Numerical Optimization of a Nanophotonic Cavity by Machine Learning for Near-Unity Photon Indistinguishability at Room Temperature.

Room-temperature (RT), on-chip deterministic generation of indistinguishable photons coupled to photonic integrated circuits is key for quantum photonic applications. Nevertheless, high indistinguishability (I) at RT is difficult to obtain due to the intrinsic dephasing of most deterministic single-photon sources (SPS). Here, we present a numerical demonstration of the design and optimization of a hybrid slot-Bragg nanophotonic cavity that achieves a theoretical near-unity I and a high coupling efficiency (ß) at RT for a variety of single-photon emitters. Our numerical simulations predict modal volumes in the order of 10-3(λ/2n)3, allowing for strong coupling of quantum photonic emitters that can be heterogeneously integrated. We show that high I and ß should be possible by fine-tuning the quality factor (Q) depending on the intrinsic properties of the single-photon emitter. Furthermore, we perform a machine learning optimization based on the combination of a deep neural network and a genetic algorithm (GA) to further decrease the modal volume by almost 3 times while relaxing the tight dimensions of the slot width required for strong coupling. The optimized device has a slot width of 20 nm. The design requires fabrication resolution in the limit of the current state-of-the-art technology. Also, the condition for high I and ß requires a positioning accuracy of the quantum emitter at the nanometer level. Although the proposal is not a scalable technology, it can be suitable for experimental demonstration of single-photon operation.

Enhancement of the indistinguishability of single photon emitters coupled to photonic waveguides.

One of the main steps towards large-scale quantum photonics consists of the integration of single photon sources (SPS) with photonic integrated circuits (PICs). For that purpose, the PICs should offer an efficient light coupling and a high preservation of the indistinguishability of photons. Therefore, optimization of the indistinguishability through waveguide design is especially relevant. In this work we have developed an analytical model that uses the Green's Dyadic of a 3D unbounded rectangular waveguide to calculate the coupling and the indistinguishability of an ideal point-source quantum emitter coupled to a photonic waveguide depending on its orientation and position. The model has been numerically evaluated through finite-difference time-domain (FDTD) simulations showing consistent results. The maximum coupling is achieved when the emitter is embedded in the center of the waveguide but somewhat surprisingly the maximum indistinguishability appears when the emitter is placed at the edge of the waveguide where the electric field is stronger due to the surface discontinuity.

Onychomadesis outbreak linked to hand, foot, and mouth disease, Spain, July 2008.

In July 2008 an onychomadesis outbreak in a nursery setting was reported in Saragossa (Spain). Some of the cases had previously suffered from hand, foot and mouth disease (HFMD). In order to study the outbreak and to determine the relation between the two diseases, two epidemiological studies were conducted: a descriptive study focused on cases and a retrospective cohort study. Samples from stool, pharynx and nails were obtained from cases for microbiological analysis. During the study period, 27 children fulfilled the case definition. The average age was 1.8 years. A case shed on average four nails (minimum one maximum twelve). Twenty-four of the 27 cases had previously presented with HFMD which started an average of 40 days before the onset of onychomadesis (relative risk: 14). Unidentified non-polio enterovirus (n=10), coxsackie B1 (n=4) and coxsackie B2 virus (n=3) were isolated in 28 specimens obtained from 14 cases. The analysis showed a strong association between HMFD and onychomadesis. Microbiological results have not been conclusive; consequently more studies are necessary to determine the causal agent of infectious onychomadesis.

[Outbreak of Legionnaires' disease in a private apartment building]. / Brote de enfermedad de los legionarios en un edificio de viviendas particulares.

BACKGROUND: An outbreak of legionnaires disease occurred in Zaragoza (Spain) in an uncommon environment such as a private apartment building was studied. METHODS: The investigation began upon notification of 3 patients admitted with pneumonia, living in the same apartment building. The suggestion of a common source of infection led to an active search for cases and a micro-environmental study of the zone where the patients lived, as well as a follow up study of other cases with hospital acquired pneumonia throughout the city. RESULTS: Six cases were detected over 9 days with a rate of 1.54%. The evolution of all the cases was favorable. The causal agent was serologically identified as Legionella pneumophilia serogroup 1 which was also found in the shower of one of the patient's bath with further confirmation that the strain isolated belonged to the Pontiac subgroup. CONCLUSIONS: The probable source of infection was the potable water. The stagnation, low temperature of the boiler and the under-chlorination of the water are factors which may have contributed to the appearance of this outbreak. The control of this type of outbreak must be based on a specific information system which treats this disease as requiring individualized declaration.