74 research outputs found
First-principles, atomistic thermodynamics for oxidation catalysis
Present knowledge of the function of materials is largely based on studies
(experimental and theoretical) that are performed at low temperatures and
ultra-low pressures. However, the majority of everyday applications, like e.g.
catalysis, operate at atmospheric pressures and temperatures at or higher than
300 K. Here we employ ab initio, atomistic thermodynamics to construct a phase
diagram of surface structures in the (T,p)-space from ultra-high vacuum to
technically-relevant pressures and temperatures. We emphasize the value of such
phase diagrams as well as the importance of the reaction kinetics that may be
crucial e.g. close to phase boundaries.Comment: 4 pages including 2 figure files. Submitted to Phys. Rev. Lett.
Related publications can be found at
http://www.fhi-berlin.mpg.de/th/paper.htm
Bilinear noise subtraction at the GEO 600 observatory
We develop a scheme to subtract off bilinear noise from the gravitational wave strain data and demonstrate it at the GEO 600 observatory. Modulations caused by test mass misalignments on longitudinal control signals are observed to have a broadband effect on the mid-frequency detector sensitivity ranging from 50 Hz to 500 Hz. We estimate this bilinear coupling by making use of narrow-band signal injections that are already in place for noise projection purposes. A coherent bilinear signal is constructed by a two-stage system identification process where the involved couplings are approximated in terms of stable rational functions. The time-domain filtering efficiency is observed to depend upon the system identification process especially when the involved transfer functions cover a large dynamic range and have multiple resonant features. We improve upon the existing filter design techniques by employing a Bayesian adaptive directed search strategy that optimizes across the several key parameters that affect the accuracy of the estimated model. The resulting post-offline subtraction leads to a suppression of modulation side-bands around the calibration lines along with a broadband reduction of the mid-frequency noise floor. The filter coefficients are updated periodically to account for any non-stationarities that can arise within the coupling. The observed increase in the astrophysical range and a reduction in the occurrence of non-astrophysical transients suggest that the above method is a viable data cleaning technique for current and future gravitational wave observatories
First demonstration of 6 dB quantum noise reduction in a kilometer scale gravitational wave observatory
Photon shot noise, arising from the quantum-mechanical nature of the light,
currently limits the sensitivity of all the gravitational wave observatories at
frequencies above one kilohertz. We report a successful application of squeezed
vacuum states of light at the GEO\,600 observatory and demonstrate for the
first time a reduction of quantum noise up to dB in a
kilometer-scale interferometer. This is equivalent at high frequencies to
increasing the laser power circulating in the interferometer by a factor of
four. Achieving this milestone, a key goal for the upgrades of the advanced
detectors, required a better understanding of the noise sources and losses, and
implementation of robust control schemes to mitigate their contributions. In
particular, we address the optical losses from beam propagation, phase noise
from the squeezing ellipse, and backscattered light from the squeezed light
source. The expertise gained from this work carried out at GEO 600 provides
insight towards the implementation of 10 dB of squeezing envisioned for
third-generation gravitational wave detectors
Alloy surface segregation in reactive environments: A first-principles atomistic thermodynamics study of Ag3Pd(111) in oxygen atmospheres
We present a first-principles atomistic thermodynamics framework to describe
the structure, composition and segregation profile of an alloy surface in
contact with a (reactive) environment. The method is illustrated with the
application to a Ag3Pd(111) surface in an oxygen atmosphere, and we analyze
trends in segregation, adsorption and surface free energies. We observe a wide
range of oxygen adsorption energies on the various alloy surface
configurations, including binding that is stronger than on a Pd(111) surface
and weaker than that on a Ag(111) surface. This and the consideration of even
small amounts of non-stoichiometries in the ordered bulk alloy are found to be
crucial to accurately model the Pd surface segregation occurring in
increasingly O-rich gas phases.Comment: 13 pages including 6 figures; related publications can be found at
http://www.fhi-berlin.mpg.de/th/th.htm
Characterization and evasion of backscattered light in the squeezed-light enhanced gravitational wave interferometer GEO 600
Squeezed light is injected into the dark port of gravitational wave
interferometers, in order to reduce the quantum noise. A fraction of the
interferometer output light can reach the OPO due to sub-optimal isolation of
the squeezing injection path. This backscattered light interacts with squeezed
light generation process, introducing additional measurement noise. We present
a theoretical description of the noise coupling mechanism. We propose a control
scheme to achieve a de-amplification of the backscattered light inside the OPO
with a consequent reduction of the noise caused by it. The scheme was
implemented at the GEO 600 detector and has proven to be crucial in maintaining
a good level of quantum noise reduction of the interferometer for high
parametric gain of the OPO. In particular, the mitigation of the backscattered
light noise helped in reaching 6dB of quantum noise reduction [Phys. Rev. Lett.
126, 041102 (2021)]. The impact of backscattered-light-induced noise on the
squeezing performance is phenomenologically equivalent to increased phase noise
of the squeezing angle control. The results discussed in this paper provide a
way for a more accurate estimation of the residual phase noise of the squeezed
light field.Comment: 14 pages, 6 figure
Composition and structure of the RuO2(110) surface in an O2 and CO environment: implications for the catalytic formation of CO2
The phase diagram of surface structures for the model catalyst RuO2(110) in
contact with a gas environment of O2 and CO is calculated by density-functional
theory and atomistic thermodynamics. Adsorption of the reactants is found to
depend crucially on temperature and partial pressures in the gas phase.
