arXiv subjects

Liang-Yan Hsu

Publications and source records attributed to Liang-Yan Hsu.

16 recordsLinked to original sources

arXiv2026

Polaron-Polariton Assisted Thermally Activated Superradiance

We predict an anomalous thermally activated superradiance in molecular aggregates within polaritonic environments. In contrast to free space, the collective emission is enhanced when either the exciton-phonon coupling or the temperature increases. This counterintuitive phenomenon is captured by a microscopic theory that combines macroscopic quantum electrodynamics with a modified polaron quantum master equation approach, revealing a nontrivial interplay among excitons, phonons, and polaritons.

physics.chem-ph↗

arXiv2025

Robust Surface-Induced Enhancement of Exciton Transport in Magic-Angle-Oriented Molecular Aggregates

Exciton transport in molecular aggregates with magic-angle orientation is expected to be strongly suppressed due to their negligible dipole-dipole interactions. However, recent reports show that light-matter interactions can significantly enhance exciton transport attributed to the effective long-range coupling mediated by the photonic fields. To elucidate their interplay, we employ the macroscopic quantum electrodynamics framework to simulate exciton transport within a chromophore array arranged in a magic-angle configuration in proximity to a silver surface. Our results show a significant enhancement of the exciton diffusion coefficient that is robust across variations in chromophore-surface separation, intermolecular distance, and molecular transition frequency. Furthermore, based on the image-dipole method, we derive analytical expressions that agree well with numerical simulations, revealing the enhancement's origin in the near-field coupling term as induced by the radiative scattering at the metallic surface. More importantly, we observe non-trivial differences in the diffusion coefficient's scaling near metallic surfaces compared to free space. Our findings highlight the potential to control exciton transport by designing coupled exciton-photon systems and engineering the dielectric environments.

physics.chem-ph↗

arXiv2024

Theory of Molecular Emission Power Spectra. III. Non-Hermitian Interactions in Multichromophoric Systems Coupled with Polaritons

Based on our previous study [S. Wang $\textit{et al}$. J. Chem. Phys. $\textbf{153}$, 184102 (2020)], we generalize the theory of molecular emission power spectra (EPS) from one molecule to multichromophoric systems in the framework of macroscopic quantum electrodynamics. This generalized theory is applicable to ensembles of molecules, providing a comprehensive description of the molecular spontaneous emission spectrum in arbitrary inhomogeneous, dispersive, and absorbing media. In the far-field region, the analytical formula of EPS can be expressed as the product of a lineshape function (LF) and an electromagnetic environment factor (EEF). To demonstrate the polaritonic effect on multichromophoric systems, we simulate the LF and EEF for one to three molecules weakly coupled to surface plasmon polaritons above a silver surface. Our analytical expressions show that the peak broadening originates from not only the spontaneous emission rates but also the imaginary part of resonant dipole-dipole interactions (non-Hermitian interactions), which is associated with the superradiance of molecular aggregates, indicating that the superradiance rate can be controlled through an intermolecular distance and the design of dielectric environments. This study presents an alternative approach to directly analyze the hybrid-state dynamics of multichromophoric systems coupled with polaritons.

physics.chem-ph↗

arXiv2024

Anomalous Giant Superradiance in Molecular Aggregates Coupled to Polaritons

In this study, we unveil an eccentric superradiance phenomenon in molecular aggregates coupled to surface plasmon polaritons. Through the quantization of electromagnetic fields in media, we demonstrate that superradiance can be significantly enhanced by polaritons and its behavior distinguishably surpasses the Dick's $N$ scaling law. To understand the mechanism of this anomalous phenomenon, we derive an analytical expression of the superradiance rate, which is general for molecular aggregates in arbitrary dispersive and absorbing media. Furthermore, we show the importance of intermolecular distance for this extraordinary superradiance.

physics.chem-ph↗

arXiv2023

Microscopic theory of exciton-polariton model involving multiple molecules: Macroscopic quantum electrodynamics formulation and essence of direct intermolecular interactions

