3,245 research outputs found
Homodyne extimation of quantum states purity by exploiting covariant uncertainty relation
We experimentally verify uncertainty relations for mixed states in the
tomographic representation by measuring the radiation field tomograms, i.e.
homodyne distributions. Thermal states of single-mode radiation field are
discussed in details as paradigm of mixed quantum state. By considering the
connection between generalised uncertainty relations and optical tomograms is
seen that the purity of the states can be retrieved by statistical analysis of
the homodyne data. The purity parameter assumes a relevant role in quantum
information where the effective fidelities of protocols depend critically on
the purity of the information carrier states. In this contest the homodyne
detector becomes an easy to handle purity-meter for the state on-line with a
running quantum information protocol.Comment: accepted for publication into Physica Script
Towards ultra-high resolution 3D reconstruction of a whole rat brain from 3D-PLI data
3D reconstruction of the fiber connectivity of the rat brain at microscopic
scale enables gaining detailed insight about the complex structural
organization of the brain. We introduce a new method for registration and 3D
reconstruction of high- and ultra-high resolution (64 m and 1.3 m
pixel size) histological images of a Wistar rat brain acquired by 3D polarized
light imaging (3D-PLI). Our method exploits multi-scale and multi-modal 3D-PLI
data up to cellular resolution. We propose a new feature transform-based
similarity measure and a weighted regularization scheme for accurate and robust
non-rigid registration. To transform the 1.3 m ultra-high resolution data
to the reference blockface images a feature-based registration method followed
by a non-rigid registration is proposed. Our approach has been successfully
applied to 278 histological sections of a rat brain and the performance has
been quantitatively evaluated using manually placed landmarks by an expert.Comment: 9 pages, Accepted at 2nd International Workshop on Connectomics in
NeuroImaging (CNI), MICCAI'201
Balancing efficiencies by squeezing in realistic eight-port homodyne detection
We address measurements of covariant phase observables (CPOs) by means of
realistic eight-port homodyne detectors. We do not assume equal quantum
efficiencies for the four photodetectors and investigate the conditions under
which the measurement of a CPO may be achieved. We show that balancing the
efficiencies using an additional beam splitter allows us to achieve a CPO at
the price of reducing the overall effective efficiency, and prove that it is
never a smearing of the ideal CPO achievable with unit quantum efficiency. An
alternative strategy based on employing a squeezed vacuum as a parameter field
is also suggested, which allows one to increase the overall efficiency in
comparison to the passive case using only a moderate amount of squeezing. Both
methods are suitable for implementantion with current technology.Comment: 8 pages, 5 figures, revised versio
Chemical characterisation of iron in dust and biomass burning aerosols during AMMA-SOP0/DABEX: implication for iron solubility
The chemical composition and the soluble fraction were determined in aerosol samples collected during flights of AMMA-SOP0/DABEX campaign, which were conducted in the West African Sahel during dry season (2006). Two aerosol types are encountered in this period: dust particles (DUST) and biomass burning aerosol (BB). Chemical analysis and microscope observations showed that the iron (Fe) found in BB samples mainly originates from dust particles mostly internally mixed in the biomass burning layer. Chemical analyses of samples showed that the Fe solubility is lower in African dust samples than in biomass burning aerosols. Our data provide a first idea of the variability of iron dust solubility in the source region (0.1% and 3.4%). We found a relationship between iron solubility/clay content/source which partly confirms that the variability of iron solubility in this source region is related to the character and origin of the aerosols themselves. In the biomass burning samples, no relationship were found between Fe solubility and either the concentrations of acidic species (SO<sub>4</sub><sup>2&minus;</sup>, NO<sub>3</sub><sup>&minus;</sup> or oxalate) or the content of carbon (TC, OC, BC). Therefore, we were unable to determine what processes are involved in this increase of iron solubility. In terms of supply of soluble Fe to oceanic ecosystems on a global scale, the higher solubility observed for Fe in biomass burning could imply an indirect source of Fe to marine ecosystems. But these aerosols are probably not significant because the Sahara is easily the dominant source of Fe to the Atlantic Ocean
Full characterization of Gaussian bipartite entangled states by a single homodyne detector
We present the full experimental reconstruction of Gaussian entangled states
generated by a type--II optical parametric oscillator (OPO) below threshold.
