230 research outputs found
Dephasing dynamics of Rydberg atom spin waves
A theory of Rydberg atom interactions is used to derive analytical forms for
the spin wave pair correlation function in laser-excited cold-atom vapors. This
function controls the quantum statistics of light emission from dense,
inhomogeneous clouds of cold atoms of various spatial dimensionalities. The
results yield distinctive scaling behaviors on the microsecond timescale,
including generalized exponential decay. A detailed comparison is presented
with a recent experiment on a cigar-shaped atomic ensemble [Y. Dudin and A.
Kuzmich, Science 336, 887 (2012)], in which Rb atoms are excited to a set of
Rydberg levels.Comment: 4 pages, Supplemental Material in Appendix, 4 figure
An efficient multi-core SIMD implementation for H.264/AVC encoder
The optimization process of a H.264/AVC encoder on three different architectures is presented. The architectures are multi- and singlecore and SIMD instruction sets have different vector registers size. The need of code optimization is fundamental when addressing HD resolutions with real-time constraints. The encoder is subdivided in functional modules in order to better understand where the optimization is a key factor and to evaluate in details the performance improvement. Common issues in both partitioning a video encoder into parallel architectures and SIMD optimization are described, and author solutions are presented for all the architectures. Besides showing efficient video encoder implementations, one of the main purposes of this paper is to discuss how the characteristics of different architectures and different set of SIMD instructions can impact on the target application performance. Results about the achieved speedup are provided in order to compare the different implementations and evaluate the more suitable solutions for present and next generation video-coding algorithms
Multimedia terminal system-on-chip design and simulation
This paper proposes a design approach based on integrated architectural and system-on-chip (SoC) simulations. The main idea is to have an efficient framework for the design and the evaluation of multimedia terminals, allowing a fast system simulation with a definable degree of accuracy. The design approach includes the simulation of very long instruction word (VLIW) digital signal processors (DSPs), the utilization of a device multiplexing the media streams, and the emulation of the real-time media acquisition. This methodology allows the evaluation of both the multimedia algorithm implementations and the hardware platform, giving feedback on the complete SoC including the interaction between modules and conflicts in accessing either the bus or shared resources. An instruction set architecture (ISA) simulator and an SoC simulation environment compose the integrated framework. In order to validate this approach, the evaluation of an audio-video multiprocessor terminal is presented, and the complete simulation test results are reported
Observation of coherent many-body Rabi oscillations
A two-level quantum system coherently driven by a resonant electromagnetic
field oscillates sinusoidally between the two levels at frequency
which is proportional to the field amplitude [1]. This phenomenon, known as the
Rabi oscillation, has been at the heart of atomic, molecular and optical
physics since the seminal work of its namesake and coauthors [2]. Notably, Rabi
oscillations in isolated single atoms or dilute gases form the basis for
metrological applications such as atomic clocks and precision measurements of
physical constants [3]. Both inhomogeneous distribution of coupling strength to
the field and interactions between individual atoms reduce the visibility of
the oscillation and may even suppress it completely. A remarkable
transformation takes place in the limit where only a single excitation can be
present in the sample due to either initial conditions or atomic interactions:
there arises a collective, many-body Rabi oscillation at a frequency
involving all N >> 1 atoms in the sample [4]. This is true even
for inhomogeneous atom-field coupling distributions, where single-atom Rabi
oscillations may be invisible. When one of the two levels is a strongly
interacting Rydberg level, many-body Rabi oscillations emerge as a consequence
of the Rydberg excitation blockade. Lukin and coauthors outlined an approach to
quantum information processing based on this effect [5]. Here we report initial
observations of coherent many-body Rabi oscillations between the ground level
and a Rydberg level using several hundred cold rubidium atoms. The strongly
pronounced oscillations indicate a nearly complete excitation blockade of the
entire mesoscopic ensemble by a single excited atom. The results pave the way
towards quantum computation and simulation using ensembles of atoms
Photon Wave-packet Manipulation via Dynamic Electromagnetically Induced Transparency in Multilayer Structures
We present a Maxwell-Bloch description of the dynamics of a light pulse
propagating through a spatially inhomogeneous system consisting of alternating
layers of EIT media and vacuum. We study the effect of a dynamical modulation
of the EIT control field on the shape of the wave packet: interesting effects
due to the presence of interfaces with group velocity mismatch are found. An
effective description based on a continuity equation is developed. Modulation
schemes that can be realized in ultracold atomic samples with standard
experimental techniques are proposed and discussed
Energy performance and climate control in mechanically ventilated greenhouses: A dynamic modelling-based assessment and investigation
Controlled environment agriculture in greenhouse is a promising solution for meeting the increasing food demand of world population. The accurate control of the indoor environmental conditions proper of greenhouses enhances high crop productivity but, contemporarily, it entails considerable energy consumption due to the adoption of mechanical systems. This work presents a new modelling approach for estimating the energy consumption for climate control of mechanically ventilated greenhouses. The novelty of the proposed energy model lies in its integrated approach in simulating the greenhouse dynamics, considering the dynamic thermal and hygric behaviour of the building and the dynamic response of the cultivated crops to the variation of the solar radiation. The presented model simulates the operation of the systems and the energy performance, considering also the variable angular speed fans that are a new promising energy-efficient technology for this productive sector. The main outputs of the model are the hourly thermal and electrical energy use for climate control and the main indoor environmental conditions. The presented modelling approach was validated against a dataset acquired in a case study of a new fully mechanically controlled greenhouse during a long-term monitoring campaign. The present work contributes to increase the knowledge about the dynamics and the energy consumption of greenhouses, and it can be a valuable decision support tool for industry, farmers, and researchers to properly address an energy efficiency optimisation in mechanically ventilated greenhouses to reach the overall objective of decreasing the rising energy consumption of the agricultural sector
Patterning Large-Scale Nanostructured Microarrays on Coverslip for Sensitive Plasmonic Detection of Aqueous Gliadin Traces
(c) The Author/sUser-friendly devices for detecting low gliadin content in commercial foods are of extreme importance for people with gluten diseases. With this concern, the present work proposes a rapid and sensitive optical nanostructured microarrays platform for the detection of gliadin using specific anti-gliadin IgG antibodies immobilized on annealed gold nanostructures (AuNPs) obtained after the high annealing process (550â—¦C) of gold thin films evaporated on commercial glass coverslips. Localized Surface Plasmon Resonance (LSPR) immunosensing of gliadin in the range of 0.1 ppm to 1000 ppm is successfully achieved. In addition, the biofunctionalization protocol was used for gluten screening in five food complex products.Publishe
Bright and dark excitons in an atom--pair filled optical lattice within a cavity
We study electronic excitations of a degenerate gas of atoms trapped in pairs
in an optical lattice. Local dipole-dipole interactions produce a long lived
antisymmetric and a short lived symmetric superposition of individual atomic
excitations as the lowest internal on-site excitations. Due to the much larger
dipole moment the symmetric states couple efficiently to neighbouring lattice
sites and can be well represented by Frenkel excitons, while the antisymmetric
dark states stay localized. Within a cavity only symmetric states couple to
cavity photons inducing long range interactions to form polaritons. We
calculate their dispersion curves as well as cavity transmission and reflection
spectra to observe them. For a lattice with aspherical sites bright and dark
states get mixed and their relative excitation energies depend on photon
polarizations. The system should allow to study new types of solid state
phenomena in atom filled optical lattices
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