321 research outputs found
Gaussian processes for choosing laser parameters for driven, dissipative Rydberg aggregates
To facilitate quantum simulation of open quantum systems at finite
temperatures, an important ingredient is to achieve thermalization on a given
time-scale. We consider a Rydberg aggregate (an arrangement of Rydberg atoms
that interact via long-range interactions) embedded in a laser-driven atomic
environment. For the smallest aggregate (two atoms), suitable laser parameters
can be found by brute force scanning of the four tunable laser parameters. For
more atoms, however, such parameter scans are too computationally costly. Here
we apply Gaussian processes to predict the thermalization performance as a
function of the laser parameters for two-atom and four-atom aggregates. These
predictions perform remarkably well using just 1000 simulations, demonstrating
the utility of Gaussian processes in an atomic physics setting. Using this
approach, we find and present effective laser parameters for generating
thermalization, the robustness of these parameters to variation, as well as
different thermalization dynamics
Flexible scheme to truncate the hierarchy of pure states
The hierarchy of pure states (HOPS) is a wavefunction-based method which can
be used for numerically modeling open quantum systems. Formally, HOPS recovers
the exact system dynamics for an infinite depth of the hierarchy. However,
truncation of the hierarchy is required to numerically implement HOPS. We want
to choose a 'good' truncation method, where by 'good' we mean that it is
numerically feasible to check convergence of the results. For the truncation
approximation used in previous applications of HOPS, convergence checks are
numerically challenging. In this work we demonstrate the application of the
'-particle approximation' (PA) to HOPS. We also introduce a new
approximation, which we call the '-mode approximation' (MA). We then
explore the convergence of these truncation approximations with respect to the
number of equations required in the hierarchy. We show that truncation
approximations can be used in combination to achieve convergence in two
exemplary problems: absorption and energy transfer of molecular aggregates.Comment: 8 pages, 3 figure
Investigations of Fluid-Structure-Coupling and Turbulence Model Effects on the DLR Results of the Fifth AIAA CFD Drag Prediction Workshop
The accurate calculation of aerodynamic forces and moments is of significant importance during the design phase of an aircraft. Reynolds-averaged Navier-Stokes (RANS) based Computational Fluid Dynamics (CFD) has been strongly developed over the last two decades regarding robustness, efficiency, and capabilities for aerodynamically complex configurations. Incremental aerodynamic coefficients of different designs can be calculated with an acceptable reliability at the cruise design point of transonic aircraft for non-separated flows. But regarding absolute values as well as increments at off-design significant challenges still exist to compute aerodynamic data and the underlying flow physics with the accuracy required. In addition to drag, pitching moments are difficult to predict because small deviations of the pressure distributions, e.g. due to neglecting wing bending and twisting caused by the aerodynamic loads can result in large discrepancies compared to experimental data. Flow separations that start to develop at off-design conditions, e.g. in corner-flows, at trailing edges, or shock induced, can have a strong impact on the predictions of aerodynamic coefficients too. Based on these challenges faced by the CFD community a working group of the AIAA Applied Aerodynamics Technical Committee initiated in 2001 the CFD Drag Prediction Workshop (DPW) series resulting in five international workshops. The results of the participants and the committee are summarized in more than 120 papers. The latest, fifth workshop took place in June 2012 in conjunction with the 30th AIAA Applied Aerodynamics Conference. The results in this paper will evaluate the influence of static aeroelastic wing deformations onto pressure distributions and overall aerodynamic coefficients based on the NASA finite element structural model and the common grids
Suppression of quantum oscillations and the dependence on site energies in electronic excitation transfer in the Fenna-Matthews-Olson trimer
Energy transfer in the photosynthetic complex of the Green Sulfur Bacteria
known as the Fenna-Matthews-Olson (FMO) complex is studied theoretically taking
all three subunits (monomers) of the FMO trimer and the recently found eighth
bacteriochlorophyll (BChl) molecule into account. We find that in all
considered cases there is very little transfer between the monomers. Since it
is believed that the eighth BChl is located near the main light harvesting
antenna we look at the differences in transfer between the situation when BChl
8 is initially excited and the usually considered case when BChl 1 or 6 is
initially excited. We find strong differences in the transfer dynamics, both
qualitatively and quantitatively. When the excited state dynamics is
initialized at site eight of the FMO complex, we see a slow exponential-like
decay of the excitation. This is in contrast to the oscillations and a
relatively fast transfer that occurs when only seven sites or initialization at
sites 1 and 6 is considered. Additionally we show that differences in the
values of the electronic transition energies found in the literature lead to a
large difference in the transfer dynamics
An efficient method to calculate excitation energy transfer in light harvesting systems. Application to the FMO complex
A master equation, derived from the non-Markovian quantum state diffusion
(NMQSD), is used to calculate excitation energy transfer in the photosynthetic
Fenna-Matthews-Olson (FMO) pigment-protein complex at various temperatures.
This approach allows us to treat spectral densities that contain explicitly the
coupling to internal vibrational modes of the chromophores. Moreover, the
method is very efficient, with the result that the transfer dynamics can be
calculated within about one minute on a standard PC, making systematic
investigations w.r.t. parameter variations tractable. After demonstrating that
our approach is able to reproduce the results of the numerically exact
hierarchical equations of motion (HEOM) approach, we show how the inclusion of
vibrational modes influences the transfer
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Perspectives on weak interactions in complex materials at different length scales
Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties
Entdeckung eines Pseudoausbruches mit Carbapenem-resistenten Acinetobacter baumannii
Am Nationalen Referenzzentrum für gramnegative Krankenhauserreger wurde im November und Dezember 2020 das gehäufte Auftreten von Isolaten des Acinetobacter baumannii-Komplex mit Carbapenemresistenz beobachtet. Der Beitrag beschreibt die in Kooperation mit dem Robert Koch-Institut durchgeführte Ausbruchsuntersuchung und die Aufklärung als Pseudoausbruch.Peer Reviewe
Perspectives on weak interactions in complex materials at different length scales
Nanocomposite materials consist of nanometer-sized quantum objects such as atoms, molecules, voids or nanoparticles embedded in a host material. These quantum objects can be exploited as a super-structure, which can be designed to create material properties targeted for specific applications. For electromagnetism, such targeted properties include field enhancements around the bandgap of a semiconductor used for solar cells, directional decay in topological insulators, high kinetic inductance in superconducting circuits, and many more. Despite very different application areas, all of these properties are united by the common aim of exploiting collective interaction effects between quantum objects. The literature on the topic spreads over very many different disciplines and scientific communities. In this review, we present a cross-disciplinary overview of different approaches for the creation, analysis and theoretical description of nanocomposites with applications related to electromagnetic properties
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