10,654 research outputs found
Efficient Spatial Redistribution of Quantum Dot Spontaneous Emission from 2D Photonic Crystals
We investigate the modification of the spontaneous emission dynamics and
external quantum efficiency for self-assembled InGaAs quantum dots coupled to
extended and localised photonic states in GaAs 2D-photonic crystals. The
2D-photonic bandgap is shown to give rise to a 5-10 times enhancement of the
external quantum efficiency whilst the spontaneous emission rate is
simultaneously reduced by a comparable factor. Our findings are quantitatively
explained by a modal redistribution of spontaneous emission due to the modified
local density of photonic states. The results suggest that quantum dots
embedded within 2D-photonic crystals are suitable for practical single photon
sources with high external efficiency
The effects of lunar dust accumulation on the performance of photovoltaic arrays
Lunar base activity, particularly rocket launch and landing, will suspend and transport lunar dust. From preliminary models, the resulting dust accumulation can be significant, even as far as 2 km from the source. For example, at 2 km approximately 0.28 mg/sq cm of dust is anticipated to accumulate after only 10 surface missions with a 26,800 N excursion vehicle. The possible associated penalties in photovoltaic array performance were therefore the subject of experimental as well as theoretical investigation. To evaluate effects of dust accumulation on relative power output, current-voltage characteristics of dust-covered silicon cells were determined under the illumination of a Spectrolab X-25L solar simulator. The dust material used in these experiments was a terrestrial basalt which approximated lunar soil in particle size and composition. Cell short circuit current, an indicator of the penetrating light intensity, was found to decrease exponentially with dust accumulation. This was predicted independently by modeling the light occlusion caused by a growing layer of dust particles. Moreover, the maximum power output of dust-covered cells, derived from the I-V curves, was also found to degrade exponentially. Experimental results are presented and potential implications discussed
Nondegenerate three-dimensional complex Euclidean superintegrable systems and algebraic varieties
A classical (or quantum) second order superintegrable system is an integrable n-dimensional Hamiltonian system with potential that admits 2n−1 functionally independent second order constants of the motion polynomial in the momenta, the maximum possible. Such systems have remarkable properties: multi-integrability and multiseparability, an algebra of higher order symmetries whose representation theory yields spectral information about the Schrödinger operator, deep connections with special functions, and with quasiexactly solvable systems. Here, we announce a complete classification of nondegenerate (i.e., four-parameter) potentials for complex Euclidean 3-space. We characterize the possible superintegrable systems as points on an algebraic variety in ten variables subject to six quadratic polynomial constraints. The Euclidean group acts on the variety such that two points determine the same superintegrable system if and only if they lie on the same leaf of the foliation. There are exactly ten nondegenerate potentials. ©2007 American Institute of Physic
Superintegrable Systems in Darboux spaces
Almost all research on superintegrable potentials concerns spaces of constant
curvature. In this paper we find by exhaustive calculation, all superintegrable
potentials in the four Darboux spaces of revolution that have at least two
integrals of motion quadratic in the momenta, in addition to the Hamiltonian.
These are two-dimensional spaces of nonconstant curvature. It turns out that
all of these potentials are equivalent to superintegrable potentials in complex
Euclidean 2-space or on the complex 2-sphere, via "coupling constant
metamorphosis" (or equivalently, via Staeckel multiplier transformations). We
present tables of the results
Second order superintegrable systems in conformally flat spaces. IV. The classical 3D Stäckel transform and 3D classification theory
This article is one of a series that lays the groundwork for a structure and classification theory of second order superintegrable systems, both classical and quantum, in conformally flat spaces. In the first part of the article we study the Stäckel transform (or coupling constant metamorphosis) as an invertible mapping between classical superintegrable systems on different three-dimensional spaces. We show first that all superintegrable systems with nondegenerate potentials are multiseparable and then that each such system on any conformally flat space is Stäckel equivalent to a system on a constant curvature space. In the second part of the article we classify all the superintegrable systems that admit separation in generic coordinates. We find that there are eight families of these systems
Debye Potentials for Maxwell and Dirac Fields from a Generalisation of the Killing-Yano Equation
By using conformal Killing-Yano tensors, and their generalisations, we obtain
scalar potentials for both the source-free Maxwell and massless Dirac
equations. For each of these equations we construct, from conformal
Killing-Yano tensors, symmetry operators that map any solution to another.Comment: 35 pages, plain Te
Direct Observation of Controlled Coupling in an Individual Quantum Dot Molecule
We report the direct observation of quantum coupling in individual quantum
dot molecules and its manipulation using static electric fields. A pronounced
anti-crossing of different excitonic transitions is observed as the electric
field is tuned. Comparison of our experimental results with theory shows that
the observed anti-crossing occurs between excitons with predominant spatially
\emph{direct} and \emph{indirect} character. The electron component of the
exciton wavefunction is shown to have molecular character at the anti-crossing
and the quantum coupling strength is deduced optically. In addition, we
determine the dependence of the coupling strength on the inter-dot separation
and identify a field driven transition of the nature of the molecular ground
state.Comment: 11 pages, 4 figures submitted to Physical Review Letter
Unified treatment and classification of superintegrable systems with integrals quadratic in momenta on a two dimensional manifold
In this paper we prove that the two dimensional superintegrable systems with
quadratic integrals of motion on a manifold can be classified by using the
Poisson algebra of the integrals of motion. There are six general fundamental
classes of superintegrable systems. Analytic formulas for the involved
integrals are calculated in all the cases. All the known superintegrable
systems are classified as special cases of these six general classes.Comment: LaTeX, 72 pages. Extended version of the published version in JM
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