Cavity quantum electrodynamics (CQED) and its extensions are widely used for the description of exciton-polariton systems. However, the exciton-polariton models based on CQED vary greatly within different contexts. One of the most significant discrepancies among these CQED models is whether one should include direct intermolecular interactions in the CQED Hamiltonian. To answer this question, in this article, we derive an effective dissipative CQED model including free-space dipole-dipole interactions (CQED-DDI) from a microscopic Hamiltonian based on macroscopic quantum electrodynamics. Dissipative CQED-DDI successfully captures the nature of vacuum fluctuations in dielectric media and separates it into the free-space effects and the dielectric-induced effects. The former include spontaneous emissions, dephasings and dipole-dipole interactions in free space; the latter include exciton-polariton interactions and photonic losses due to dielectric media. We apply dissipative CQED-DDI to investigate the exciton-polariton dynamics (the population dynamics of molecules above a plasmonic surface) and compare the results with those based on the methods proposed by several previous studies. We find that direct intermolecular interactions are a crucial element when employing CQED-like models to study exciton-polariton systems involving multiple molecules.

quant-ph↗

arXiv2023

Wide-Dynamic-Range Control of Quantum-Electrodynamic Electron Transfer Reactions in the Weak Coupling Regime

Catalyzing reactions effectively by vacuum fluctuations of electromagnetic fields is a significant challenge within the realm of chemistry. Different from most studies based on vibrational strong coupling, we introduce an innovative catalytic mechanism driven by weakly coupled polaritonic fields. Through the amalgamation of macroscopic quantum electrodynamics (QED) principles with Marcus electron transfer (ET) theory, our results reveal that ET reaction rates can be precisely modulated across a wide dynamic range by controlling the size and structure of nanocavities. Comparing to QED-driven radiative ET rates in free space, plasmonic cavities induce substantial rate enhancements spanning from orders of magnitude ranging from 10^3-fold to 10^1-fold. By contrast, Fabry-Perot cavities engender rate suppression spanning from 10^{-2}-fold to 10^{-1}-fold. This work overcomes the necessity of using strong light-matter interactions in QED chemistry, opening up a new era of manipulating QED-based chemical reactions in a wide dynamic range.

physics.chem-ph↗

arXiv2023

Many-Body Coherence in Quantum Transport

In this study, we propose the concept of harnessing quantum coherence to control electron transport in a many-body system. Combining an open quantum system technique based on Hubbard operators, we show that many-body coherence can eliminate the well-known Coulomb staircase and cause strong negative differential resistance. To explore the mechanism, we analytically derive the current-coherence relationship in the zero electron-phonon coupling limit. Furthermore, by incorporating a gate field, we demonstrate the possibility of constructing a coherence-controlled transistor. This development opens up a new direction for exploring quantum electronic devices based on many-body coherence.

cond-mat.mes-hall↗

arXiv2023

Quantum dynamics of molecular ensembles coupled with quantum light: Counter-rotating interactions as an essential component

The rotating-wave approximation to light-matter interactions is widely used in the quantum electrodynamics Hamiltonian; however, its validity has long been a matter of debate. In this article, we explore the impact of the rotating-wave approximation on the quantum dynamics of multiple molecules in complex dielectric environments within the framework of macroscopic quantum electrodynamics. In general, we find that the energy shifts of the molecules and the inter-molecule dipole-dipole interaction obtained in the weak coupling regime are correct only when the counter-rotating interactions are considered. Moreover, under the rotating-wave approximation, the energy shifts of the ground-state molecules and a portion of the inter-molecule interaction are discarded. Notably, in the near-field zone (short inter-molecular distance), the reduction of inter-molecule interaction can reach up to 50 percent. We also conduct a case study on the population dynamics of a pair of identical molecules above a plasmonic surface. Through analytical and numerical analysis, it is revealed that the rotating-wave approximation can profoundly affect the dynamics of the molecules in both strong and weak coupling regimes, emphasizing the need for careful consideration when making the rotating-wave approximation in a multiple-molecule system coupled with quantum light.