Assuming that a catalyst surface under steady-state operation conditions is
close to a constrained thermodynamic equilibrium, we are able to rationalize a
number of experimental findings on the CO oxidation over RuO2(110). We also
calculated reaction pathways and energy barriers. Based on the various results
the importance of phase coexistence conditions is emphasized as these will lead
to an enhanced dynamics at the catalyst surface. Such conditions may actuate an
additional, kinetically controlled reaction mechanism on RuO2(110).Comment: 12 pages including 8 figure files. Submitted to Phys. Rev. B. Related
publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm
Direct limits for scalar field dark matter from a gravitational-wave detector
The nature of dark matter remains unknown to date, although several candidate particles are being considered in a dynamically changing research landscape1. Scalar field dark matter is a prominent option that is being explored with precision instruments, such as atomic clocks and optical cavities2–8. Here we describe a direct search for scalar field dark matter using a gravitational-wave detector, which operates beyond the quantum shot-noise limit. We set new upper limits on the coupling constants of scalar field dark matter as a function of its mass, by excluding the presence of signals that would be produced through the direct coupling of this dark matter to the beam splitter of the GEO600 interferometer. These constraints improve on bounds from previous direct searches by more than six orders of magnitude and are, in some cases, more stringent than limits obtained in tests of the equivalence principle by up to four orders of magnitude. Our work demonstrates that scalar field dark matter can be investigated or constrained with direct searches using gravitational-wave detectors and highlights the potential of quantum-enhanced interferometry for dark matter detection. © 2021, The Author(s)
Direct limits for scalar field dark matter from a gravitational-wave detector
The nature of dark matter remains unknown to date; several candidate
particles are being considered in a dynamically changing research landscape.
Scalar field dark matter is a prominent option that is being explored with
precision instruments, such as atomic clocks and optical cavities. Here we
report on the first direct search for scalar field dark matter utilising a
gravitational-wave detector, which operates beyond the quantum shot-noise
limit. We set new upper limits for the coupling constants of scalar field dark
matter as a function of its mass, by excluding the presence of signals that
would be produced through the direct coupling of this dark matter to the
beamsplitter of the GEO600 interferometer. The new constraints improve upon
bounds from previous direct searches by more than six orders of magnitude, and
are in some cases more stringent than limits obtained in tests of the
equivalence principle by up to four orders of magnitude. Our work demonstrates
that scalar field dark matter can be probed or constrained with direct searches
using gravitational-wave detectors, and highlights the potential of
quantum-enhanced interferometry for dark matter detection
Wirkung der MaĂźnahmen der Bundesregierung innerhalb der Zielarchitektur zum Umbau der Energieversorgung
Um die weitere Entwicklung der Energiewende zu gestalten, wurde mit dem Ersten Fortschrittsbericht zur Energiewende eine Strukturierung der verschiedenen Energiewendeziele nach Sektoren und Kategorien vorgenommen und in eine Hierarchie nach Strategie- und Steuerungsebene gebracht. Diese Strukturierung der Ziele wird in dieser Studie (und auch darüber hinaus) als Zielarchitektur bezeichnet. In der vorliegenden Studie werden die Wirkungen der Instrumente innerhalb der Zielarchitektur und ihr Zusammenspiel zur Erreichung der energiepolitischen Ziele analysiert. Auf Basis der erzielten Ergebnisse wird die Zielarchitektur im Hinblick auf die Erreichung der energie- und klimapolitischen Ziele sowie einer weiteren Optimierung der Energiewende hin untersucht. Dabei sollen insbesondere anhand der beiden Leitkriterien Kosteneffizienz und Systemintegration mögliche Korridore für Steuerungsziele wie auch Flexibilisierungsoptionen der Ziele identifiziert werden
Quantum state preparation and macroscopic entanglement in gravitational-wave detectors
Long-baseline laser-interferometer gravitational-wave detectors are operating
at a factor of 10 (in amplitude) above the standard quantum limit (SQL) within
a broad frequency band. Such a low classical noise budget has already allowed
the creation of a controlled 2.7 kg macroscopic oscillator with an effective
eigenfrequency of 150 Hz and an occupation number of 200. This result, along
with the prospect for further improvements, heralds the new possibility of
experimentally probing macroscopic quantum mechanics (MQM) - quantum mechanical
behavior of objects in the realm of everyday experience - using
gravitational-wave detectors. In this paper, we provide the mathematical
foundation for the first step of a MQM experiment: the preparation of a
macroscopic test mass into a nearly minimum-Heisenberg-limited Gaussian quantum
state, which is possible if the interferometer's classical noise beats the SQL
in a broad frequency band. Our formalism, based on Wiener filtering, allows a
straightforward conversion from the classical noise budget of a laser
interferometer, in terms of noise spectra, into the strategy for quantum state
preparation, and the quality of the prepared state. Using this formalism, we
consider how Gaussian entanglement can be built among two macroscopic test
masses, and the performance of the planned Advanced LIGO interferometers in
quantum-state preparation
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