1,720,964 research outputs found
Theoretical and Computational Insights into Non-Linear Response in Action-2D Electronic Spectroscopy
Full text linkTwo-Dimensional Electronic Spectroscopy (2DES) is a powerful tool for investigating the properties of complex molecular aggregates and nanostructures. By probing the system with a sequence of ultrafast laser pulses, spectral and temporal information are dissected along multiple dimensions, allowing to track energy and charge transfer pathways within multichromophoric systems. Because of the wealth of information contained in the spectra, the origin of certain spectral features can be ambiguous. Therefore, the development of theoretical models and numerical simulations is essential to support their correct interpretation.
Recently, a novel implementation of the technique has been realized, known as Action-2DES (A-2DES), calling for theoretical and numerical efforts to establish the correlation between spectral features and the dynamical processes occurring at the molecular scale. While probing the coherent dynamics induced by the interaction with four collinear laser pulses, the technique relies on the measurement of an incoherent signal proportional to the excited-state population, e.g., fluorescence or photocurrent, allowing the investigation of functional dynamics of systems in operando conditions.
In this Thesis, we delve into the theory of A-2DES and its numerical simulation to clarify essential aspects of the incoherent signal detected with this technique. To this end, we employed a combination of perturbative and non-perturbative approaches to describe the light-matter interaction. While the former provides the conceptual basis for the analysis of the response in terms of several dynamical pathways, the latter allows the complete simulation of the entire spectroscopic experiment.
In A-2DES, the signal is detected over a timescale during which the excited-state population may undergo several processes. We investigated the effects of such population dynamics on the spectra by characterizing the spectroscopic response of a model of quantum dot featuring the interplay between exciton and biexciton contributions to the signal.
The involvement of the double-excited manifold in the signal represents a crucial factor shaping the signal in A-2DES. Thus, we analyzed the case in which the double-excited manifold consists of excited states localized on different weakly interacting chromophores. This setting allows to discuss the origin of cross-peaks and incoherent mixing in the signal, first considering the case of a simple molecular dimer and then in a larger molecular assembly. The analysis shows that mixing effects are intrinsic in the A-2DES, and they must be carefully addressed in the design of the sample and the choice of the detection scheme.
Our investigation further proceeded by focusing on the dependence of the spectral features on varying the excitonic coupling strength, showing how cross-peaks can either reflect the presence of exciton-exciton annihilation or excitonic delocalization between chromophores, depending on the coupling regime.
Finally, we shifted the focus toward a related yet distinct subject, wondering whether emerging quantum computing technologies could contribute to the efficient simulation of 2DES spectra. Accordingly, we designed a quantum algorithm for simulating the non-linear response of multichromophoric systems and provided a proof-of-concept computation considering an excitonic dimer model
A Quantum Algorithm from Response Theory: Digital Quantum Simulation of Two-Dimensional Electronic Spectroscopy
No full textMultidimensional optical spectroscopies are powerful techniques to investigate energy transfer pathways in natural and artificial systems. Because of the high information content of the spectra, numerical simulations of the optical response are of primary importance to assist the interpretation of spectral features. However, the increasing complexity of the investigated systems and their quantum dynamics call for the development of novel simulation strategies. In this work, we consider using digital quantum computers. By combining quantum dynamical simulation and nonlinear response theory, we present a quantum algorithm for computing the optical response of molecular systems. The quantum advantage stems from the efficient quantum simulation of the dynamics governed by the molecular Hamiltonian, and it is demonstrated by explicitly considering exciton-vibrational coupling. The protocol is tested on a near-term quantum device, providing the digital quantum simulation of the linear and nonlinear response of simple molecular models
Simulating action-2D electronic spectroscopy of quantum dots: insights on the exciton and biexciton interplay from detection-mode and time-gating
Full text linkUnifying Nonlinear Response and Incoherent Mixing in Action-2D Electronic Spectroscopy
