical open quantum system dynamics method for studying rate modifications of ground-state chemical reactions in an optical cavity under vibrational strong-coupling conditions. In this approach, the cavity radiation mode is treated classically with a mean-field nuclear force averaging over the remaining degrees of freedom, both within the system and the environment, which are handled quantum mechanically within the hierarchical equations of motion framework. Using this approach, we conduct a comparative analysis by juxtaposing the mixed quantum-classical results with fully quantum-mechanical simulations. After eliminating spurious peaks that can occur when not using the rigorous definition of the rate constant, we confirm the crucial role of the quantum nature of the cavity radiation mode in reproducing the resonant peak observed in the cavity frequency-dependent rate profile. In other words, it appears necessary to explicitly consider the quantized photonic states in studying reactivity modification in vibrational polariton chemistry (at least for the model systems studied in this work), as these phenomena stem from cavity-induced reaction pathways involving resonant energy exchanges between photons and molecular vibrational transitions.

Weak to strong coupling conditions for a microcavity–quantum dot system under incoherent pumping

We theoretically study the power spectra of a microcavity–quantum dot system under incoherent pumping of photons and excitons, considering two models: one with linked cavity loss rate and pumping, and one with independent cavity loss rate and pumping. We investigate the transition from strong to weak coupling under low and high incoherent pumping in each model and determine sets of parameters necessary to achieve these regimes of light–matter interaction. Despite their differences, both models exhibit a sequence of transitions between weak, strong, and weak coupling as the pumping is increased. This prediction has not yet been observed.

Spatially Resolved Near Field Spectroscopy of Vibrational Polaritons at the Small N Limit.

Vibrational polaritons, which have been primarily studied in Fabry-Pérot cavities with a large number of molecules (N ∼ 106-1010) coupled to the resonator mode, exhibit various experimentally observed effects on chemical reactions. However, the exact mechanism is elusively understood from the theoretical side, as the large number of molecules involved in an experimental strong coupling condition cannot be represented completely in simulations. This discrepancy between theory and experiment arises from computational descriptions of polariton systems typically being limited to only a few molecules, thus failing to represent the experimental conditions adequately. To address this mismatch, we used surface phonon polariton (SPhP) resonators as an alternative platform for vibrational strong coupling. SPhPs exhibit strong electromagnetic confinement on the surface and thus allow for coupling to a small number of molecules. As a result, this platform can enhance nonlinearity and slow down relaxation to the dark modes. In this study, we fabricated a pillar-shaped quartz resonator and then coated it with a thin layer of cobalt phthalocyanine (CoPc). By employing scattering-type scanning near-field optical microscopy (s-SNOM), we spatially investigated the dependency of vibrational strong coupling on the spatially varying electromagnetic field strength and demonstrated strong coupling with 38,000 molecules only-reaching to the small N limit. Through s-SNOM analysis, we found that strong coupling was observed primarily on the edge of the quartz pillar and the apex of the s-SNOM tip, where the maximum field enhancement occurs. In contrast, a weak resonance signal and lack of coupling were observed closer to the center of the pillar. This work demonstrates the importance of spatially resolved polariton systems in nanophotonic platforms and lays a foundation to explore polariton chemistry and chemical dynamics at the small N limit-one step closer to reconcile with high-level quantum calculations.

An Effective Model for Capturing the Role of Excitonic Interactions in the Wave-Packet Dynamics of DNA Nucleobases

Investigating exciton dynamics within DNA nucleobases is essential for comprehensively understanding how inherent photostability mechanisms function at the molecular level, particularly in the context of life’s resilience to solar radiation. In this paper, we introduce a mathematical model that effectively simulates the photoexcitation and deactivation dynamics of nucleobases within an ultrafast timeframe, particularly focusing on wave-packet dynamics under conditions of strong nonadiabatic coupling. Employing the hierarchy equation of motion, we simulate two-dimensional electronic spectra (2DES) and calibrate our model by comparing it with experimentally obtained spectra. This study also explores the effects of base stacking on the photo-deactivation dynamics in DNA. Our results demonstrate that, while strong excitonic interactions between nucleobases are present, they have a minimal impact on the deactivation dynamics of the wave packet in the electronic excited states. We further observe that the longevity of electronic excited states increases with additional base stacking and pairing, a phenomenon accurately depicted by our excitonic model. This model enables a detailed examination of the wave packet’s motion on electronic excited states and its rapid transition to the ground state. Additionally, using this model, we studied base stacks in DNA hairpins to effectively capture the primary exciton dynamics at a reasonable computational scale. Overall, this work provides a valuable framework for studying exciton dynamics from single nucleobases to complex structures such as DNA hairpins.

