240 research outputs found
Molecules as Sources for Indistinguishable Single Photons
We report on the triggered generation of indistinguishable photons by
solid-state single-photon sources in two separate cryogenic laser scanning
microscopes. Organic fluorescent molecules were used as emitters and
investigated by means of high resolution laser spectroscopy. Continuous-wave
photon correlation measurements on individual molecules proved the isolation of
single quantum systems. By using frequency selective pulsed excitation of the
molecule and efficient spectral filtering of its emission, we produced
triggered Fourier-limited single photons. In a further step, local electric
fields were applied to match the emission wavelengths of two different
molecules via Stark effect. Identical single photons are indispensible for the
realization of various quantum information processing schemes proposed. The
solid-state approach presented here prepares the way towards the integration of
multiple bright sources of single photons on a single chip.Comment: Accepted for publication in J. Mod. Opt. This is the original
submitted versio
Realization of two Fourier-limited solid-state single-photon sources
We demonstrate two solid-state sources of indistinguishable single photons.
High resolution laser spectroscopy and optical microscopy were combined at T =
1.4 K to identify individual molecules in two independent microscopes. The
Stark effect was exploited to shift the transition frequency of a given
molecule and thus obtain single photon sources with perfect spectral overlap.
Our experimental arrangement sets the ground for the realization of various
quantum interference and information processing experiments.Comment: 6 page
Strong extinction of a laser beam by a single molecule
We present an experiment where a single molecule strongly affects the
amplitude and phase of a laser field emerging from a subwavelength aperture. We
achieve a visibility of -6% in direct and +10% in cross-polarized detection
schemes. Our analysis shows that a close to full extinction should be possible
using near-field excitation.Comment: 5 pages, 4 figures, submitted to PR
Einfluss von N-Düngermenge und Nitrifikationshemmung auf die direkten N2O-Emissionen eines gemüsebaulich genutzten Ackerbodens
Lachgas (N2O) ist ein klimarelevantes Spurengas, es trägt zum Ozonabbau in der Stratosphäre sowie zu 8% am anthropogenen Treibhauseffekt bei und stammt zum Großteil aus landwirtschaftlich genutzten Böden. Ziel dieser Studie war die Ermittlung belastbarer annueller Daten zur N2O-Freisetzung aus gemüsebaulich genutzten Ackerböden Mitteleuropas, d.h. aus einer Gegend mit ausgeprägten Frost-Tau-Zyklen. Ferner sollte das Potential zur Minderung der direkten N2O-Emissionen untersucht werden. Hierzu wurde sowohl eine reduzierte Düngung als auch der Zusatz eines Nitrifikationshemmstoffs getestet. Die Beiträge von N-Dünger und Ernterückständen an den untersuchten Emissionen wurden mittels 15N-markiertem Dünger ermittelt. Die Emissionsfaktoren der verschiedenen Düngerstufen lagen zwischen 0,9 und 1,7. Durch Düngerreduktion bzw. Zusatz von Nitrifikationshemmstoff wurde bei konstantem Ertrag die N2O-Freisetzung um 24 bzw 43% reduziert. Die Blumenkohlernterückstände verursachten 21% der Jahresemissionen und sorgten für hohe Winteremissionen, während Tau-Peaks kaum ausgeprägt waren
Resolution and enhancement in nanoantenna-based fluorescence microscopy
Single gold nanoparticles can act as nanoantennas for enhancing the
fluorescence of emitters in their near-fields. Here we present experimental and
theoretical studies of scanning antenna-based fluorescence microscopy as a
function of the diameter of the gold nanoparticle. We examine the interplay
between fluorescence enhancement and spatial resolution and discuss the
requirements for deciphering single molecules in a dense sample. Resolutions
better than 20 nm and fluorescence enhancement up to 30 times are demonstrated
experimentally. By accounting for the tip shaft and the sample interface in
finite-difference time-domain calculations, we explain why the measured
fluorescence enhancements are higher in the presence of an interface than the
values predicted for a homogeneous environment.Comment: 10 pages, 3 figures. accepted for publication in Nano Letter
Evoked itch perception is associated with changes in functional brain connectivity