quant-ph↗

arXiv2023

Polariton-Assisted Resonance Energy Transfer Beyond Resonant Dipole-Dipole Interaction: A Transition Current Density Approach

Using electric dipoles to describe light-matter interactions between two entities is a conventional approximation in physics, chemistry, and material sciences. However, the lack of material structures makes the approximation inadequate when the size of an entity is comparable to the spatial extent of electromagnetic fields or the distance between two entities. In this study, we develop a unified theory of radiative and non-radiative resonance energy transfer based on transition current density in a theoretical framework of macroscopic quantum electrodynamics. The proposed theory allows us to describe polariton-assisted resonance energy transfer between two entities with arbitrary material structures in spatially dependent vacuum electric fields. To demonstrate the generality of the proposed theory, we rigorously prove that our theory can cover the main results of the transition density cube method and the plasmon-coupled resonance energy transfer. We believe that this study opens a promising direction for exploring light-matter interactions beyond the scope of electric dipoles and provides new insights into material physics.

physics.chem-ph↗

arXiv2022

Polaritonic Huang-Rhys Factor: Basic Concepts and Quantifying Light-Matter Interaction in Medium

Huang-Rhys (HR) factor, a dimensionless factor that characterizes electron-phonon coupling, has been extensively employed to investigate material properties in various fields. In the same spirit, we present a quantity called polaritonic HR factor to quantitatively describe the effects of (i) light-matter coupling induced by permanent dipoles and (ii) dipole self-energy. The former can be viewed as polaritonic displacements, while the latter is associated with the electronic coupling shift. In the framework of macroscopic quantum electrodynamics, the polaritonic HR factor, coupling shift, and modified light-matter coupling strength in an arbitrary dielectric environment can be evaluated without free parameters, whose magnitudes are in good agreement with the previous experimental results. In addition, polaritonic progression developed in our theory indicates that large polaritonic HR factors can result in light-matter decoupling, multipolariton formation, and non-radiative transition. We believe that this study provides a useful perspective to understand and quantify light-matter interaction in medium.

physics.chem-ph↗

arXiv2021

Simple but accurate estimation of light-matter coupling strength and optical loss for a molecular emitter coupled with photonic modes

Light-matter coupling strength and optical loss are two key physical quantities in cavity quantum electrodynamics (cQED), and their interplay determines whether light-matter hybrid states can be formed or not in chemical systems. In this study, by using macroscopic quantum electrodynamics (mQED) combined with a pseudomode approach, we present a simple but accurate method which allows us to quickly estimate the light-matter coupling strength and optical loss without free parameters. Moreover, for a molecular emitter coupled with photonic modes (including cavity modes and plasmon polartion modes), we analytically and numerically prove that the dynamics derived from the mQED-based wavefunction approach is mathematically equivalent to the dynamics governed by the cQED-based Lindblad master equation when the Purcell factor behaves like Lorentzians.

physics.chem-ph↗

arXiv2019

Photoinduced Anomalous Coulomb Blockade and the Role of Triplet States in Electron Transport through an Irradiated Molecular Transistor II: Effects of Electron-Phonon Coupling and Vibrational Relaxation

We generalize our previous theory [Nano Lett. \textbf{18}, 5015-5023 (2018)] to investigate the influence of electron-phonon (e-p) coupling and vibrational relaxation on photoinduced \textit{anomalous Coulomb blockade}, which originates from the triplet states and the energy level alignment. We derive the master equation for an irradiated molecular transistor and obtain the relevant rates via the Redfield theory instead of the phenomenological Fermi golden rule approach. To explore the interplay between e-p coupling and vibrational relaxation, we analyze the charge stability diagrams and the current-voltage characteristics (both gate voltage and source-drain bias voltage) under different e-p coupling strengths in two extreme limits of vibrational relaxation (equilibrated and unequilibrated phonon regimes). From the perspective of energy level alignment, we choose four representative situations and derive the analytical formulas of the photoinduced current in the equilibrated regime. The analytical solution reveals a new type of photocurrent due to e-p coupling that does not require the perfect energy level alignment between charged states and triplet states. In general, our study indicates that photoinduced current and anomalous Coulomb blockade caused by the triplet states are supposed to be experimentally observed.

