440 research outputs found
Controlling the magnetism of adsorbed metal–organic molecules
Gaining control on the size or the direction of the magnetic moment of
adsorbed metal–organic molecules constitutes an important step towards the
realization of a surface-mounted molecular spin electronics. Such control can
be gained by taking advantage of interactions of the molecule's magnetic
moment with the environment. The paramagnetic moments of adsorbed metal-
organic molecules, for example, can be controlled by the interaction with
magnetically ordered substrates. Metalloporphyrins and -phthalocyanines
display a quasi-planar geometry, allowing the central metal ion to interact
with substrate electronic states. This can lead to magnetic coupling with a
ferromagnetic or even antiferromagnetic substrate. The molecule–substrate
coupling can be mediated and controlled by insertion layers such as oxygen
atoms, graphene, or nonmagnetic metal layers. Control on the magnetic
properties of adsorbed metalloporphyrins or -phthalocyanines can also be
gained by on-surface chemical modification of the molecules. The magnetic
moment or the magnetic coupling to ferromagnetic substrates can be changed by
adsorption and thermal desorption of small molecules that interact with the
fourfold-coordinated metal center via the remaining axial coordination site.
Spin-crossover molecules, which possess a metastable spin state that can be
switched by external stimuli such as temperature or light, are another
promising class of candidates for control of magnetic properties. However, the
immobilization of such molecules on a solid surface often results in a quench
of the spin transition due to the interaction with the substrate. We present
examples of Fe(II) spin-crossover complexes in direct contact with a solid
surface that undergo a reversible spin-crossover transition as a function of
temperature, by illumination with visible light, or can be switched by the tip
of a scanning tunneling microscope
Raman quantum memory based on an ensemble of nitrogen-vacancy centers coupled to a microcavity
We propose a scheme to realize optical quantum memories in an ensemble of
nitrogen-vacancy centers in diamond that are coupled to a micro-cavity. The
scheme is based on off-resonant Raman coupling, which allows one to circumvent
optical inhomogeneous broadening and store optical photons in the electronic
spin coherence. This approach promises a storage time of order one second and a
time-bandwidth product of order 10. We include all possible optical
transitions in a 9-level configuration, numerically evaluate the efficiencies
and discuss the requirements for achieving high efficiency and fidelity
Control and coherence of the optical transition of single defect centers in diamond
We demonstrate coherent control of the optical transition of single
Nitrogen-Vacancy defect centers in diamond. On applying short resonant laser
pulses, we observe optical Rabi oscillations with a half-period as short as 1
nanosecond, an order of magnitude shorter than the spontaneous emission time.
By studying the decay of Rabi oscillations, we find that the decoherence is
dominated by laser-induced spectral jumps. By using a low-power probe pulse as
a detuning sensor and applying post-selection, we demonstrate that spectral
diffusion can be overcome in this system to generate coherent photons.Comment: 5 pages,4 figure
Towards a Taxonomic Benchmarking Framework for Predictive Maintenance: The Case of NASA’s Turbofan Degradation
The availability of datasets for analytical solution development is a common bottleneck in data-driven predictive maintenance. Therefore, novel solutions are mostly based on synthetic benchmarking examples, such as NASA’s C-MAPSS datasets, where researchers from various disciplines like artificial intelligence and statistics apply and test their methodical approaches. The majority of studies, however, only evaluate the overall solution against a final prediction score, where we argue that a more fine-grained consideration is required distinguishing between detailed method components to measure their particular impact along the prognostic development process. To address this issue, we first conduct a literature review resulting in more than one hundred studies using the C-MAPSS datasets. Subsequently, we apply a taxonomy approach to receive dimensions and characteristics that decompose complex analytical solutions into more manageable components. The result is a first draft of a systematic benchmarking framework as a more comparable basis for future development and evaluation purposes
Optical differential reflectance spectroscopy for photochromic molecules on solid surfaces
Optical reflectance of thin adsorbates on solid surfaces is able to reveal fundamental changes of molecular properties compared to bulk systems. The detection of very small changes in the optical reflectance required several technical improvements in the past decades. We present an experimental setup that is capable of high-quality measurements of submonolayers and ultrathin layers of photochromic molecules on surfaces as well as quantifying their isomerization kinetics. By using photomultipliers as detectors, an enhancement of the signal-to-noise ratio by a factor of three with a total reduction of light exposure on the sample by at least four orders of magnitude is achieved. The potential of the experimental setup is demonstrated by a characterization of the photoswitching and thermal switching of a spirooxazine derivate on a bismuth surface
Ammonia coordination introducing a magnetic moment in an on-surface low-spin porphyrin
Amazing ammonia: The molecular spin state of Ni(II) porphyrin, supported on a ferromagnetic Co surface, can be reversibly switched between spin-off (S = 0) and spin-on (S = 1) states upon coordination and decoordination of the gaseous ligand NH3, respectively (see picture). This finding clearly indicates the possible use of the system as a single-molecule-based magnetochemical sensor and in spintronics
Quantum networks with neutral atom processing nodes
Quantum networks providing shared entanglement over a mesh of quantum nodes
will revolutionize the field of quantum information science by offering novel
applications in quantum computation, enhanced precision in networks of sensors
and clocks, and efficient quantum communication over large distances. Recent
experimental progress with individual neutral atoms demonstrates a high
potential for implementing the crucial components of such networks. We
highlight latest developments and near-term prospects on how arrays of
individually controlled neutral atoms are suited for both efficient remote
entanglement generation and large-scale quantum information processing, thereby
providing the necessary features for sharing high-fidelity and error-corrected
multi-qubit entangled states between the nodes. We describe both the
functionality requirements and several examples for advanced, large-scale
quantum networks composed of neutral atom processing nodes.Comment: 10 pages, 5 figure
Electron spin relaxation in bulk GaAs for doping densities close to the metal-to-insulator transition
We have measured the electron spin relaxation rate and the integrated spin
noise power in n-doped GaAs for temperatures between 4 K and 80 K and for
doping concentrations ranging from 2.7 x 10^{-15} cm^{-3} to 8.8 x 10^{-16}
cm^{-3} using spin noise spectroscopy. The temperature dependent measurements
show a clear transition from localized to free electrons for the lower doped
samples and confirm mainly free electrons at all temperatures for the highest
doped sample. While the sample at the metal-insulator-transition shows the
longest spin relaxation time at low temperatures, a clear crossing of the spin
relaxation rates is observed at 70 K and the highest doped sample reveals the
longest spin relaxation time above 70 K.Comment: 6 pages, 4 figure
Spin-Crossover Molecules on Surfaces: From Isolated Molecules to Ultrathin Films
Molecular spintronics seeks to use single or few molecules as functional building blocks for spintronic applications, directly relying on molecular properties or properties of interfaces between molecules and inorganic electrodes. Spin-crossover molecules (SCMs) are one of the most promising classes of candidates for molecular spintronics due to their bistability deriving from the existence of two spin states that can be reversibly switched by temperature, light, electric fields, etc. Building devices based on single or few molecules would entail connecting the molecule(s) with solid surfaces and understanding the fundamental behavior of the resulting assemblies. Herein, the investigations of SCMs on solid surfaces, ranging from isolated single molecules (submonolayers) to ultrathin films (mainly in the sub-10 nm range) are summarized. The achievements, challenges and prospects in this field are highlighted
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