980 research outputs found
Buried heterostructure vertical-cavity surface-emitting laser with semiconductor mirrors
We report a buried heterostructure vertical-cavity surface-emitting laser
fabricated by epitaxial regrowth over an InGaAs quantum well gain medium. The
regrowth technique enables microscale lateral confinement that preserves a high
cavity quality factor (loaded 4000) and eliminates parasitic
charging effects found in existing approaches. Under optimal spectral overlap
between gain medium and cavity mode (achieved here at = 40 K) lasing was
obtained with an incident optical power as low as = 10 mW
( = 808 nm). The laser linewidth was found to be 3
GHz at 5
Challenges in Open-air Microwave Quantum Communication and Sensing
Quantum communication is a holy grail to achieve secure communication among a
set of partners, since it is provably unbreakable by physical laws. Quantum
sensing employs quantum entanglement as an extra resource to determine
parameters by either using less resources or attaining a precision unachievable
in classical protocols. A paradigmatic example is the quantum radar, which
allows one to detect an object without being detected oneself, by making use of
the additional asset provided by quantum entanglement to reduce the intensity
of the signal. In the optical regime, impressive technological advances have
been reached in the last years, such as the first quantum communication between
ground and satellites, as well as the first proof-of-principle experiments in
quantum sensing. The development of microwave quantum technologies turned out,
nonetheless, to be more challenging. Here, we will discuss the challenges
regarding the use of microwaves for quantum communication and sensing. Based on
this analysis, we propose a roadmap to achieve real-life applications in these
fields.Comment: Long version of the article published in the Proceeding
Quantum dot photonic crystal lasers
Coupled cavity designs on two-dimensional square lattice photonic crystal slabs were used to demonstrate optically pumped indium arsenide quantum dot photonic crystal lasers at room temperature. Threshold pump powers of 120 and 370 μW were observed for coupled cavities including two and four defect cavities defined in optimised photonic crystals
Large size cryogenic turbine type flowmeter technology
Procurement, calibration, installation, and use of cryogenic turbine flowmeters for M-1 engin
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Optoelectronic and electronic devices based on quantum dots having proximity-placed acceptor impurities, and methods therefor
Solid-state optoelectronic and electronic devices that use semiconductor quantum dots for manipulation of photonic or electronic properties include a semiconductor active region forming a quantum dot heterostructure having a plurality of quantum dot layers each having discrete quantum hole states and a p-type impurity layer formed proximate to at least one of the quantum dot layers to provide excess equilibrium hole charge to occupy at least some of the discrete quantum hole states to improve To and other performance characteristics of quantum dot devices.Board of Regents, University of Texas Syste
Critical Collapse in Einstein-Gauss-Bonnet Gravity in Five and Six Dimensions
Einstein-Gauss-Bonnet gravity (EGB) provides a natural higher dimensional and
higher order curvature generalization of Einstein gravity. It contains a new,
presumably microscopic, length scale that should affect short distance
properties of the dynamics, such as Choptuik scaling. We present the results of
a numerical analysis in generalized flat slice co-ordinates of self-gravitating
massless scalar spherical collapse in five and six dimensional EGB gravity near
the threshold of black hole formation. Remarkably, the behaviour is universal
(i.e. independent of initial data) but qualitatively different in five and six
dimensions. In five dimensions there is a minimum horizon radius, suggestive of
a first order transition between black hole and dispersive initial data. In six
dimensions no radius gap is evident. Instead, below the GB scale there is a
change in the critical exponent and echoing period.Comment: 21 pages, 39 figures, a couple of references and two new figures
adde
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Development of an Economic Decision Support for the Application of Additive Manufacture in Aerospace
Additive Manufacturing offers a high potential in aerospace industry due to its freedom of
design and the ability to manufacture complex and lightweight parts. The low number of
units, high quality standards and fast response time are special challenges that have to be met
especially in the Maintenance, Repair and Overhaul sector. Thus, companies have to decide at
which point it is economic to apply Additive Manufacturing. However, companies lack
experience on this new technology. This is why a tool is required that takes into account the
above mentioned crucial points and supports the decision process. The paper analyzes
aviation’s characteristics with regard to Additive Manufacturing. The structure of current
MRO repair workflows is investigated to identify a feasible application for Additive
Manufacturing. Additionally the supply chain will be examined to indicate the benefit which
the technology can generate in this highly demanding field. The findings are integrated into a
methodology that supports the decision whether to apply Additive Manufacturing on the basis
of costs, time and quality.Mechanical Engineerin
Semiconductor laser monolithically pumped with a light emitting diode operating in the thermoelectrophotonic regime
Data are presented on a monolithic chip that integrates a quantum well semiconductor laser with a high efficiency light emitting diode (LED), with the LED used to optically pump the laser. The LED operates in the thermoelectrophotonic regime that can produce heat absorption, offering the possibility of heat pump action. The internal optical pumping also offers the possibility of very low internal loss in the laser and the prospect of reaching greater than unity power conversion efficiency in the laser chip. The integrated laser chip is operated and tested under continuous-wave room temperature operation
Non-Fermi liquid states in the pressurized system: two critical points
In the archetypal strongly correlated electron superconductor CeCuSi
and its Ge-substituted alloys CeCu(SiGe) two quantum
phase transitions -- one magnetic and one of so far unknown origin -- can be
crossed as a function of pressure \cite{Yuan 2003a}. We examine the associated
anomalous normal state by detailed measurements of the low temperature
resistivity () power law exponent . At the lower critical point
(at , ) depends strongly on Ge
concentration and thereby on disorder level, consistent with a
Hlubina-Rice-Rosch scenario of critical scattering off antiferromagnetic
fluctuations. By contrast, is independent of at the upper quantum
phase transition (at , ), suggesting critical
scattering from local or Q=0 modes, in agreement with a density/valence
fluctuation approach.Comment: 4 pages, including 4 figures. New results added. Significant changes
on the text and Fig.
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