Insights into the mechanisms of optical cavity-modified ground-state chemical reactions

In this work, we systematically investigate the mechanisms underlying the rate modification of ground-state chemical reactions in an optical cavity under vibrational strong-coupling conditions. We employ a symmetric double-well description of the molecular potential energy surface and a numerically exact open quantum system approach—the hierarchical equations of motion in twin space with a matrix product state solver. Our results predict the existence of multiple peaks in the photon frequency-dependent rate profile for a strongly anharmonic molecular system with multiple vibrational transition energies. The emergence of a new peak in the rate profile is attributed to the opening of an intramolecular reaction pathway, energetically fueled by the cavity photon bath through a resonant cavity mode. The peak intensity is determined jointly by kinetic factors. Going beyond the single-molecule limit, we examine the effects of the collective coupling of two molecules to the cavity. We find that when two identical molecules are simultaneously coupled to the same resonant cavity mode, the reaction rate is further increased. This additional increase is associated with the activation of a cavity-induced intermolecular reaction channel. Furthermore, the rate modification due to these cavity-promoted reaction pathways remains unaffected, regardless of whether the molecular dipole moments are aligned in the same or opposite direction as the light polarization.

Wireless Power Transfer System Model Reduction with Split Frequency Matching

Reduced-order dynamic models of wireless power transfer (WPT) systems are desired to simplify the analysis and design of power control, phase synchronization, and maximum efficiency tracking. The reduced-order dynamic phasor model is a good choice because of its straightforward physical meaning and concise mathematical formula. However, the model relies on the assumption of loose coupling and loses accuracy when the coupling becomes stronger. In this paper, a model reduction method with split frequency matching is proposed to improve model accuracy under relatively strong coupling conditions, which is suitable for most short-distance WPT applications, such as wireless electrical vehicle charging. Split frequency matching is achieved through a pair of conjugate equivalent mutual inductances, which are derived from the asymmetry characteristics of the full-order dynamic phasor model in the positive and negative frequency domains. The proposed model retains the advantages of the existing model while significantly improving the accuracy under strong coupling conditions. Its characteristics are verified by comparing the experimental results and model predictions under both large step changes and small-signal perturbations.

High-efficiency all-optical switching based on broadband coherent perfect absorption in an atom-cavity system

We propose an ultrahigh-efficiency and broadband all-optical switching scheme based on coherent perfect absorption (CPA) in linear and nonlinear excitation regimes in a cavity quantum electrodynamics (CQED) system. Two separate atomic transitions are excited simultaneously by two signal fields coupled from two ends of an optical cavity under the collective strong coupling condition. Three polariton eigenstates are produced which can be tuned freely by varying system parameters. The output field intensities of multiple channels are zero when the CPA criterion is satisfied. However, destructive quantum interference can be induced by a free-space weak control laser when it is tuned to be resonant to the polariton state. As a consequence, the CQED system acts as a coherent perfect light absorber/transmitter as the control field is turned on/off the polariton resonances. In particular, the proposed scheme may be used to realize broadband multi-throw all-optical switching in the nonlinear excitation regime. The proposed scheme is useful for constructing all-optical routing, all-optical communication networks and various all-optical logic elements.

Making 1H-1H Couplings More Accessible and Accurate with Selective 2DJ NMR Experiments Aided by 13C Satellites.

