arXiv subjects

Chern Chuang

Publications and source records attributed to Chern Chuang.

At least 19 recordsLinked to original sources

arXiv2026

Simulating Exciton Transport with Complex Absorbing Potentials

We introduce a stochastic framework based on complex absorbing potentials (CAPs) to investigate exciton transport in large molecular aggregates. Within this approach, CAPs act as non-Hermitian reservoirs and sinks that enable effective measurement of transport efficiency. We apply this framework to cyanine dye aggregates and examine how vacancy defects and system size influence exciton dynamics in two-dimensional sheets and quasi-one-dimensional tubes. We also introduce a CAPs-based classification scheme that links molecular packing in 2D aggregates to transport behavior. Our results demonstrate how aggregate topology and structural disorder govern exciton dynamics and provide guidance for designing materials with enhanced energy transport.

physics.chem-ph↗

arXiv2026

Coherent Biexciton Transport in the Presence of Exciton-Exciton Annihilation in Molecular Aggregates

We present a theoretical framework for biexciton dynamics in molecular aggregates that explicitly treats populations and coherences across excitation manifolds within a reduced density-matrix formalism. By extending kinetic descriptions beyond the weak-coupling limit, the approach captures the influence of exciton delocalization and exciton-exciton annihilation while remaining computationally tractable within a Markovian description of environmental relaxation. Using this framework, we investigate how the spatial profile and momentum composition of the initial biexciton state govern fluorescence decay and transport. Incoherent initial conditions lead to strongly non-exponential relaxation and time-dependent diffusion driven by nonlinear population kinetics. In contrast, coherently prepared biexciton states exhibit pronounced early-time coherent transport, whose character depends sensitively on whether the initial state is prepared as a standing-wave or traveling-wave superposition of single-exciton modes. Despite nearly identical emission dynamics for J and H aggregate, biexciton transport properties differ markedly due to band structure-dependent interference effect. Our results demonstrate that biexciton dynamics remains strongly influenced by initial-state coherence and momentum composition. Besides initial-state preparation, the coherent-to-incoherent crossover and the diffusive spreading of the exciton density are sensitive to internal conversion processes such as exciton fusion and the decay to the first excited state. The present work establishes initial-state preparation as a key control parameter for many-exciton transport in excitonic systems and provides a general framework for interpreting nonlinear optical experiments beyond population-based descriptions.

cond-mat.mes-hall↗

arXiv2025

Transfer tensor analysis of localization in the Anderson and Aubry-Andr\'e-Harper models

We use the transfer tensor method to analyze localization and transport in simple disordered systems, specifically the Anderson and Aubry-Andr\'e-Harper models. Emphasis is placed on the memory effects that emerge when ensemble-averaging over disorder, even when individual trajectories are strictly Markovian. We find that transfer tensor memory effects arise to remove fictitious terms that would correspond to redrawing static disorder at each time step, which would create a temporally uncorrelated dynamic disorder. Our results show that while eternal memory is a necessary condition for localization, it is not sufficient. We determine that signatures of localization and transport can be found within the transfer tensors themselves by defining a metric called "outgoing-pseudoflux". This work establishes connections between theoretical research on dynamical maps and Markovianity and localization phenomena in physically realizable model systems.

cond-mat.dis-nn↗

arXiv2025

Mixed State Entanglement Via the Cauchy-Schwarz Inequality

The entanglement properties of mixed states are of great importance in the study of open quantum systems and quantum information science, but commonly used entanglement measures, such as negativity, can be difficult to apply or connect to physical properties of the system. We introduce the Cauchy-Schwarz Violation (CSV) Condition, which has a simple dependence on the populations and coherences of the density operator. A sufficient condition for entanglement, it provides a more direct connection to the physical characteristics of the system such as its symmetries. We illustrate the often surprising insights gained from the CSV condition by applying it to the Jaynes-Cummings Model, the Quantum Rabi Model, and an open-system Quantum Rabi Model.

quant-ph↗

arXiv2025

Parametric Hypersensitivity and Transport in the Steady-State Open-System Holstein Model

