Analysis of detector performance in a gigahertz clock rate quantum key distribution system

We present a detailed analysis of a gigahertz clock rate environmentally robust phase-encoded quantum key distribution (QKD) system utilizing several different single-photon detectors, including the first implementation of an experimental resonant cavity thin-junction silicon single-photon avalanche diode. The system operates at a wavelength of 850 nm using standard telecommunications optical fibre. A general-purpose theoretical model for the performance of QKD systems is presented with reference to these experimental results before predictions are made about realistic detector developments in this system. We discuss, with reference to the theoretical model, how detector operating parameters can be further optimized to maximize key exchange rates

Enhancing the fill-factor of CMOS SPAD arrays using microlens integration

Arrays of single-photon avalanche diode (SPAD) detectors were fabricated, using a 0.35 μm CMOS technology process, for use in applications such as time-of-flight 3D ranging and microscopy. Each 150 x 150 μm pixel comprises a 30 μm active area diameter SPAD and its associated circuitry for counting, timing and quenching, resulting in a fill-factor of 3.14%. This paper reports how a higher effective fill-factor was achieved as a result of integrating microlens arrays on top of the 32 x 32 SPAD arrays. Diffractive and refractive microlens arrays were designed to concentrate the incoming light onto the active area of each pixel. A telecentric imaging system was used to measure the improvement factor (IF) resulting from microlens integration, whilst varying the f-number of incident light from f/2 to f/22 in one-stop increments across a spectral range of 500-900 nm. These measurements have demonstrated an increasing IF with fnumber, and a maximum of ~16 at the peak wavelength, showing a good agreement with theoretical values. An IF of 16 represents the highest value reported in the literature for microlenses integrated onto a SPAD detector array. The results from statistical analysis indicated the variation of detector efficiency was between 3-10% across the whole f-number range, demonstrating excellent uniformity across the detector plane with and without microlenses

Manipulating thermal light via displaced-photon subtraction

Thermal radiation played a pivotal role in the preliminary development of quantum physics where it helped resolve the apparent incongruity of the ultraviolet catastrophe. In contemporary physics, thermal state generation and manipulation finds new application in fields such as quantum imaging and quantum illumination and as a practical realization of Maxwell's demon. These applications often go hand in hand with photon subtraction operations which probabilistically amplify the mean photon number (MPN) of thermal light as a result of its super-Poissonian photon statistics. In this article, we introduce an operation for thermal states of light based on a generalized photon subtraction scheme. Displaced-photon subtraction (DPS) makes use of coherent state displacement followed by a subsequent anti-displacement in combination with single-photon detection to probe the MPN of a thermal state. We find regimes in which the output of a successful DPS is amplified, unchanged, or attenuated relative to the unconditioned output state. The regime of operation is controlled via the magnitude of the coherent displacement. A theoretical description of generalized photon subtraction of a displaced thermal state is derived via a two-mode moment-generating function (MGF) and used to describe generalized DPS. We perform a proof of principle experimental implementation of DPS for the case of a balanced beam splitter for which results demonstrate good agreement with the model

Whole-genome sequencing of a quarter-century melioidosis outbreak in temperate Australia uncovers a region of low-prevalence endemicity

This study was funded by the National Health and Medical Research Council via awards 1046812 and 1098337, and the Wellcome Trust Sanger Institute via award 098051. S.J.P. receives funding from the NIHR Cambridge Biomedical Research Centre.Melioidosis, caused by the highly recombinogenic bacterium Burkholderia pseudomallei, is a disease with high mortality. Tracing the origin of melioidosis outbreaks and understanding how the bacterium spreads and persists in the environment are essential to protecting public and veterinary health and reducing mortality associated with outbreaks. We used whole-genome sequencing to compare isolates from a historical quarter-century outbreak that occurred between 1966 and 1991 in the Avon Valley, Western Australia, a region far outside the known range of B. pseudomallei endemicity. All Avon Valley outbreak isolates shared the same multilocus sequence type (ST-284), which has not been identified outside this region. We found substantial genetic diversity among isolates based on a comparison of genome-wide variants, with no clear correlation between genotypes and temporal, geographical or source data. We observed little evidence of recombination in the outbreak strains, indicating that genetic diversity among these isolates has primarily accrued by mutation. Phylogenomic analysis demonstrated that the isolates confidently grouped within the Australian B. pseudomallei clade, thereby ruling out introduction from a melioidosis-endemic region outside Australia. Collectively, our results point to B. pseudomallei ST-284 being present in the Avon Valley for longer than previously recognized, with its persistence and genomic diversity suggesting long-term, low-prevalence endemicity in this temperate region. Our findings provide a concerning demonstration of the potential for environmental persistence of B. pseudomallei far outside the conventional endemic regions. An expected increase in extreme weather events may reactivate latent B. pseudomallei populations in this region.Publisher PDFPeer reviewe

Statin treatment and risk of recurrent venous thromboembolism: a nationwide cohort study

Statins may decrease the risk of primary venous thromboembolism (VTE), that is, deep vein thrombosis (DVT) and pulmonary embolism (PE) but the effect of statins in preventing recurrent VTE is less clear. The aim of this study was therefore to investigate the association between statin therapy and risk of recurrent VTE. A prospective cohort study. All hospitals in Denmark. All patients with a hospital diagnosis of VTE in Denmark during 1997-2009 associated with a warfarin or heparin prescription were identified. Adjusted HR of recurrent hospitalised VTE (ie, fatal or non-fatal DVT or PE) associated with use of statins. 44 330 patients with VTE were included in the study. Of these 3914 were receiving statin therapy at baseline. Patients receiving statins were older (68±11 compared to 62±18 years), had more comorbidity and used more medications. The incidence rate for recurrent VTE was 24.4 (95% CI 22.8 to 26.2) per 1000 person-years among statin users and 48.5 (95% CI 47.4 to 49.7) per 1000 person-years among non-statin users. Statin use was associated with a significantly lower risk of a recurrent VTE, adjusted HR 0.74 (95% CI 0.68 to 0.80), compared with no statin use. The association between statin use and risk of recurrent VTE was significantly affected by age. Among younger individuals (≤80 years), statin use was associated with lower risk of recurrent VTE, HR 0.70 (95% CI 0.65 to 0.76) whereas in older individuals (>80 years) statin use was significantly associated with higher risk of recurrent VTE, HR 1.28 (95% CI 1.02 to 1.60), p for interaction= <0.0001. Statin use was associated with a decreased risk of recurrent VT