1H-1H coupling constants are one of the primary sources of information for nuclear magnetic resonance (NMR) structural analysis. Several selective 2DJ experiments have been proposed that allow for their individual measurement at pure shift resolution. However, all of these experiments fail in the not uncommon case when coupled protons have very close chemical shifts. First, the coupling between protons with overlapping multiplets is inaccessible due to the inability of a frequency-selective pulse to invert just one of them. Second, the strong coupling condition affects the accuracy of coupling measurements involving third spins. These shortcomings impose a limit on the effectiveness of state-of-the-art experiments, such as G-SERF or PSYCHEDELIC. Here, we introduce two new and complementary selective 2DJ experiments that we coin SERFBIRD and SATASERF. These experiments overcome the aforementioned issues by utilizing the 13C satellite signals at natural isotope abundance, which resolves the chemical shift degeneracy. We demonstrate the utility of these experiments on the tetrasaccharide stachyose and the challenging case of norcamphor, for the latter achieving measurement of all JHH couplings, while only a few were accessible with PSYCHEDELIC. The new experiments are applicable to any organic compound and will prove valuable for configurational and conformational analyses.

Consequences of Vibrational Strong Coupling on Supramolecular Polymerization of Porphyrins.

Supramolecular polymers display interesting optoelectronic properties and, thus, deploy multiple applications based on their molecular arrangement. However, controlling supramolecular interactions to achieve a desirable molecular organization is not straightforward. Over the past decade, light-matter strong coupling has emerged as a new tool for modifying chemical and material properties. This novel approach has also been shown to alter the morphology of supramolecular organization by coupling the vibrational bands of solute and solvent to the optical modes of a Fabry-Perot cavity (vibrational strong coupling, VSC). Here, we study the effect of VSC on the supramolecular polymerization of chiral zinc-porphyrins (S-Zn) via a cooperative effect. Electronic circular dichroism (ECD) measurements indicate that the elongation temperature (Te) of the supramolecular polymerization is lowered by ∼10 °C under VSC. We have also generalized this effect by exploring other supramolecular systems under strong coupling conditions. The results indicate that the solute-solvent interactions are modified under VSC, which destabilizes the nuclei of the supramolecular polymer at higher temperatures. These findings demonstrate that the VSC can indeed be used as a tool to control the energy landscape of supramolecular polymerization. Furthermore, we use this unique approach to switch between the states formed under ON- and OFF-resonance conditions, achieved by simply tuning the optical cavity in and out of resonance.

From weak to strong coupling: quasi-BIC metasurfaces for mid-infrared light-matter interactions.

Thanks to their giant, yet tunable, Q-factor resonances, all-dielectric metasurfaces supporting the quasi-bound states in the continuum (q-BIC) resonances are well-suited to provide a promising platform for quantum-coherent light-matter interactions. Yet, the strong coupling regime, characterized by the hybrid light-matter states - polaritons, has not yet been fully explored in the mid-infrared regime. This paper investigates the parameter space of vibrational strong coupling (VSC) between material and metasurface cavities supporting q-BIC resonances in the mid-infrared spectral range. We outline the effects of transition dipole strength, damping rate, and the number of molecules coupled to a single cavity, as well as the cavity damping rates, to understand their respective impacts on VSC. By tuning the Q-factor of the metasurface and material parameters, a new transition light-matter coupling zone is introduced, bridging the gap between weak and strong coupling, where polaritons form but their linewidths prohibit their spectral identification. The study further identifies the effects of cavity linewidth on polariton peak separability in strongly coupled systems, highlighting that the cavities with smaller nonradiative losses and narrower linewidths facilitate better polariton separability. Moreover, we found that matching cavity and material loss, satisfying the critical strong coupling condition, enhances the coupling strength between cavity and material. Overall, these findings can guide the design of photonic cavities suited for VSC experiments, contributing to the burgeoning fields of polaritonic chemistry, light-mediated modulation of chemical reactivity, and highly sensitive molecular spectroscopy.

Quantum nonlinear effect in a dissipatively coupled optomechanical system.