We demonstrate that the nonequilibrium steady state (NESS) of an open-system Holstein model with linear bias displays extreme sensitivity to the closed system parameters. This sensitivity is shown to correspond to avoided crossings in the closed system spectrum, as previously demonstrated in the Rabi model. We then develop a kinetic model to analyze the effects of environmental parameters on NESS hypersensitivity. This reveals that hypersensitivity only exists in intermediate environmental parameter regimes, a prediction that is verified numerically. The inherent spatial character of the Holstein model offers a natural connection to transport, revealing that transport properties in the steady-state regime can be optimized by simultaneously coordinating the closed- and open-system parameters.

quant-ph↗

arXiv2024

Mixtures and grain boundaries of P, D, and G triply periodic minimal surfaces

We introduce a square tiling/tetragonal strip representation to the P, D, and G triply periodic minimal surfaces. This approach is useful in identifying mixtures and grain boundaries of these surfaces that might be useful for material sciences or advanced manufacturing purposes. Generalizations to more complicated strip topology (multi-strand) as well as other regular and semi-regular tilings are discussed. Examples of these include double diamond, double gyroid, and triangular P/D/G surfaces.

cond-mat.mtrl-sci↗

arXiv2024

Machine Learning Optimization of non-Kasha Behavior and of Transient Dynamics in Model Retinal Isomerization

Designing a model of retinal isomerization in Rhodopsin, the first step in vision, that accounts for both experimental transient and stationary state observables is challenging. Here, multi-objective Bayesian optimization is employed to refine the parameters of a minimal two-state-two-mode (TM) model describing the photoisomerization of retinal in Rhodopsin. With an appropriate selection of objectives, the optimized retinal model predicts excitation wavelength-dependent fluorescence spectra that closely align with experimentally observed non-Kasha behavior in the non-equilibrium steady state. Further, adjustments to the potential energy surface within the TM model reduce the discrepancies across the time domain. Overall, agreement with experimental data is excellent.

physics.bio-ph↗

arXiv2023

Coherent spatial control of wave packet dynamics on quantum lattices

Quantum lattices are pivotal in the burgeoning fields of quantum materials and information science. Rapid developments in microscopy and quantum engineering allow for preparing and monitoring wave-packet dynamics on quantum lattices with increasing spatial and temporal resolution. Motivated by these emerging research interests, we present an analytical study of wave packet diffusivity and diffusion length on tight-binding quantum lattices subject to stochastic noise. Our analysis points to the crucial role of spatial coherence and predicts a set of novel phenomena: noise can enhance the transient diffusivity and diffusion length of sufficiently extended initial states; A smooth Gaussian initial state spreads slower than a localized initial state; A standing or traveling initial state with large momentum spreads faster than a localized initial state and exhibits a noise-induced peak in the transient diffusivity; The change in the time-dependent diffusivity and diffusion length relative to a localized initial state follows a universal dependence on the Gaussian width. These theoretical predictions and the underlying mechanism of spatial coherence suggest the possibility of controlling the wave packet dynamics on quantum lattices by spatial manipulations, which will have implications for materials science and quantum technologies.

quant-ph↗

arXiv2022

Electronic-vibrational resonance does not alter steady-state transport in natural light-harvesting systems

Oscillations in time-dependent 2D electronic spectra appear as evidence of quantum coherence in light-harvesting systems related to electronic-vibrational resonant interactions. Nature, however, takes place in a non-equilibrium steady-state, so the relevance of these arguments to the natural process is unclear. Here we examine the role of intramolecular vibrations in the non-equilibrium steady-state of photosynthetic dimers in the natural scenario of incoherent light excitation. It is found that vibrations resonant with the energy difference between exciton states do not increase the quantum yield nor the imaginary part of the intersite coherence that is relevant for transport compared with non-resonant vibrations in the natural non-equilibrium steady state. That is, the vibration-electronic resonance interaction does not alter energy transport under natural incoherent-light excitation conditions.

quant-ph↗

arXiv2022

Parametric hypersensitivity in many-body bath-mediated transport: The quantum Rabi model

We demonstrate that non-equilibrium steady states of the dissipative Rabi model show dramatic spikes in transport rates over narrow parameter ranges. Similar results are found for the Holstein and Dicke models. This is found to be due to avoided energy level crossings in the corresponding closed systems, and correlates with spikes in the entanglement entropy of key eigenstates, a signature of strong mixing and resonance among system degrees of freedom. Further, contrasting the Rabi model with the Jaynes-Cummings model reveals this behavior as being related to quantum integrability.

quant-ph↗

arXiv2022

Steady State Photoisomerization Quantum Yield of Model Rhodopsin: Insights from Wavepacket Dynamics?

