247 research outputs found
Simulation of emission spectra of transition-metal dichalcogenide monolayers with the multimode Brownian oscillator model
The multimode Brownian oscillator model is employed to simulate the emission
spectra of transition metal dichalcogenide monolayers. Good agreement is
obtained between measured and simulated photoluminescence spectra of WSe2, WS2,
MoSe2 and MoS2 at various temperatures. The Huang-Rhys factor extracted from
the model can be associated with that from the modified semi-empirical Varshni
equation at high temperatures. Individual mechanisms leading to the unique
temperature-dependent emission spectra of those TMDs are validated by the MBO
fitting, while it is in turn confirmed that the MBO analysis is an effective
method for studying the optical properties of TMD monolayers. Parameters
extractd from the MBO fitting can be used to explore exciton-photon-phonon
dynamics of TMDs in a more comprehensive model
Photon-assisted Landau-Zener transitions in a periodically driven Rabi dimer coupled to a dissipative mode
We investigate multiple photon-assisted Landau-Zener (LZ) transitions in a
hybrid circuit quantum electrodynamics device in which each of two interacting
transmission-line resonators is coupled to a qubit, and the qubits are driven
by periodic driving fields and also coupled to a common phonon mode. The
quantum state of the entire composite system is modeled using the multi- Ansatz in combination with the time-dependent Dirac-Frenkel variational
principle. Applying a sinusoidal driving field to one of the qubits, this
device is an ideal platform to study the photon-assisted LZ transitions by
comparing the dynamics of the two qubits. A series of interfering
photon-assisted LZ transitions take place if the photon frequency is much
smaller than the driving amplitude. Once the two energy scales are comparable,
independent LZ transitions arise and a transition pathway is revealed using an
energy diagram. It is found that both adiabatic and nonadiabatic transitions
are involved in the dynamics. Used to model environmental effects on the LZ
transitions, the common phonon mode coupled to the qubits allows for more
available states to facilitate the LZ transitions. An analytical formula is
obtained to estimate the short-time phonon population and produces results in
reasonable agreement with numerical calculations. Equipped with the knowledge
of the photon-assisted LZ transitions in the system, we can precisely
manipulate the qubit state and successfully generate the qubit dynamics with a
square-wave pattern by applying driving fields to both qubits, opening up new
venues to manipulate the states of qubits and photons in quantum information
devices and quantum computer
Optical-Cavity Manipulation Strategies of Conical Intersections Mediated Singlet Fission Systems
We offer a theoretical perspective on simulation and engineering of
polaritonic conical-intersection-driven singlet-fission (SF) materials. Using
rubrene as an example and applying the numerically accurate Davydov-Ansatz
methodology, we derive dynamic and spectroscopic responses of the system and
demonstrate key mechanisms capable of SF manipulation, viz. cavity-induced
enhancement/weakening/suppression of SF, population localization on the singlet
state via engineering of the cavity-mode excitation, polaron/polariton
decoupling, collective enhancement of SF. We outline unsolved problems and
challenges in the field, and share our views on the development of the future
lines of research. We emphasize the significance of careful modeling of
cascades of polaritonic conical intersections in high excitation manifolds and
envisage that collective geometric phase effects may remarkably affect the SF
dynamics and yield. We argue that microscopic interpretation of the main
regulatory mechanisms of the polaritonic conical-intersection-driven SF can
substantially deepen our understanding of this process, thereby providing novel
ideas and solutions for improving conversion efficiency in photovoltaics.Comment: 14 pages, 6 figure
A DeepāLearning Approach to the Dynamics of LandauāZenner Transitions
Traditional approaches to the dynamics of the open quantum systems with high precision are often resource intensive. How to improve computation accuracy and efficiency for target systems is an extremely difficult challenge. In this work, combining unsupervised and supervised learning algorithms, a deep-learning approach is introduced to simulate and predict LandauāZenner dynamics. Data obtained from multiple Davydov (Formula presented.) Ansatz with a low multiplicity of four are used for training, while the data from the trial state with a high multiplicity of ten are adopted as target data to assess the accuracy of prediction. After proper training, our method can successfully predict and simulate LandauāZenner dynamics using only random noise and two adjustable model parameters. Compared to the high-precision dynamics data from multiple Davydov (Formula presented.) Ansatz with a multiplicity of ten, the error rate falls below 0.6%.Ministry of Education (MOE)Accepted versionThe authors gratefully acknowledge the support of the Singapore Ministry of Education Academic Research Fund (Grant Nos. 2018-T1-002-175 and 2020-T1-002- 075)). K. Sun would also like to thank the Natural Science Foundation of Zhejiang Province (Grant No. LY18A040005) for partial support. L.L. Gao acknowledges the support of the Graduate Scientific Research Foundation of Hangzhou Dianzi University
Quantifying non-Markovianity for a chromophore-qubit pair in a super-Ohmic bath
An approach based on a non-Markovian time-convolutionless polaron master
equation is used to probe the quantum dynamics of a chromophore-qubit in a
super-Ohmic bath. Utilizing a measure of non-Markovianity based on dynamical
fixed points, we study the effects of the environment temperature and the
coupling strength on the non-Markovian behavior of the chromophore in a
super-Ohmic bath. It is found that an increase in the temperature results in a
reduction in the backflow information from the environment to the chromophore,
and therefore, a suppression of non-Markovianity. In the weak coupling regime,
increasing coupling strength will enhance the non- Markovianity, while the
effect is reversed in the strong coupling regime.Comment: 10 pages, 9 figure
Exciton Dynamics and Time-Resolved Fluorescence in Nanocavity-Integrated Monolayers of Transition-Metal Dichalcogenides
We have developed an ab-initio-based fully-quantum numerically-accurate
methodology for the simulation of the exciton dynamics and time- and
frequency-resolved fluorescence spectra of the cavity-controlled
two-dimensional materials at finite temperature and applied this methodology to
the single-layer WSe2 system. This allowed us to establish dynamical and
spectroscopic signatures of the polaronic and polaritonic effects as well as
uncover their characteristic timescales in the relevant range of temperatures
Excitonic energy transfer in light-harvesting complexes in purple bacteria
Two distinct approaches, the Frenkel-Dirac time-dependent variation and the
Haken-Strobl model, are adopted to study energy transfer dynamics in
single-ring and double-ring light-harvesting systems in purple bacteria. It is
found that inclusion of long-range dipolar interactions in the two methods
results in significant increases in intra- or inter-ring exciton transfer
efficiency. The dependence of exciton transfer efficiency on trapping positions
on single rings of LH2 (B850) and LH1 is similar to that in toy models with
nearest-neighbor coupling only. However, owing to the symmetry breaking caused
by the dimerization of BChls and dipolar couplings, such dependence has been
largely suppressed. In the studies of coupled-ring systems, both methods reveal
interesting role of dipolar interaction in increasing energy transfer
efficiency by introducing multiple intra/inter-ring transfer paths.
Importantly, the time scale (~4ps) of inter-ring exciton transfer obtained from
polaron dynamics is in good agreement with previous studies. In a double-ring
LH2 system, dipole-induced symmetry breaking leads to global minima and local
minima of the average trapping time when there is a finite value of non-zero
dephasing rate, suggesting that environment plays a role in preserving quantum
coherent energy transfer. In contrast, dephasing comes into play only when the
perfect cylindrical symmetry in the hypothetic system is broken. This study has
revealed that dipolar interaction between chromophores may play an important
part in the high energy transfer efficiency in the LH2 system and many other
natural photosynthetic systems.Comment: 14 pages 9 figure
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