arXiv subjects

Wenxiang Ying

Publications and source records attributed to Wenxiang Ying.

8 recordsLinked to original sources

arXiv2026

A Mesoscopic Ginzburg--Landau Model for Vibrational Strong Coupling Enhanced Rayleigh Scattering in Molecular Liquids

Recent experiments by Sandeep \textit{et al.} [Angew. Chem. Int. Ed. 65, e16917 (2026)] suggest that vibrational strong coupling (VSC) in molecular liquids can generate mesoscopic phenomena beyond single-molecule observables, including resonantly enhanced Rayleigh scattering, abrupt concentration thresholds, and thermal collapse. Motivated by these observations, we construct a mesoscopic Ginzburg--Landau model with two coupled fields: a cavity-controlled collective vibrational polarization $P$ and a secondary structural field $m$ whose long-wavelength susceptibility is renormalized by the collective vibrational polarization intensity $P^2$, assumed to govern long-wavelength density/dielectric fluctuations. With calibrated parameters, the model captures the observed Rayleigh enhancement, collective scaling relations, and threshold-like behavior, while explaining why polaritonic/IR signatures may persist when Rayleigh scattering disappears. The model further predicts enhanced long-wavelength density/dielectric correlations, enlarged mesoscopic correlation lengths, and slowed structural dynamics in the regime with strong Rayleigh enhancement, providing direct experimental tests through small-angle X-ray/neutron scattering and dynamic light-scattering probes.

physics.chem-ph↗

arXiv2026

Excitation density controlled regimes of collective light--matter dynamics

Theoretical descriptions of collective light--matter dynamics often rely on the mean-field (MF) or single-excitation (SE) approximations, yet the parameter regimes where they apply are rarely clearly delineated. Here we show that representative limiting regimes are characterized by two independent parameters: the number of molecules $N$ and the excitation number $N_{\rm exc}$. In the Tavis--Cummings model, when $N\gg 1$ and the excitation density $N_{\rm exc} / N \to 0$, MF and SE descriptions agree and yield linear collective dynamics, showing harmonic Rabi oscillations. At finite excitation density ($N_{\rm exc} / N \sim \mathcal{O}(1)$), the large-$N$ limit remains accurately described by MF dynamics but becomes nonlinear in $N_{\rm exc} / N$, manifested by a Duffing equation for the cavity amplitude with anharmonic Rabi frequency. We further show that cluster expansion systematically restores finite-$N$ correlations beyond MF. When local vibronic interactions are included, the same linear collective limit is reached by both approximations, with SE reaching it through polaron decoupling and MF through linearization. This two-parameter regime map clarifies the limits in which different theoretical descriptions provide controlled descriptions of collective light--matter dynamics.

physics.chem-ph↗

arXiv2026

Linear and nonlinear vibrational excitation driven by molecular polaritons

Following our recent numerical study [arXiv:2601.16299 (2026)], we investigate vibrational excitation induced by transient optical driving in molecular ensembles strongly coupled to a cavity mode using the field-driven Holstein--Tavis--Cummings model. We analyze how pulsed excitation redistributes energy among electronic, photonic, and vibrational degrees of freedom in molecular polaritons. Vibrational dynamics are examined over a broad range of pulse durations and intensities within both the single-excitation approximation and a mean-field description of collective light--matter coupling. Despite their distinct formulations and microscopic descriptions, these two approaches yield consistent scaling relations for vibrational excitation. In particular, we disentangle linear and nonlinear contributions to vibrational excitation, which are reflected in distinct quadratic and quartic scaling behaviors with respect to the driving field amplitude (that is, linear and quadratic dependence on the incident pulse intensity). The microscopic origin of the nonlinear component is identified as a polariton-mediated intrapulse stimulated Raman-like process, enabled by a pulse spectral bandwidth large enough to overlap both upper and lower polaritons (rather than a conventional multi-pulse scheme). These results establish a unified framework for understanding vibrational excitation under pulsed polariton driving and provide guidance for the interpretation and control of ultrafast polariton experiments. Discrepancies between the mean-field and single-excitation approaches under certain pulsed conditions are identified and analyzed.

physics.chem-ph↗

arXiv2026

Collective Rabi-driven vibrational activation in molecular polaritons

Molecular polaritons arise from electronic or vibrational strong coupling (ESC and VSC) with confined electromagnetic fields. While these have been widely studied, the influence of electron-nuclear dynamics in driven cavities remains largely unknown. Here, we report a previously unrecognized mechanism of vibrational activation that emerges under collective ESC in driven optical cavities. Using simulations that self-consistently combine Maxwell's equations with quantum molecular dynamics, we show that collective electronic Rabi oscillations coherently drive nuclear motion. This effect is captured using both vibrational wave-packet dynamics in a minimal two-level model and atomistic simulations based on time-dependent density-functional tight-binding theory. Vibrational activation depends non-monotonically on the Rabi frequency and is maximized when the collective polaritonic splitting resonates with a molecular vibrational mode. The mechanism exhibits features consistent with a stimulated Raman-like relaxation mechanism. Our predictions are robust under realistic cavity conditions and provide the conditions in which they could be verified experimentally.