We simulate the nonequilibrium steady state \textit{cis-trans} photoisomerization of retinal chromophore in rhodopsin based on a two-state-two-mode model coupled to a thermal environment. By analyzing the systematic trends within an inhomogeneously broadened ensemble of systems, we find that the steady state reaction quantum yield (QY) correlates strongly with the excess energy above the crossing point of the system, in agreement with the prediction of the short time dynamical wavepacket picture. However, the nontrivial dependence of the QY on the system-environment interaction indicates that a pure dynamical picture is insufficient and that environment-induced partial internal energy redistribution takes place before the reaction concludes. These results imply that a proper treatment of the photoisomerization reaction, particularly its high QY, must account for the redistribution and dissipation of energy beyond the dynamical wavepacket motion that is typically employed in the literature and that is appropriate only in the transient regime.

physics.chem-ph↗

arXiv2021

Multi-objective optimization for retinal photoisomerization models with respect to experimental observables

The fitting of physical models is often done only using a single target observable. However, when multiple targets are considered, the fitting procedure becomes cumbersome, there being no easy way to quantify the robustness of the model for all different observables. Here, we illustrate that one can jointly search for the best model for each desired observable through multi-objective optimization. To do so we construct the Pareto front to study if there exists a set of parameters of the model that can jointly describe multiple, or all, observables. To alleviate the computational cost, the predicted error for each targeted objective is approximated with a Gaussian process model, as it is commonly done in the Bayesian optimization framework. We applied this methodology to improve three different models used in the simulation of stationary state $cis-trans$ photoisomerization of retinal in rhodopsin. Optimization was done with respect to different experimental measurements, including emission spectra, peak absorption frequencies for the $cis$ and $trans$ conformers, and the energy storage.

physics.chem-ph↗

arXiv2021

Universal Scalings in 2D Anisotropic Dipolar Excitonic Systems

Low-dimensional excitonic materials have inspired much interest owing to their novel physical and technological prospects. In particular, those with strong in-plane anisotropy are among the most intriguing but short of general analyses. We establish the universal functional form of the anisotropic dispersion in the small $k$ limit for 2D dipolar excitonic systems. While the energy is linearly dispersed in the direction parallel to the dipole in-plane, the perpendicular direction is dispersionless up to linear order, which can be explained by the quantum interference effect of the interaction among the constituents of 1D subsystems. The anisotropic dispersion results in a $E^{\sim0.5}$ scaling of the system density of states and predicts unique spectroscopic signatures including: (1) disorder-induced absorption linewidth, $W(\sigma)\sim\sigma^{2.8}$, with $\sigma$ the disorder strength, (2) temperature dependent absorption linewidth, $W(T)\sim T^{s+1.5}$, with $s$ the exponent of the environment spectral density, and (3) the out-of-plane angular $\theta$ dependence of the peak splittings in absorption spectra, $\Delta E(\theta)\propto\sin^2\theta$. These predictions are confirmed quantitatively with numerical simulations of molecular thin films and tubules.

cond-mat.mes-hall↗

arXiv2020

Extreme Parametric Sensitivity in the Steady-State Photoisomerization of Model Retinal

The photoisomerization reaction of the retinal chromophore in rhodopsin was computationally studied using a two-state two-mode model coupled to thermal baths. Reaction quantum yields at the steady state (10 ps and beyond) were found to be considerably different than their transient values, suggesting a weak correlation between transient and steady-state dynamics in these systems. Significantly, the steady-state quantum yield was highly sensitive to minute changes in system parameters, while transient dynamics was nearly unaffected. Correlation of such sensitivity with standard level spacing statistics of the nonadiabatic vibronic system suggests a possible origin in quantum chaos. The feasibility of experimental observation of this phenomenon and its implications in condensed-phase photochemistry and biological light sensing are discussed.

