High-yield fabrication of entangled photon emitters for hybrid quantum networking using high-temperature droplet epitaxy

Several semiconductor quantum dot techniques have been investigated for the generation of entangled photon pairs. Among the other techniques, droplet epitaxy enables the control of the shape, size, density, and emission wavelength of the quantum emitters. However, the fraction of the entanglement-ready quantum dots that can be fabricated with this method is still limited to around 5%, and matching the energy of the entangled photons to atomic transitions (a promising route towards quantum networking) remains an outstanding challenge. Here, we overcome these obstacles by introducing a modified approach to droplet epitaxy on a high symmetry (111)A substrate, where the fundamental crystallization step is performed at a significantly higher temperature as compared to previous reports. Our method drastically improves the yield of entanglement-ready photon sources near the emission wavelength of interest, which can be as high as 95% due to the low values of fine structure splitting and radiative lifetime, together with the reduced exciton dephasing offered by the choice of GaAs/AlGaAs materials. The quantum dots are designed to emit in the operating spectral region of Rb-based slow-light media, providing a viable technology for quantum repeater stations.Comment: 14 pages, 3 figure

Strain-Tunable GaAs Quantum dot: A Nearly Dephasing-Free Source of Entangled Photon Pairs on Demand

Entangled photon generation from semiconductor quantum dots via the biexciton-exciton cascade underlies various decoherence mechanisms related to the solid-state nature of the quantum emitters. So far, this has prevented the demonstration of nearly-maximally entangled photons without the aid of inefficient and complex post-selection techniques that are hardly suitable for quantum communication technologies. Here, we tackle this challenge using strain-tunable GaAs quantum dots driven under two-photon resonant excitation and with strictly-degenerate exciton states. We demonstrate experimentally that our on-demand source generates polarization-entangled photons with fidelity of 0.978(5) and concurrence of 0.97(1) without resorting to post-selection techniques. Moreover, we show that the remaining decoherence mechanisms can be overcome using a modest Purcell enhancement so as to achieve a degree of entanglement >0.99. Our results highlight that GaAs quantum dots can be readily used in advanced communication protocols relying on the non-local properties of quantum entanglement

Highly indistinguishable single photons from incoherently and coherently excited GaAs quantum dots

Semiconductor quantum dots are converging towards the demanding requirements of photonic quantum technologies. Among different systems, quantum dots with dimensions exceeding the free-exciton Bohr radius are appealing because of their high oscillator strengths. While this property has received much attention in the context of cavity quantum electrodynamics, little is known about the degree of indistinguishability of single photons consecutively emitted by such dots and on the proper excitation schemes to achieve high indistinguishability. A prominent example is represented by GaAs quantum dots obtained by local droplet etching, which recently outperformed other systems as triggered sources of entangled photon pairs. On these dots, we compare different single-photon excitation mechanisms, and we find (i) a "phonon bottleneck" and poor indistinguishability for conventional excitation via excited states and (ii) photon indistinguishablilities above 90% for both strictly resonant and for incoherent acoustic- and optical-phonon-assisted excitation. Among the excitation schemes, optical phonon-assisted excitation enables straightforward laser rejection without a compromise on the source brightness together with a high photon indistinguishability

Estimating credit and profit scoring of a Brazilian credit union with logistic regression and machine-learning techniques

Purpose – Although credit unions are nonprofit organizations, their objectives depend on the efficient management of their resources and credit risk aligned with the principles of the cooperative doctrine. This paper aims to propose the combined use of credit scoring and profit scoring to increase the effectiveness of the loan-granting process in credit unions. Design/methodology/approach – This sample is composed by the data of personal loans transactions of a Brazilian credit union. Findings – The analysis reveals that the use of statistical methods improves significantly the predictability of default when compared to the use of subjective techniques and the superiority of the random forests model in estimating credit scoring and profit scoring when compared to logit and ordinary least squares method (OLS) regression. The study also illustrates how both analyses can be used jointly for more effective decision-making. Originality/value – Replacing subjective analysis with objective credit analysis using deterministic models will benefit Brazilian credit unions. The credit decision will be based on the input variables and on clear criteria, turning the decision-making process impartial. The joint use of credit scoring and profit scoring allows granting credit for the clients with the highest potential to pay debt obligation and, at the same time, to certify that the transaction profitability meets the goals of the organization: to be sustainable and to provide loans and investment opportunities at attractive rates to members

High voltage pulsed stimulation increases cicatrization of chronic cutaneous ulcers: analysis of six cases