A full-quantum approach is used to study the quantum nonlinear properties of a compound Michelson-Sagnac interferometer optomechanical system. By deriving the effective Hamiltonian, we find that the reduced system exhibits a Kerr nonlinear term with a complex coefficient, entirely induced by the dissipative and dispersive couplings. Unexpectedly, the nonlinearities resulting from the dissipative coupling possess non-Hermitian Hamiltonian-like properties preserving the quantum nature of the dispersive coupling beyond the traditional system dissipation. This protective mechanism allows the system to exhibit strong quantum nonlinear effects when the detuning (the compound cavity detuning Δc and the auxiliary cavity detuning Δe) and the tunneling coupling strength (J) of two cavities satisfy the relation J2 = ΔcΔe. Moreover, the additive effects of dispersive and dissipative couplings can produce strong anti-bunching effects, which exist in both strong and weak coupling conditions. Our work may provide a new way to study and produce strong quantum nonlinear effects in dissipatively coupled optomechanical systems.

Shaping the laser control landscape of a hydrogen transfer reaction by vibrational strong coupling. A direct optimal control approach.

Controlling molecular reactivity by shaped laser pulses is a long-standing goal in chemistry. Here, we suggest a direct optimal control approach that combines external pulse optimization with other control parameters arising in the upcoming field of vibro-polaritonic chemistry for enhanced controllability. The direct optimal control approach is characterized by a simultaneous simulation and optimization paradigm, meaning that the equations of motion are discretized and converted into a set of holonomic constraints for a nonlinear optimization problem given by the control functional. Compared with indirect optimal control, this procedure offers great flexibility, such as final time or Hamiltonian parameter optimization. A simultaneous direct optimal control theory will be applied to a model system describing H-atom transfer in a lossy Fabry-Pérot cavity under vibrational strong coupling conditions. Specifically, optimization of the cavity coupling strength and, thus, of the control landscape will be demonstrated.

Strong coupling in metal-semiconductor microcavities featuring Ge quantum wells: a perspective study

Abstract In this work we theoretically investigate the possibility of observing strong coupling at mid-infrared frequencies within the group-IV semiconductor material platform. Our results show that the strong coupling condition is attainable in Ge/SiGe quantum wells integrated in hybrid metal-semiconductor microcavities, featuring a highly n-doped SiGe layer as one of the mirrors.

A Two‐Step Entanglement Concentration for the Less‐Entangled Four‐Photon Cluster States

AbstractEntanglement concentration serves as an essential tool to obtain the maximally entangled states from the less‐entangled states in quantum information processing tasks. An efficient two‐step entanglement concentration protocol (ECP) is proposed to concentrate the less‐entangled four‐photon cluster states with four unknown coefficients into the maximally entangled states in this paper. The protocol utilizes parity‐check gate and photon‐polarized controlled‐Z gate, constructed with a single semiconductor quantum dot in a single optical microcavity (quantum dot‐cavity coupled system) and several linear optical elements. The discarded quantum states can be recycled in the next round concentration to achieve a higher success probability. Under conditions of strong coupling and weak side leakage rate, the ECP can tend toward ideal fidelity and efficiency. Compared to the previously proposed ECPs that utilize various auxiliary tools such as additional entangled states and complex quantum logic gates, the ECP significantly simplifies the analysis process and enables efficient implementation. Thus, the ECP is more economical and feasible in future optical systems.

Thermal transport mechanism of 4H–SiC/SiO2 heterostructures: a molecular dynamics study

Silicon carbide (SiC) is widely used in high-frequency, high-speed, and high-power applications such as power electronics, rail transportation, new energy vehicles, and aerospace. However, the thermal properties of the SiC/SiO2 interface, which is commonly found in SiC-based devices, are not yet fully understood. This study aims to investigate the influence of temperature and interface coupling strength on the interface thermal resistance (ITR) of 4H-SiC/SiO2 using non-equilibrium molecular dynamics simulations. Both crystalline and amorphous SiO2, as well as two interface contact modes (Si-terminated and C-terminated), have also been considered. The results reveal that the ITR of 4H-SiC/SiO2 is significantly affected by the interface coupling strength and contact modes. Under strong interface coupling conditions, the ITR for Si-terminated and C-terminated contacts modes of 4H-SiC/SiO2 interfaces are 8.077 × 10−10 m2KW−1 and 6.835 × 10−10 m2KW−1, respectively. However, under weak interface coupling conditions, these values increase to 10.142 × 10−10 m2KW−1 and 7.785 × 10−10 m2KW−1, respectively. Regardless of whether SiO2 is crystalline or amorphous, the ITR of the 4H-SiC/SiO2 interface exhibits a similar trend with increasing temperature (from 300 to 700 K). Additionally, the ITR of the amorphous SiO2 interface is smaller than that of the crystalline SiO2 interface under both strong and weak coupling conditions. To gain insights into the heat transport mechanism, the phonon density of states was analyzed to examine the phonon spectral characteristics under varying coupling strengths. These findings have implications for enhancing the thermal management and heat dissipation of SiC devices, providing a framework for controlling interface phonon scattering, and informing the thermal design of nanodevices.