quant-ph↗

arXiv2020

Stochastically Realized Observables for Excitonic Molecular Aggregates

We show that a stochastic approach enables calculations of the optical properties of large 2-dimensional and nanotubular excitonic molecular aggregates. Previous studies of such systems relied on numerically diagonalizing the dense and disordered Frenkel Hamiltonian, which scales approximately as $\mathcal{O}(N^3)$ for $N$ dye molecules. Our approach scales much more efficiently as $\mathcal{O}(N\log(N))$, enabling quick study of systems with a million of coupled molecules on the micron size scale. We calculate several important experimental observable including the optical absorption spectrum and density of states, and develop a stochastic formalism for the participation ratio. Quantitative agreement with traditional matrix diagonalization methods is demonstrated for both small- and intermediate-size systems. The stochastic methodology enables the study of the effects of spatial-correlation in site energies on the optical signatures of large 2D aggregates. Our results demonstrate that stochastic methods present a path forward for screening structural parameters and validating experiments and theoretical predictions in large excitonic aggregates.

physics.chem-ph↗

arXiv2019

Generalized Kasha's Scheme for Classifying Two-Dimensional Excitonic Molecular Aggregates: Temperature Dependent Absorption Peak Frequency Shift

We propose a generalized theoretical framework for classifying two-dimensional (2D) excitonic molecular aggregates based on an analysis of temperature dependent spectra. In addition to the monomer-aggregate absorption peak shift, which defines the conventional J- and H-aggregates, we incorporate the peak shift associated with increasing temperature as a measure to characterize the exciton band structure. First we show that there is a one-to-one correspondence between the monomer-aggregate and the T-dependent peak shifts for Kasha's well-established model of 1D aggregates, where J-aggregates exhibit further redshift upon increasing temperature and H-aggregates exhibit further blueshift. On the contrary, 2D aggregate structures are capable of supporting the two other combinations: blueshifting J-aggregates and redshifting H-aggregates, owing to their more complex exciton band structures. Secondly, using spectral lineshape theory, the T-dependent shift is associated with the relative abundance of states on each side of the bright state. We further establish that the density of states can be connected to the microscopic packing condition leading to these four classes of aggregates by separately considering the short and long-range contribution to the excitonic couplings. In particular the T-dependent shift is shown to be an unambiguous signature for the sign of net short-range couplings: Aggregates with net negative (positive) short-range couplings redshift (blueshift) with increasing temperature. Lastly, comparison with experiments shows that our theory can be utilized to quantitatively account for the observed but previously unexplained T-dependent absorption lineshapes. Thus, our work provides a firm ground for elucidating the structure-function relationships for molecular aggregates and is fully compatible with existing experimental and theoretical structure characterization tools.

physics.chem-ph↗

arXiv2015

Quantum Diffusion on Molecular Tubes: Universal Scaling of the 1D to 2D Transition

The transport properties of disordered systems are known to depend critically on dimensionality. We study the diffusion coefficient of a quantum particle confined to a lattice on the surface of a tube, where it scales between the 1D and 2D limits. It is found that the scaling relation is universal and independent of the disorder and noise parameters, and the essential order parameter is the ratio between the localization length in 2D and the circumference of the tube. Phenomenological and quantitative expressions for transport properties as functions of disorder and noise are obtained and applied to real systems: In the natural chlorosomes found in light-harvesting bacteria the exciton transfer dynamics is predicted to be in the 2D limit, whereas a family of synthetic molecular aggregates is found to be in the homogeneous limit and is independent of dimensionality.

cond-mat.mes-hall↗

arXiv2015

Quantum transport in d-dimensional lattices

We prove analytically that both fermionic and bosonic uniform d-dimensional lattices can be reduced to a set of independent one-dimensional modes. This reduction leads to the conclusion that the dynamics in uniform fermionic and bosonic lattices is always ballistic. By the use of the Jordan-Wigner transformation we extend our analysis to spin lattices, proving the existence of both ballistic and non-ballistic subspaces in any dimension and for any system size. We then relate the nature of transport with the number of excitations in the spin lattice, indicating that a single excitation propagates always ballistically and that the non-ballistic behavior of uniform spin lattices is a consequence of the interaction between different excitations.

quant-ph↗