Full text linkAction-detection has expanded the scope and applicability of 2D electronic spectroscopy, while posing new challenges for the unambiguous interpretation of spectral features. In this context, identifying the origin of cross-peaks at early waiting times is not trivial, and incoherent mixing is often invoked as an unwanted contribution masking the nonlinear signal. In this work, we elaborate on the relation between the nonlinear response and the incoherent mixing contribution by analyzing the action signal in terms of one- and two-particle observables. Considering a weakly interacting molecular dimer, we show how cross-peaks at early waiting times, reflecting exciton-exciton annihilation dynamics, can be equivalently interpreted as arising from incoherent mixing. This equivalence, on the one hand, highlights the information content of spectral features related to incoherent mixing and, on the other hand, provides an efficient numerical scheme to simulate the action response of weakly interacting systems
From stochastic Hamiltonian to quantum simulation: exploring memory effects in exciton dynamics
Full text linkThe unraveling of open quantum system dynamics in terms of stochastic quantum trajectories offers a picture of open system dynamics that consistently considers memory effects stemming from the finite correlation time of environment fluctuations. These fluctuations significantly influence the coherence and energy transport properties of excitonic systems. When their correlation time is comparable to the timescale of the Hamiltonian evolution, it leads to the departure of open system dynamics from the Markovian limit. In this work, we leverage the unraveling of exciton dynamics through stochastic Hamiltonian propagators to design quantum circuits that simulate exciton transport, capturing finite memory effects. In addition to enabling the synthesis of parametrizable quantum circuits, stochastic unitary propagators provide a transparent framework for investigating non-Markovian effects on exciton transport. Our analysis reveals a nuanced relationship between environment correlation time and transport efficiency, identifying a regime of 'memory-assisted' quantum transport where time-correlated fluctuations allow the system to reach higher efficiency. However, this property is not universal and can only be realized in conjunction with specific features of the system Hamiltonian
Strategies to simulate dephasing-assisted quantum transport on digital quantum computers
No full textSimulating charge and energy transfer in extended molecular networks requires an effective model to include the environment because it significantly affects the quantum dynamics. A prototypical effect known as environment-assisted quantum transport (ENAQT) consists in the enhancement of the transfer efficiency by the interaction with an environment. A simple description of this phenomenon is obtained by a quantum master equation describing a quantum walk over the molecular network in the presence of inter-site decoherence. We consider the problem of simulating the dynamics underlying ENAQT in a digital quantum computer. Two different quantum algorithms are introduced, the first one based on stochastic Hamiltonians and the second one based on a collision scheme. We test both algorithms by simulating ENAQT in a small molecular network on a quantum computer emulator and provide a comparative analysis of the two approaches. Both algorithms can be implemented in a memory efficient encoding with the number of required qubits scaling logarithmically with the size of the simulated system while the number of gates increases quadratically. We discuss the algorithmic quantum trajectories generated by the two simulation strategies showing that they realize distinct unravellings of the site-dephasing master equation. In our approach, the non-unitary dynamics of the open system is obtained through effective representations of the environment, paving the way to digital quantum simulations of quantum transport influenced by structured environments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Identification of Design Principles for the Preparation of Colloidal Plexcitonic Materials
Full text link: Colloidal plexcitonic materials (CPMs) are a class of nanosystems where molecular dyes are strongly coupled with colloidal plasmonic nanoparticles, acting as nanocavities that enhance the light field. As a result of this strong coupling, new hybrid states are formed, called plexcitons, belonging to the broader family of polaritons. With respect to other families of polaritonic materials, CPMs are cheap and easy to prepare through wet chemistry methodologies. Still, clear structure-to-properties relationships are not available, and precise rules to drive the materials' design to obtain the desired optical properties are still missing. To fill this gap, in this article, we prepared a dataset with all CPMs reported in the literature, rationalizing their design by focusing on their three main relevant components (the plasmonic nanoparticles, the molecular dyes, and the capping layers) and identifying the most used and efficient combinations. With the help of statistical analysis, we also found valuable correlations between structure, coupling regime, and optical properties. The results of this analysis are expected to be relevant for the rational design of new CPMs with controllable and predictable photophysical properties to be exploited in a vast range of technological fields
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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