10,962 research outputs found
Metallic nanorings for broadband, enhanced extraction of light from solid-state emitters
We report on the increased extraction of light emitted by solid-state sources
embedded within high refractive index materials. This is achieved by making use
of a local lensing effect by sub-micron metallic rings deposited on the sample
surface and centered around single emitters. We show enhancements in the
intensity of the light emitted by InAs/GaAs single quantum dot lines into free
space as high as a factor 20. Such a device is intrinsically broadband and
therefore compatible with any kind of solid-state light source. We foresee the
fabrication of metallic rings via scalable techniques, like nano-imprint, and
their implementation to improve the emission of classical and quantum light
from solid-state sources. Furthermore, while increasing the brightness of the
devices, the metallic rings can also act as top contacts for the local
application of electric fields for carrier injection or wavelength tuning.Comment: 10 pages, 3 figure
Fabrication and tuning of plasmonic optical nanoantennas around droplet epitaxy quantum dots by cathodoluminescence
We use cathodoluminescence to locate droplet epitaxy quantum dots with a
precision nm before fabricating nanoantennas in their vicinity by
electron-beam lithography. Cathodoluminescence is further used to evidence the
effect of the antennas as a function of their length on the light emitted by
the dot. Experimental results are in good agreement with numerical simulations
of the structures
Universal expansions of scattering amplitudes for gravitons, gluons and Goldstone particles
Tree-level scattering amplitudes for gravitons, gluons and Goldstone
particles in any dimensions are strongly constrained by basic principles, and
they are intimately related to each other via various relations. We study two
types of "universal expansions" with respect to gauge bosons and Goldstone
bosons: the former express tree amplitudes in Einstein gravity (Yang-Mills) as
linear combinations of single-trace Einstein-Yang-Mills (Yang-Mills-)
amplitudes with coefficients given by Lorentz products of polarizations and
momenta; the latter express tree amplitudes in non-linear sigma model,
(Dirac-)Born-Infeld and a special Galileon theory, as linear combinations of
single-trace mixed amplitudes with particles of lower "degree of Adler's zero"
and coefficients given by products of Mandelstam variables. We trace the origin
of gauge-theory expansions to the powerful uniqueness theorem based on gauge
invariance, and expansions in effective field theories can be derived from
gauge-theory ones via a special dimension reduction.Comment: 8 pages, 1 figur
Moving boundary and photoelastic coupling in GaAs optomechanical resonators
Chip-based cavity optomechanical systems are being considered for
applications in sensing, metrology, and quantum information science. Critical
to their development is an understanding of how the optical and mechanical
modes interact, quantified by the coupling rate . Here, we develop GaAs
optomechanical resonators and investigate the moving dielectric boundary and
photoelastic contributions to . First, we consider coupling between the
fundamental radial breathing mechanical mode and a 1550 nm band optical
whispering gallery mode in microdisks. For decreasing disk radius from
m to m, simulations and measurements show that changes
from being dominated by the moving boundary contribution to having an equal
photoelastic contribution. Next, we design and demonstrate nanobeam
optomechanical crystals in which a GHz mechanical breathing mode couples
to a 1550 nm optical mode predominantly through the photoelastic effect. We
show a significant (30 ) dependence of on the device's in-plane
orientation, resulting from the difference in GaAs photoelastic coefficients
along different crystalline axes, with fabricated devices exhibiting
as high as 1.1 MHz for orientation along the [110] axis.
GaAs nanobeam optomechanical crystals are a promising system which can combine
the demonstrated large optomechanical coupling strength with additional
functionality, such as piezoelectric actuation and incorporation of optical
gain media
A formal framework for modeling and validating Simulink diagrams
10.1007/s00165-009-0108-9Formal Aspects of Computing215451-483FACM
Decay dynamics and exciton localization in large GaAs quantum dots grown by droplet epitaxy
We investigate the optical emission and decay dynamics of excitons confined
in large strain-free GaAs quantum dots grown by droplet epitaxy. From
time-resolved measurements combined with a theoretical model we show that
droplet-epitaxy quantum dots have a quantum efficiency of about 75% and an
oscillator strength between 8 and 10. The quantum dots are found to be fully
described by a model for strongly-confined excitons, in contrast to the
theoretical prediction that excitons in large quantum dots exhibit the
so-called giant oscillator strength. We attribute these findings to localized
ground-state excitons in potential minima created by material intermixing
during growth. We provide further evidence for the strong-confinement regime of
excitons by extracting the size of electron and hole wavefunctions from the
phonon-broadened photoluminescence spectra. Furthermore, we explore the
temperature dependence of the decay dynamics and, for some quantum dots,
observe a pronounced reduction in the effective transition strength with
temperature. We quantify and explain these effects as being an intrinsic
property of large quantum dots owing to thermal excitation of the ground-state
exciton. Our results provide a detailed understanding of the optical properties
of large quantum dots in general, and of quantum dots grown by droplet epitaxy
in particular.Comment: 13 pages, 7 figure
SCC-based improved reachability analysis for Markov decision processes
Markov decision processes (MDPs) are extensively used to model systems with both probabilistic and nondeterministic behavior. The problem of calculating the probability of reaching certain system states (hereafter reachability analysis) is central to the MDP-based system analysis. It is known that existing approaches on reachability analysis for MDPs are often inefficient when a given MDP contains a large number of states and loops, especially with the existence of multiple probability distributions. In this work, we propose a method to eliminate strongly connected components (SCCs) in an MDP using a divide-and-conquer algorithm, and actively remove redundant probability distributions in the MDP based on the convex property. With the removal of loops and parts of probability distributions, the probabilistic reachability analysis can be accelerated, as evidenced by our experiment results.No Full Tex
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