422 research outputs found
On the indistinguishability of Raman photons
We provide a theoretical framework to study the effect of dephasing on the
quantum indistinguishability of single photons emitted from a coherently driven
cavity QED -system. We show that with a large excited-state detuning,
the photon indistinguishability can be drastically improved provided that the
fluctuation rate of the noise source affecting the excited state is fast
compared with the photon emission rate. In some cases a spectral filter is
required to realize this improvement, but the cost in efficiency can be made
small.Comment: 18 pages, 3 figures, final versio
Coherent Population Trapping of Single Spins in Diamond Under Optical Excitation
Coherent population trapping is demonstrated in single nitrogen-vacancy
centers in diamond under optical excitation. For sufficient excitation power,
the fluorescence intensity drops almost to the background level when the laser
modulation frequency matches the 2.88 GHz splitting of the ground states. The
results are well described theoretically by a four-level model, allowing the
relative transition strengths to be determined for individual centers. The
results show that all-optical control of single spins is possible in diamond.Comment: minor correction
Photoluminescence of single colour defects in 50 nm diamond nanocrystals
We used optical confocal microscopy to study optical properties of diamond 50
nm nanocrystals first irradiated with an electron beam, then dispersed as a
colloidal solution and finally deposited on a silica slide. At room
temperature, under CW laser excitation at a wavelength of 514.5 nm we observed
perfectly photostable single Nitrogen-Vacancy (NV) colour defects embedded in
the nanocrystals. From the zero-phonon line around 575 nm in the spectrum of
emitted light, we infer a neutral NV0 type of defect. Such nanoparticle with
intrinsic fluorescence are highly promising for applications in biology where
long-term emitting fluorescent bio-compatible nanoprobes are still missing.Comment: proceedings of ICDS 23 conference (23rd International Conference on
Defects in Semiconductors, July 24 - July 29, 2005, Awaji Island, Hyogo,
Japan); to appear in "Physica B
Quality and Safety Aspects of Infant Nutrition
Quality and safety aspects of infant nutrition are of key importance for child health, but oftentimes they do not get much attention by health care professionals whose interest tends to focus on functional benefits of early nutrition. Unbalanced diets and harmful food components induce particularly high risks for untoward effects in infants because of their rapid growth, high nutrient needs, and their typical dependence on only one or few foods during the first months of life. The concepts, standards and practices that relate to infant food quality and safety were discussed at a scientific workshop organized by the Child Health Foundation and the Early Nutrition Academy jointly with the European Society for Paediatric Gastroenterology, Hepatology and Nutrition, and a summary is provided here. The participants reviewed past and current issues on quality and safety, the role of different stakeholders, and recommendations to avert future issues. It was concluded that a high level of quality and safety is currently achieved, but this is no reason for complacency. The food industry carries the primary responsibility for the safety and suitability of their products, including the quality of composition, raw materials and production processes. Introduction of new or modified products should be preceded by a thorough science based review of suitability and safety by an independent authority. Food safety events should be managed on an international basis. Global collaboration of food producers, food-safety authorities, paediatricians and scientists is needed to efficiently exchange information and to best protect public health. Copyright (C) 2012 S. Karger AG, Base
Properties of a single photon generated by a solid-state emitter: effects of pure dephasing
We investigate the properties of a single photon generated by a solid-state
emitter subject to strong pure dephasing. We employ a model in which all the
elements of the system, including the propagating fields, are treated quantum
mechanically. We analytically derive the density matrix of the emitted photon,
which contains full information about the photon, such as its pulse profile,
power spectrum, and purity. We visualize these analytical results using
realistic parameters and reveal the conditions for maximizing the purity of
generated photons.Comment: 25pages(one column), 10 figure
Aberration-free ultra-thin flat lenses and axicons at telecom wavelengths based on plasmonic metasurfaces
The concept of optical phase discontinuities is applied to the design and
demonstration of aberration-free planar lenses and axicons, comprising a phased
array of ultrathin subwavelength spaced optical antennas. The lenses and
axicons consist of radial distributions of V-shaped nanoantennas that generate
respectively spherical wavefronts and non-diffracting Bessel beams at telecom
wavelengths. Simulations are also presented to show that our aberration-free
designs are applicable to high numerical aperture lenses such as flat
microscope objectives
A framework for digital sunken relief generation based on 3D geometric models
Sunken relief is a special art form of sculpture whereby the depicted shapes are sunk into a given surface. This is traditionally created by laboriously carving materials such as stone. Sunken reliefs often utilize the engraved lines or strokes to strengthen the impressions of a 3D presence and to highlight the features which otherwise are unrevealed. In other types of reliefs, smooth surfaces and their shadows convey such information in a coherent manner. Existing methods for relief generation are focused on forming a smooth surface with a shallow depth which provides the presence of 3D figures. Such methods unfortunately do not help the art form of sunken reliefs as they omit the presence of feature lines. We propose a framework to produce sunken reliefs from a known 3D geometry, which transforms the 3D objects into three layers of input to incorporate the contour lines seamlessly with the smooth surfaces. The three input layers take the advantages of the geometric information and the visual cues to assist the relief generation. This framework alters existing techniques in line drawings and relief generation, and then combines them organically for this particular purpose
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