25 research outputs found
Strain-Tunable GaAs Quantum dot: A Nearly Dephasing-Free Source of Entangled Photon Pairs on Demand
Entangled photon generation from semiconductor quantum dots via the
biexciton-exciton cascade underlies various decoherence mechanisms related to
the solid-state nature of the quantum emitters. So far, this has prevented the
demonstration of nearly-maximally entangled photons without the aid of
inefficient and complex post-selection techniques that are hardly suitable for
quantum communication technologies. Here, we tackle this challenge using
strain-tunable GaAs quantum dots driven under two-photon resonant excitation
and with strictly-degenerate exciton states. We demonstrate experimentally that
our on-demand source generates polarization-entangled photons with fidelity of
0.978(5) and concurrence of 0.97(1) without resorting to post-selection
techniques. Moreover, we show that the remaining decoherence mechanisms can be
overcome using a modest Purcell enhancement so as to achieve a degree of
entanglement >0.99. Our results highlight that GaAs quantum dots can be readily
used in advanced communication protocols relying on the non-local properties of
quantum entanglement
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Wavelength-tunable sources of entangled photons interfaced with atomic vapours
The prospect of using the quantum nature of light for secure communication keeps spurring
the search and investigation of suitable sources of entangled photons. A single semiconductor
quantum dot is one of the most attractive, as it can generate indistinguishable
entangled photons deterministically and is compatible with current photonic-integration
technologies. However, the lack of control over the energy of the entangled photons is
hampering the exploitation of dissimilar quantum dots in protocols requiring the teleportation
of quantum entanglement over remote locations. Here we introduce quantum dot-based
sources of polarization-entangled photons whose energy can be tuned via three-directional
strain engineering without degrading the degree of entanglement of the photon pairs. As a
test-bench for quantum communication, we interface quantum dots with clouds of atomic
vapours, and we demonstrate slow-entangled photons from a single quantum emitter. These
results pave the way towards the implementation of hybrid quantum networks where
entanglement is distributed among distant parties using optoelectronic devices
Strain-Tuning of the Optical Properties of Semiconductor Nanomaterials by Integration onto Piezoelectric Actuators
The tailoring of the physical properties of semiconductor nanomaterials by
strain has been gaining increasing attention over the last years for a wide
range of applications such as electronics, optoelectronics and photonics. The
ability to introduce deliberate strain fields with controlled magnitude and in
a reversible manner is essential for fundamental studies of novel materials and
may lead to the realization of advanced multi-functional devices. A prominent
approach consists in the integration of active nanomaterials, in thin epitaxial
films or embedded within carrier nanomembranes, onto
Pb(Mg1/3Nb2/3)O3-PbTiO3-based piezoelectric actuators, which convert electrical
signals into mechanical deformation (strain). In this review, we mainly focus
on recent advances in strain-tunable properties of self-assembled InAs quantum
dots embedded in semiconductor nanomembranes and photonic structures.
Additionally, recent works on other nanomaterials like rare-earth and metal-ion
doped thin films, graphene and MoS2 or WSe2 semiconductor two-dimensional
materials are also reviewed. For the sake of completeness, a comprehensive
comparison between different procedures employed throughout the literature to
fabricate such hybrid piezoelectric-semiconductor devices is presented. Very
recently, a novel class of micro-machined piezoelectric actuators have been
demonstrated for a full control of in-plane stress fields in nanomembranes,
which enables producing energy-tunable sources of polarization-entangled
photons in arbitrary quantum dots. Future research directions and prospects are
discussed.Comment: review manuscript, 78 pages, 27 figure
Biochemical consequences of two clinically relevant ND-gene mutations in Escherichia coli respiratory complex I.