The treatment of cutaneous ulcers by electrical stimulation in clinical practice has grown, however there are few studies investigating the effectiveness of these individual resources in monitoring and complete healing of the lesions. Thus, High Voltage Pulsed Stimulation (HVPS) was used in chronic skin ulcers with the aim of reduce the area of the lesion. Four male subjects with chronic cutaneous ulcers participated in the study. The treatment of the injury consisted on HVPS application (15 microseconds, 100/150 V, 100 Hz) for 30 minutes, 2 times weekly. The electrode with negative polarity was placed on the lesion and positive on vascular path. The ulcers were assessed pre and post-intervention by photogrammetry, and it was calculated the area of the lesion. As a result, we observed the complete healing in the subjects I and II (respectively, area of 4.66 cm² to 0 after 21 sessions and 1.74 cm² to 0 after 16 sessions). The area of subject III right ulcer obtained reduction of 93% after 100° session (2.02 to 0.14 cm²) and left ulcer obtained reduction of 80.40% (2.50 to 0.49 cm²). In subject IV there was a complete healing of the sacral lesion after 75 sessions (10.74 cm² to 0) and decrease sciatic lesion of 11.01 to 2.43 cm². Thus we conclude that HVPS facilitated the healing process of stimulated ulcers because the areas of all ulcers had decreased more than 78%, and in three of them there was complete healing.O tratamento de úlceras cutâneas por estimulação elétrica tem crescido na prática clínica, no entanto, faltam estudos que investiguem a efetividade desse recurso em acompanhamento prolongado ou até que ocorra a cicatrização completa das lesões. Assim, a estimulação elétrica de alta voltagem (EEAV) foi aplicada em úlceras cutâneas crônicas com o objetivo de reduzir a área da lesão. Para tanto, participaram do estudo quatro homens que apresentavam seis úlceras cutâneas que receberam a EEAV (fase=15ms; F=100 Hz; T: 100 a 150 V; fases gêmeas), 2 vezes por semana, durante 30 minutos. O eletrodo com polaridade negativa foi colocado sobre a lesão e o positivo no trajeto vascular. As úlceras foram avaliadas pré e pós-intervenção por meio da fotogrametria, sendo calculada a área da lesão. Como resultado, observamos o fechamento completo da lesão nos sujeitos I e II (área de 4,66 cm² para 0 após 21 sessões e de 1,74 cm² para 0 após 16 sessões, respectivamente). O sujeito III obteve redução de 93% na área da lesão direita (de 2,02 para 0,14 cm²) e na esquerda de 80,40% (de 2,50 para 0,49 cm²), após 100 sessões. No sujeito IV ocorreu o fechamento completo da lesão sacral (de 10,74 cm² para 0) e a redução da lesão isquiática de 11,01 para 2,43 cm², após 75 sessões. Desse modo, concluímos que a EEAV facilitou o processo de cicatrização das úlceras estimuladas, pois as áreas de todas as úlceras apresentaram diminuição superior a 78%, havendo cicatrização completa em três delas.El tratamiento de úlceras cutáneas con el uso de estimulación eléctrica tiene crecido en la práctica clínica, pero no hay muchos estudios que investigaron la efectividad de eso recurso en el acompañamiento prolongado o hasta la ocurrencia de la cicatrización completa de las lesiones. Así, la estimulación eléctrica de alto voltaje (EEAV) fue aplicada en úlceras cutáneas crónicas con el objetivo de reducir la área de la lesión. Para eso, cuatro hombres con seis úlceras cutáneas crónicas participaron del estudio, los cuales habían recibido la EEAV (fase=15ms; F=100 Hz; T: el 100 al 150 V; fases), dos veces por semana, por 30 minutos. Lo electrodo con polaridad negativa fue posicionado sobre la lesión y lo positivo en el trayecto vascular. Las úlceras fueron evaluadas antes y después de la intervención por medio de la fotogrametría, y la área de la lesión fue calculada. Se observó, como resultado, el cierre completo de la lesión en los sujetos I y II (área de 4,66 cm² para 0 después de 21 sesiones y de 1,74 cm² para 0 después de 16 sesiones, respectivamente). El sujeto III obtuvo reducción del 93% en el local de la lesión derecha (de 2,02 para 0,14 cm²) y en la izquierda del 80,40% (del 2,50 para 0,49 cm²) después de 100 sesiones. El cierre completo de la lesión del sacro (del 10,74 cm² para 0) y la reducción de la isquiática del 11,01 para 2,43 cm² ocurrieron en el sujeto IV después de 75 sesiones. Por lo tanto, se concluyo que la EEAV ha facilitado el proceso de cicatrización de las úlceras estimuladas, pues las áreas de todas las úlceras presentaron disminución superior al 78% con cicatrización completa en tres de ellas.28629

