1,879 research outputs found
Flat Thomas-Fermi artificial atoms
We consider two-dimensional (2D) "artificial atoms" confined by an axially
symmetric potential . Such configurations arise in circular quantum
dots and other systems effectively restricted to a 2D layer. Using the
semiclassical method, we present the first fully self-consistent and analytic
solution yielding equations describing the density distribution, energy, and
other quantities for any form of and an arbitrary number of confined
particles. An essential and nontrivial aspect of the problem is that the 2D
density of states must be properly combined with 3D electrostatics. The
solution turns out to have a universal form, with scaling parameters
and ( is the dot radius and is the effective
Bohr radius)
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Interpreting the Operando XANES of Surface-Supported Subnanometer Clusters: When Fluxionality, Oxidation State, and Size Effect Fight
Detector imperfections in photon-pair source characterization
We analyze how imperfections in single-photon detectors impact the
characterization of photon-pair sources. We perform exact calculations to
reveal the effects of multi-pair emissions and of noisy, non-unit efficiency,
non photon-number resolving detections on the Cauchy-Schwarz parameter, on the
second order auto-correlation and cross-correlation functions, and on the
visibilities of both Hong-Ou-Mandel and Bell-like interferences. We consider
sources producing either two-mode squeezed states or states with a Poissonian
photon distribution. The proposed formulas are useful in practice to determine
the impacts of multi-pair emissions and dark counts in standard tests used in
quantum optics.Comment: 9 pages, 11 figure
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Oxidative Dehydrogenation of Cyclohexane by Cu vs Pd Clusters: Selectivity Control by Specific Cluster Dynamics
Photon-bunching measurement after 2x25km of standard optical fibers
To show the feasibility of a long distance partial Bell-State measurement, a
Hong-Ou-Mandel experiment with coherent photons is reported. Pairs of
degenerate photons at telecom wavelength are created by parametric down
conversion in a periodically poled lithium niobate waveguide. The photon pairs
are separated in a beam-splitter and transmitted via two fibers of 25km. The
wave-packets are relatively delayed and recombined on a second beam-splitter,
forming a large Mach-Zehnder interferometer. Coincidence counts between the
photons at the two output modes are registered. The main challenge consists in
the trade-off between low count rates due to narrow filtering and length
fluctuations of the 25km long arms during the measurement. For balanced paths a
Hong-Ou-Mandel dip with a visibility of 47.3% is observed, which is close to
the maximal theoretical value of 50% developed here. This proves the
practicability of a long distance Bell state measurement with two independent
sources, as e.g. required in an entanglement swapping configuration in the
scale of tens of km.Comment: 6 pages, 5 figure
The integrated 3-point correlation function of cosmic shear
We present the integrated 3-point shear correlation function
-- a higher-order statistic of the cosmic shear field -- which can be directly
estimated in wide-area weak lensing surveys without measuring the full 3-point
shear correlation function, making this a practical and complementary tool to
2-point statistics for weak lensing cosmology. We define it as the 1-point
aperture mass statistic measured at different locations on
the shear field correlated with the corresponding local 2-point shear
correlation function . Building upon existing work on the integrated
bispectrum of the weak lensing convergence field, we present a theoretical
framework for computing the integrated 3-point function in real space for any
projected field within the flat-sky approximation and apply it to cosmic shear.
Using analytical formulae for the non-linear matter power spectrum and
bispectrum, we model and validate it on N-body simulations
within the uncertainties expected from the sixth year cosmic shear data of the
Dark Energy Survey. We also explore the Fisher information content of
and perform a joint analysis with for two
tomographic source redshift bins with realistic shape-noise to analyse its
power in constraining cosmological parameters. We find that the joint analysis
of and has the potential to considerably improve
parameter constraints from alone, and can be particularly useful in
improving the figure of merit of the dynamical dark energy equation of state
parameters from cosmic shear data.Comment: Accepted for publication in MNRAS; v2 matches the accepted
manuscript; 18 pages + appendi
Modulation of ISOs by land-atmosphere feedback and contribution to the interannual variability of Indian summer monsoon
A mechanism of internal variability of Indian summer monsoon through the modulation of intraseasonal oscillation (ISO) by land-atmosphere feedback is proposed. Evidence of feedback between surface soil moisture and ISOs is seen in the soil moisture data from GSWP-2 and rainfall data from observations. Using two sets of internal simulation by a regional climate model (RCM), it is shown that internally generated anomalous soil moisture interacts with the following ISO and generates interannual variability. To gain further insight, 27 years of sensitivity experiment by prescribing wet (dry) soil moisture condition during break (active) period along with a control simulation are carried out. The sensitivity experiment reveals the large-scale nature of soil moisture and ISO feedback which takes place through the changes in atmospheric stability by altering lower-level atmospheric conditions. The feedback is inherent to the monsoon system and a part of it acts through the intraseasonal varying memory of soil moisture. The RCM used to test the hypothesis is constrained by one-way interactions at the lateral boundary. Experiments with a much larger domain upheld the findings and hence suggest the true nature of soil moisture and ISO feedback present in the monsoon system
A versatile source of polarisation entangled photons for quantum network applications
We report a versatile and practical approach for generating high-quality
polarization entanglement in a fully guided-wave fashion. Our setup relies on a
high-brilliance type-0 waveguide generator producing paired photon at a telecom
wavelength associated with an advanced energy-time to polarisation transcriber.
The latter is capable of creating any pure polarization entangled state, and
allows manipulating single photon bandwidths that can be chosen at will over
five orders of magnitude, ranging from tens of MHz to several THz. We achieve
excellent entanglement fidelities for particular spectral bandwidths, i.e. 25
MHz, 540 MHz and 100 GHz, proving the relevance of our approach. Our scheme
stands as an ideal candidate for a wide range of network applications, ranging
from dense division multiplexing quantum key distribution to heralded optical
quantum memories and repeaters.Comment: 5 figure
Experimental polarization encoded quantum key distribution over optical fibres with real-time continuous birefringence compensation
In this paper we demonstrate an active polarization drift compensation scheme
for optical fibres employed in a quantum key distribution experiment with
polarization encoded qubits. The quantum signals are wavelength multiplexed in
one fibre along with two classical optical side channels that provide the
control information for the polarization compensation scheme. This set-up
allows us to continuously track any polarization change without the need to
interrupt the key exchange. The results obtained show that fast polarization
rotations of the order of 40*pi rad/s are effectively compensated for. We
demonstrate that our set-up allows continuous quantum key distribution even in
a fibre stressed by random polarization fluctuations. Our results pave the way
for Bell-state measurements using only linear optics with parties separated by
long-distance optical fibres
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