physics.chem-ph↗

arXiv2015

Entropy-based Time-Varying Window Width Selection for Nonlinear type Time-Frequency Analysis

We propose a time-varying optimal window width (TVOWW) selection scheme to optimize the performance of several nonlinear-type time-frequency analyses, including the reassignment method, and the synchrosqueezing transform (SST) and its variations. A window rendering the most concentrated distribution in the time-frequency representation (TFR) is regarded as the optimal window. The TVOWW selection scheme is particularly useful for signals that comprise fast-varying instantaneous frequencies and small spectral gaps. To demonstrate the efficacy of the method, in addition to analyzing a synthetic signal, we study an atomic time-varying dipole moment driven by two-color mid-infrared laser fields in attosecond physics.

physics.data-an↗

arXiv2015

Exploring laser-driven quantum phenomena from a time-frequency analysis perspective: A comprehensive study

Time-frequency (TF) analysis is a powerful tool for exploring ultrafast dynamics in atoms and molecules. While some TF methods have demonstrated their usefulness and potential in several of quantum systems, a systematic comparison among these methods is still lacking. To this end, we compare a series of classical and contemporary TF methods by taking hydrogen atom in a strong laser field as a benchmark. In addition, several TF methods such as Cohen class distribution other than the Wigner-Ville distribution, reassignment methods, and the empirical mode decomposition method are first introduced to exploration of ultrafast dynamics. Among these TF methods, the synchrosqueezing transform successfully illustrates the physical mechanisms in the multiphoton ionization regime and in the tunneling ionization regime. Furthermore, an empirical procedure to analyze an unknown complicated quantum system is provided, indicating the versatility of TF analysis as a new viable venue for exploring quantum dynamics.

physics.data-an↗

arXiv2014

A new time-frequency method to reveal quantum dynamics of atomic hydrogen in intense laser pulses: Synchrosqueezing Transform

This study introduces a new adaptive time-frequency (TF) analysis technique, synchrosqueezing transform (SST), to explore the dynamics of a laser-driven hydrogen atom at an {\it ab initio} level, upon which we have demonstrated its versatility as a new viable venue for further exploring quantum dynamics. For a signal composed of oscillatory components which can be characterized by instantaneous frequency, the SST enables rendering the decomposed signal based on the phase information inherited in the linear TF representation with mathematical support. Compared with the classical type TF methods, the SST clearly depicts several intrinsic quantum dynamical processes such as selection rules, AC Stark effects, and high harmonic generation.

physics.data-an↗

arXiv2014

Electron transport through a single-molecule junction with multiple pathways under time-periodic fields: A Floquet-scattering formalism

We develop a new general formulation to explore light-driven electron transport through a single-molecule device with multiple pathways. Three individual systems are proposed including (i) a two-terminal molecular junction based on phenyl-acetylene macrocycle (PAM), (ii) PAM with three terminals, and (iii) a parallel molecular circuit. The computations show that PAM-based optoelectronic switches have robust large on-off ratios and weak-field operating conditions, which are not sensitive to asymmetric molecule-lead couplings. In addition, field-amplitude power laws for one- and two-photon assisted tunneling are evident in the computational results, and the laws can be proven by using perturbation analysis. For PAM-based optoelectronic routers, we show that it is possible to manipulate the direction of electric current through the PAM molecule by using a weak linearly polarized laser field. For parallel circuits made of molecular quantum dots, the condition of coherent destruction of tunneling is derived by using the rotating wave approximation and the high-frequency approximation.

cond-mat.mes-hall↗