Phonon-Assisted Two-Photon Interference from Remote Quantum Emitters

Photonic quantum technologies are on the verge of finding applications in everyday life with quantum cryptography and quantum simulators on the horizon. Extensive research has been carried out to identify suitable quantum emitters and single epitaxial quantum dots have emerged as near-optimal sources of bright, on-demand, highly indistinguishable single photons and entangled photon-pairs. In order to build up quantum networks, it is essential to interface remote quantum emitters. However, this is still an outstanding challenge, as the quantum states of dissimilar “artificial atoms” have to be prepared on-demand with high fidelity and the generated photons have to be made indistinguishable in all possible degrees of freedom. Here, we overcome this major obstacle and show an unprecedented two-photon interference (visibility of 51 ± 5%) from remote strain-tunable GaAs quantum dots emitting on-demand photon-pairs. We achieve this result by exploiting for the first time the full potential of a novel phonon-assisted two-photon excitation scheme, which allows for the generation of highly indistinguishable (visibility of 71 ± 9%) entangled photon-pairs (fidelity of 90 ± 2%), enables push-button biexciton state preparation (fidelity of 80 ± 2%) and outperforms conventional resonant two-photon excitation schemes in terms of robustness against environmental decoherence. Our results mark an important milestone for the practical realization of quantum repeaters and complex multiphoton entanglement experiments involving dissimilar artificial atoms

Combustion of Sugarcane Bagasse Pellets Produced with/without Glycerol: Chemical, Thermal and Emission Analyses

Purpose: Use of agricultural biomass in the form of pellets has gained worldwide prominence in recent decades, as part of the search for cleaner and renewable energy sources. Brazil is the largest sugarcane producer in the world, a fact that also places it as a major producer of residues from processing this crop. Methods: In this study, sugarcane bagasse pellets (SBP100) were handcrafted using glycerol as binder (30% - SBP30G) and, subsequently, analyses of their chemical and thermal properties, as well as those of the thermal decomposition exhaust gases, were conducted. Results: Average temperatures in the combustion range were 213.62±137.07° C (SBP100) and 211.97±86.85 °C (SBP30G). Combustion exhaust gas values were 20.04±0.15% (SBP100) and 19.95±0.19% (SBP30G) for O2; 1739.58±156.17 ppm (SBP100) and 1575±466.85 ppm (SBP30G) for CO; 19.92 ± 2.47 ppm (SBP100) and 17.33±4.69 ppm (SBP30G) for NOx; 341.67±134.37 ppm (SBP100) and 491.67±341.42 ppm (SBP30G) for CH4. SBP30G combustion proved to be less polluting with respect to CO and NOx generation than SBP100, but not for CH4. However, average thermal performance was similar for both. Conclusion: Use of glycerol contributed considerably to the changes in the pellets’ physical parameters. Exhaust gas analyses of the combustion of these substrates can serve as a basis for creating safety parameters and public policies to regulate the use of biomass for energy purposes

MamoSite® RTS

Resumo: Pretende-se analisar o procedimento da técnica MammoSite® RTS, assim como as suas vantagens e desvantagens, através de uma pesquisa bibliográfica. Verificou-se que é uma técnica relativamente simples e com melhores resultados, quando comparada com outras técnicas de tratamento. No entanto é importante continuar a investigar, para que se possa comprovar a sua eficácia. Introdução/Objectivos: A técnica MammoSite® RTS é utilizada no tratamento de doentes com carcinomas da mama em estadios precoces (T1/T2 e N0 ou N1), previamente submetidas a lumpectomia e dissecação ganglionar. Esta é uma técnica relativamente recente e que introduz uma nova abordagem da radiação aos tecidos adjacentes à loca tumoral. Pretende-se compreender o procedimento necessário à realização desta técnica, bem com as suas principais vantagens e desvantagens

High yield and ultrafast sources of electrically triggered entangled-photon pairs based on strain-tunable quantum dots

Triggered sources of entangled photon pairs are key components in most quantum communication protocols. For practical quantum applications, electrical triggering would allow the realization of compact and deterministic sources of entangled photons. Entangled-light-emitting-diodes based on semiconductor quantum dots are among the most promising sources that can potentially address this task. However, entangled-light-emitting-diodes are plagued by a source of randomness, which results in a very low probability of finding quantum dots with sufficiently small fine structure splitting for entangled-photon generation (∼10−2). Here we introduce strain-tunable entangled-light-emitting-diodes that exploit piezoelectric-induced strains to tune quantum dots for entangled-photon generation. We demonstrate that up to 30% of the quantum dots in strain-tunable entangled-light-emitting-diodes emit polarization-entangled photons. An entanglement fidelity as high as 0.83 is achieved with fast temporal post selection. Driven at high speed, that is 400 MHz, strain-tunable entangled-light-emitting-diodes emerge as promising devices for high data-rate quantum applications