Chronic itch, a highly debilitating condition, has received relatively little attention in the neuroimaging literature. Recent studies suggest that brain regions supporting itch in chronic itch patients encompass sensorimotor and salience networks, and corticostriatal circuits involved in motor preparation for scratching. However, how these different brain areas interact with one another in the context of itch is still unknown. We acquired BOLD fMRI scans in 14 atopic dermatitis patients to investigate resting-state functional connectivity before and after allergen-induced itch exacerbated the clinical itch perception in these patients. A seed-based analysis revealed decreased functional connectivity from baseline resting state to the evoked-itch state between several itch-related brain regions, particularly the insular and cingulate cortices and basal ganglia, where decreased connectivity was significantly correlated with increased levels of perceived itch. In contrast, evoked itch increased connectivity between key nodes of the frontoparietal control network (superior parietal lobule and dorsolateral prefrontal cortex), where higher increase in connectivity was correlated with a lesser increase in perceived itch, suggesting that greater interaction between nodes of this executive attention network serves to limit itch sensation via enhanced top-down regulation. Overall, our results provide the first evidence of itch-dependent changes in functional connectivity across multiple brain regions
Efficient coupling of photons to a single molecule and the observation of its resonance fluorescence
Single dye molecules at cryogenic temperatures display many spectroscopic
phenomena known from free atoms and are thus promising candidates for
fundamental quantum optical studies. However, the existing techniques for the
detection of single molecules have either sacrificed the information on the
coherence of the excited state or have been inefficient. Here we show that
these problems can be addressed by focusing the excitation light near to the
absorption cross section of a molecule. Our detection scheme allows us to
explore resonance fluorescence over 9 orders of magnitude of excitation
intensity and to separate its coherent and incoherent parts. In the strong
excitation regime, we demonstrate the first observation of the Mollow triplet
from a single solid-state emitter. Under weak excitation we report the
detection of a single molecule with an incident power as faint as 150 attoWatt,
paving the way for studying nonlinear effects with only a few photons.Comment: 6 figure
A 20-year prospective study of mortality and causes of death among hospitalized opioid addicts in Oslo
<p>Abstract</p> <p>Background</p> <p>To study mortality rate and causes of death among all hospitalized opioid addicts treated for self-poisoning or admitted for voluntary detoxification in Oslo between 1980 and 1981, and to compare their mortality to that of the general population.</p> <p>Methods</p> <p>A prospective cohort study was conducted on 185 opioid addicts from all medical departments in Oslo who were treated for either self-poisoning (<it>n </it>= 93, 1980), voluntary detoxification (<it>n </it>= 75, 1980/1981) or both (<it>n </it>= 17). Their median age was 24 years; with a range from 16 to 41, and 53% were males. All deaths that had occurred by the end of 2000 were identified from the Central Population Register. Causes of death were obtained from Statistics Norway. Standardized mortality ratios (SMRs) were computed for mortality, in general, and in particular, for different causes of death.</p> <p>Results</p> <p>During a period of 20 years, 70 opioid addicts died (37.8%), with a standardized mortality ratio (SMR) equal to 23.6 (95% CI, 18.7–29.9). The SMR remained high during the whole period, ranging from 32.4 in the first five-year period, to 13.4 in the last five-year period. There were no significant differences in SMR between self-poisonings and those admitted for voluntarily detoxification. The registered causes of death were accidents (11.4%), suicide (7.1%), cancer (4.3%), cardiovascular disease (2.9%), other violent deaths (2.9%), other diseases (71.4%). Among the 50 deaths classified as other diseases, the category "drug dependence" was listed in the vast majority of cases (37 deaths, 52.9% of the total). SMRs increased significantly for all causes of death, with the other diseases group having the highest SMR; 65.8 (95% CI, 49.9–86.9). The SMR was 5.4 (95% CI, 1.3–21.5) for cardiovascular diseases, and 4.3 (95% CI, 1.4–13.5) for cancer. The SMR was 13.2 (95% CI, 6.6–26.4) for accidents, 10.7 (95% CI, 4.5–25.8) for suicides, and 28.6 (95% CI, 7.1–114.4) for other violent deaths.</p> <p>Conclusion</p> <p>The risk of death among opioid addicts was significantly higher for all causes of death compared with the general population, implying a poor prognosis over a 20-year period for this young patient group.</p
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