NADH:ubiquinone oxidoreductase (respiratory complex I) plays a major role in energy metabolism by coupling electron transfer from NADH to quinone with proton translocation across the membrane. Complex I deficiencies were found to be the most common source of human mitochondrial dysfunction that manifest in a wide variety of neurodegenerative diseases. Seven subunits of human complex I are encoded by mitochondrial DNA (mtDNA) that carry an unexpectedly large number of mutations discovered in mitochondria from patients' tissues. However, whether or how these genetic aberrations affect complex I at a molecular level is unknown. Here, we used Escherichia coli as a model system to biochemically characterize two mutations that were found in mtDNA of patients. The V253AMT-ND5 mutation completely disturbed the assembly of complex I, while the mutation D199GMT-ND1 led to the assembly of a stable complex capable to catalyze redox-driven proton translocation. However, the latter mutation perturbs quinone reduction leading to a diminished activity. D199MT-ND1 is part of a cluster of charged amino acid residues that are suggested to be important for efficient coupling of quinone reduction and proton translocation. A mechanism considering the role of D199MT-ND1 for energy conservation in complex I is discussed
ОСОБЕННОСТИ ЧИСЛЕННЫХ МЕТОДОВ РЕШЕНИЯ НЕСТАЦИОНАРНЫХ ЗАДАЧ ГЕОМЕХАНИКИ И ИХ ПРОГРАММНОЙ РЕАЛИЗАЦИИ
Приведен способ решения нестационарных задач геомеханики с применением
методов крупных частиц и прогонки. Реализация способов осуществляется в среде разработки Visual Studio 2008
Mass Photometry of Membrane Proteins
Integral membrane proteins (IMPs) are biologically highly significant but challenging to study because they require maintaining a cellular lipid-like environment. Here, we explore the application of mass photometry (MP) to IMPs and membrane-mimetic systems at the single-particle level. We apply MP to amphipathic vehicles, such as detergents and amphipols, as well as to lipid and native nanodiscs, characterizing the particle size, sample purity, and heterogeneity. Using methods established for cryogenic electron microscopy, we eliminate detergent background, enabling high-resolution studies of membrane-protein structure and interactions. We find evidence that, when extracted from native membranes using native styrene-maleic acid nanodiscs, the potassium channel KcsA is present as a dimer of tetramers—in contrast to results obtained using detergent purification. Finally, using lipid nanodiscs, we show that MP can help distinguish between functional and non-functional nanodisc assemblies, as well as determine the critical factors for lipid nanodisc formation
Wirkungsforschung – über Allianzen von Evaluation und Managerialismus und die Möglichkeit erklärender Kritik
Ziegler H. Wirkungsforschung – über Allianzen von Evaluation und Managerialismus und die Möglichkeit erklärender Kritik. In: Schimpf E, Stehr J, eds. Kritisches Forschen in der Sozialen Arbeit. Gegenstandsbereiche – Kontextbedingungen – Positionierungen – Perspektiven. Wiesbaden: VS Verlag für Sozialwissenschaften; 2012: 93-105
Polarimetric millimetre wave SAR for precision farming applications
A high resolution imaging millimetre wave SAR delivers three key parameters important for precision farming applications, namely range, reflectivity and polarization state. The reflectivity gives information upon the type of crop and its humidity. Especially in the millimeter wave region young growing green plants exhibit a considerably higher reflectivity than older, dry leaves. Dependent on the transmit-receive polarization also indications are given upon the humidity of the underlying soil. Polarimetry also allows to judge the ripeness of the grain as the geometry of the ear is changing during the ripening process
Exploring ND-011992, a quinazoline-type inhibitor targeting quinone reductases and quinol oxidases
Abstract Bacterial energy metabolism has become a promising target for next-generation tuberculosis chemotherapy. One strategy to hamper ATP production is to inhibit the respiratory oxidases. The respiratory chain of Mycobacterium tuberculosis comprises a cytochrome bcc:aa 3 and a cytochrome bd ubiquinol oxidase that require a combined approach to block their activity. A quinazoline-type compound called ND-011992 has previously been reported to ineffectively inhibit bd oxidases, but to act bactericidal in combination with inhibitors of cytochrome bcc:aa 3 oxidase. Due to the structural similarity of ND-011992 to quinazoline-type inhibitors of respiratory complex I, we suspected that this compound is also capable of blocking other respiratory chain complexes. Here, we synthesized ND-011992 and a bromine derivative to study their effect on the respiratory chain complexes of Escherichia coli. And indeed, ND-011992 was found to inhibit respiratory complex I and bo 3 oxidase in addition to bd-I and bd-II oxidases. The IC50 values are all in the low micromolar range, with inhibition of complex I providing the lowest value with an IC50 of 0.12 µM. Thus, ND-011992 acts on both, quinone reductases and quinol oxidases and could be very well suited to regulate the activity of the entire respiratory chain