Our scheme provides the entire covariance matrix using a single homodyne
detector and allows for the complete characterization of bipartite Gaussian
states, including the evaluation of purity, entanglement and nonclassical
photon correlations, without a priori assumptions on the state under
investigation. Our results show that single homodyne schemes are convenient and
robust setups for the full characterization of OPO signals and represent a tool
for quantum technology based on continuous variable entanglement.Comment: 4 pages, 3 figures, slightly longer version of published PR
Pre-discovery observations of CoRoT-1b and CoRoT-2b with the BEST survey
The BEST wide-angle telescope installed at the Observatoire de Haute-Provence
and operated in remote control from Berlin by the Institut fuer
Planetenforschung, DLR, has observed the CoRoT target fields prior to the
mission. The resulting archive of stellar photometric lightcurves is used to
search for deep transit events announced during CoRoT's alarm-mode to aid in
fast photometric confirmation of these events. The "initial run" field of CoRoT
(IRa01) has been observed with BEST in November and December 2006 for 12
nights. The first "long run" field (LRc01) was observed from June to September
2005 for 35 nights. After standard CCD data reduction, aperture photometry has
been performed using the ISIS image subtraction method. About 30,000
lightcurves were obtained in each field. Transits of the first detected planets
by the CoRoT mission, CoRoT-1b and CoRoT-2b, were found in archived data of the
BEST survey and their lightcurves are presented here. Such detections provide
useful information at the early stage of the organization of follow-up
observations of satellite alarm-mode planet candidates. In addition, no period
change was found over ~4 years between the first BEST observation and last
available transit observations.Comment: AJ, accepte
Wildfire smoke in the Siberian Arctic in summer: source characterization and plume evolution from airborne measurements
We present airborne measurements of carbon dioxide (CO<sub>2</sub>), carbon monoxide (CO), ozone (O<sub>3</sub>), equivalent black carbon (EBC) and ultra fine particles over North-Eastern Siberia in July 2008 performed during the YAK-AEROSIB/POLARCAT experiment. During a "golden day" (11 July 2008) a number of biomass burning plumes were encountered with CO mixing ratio enhancements of up to 500 ppb relative to a background of 90 ppb. Number concentrations of aerosols in the size range 3.5–200 nm peaked at 4000 cm<sup>&minus;3</sup> and the EBC content reached 1.4 &mu;g m<sup>&minus;3</sup>. These high concentrations were caused by forest fires in the vicinity of the landing airport in Yakutsk where measurements in fresh smoke could be made during the descent. We estimate a combustion efficiency of 90 &plusmn; 3% based on CO and CO<sub>2</sub> measurements and a CO emission factor of 65.5 &plusmn; 10.8 g CO per kilogram of dry matter burned. This suggests a potential increase in the average northern hemispheric CO mixing ratio of 3.0–7.2 ppb per million hectares of Siberian forest burned. For BC, we estimate an emission factor of 0.52 &plusmn; 0.07 g BC kg<sup>&minus;1</sup>, comparable to values reported in the literature. The emission ratio of ultra-fine particles (3.5–200 nm) was 26 cm<sup>&minus;3</sup> (ppb CO)<sup>&minus;1</sup>, consistent with other airborne studies. <br><br> The transport of identified biomass burning plumes was investigated using the FLEXPART Lagrangian model. Based on sampling of wildfire plumes from the same source but with different atmospheric ages derived from FLEXPART, we estimate that the e-folding lifetimes of EBC and ultra fine particles (between 3.5 and 200 nm in size) against removal and growth processes are 5.1 and 5.5 days respectively, supporting lifetime estimates used in various modelling studies
Quantum state engineering assisted by entanglement
We suggest a general scheme for quantum state engineering based on
conditional measurements carried out on entangled twin-beam of radiation.
Realistic detection schemes such as {\sc on/off} photodetection, homodyne
detection and joint measurement of two-mode quadratures are analyzed in
details. Imperfections of the apparatuses, such as nonunit quantum efficiency
and finite resolution, are taken into account. We show that conditional {\sc
on/off} photodetection provides a reliable scheme to verify nonclassicality,
whereas conditional homodyning represents a tunable and robust source of
squeezed light. We also describe optical teleportation as a conditional
measurement, and evaluate the degrading effects of finite amount of
entanglement, decoherence due to losses, and nonunit quantum efficiency.Comment: Some pics with low resolution. Originals at http://www.qubit.i
- …