Optical Cavity Design and Functionality for Molecular Strong Coupling.

Optical cavity/molecule strong coupling offers attractive opportunities to modulate photochemical or photophysical processes. When atoms or molecules are placed in an optical cavity, they can coherently exchange photonic energy with optical cavity vacuum fields, entering the strong coupling interaction regime. Recent work suggests that the thermodynamic and kinetic properties of molecules can be significantly changed by strong coupling, resulting in the emergence of intriguing photochemical and photophysical phenomena. As more and more physico-chemical systems are studied under strong coupling conditions, optical cavities have also advanced in their sophistication, responsiveness, and (multi)functionality. In this review, we highlight some of these recent developments, particularly focusing on Fabry-Perot microcavities.

Cross-Space Conduction Assessment Method of Network Attack Risk under the Strong Coupling Characteristics of Electric Power Cyber Physics

With the deep integration and wide application of advanced digital sensing, Internet of Things technology, and energy technology in power systems. Power information systems and physical systems are gradually being coupled and developed into power cyber–physical systems (CPS). A number of blackouts in recent years have shown that cyberspace cyber attacks on CPS can lead to the intensification and rapid spread of faults in the physical space of the power grid, and even system collapse. Aiming at the difficulty of analyzing the evolution of cyber–physical cross-space impacts of cyber-attacks, this paper proposes a cross-domain propagation impact assessment method that considers cyber–physical coupling risks caused by attacks. First, according to the multiple coupling relationship between the power system information space and physical space, the monitoring function model and the control function model are established. Second, under the effect of high-concealment attack, analyze the impact of the risk caused by its failure after it is transmitted to the physical space with different propagation probabilities. Finally, the experimental verification was carried out using the IEEE RTS79 standard test system. The simulation results show that the proposed method can comprehensively consider the cyber–physical energy supply coupling relationship, the risk propagation probability, and the operating characteristics of the information system, and effectively quantify and evaluate the impact of information space network attacks on the physical space entity power grid. It further reveals the objective law that information space risks can evolve and spread across domains under the condition of strong coupling of information physics.

Evidence for Hybrid Inorganic–Organic Transitions at the WS2/Terrylene Interface

The realization of the potential of hybrid inorganic organic systems requires an understanding of the coupling between the constituents: its nature and its strength. The observation of hybrid optical transitions in the monolayer WS2/terrylene hybrid is reported. The first‐principle calculations, linear optical, and transient absorption spectroscopy are employed to investigate the optical spectrum of the hybrid, which exhibits a new transition that does not appear in the constituents’ spectra. The calculations indicate type II level alignment, with the highest occupied level of terrylene in the gap of WS2. Exploiting state‐resolved transient absorption, the response of the hybrid interface to optical excitation is selectively probed. The dynamics reveal rapid hole transfer from WS2 to the terrylene layer, with a decay time of 88 ps. This hole transfer induces a bleach of the hybrid transition, which indicates that terrylene contributes to its initial state. Based on this, the hybrid resonance energy, and on our calculations, we assign the hybrid feature to a transition from the highest occupied molecular orbital of terrylene to the conduction band of WS2 close to the Γ point. The results indicate that the conditions for strong electronic coupling are met in this hybrid system.

Spontaneous Raman scattering from vibrational polaritons is obscured by reservoir states.

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