physics.comp-ph↗

arXiv2025

Electron transfer in confined electromagnetic fields: a unified Fermi's golden rule rate theory and extension to lossy cavities

With the rapid development of nanophotonics and cavity quantum electrodynamics, there has been growing interest in how confined electromagnetic fields modify fundamental molecular processes such as electron transfer. In this paper, we revisit the problem of nonadiabatic electron transfer (ET) in confined electromagnetic fields studied in [J. Chem. Phys. 150, 174122 (2019)] and present a unified rate theory based on Fermi's golden rule (FGR). By employing a polaron-transformed Hamiltonian, we derive analytic expressions for the ET rate correlation functions that are valid across all temperature regimes and all cavity mode time scales. In the high-temperature limit, our formalism recovers the Marcus and Marcus-Jortner results, while in the low-temperature limit it reveals the emergence of the energy gap law. We further extend the theory to include cavity loss by using an effective Brownian oscillator spectral density, which enables closed-form expressions for the ET rate in lossy cavities. As applications, we demonstrate two key cavity-induced phenomena: (i) resonance effects, where the ET rate is strongly enhanced at certain cavity mode frequencies, and (ii) electron-transfer-induced photon emission, arising from the population of cavity photon Fock states during the ET process. These results establish a general framework for understanding how confined electromagnetic fields reshape charge transfer dynamics, and suggest novel opportunities for controlling and probing ET reactions in nanophotonic environments.

physics.chem-ph↗

arXiv2025

Microscopic Theory of Polariton Group Velocity Renormalization

Cavity exciton-polaritons exhibit ballistic transport and can achieve a distance of 100 $μ$m in one picosecond. This ballistic transport significantly enhances mobility compared to that of bare excitons, which often move diffusively and become the bottleneck for energy conversion and transfer devices. Despite being robustly reproduced in experiments and simulations, there is no comprehensive microscopic theory addressing the group velocity of polariton transport, and its renormalization due to phonon scattering while still preserving this ballistic behavior. In this work, we develop a microscopic theory to describe the group velocity renormalization using a finite-temperature Green's function approach. Utilizing the generalized Holstein-Tavis-Cummings Hamiltonian, we analytically derive an expression for the group velocity renormalization and find that it is caused by phonon-mediated transitions from the lower polariton (LP) states to the dark states, then scattering from dark states back to LP. The dark states do not have to be populated in this process, serving as the virtual state for super-exchange (especially true for a large light-matter detuning). The theory predicts that the magnitude of group velocity renormalization scales linearly with the phonon bath reorganization energy under weak coupling conditions (perturbative regime for exciton-phonon coupling) and also linearly depends on the temperature in the high-temperature regime. These predictions are numerically verified using quantum dynamics simulations, demonstrating quantitative agreement. Our findings provide theoretical insights and a predictive analytical framework that advance the understanding and design of cavity-modified semiconductors and molecular ensembles, opening new avenues for engineered polaritonic devices.

quant-ph↗

arXiv2023

Microscopic Theory of Vibrational Polariton Chemistry

We present a microscopic theory that aims to explain the vibrational strong coupling (VSC) modified reaction rate constant. The analytic theory is based on a mechanistic conjecture that cavity modes promote the transition from the ground state to the vibrational excited state of the reactant, which is the rate-limiting step of the reaction. The theory explains the observed resonance effect at the normal incident angle. Assuming the coherent vibrational energy transfer picture, the theory can also explain the collective effect and makes several predictions that are experimentally verifiable.

quant-ph↗

arXiv2023

Spin relaxation dynamics with a continuous spin environment: the dissipaton equation of motion approach

We present the quantum dynamics of a spin coupling to a bath of independent spins via the dissipaton equation of motion (DEOM) approach. The bath, characterized by a continuous spectral density function, is composed of spins that are independent level systems described by the su(2) Lie algebra. This represents an extreme class of anharmonic environment. Based on the conclusion drawn by Suarez and Silbey [J. Chem. Phys. 95, 9115 (1991)] and Makri [J. Chem. Phys. 111, 6164 (1999)] that the spin bath can be mapped to a Gaussian environment under its linear response limit, we derive the fluctuation-dissipation theorem (FDT) of the spin bath from a microscopic perspective, and generalize the discussion to the case of arbitrary bath spin quantum number S. Next, the time-domain Prony fitting decomposition scheme is applied to the bare-bath time correlation function (TCF) given by FDT to generate the exponential decay basis (or pseudo modes) for DEOM construction. The accuracy and efficiency of this strategy has been justified by a variety of numerical results. We envision this work provides new insights to extend the hierarchical equations of motion (HEOM) and DEOM approach to certain types of anharmonic enviroments with arbitrary TCF or spectral density

quant-ph↗