Fertirrigação e agricultura de baixa emissão de carbono: resultados do projeto CNPq/REPENSA em São Gabriel do Oeste.

Este trabalho apresenta no âmbito do CNPq/REPENSA (Redes Nacionais de Pesquisa em Agrobiodiversidade e Sustentabilidade Agropecuária), Projeto número 562441/2010-7, ?Estruturação de rede de monitoramento e base compartilhada de dados de sistemas de produção integrada e intensiva sustentável (suinocultura-agrosilvipastoril) em assentamento de reforma agrária visando balanços favoráveis de água, energia e nutrientes?, informações norteadoras para projetos de fertirrigação para uma agricultura de baixa emissão de carbono. A fertirrigação vem se consolidando como atividade integradora de cadeias produtivas outrora dissociadas, sendo ferramenta importante de inclusão social no meio rural na borda do Pantanal (Bacia do Alto Taquari), transformando externalidades ambientais em fonte de renda e ganhos de produtividade agropecuária. Os resultados e indicadores aqui apresentados mostram que a fertirrigação com efluente de biodigestor de granjas de suínos, aqui convencionado de biofertilizante, gera impactos negativos e positivos. Os negativos recaem no potencial para eutrofização de corpos d?água por nitrogênio reativo na forma de nitratos (NO3); ambos os processos podem e devem ser substancialmente minimizados pelo uso controlado e eficiente do biofertilizante na agropecuária com doses adequadas de macro (especialmente N, P, K) e micronutrientes (Cu e Zn, entre outros) para diversasculturas, conforme discutido neste trabalho. Os impactos positivos são a manutenção do estoque de carbono no solo no longo prazo mediante manejo adequado da produção de forragem para gado (corte ou leite) ou na produção de grãos com tecnologias de conservação de solo, e o balanço favorável das emissões de gases de efeito estufa do agroecossistema como um todo pela substituição de diesel por biogás em motogeradores e motobombas, pela substituição da adubação mineral e de agrotóxicos (ambos não renováveis) e pela possibilidade de recomposição de mata proporcional à um terço dos ganhos de produtividade. Em termos de mecanismo de adaptação à mudança do clima, a restauração relativa de áreas de mata nativa favorece a recuperação e/ou manutenção de outros importantes serviços ambientais, como o aumento da agrobiodiversidade, a produção de água e incremento da polinização por insetos.bitstream/item/111107/1/BP116.pd

Quantum key distribution system in standard telecommunications fiber using a short wavelength single-photon source

A demonstration of the principles of quantum key distribution is performed using a single-photon source in a proof of concept test-bed over a distance of 2 km in standard telecommunications optical fiber. The single-photon source was an optically-pumped quantum dot in a microcavity emitting at a wavelength of 895 nm. Characterization of the quantum key distribution parameters was performed at a range of different optical excitation powers. An investigation of the effect of varying the optical excitation power of the quantum dot microcavity on the quantum bit error rate and cryptographic key exchange rate of the system are presented.Comment: Final manuscript version, some grammatical differences from the published version. 26 pages including 7 figures

Experimental demonstration of kilometer-range quantum digital signatures

We present an experimental realization of a quantum digital signature protocol which, together with a standard quantum key distribution link, increases transmission distance to kilometer ranges, three orders of magnitude larger than in previous realizations. The bit rate is also significantly increased compared with previous quantum signature demonstrations. This work illustrates that quantum digital signatures can be realized with optical components similar to those used for quantum key distribution and could be implemented in existing quantum optical fiber networks

Thrombolysis for massive pulmonary embolism in pregnancy: a case report

Mortality from pulmonary embolism (PE) in pregnancy might be related to challenges in targeting the right population for prevention. Such targeting could help ensure that the correct diagnosis is suspected and adequately investigated, and allow the initiation of the timely and best possible treatment of this disease. In the literature to date only 18 case reports of thrombolysis in pregnant women with PE have been reported, and showed beneficial effects for both mother and fetus in terms of mortality and complications with acceptable bleeding risks. We present here the case of a pregnant patient with massive PE who underwent successful thrombolysis. A 26-year-old pregnant (at 24 weeks) woman was admitted 4 h after onset of sudden acute dyspnea and chest pain. An immediate electrocardiogram showed a typical S1-Q3-T3 pattern. The echocardiogram showed a distended right ventricle with free-wall hypokinesia and displacement of the interventricular septum toward the left ventricle. Thrombolysis with recombinant tissue plasminogen activator (alteplase 10 mg bolus, then 90 mg over 2 h) was administered. Pelvic examination and ultrasound showed regular fetal heart beat, and regular placental and liquid presence. No problems developed for the mother or fetus in the subsequent days or at discharge. In conclusion, in pregnant patients with life-threatening massive PE, thrombolytic therapy can be administered, and the use of echocardiographic, laboratory, and clinical data can be useful tools to achieve a rapid diagnosis and make a therapeutic decision, but additional studies need to be performed to further define its use