Optical refrigeration with coupled quantum wells

Refrigeration of a solid-state system with light has potential applications for cooling small-scale electronics and photonics. We show theoretically that two coupled semiconductor quantum wells are efficient cooling media for optical refrigeration because they support long-lived indirect electron-hole pairs. Thermal excitation of these pairs to distinct higher-energy states with faster radiative recombination allows an efficient escape channel to remove thermal energy from the system. This allows reaching much higher cooling efficiencies than with single quantum wells. From band-diagram calculations along with an experimentally realistic level scheme we calculate the cooling efficiency and cooling yield of different devices with coupled quantum wells embedded in a suspended nanomembrane. The dimension and composition of the quantum wells allow optimizing either of these quantities, which cannot, however, be maximized simultaneously. Quantum-well structures with electrical control allow tunability of carrier lifetimes and energy levels so that the cooling efficiency can be optimized over time as the thermal population decreases due to the cooling.Comment: 10 pages, 5 figure

Заболеваемость желудочно-кишечного тракта у детей Республики Молдова

The article presents the morbidity analysis of gastrointestinal pathologies among the children’s population in Moldova during the period of 2006-2011 in terms of statistical indicators of such digestive diseases as gastritis and duodenitis, gallstones, pancreatitis, stomach and duodenal ulcers as well as inflammatory bowel diseases (ulcerative colitis and Crohn’s disease). The data of National Bureau of Statistics, National Center of Health Management and other investigations, containing official data, have been used. During these 5 years both the prevalence and incidence of the digestive pathologies were rising, taking the second and the third places in the rating of the first three nosologies being after respiratory diseases and injuries. Yet, the trigger factors as well as the relapses of gastrointestinal and hepatobiliary diseases remain completely neglected in clinical assessments and in the management of children’s behaviour. Thus, maintaining the health of children is crucial to the health condition and longevity of future adults. After the multidimensional analysis of the indicators a number of proposals have been outlined to reduce the level of digestive diseases morbidity.В статье приводится анализ патологий желудочно-кишечного тракта у детей Республики Молдова на период 2006-2011 гг. Использованы статистические показатели таких пищеварительных заболеваний как гастрит, язва желудка и двенадцатиперстной кишки, желчно-каменная болезнь, панкреатит, язва и воспалительные заболевания кишечника (язвенный колит и болезнь Крона). Задействованы данные Национального Бюро Статистики, Национального Центра Менеджмента Здравоохранения, а также результаты других исследований, содержащих официальные данные. На протяжении этих 5-ти лет, как распространенность, так и рост заболеваемости патологиями пищеварительной системы постоянно увеличиваются, занимая вторую и третью позиции после заболеваний дыхательных путей и травм в рейтинге первых трех нозологий. Несмотря на это, факторы вызывающие данные патологии, а также рецидивирующие желудочно-кишечные и гепатобилиарные заболевания остаются полностью без внимания в. клинических исследованиях и, соответственно, терапевтическое поведение детей не корректируется должным образом. А поддержание здоровья ребенка является решающим для состояния здоровья и долголетия будущего взрослого. После многомерного анализа показателей приведен ряд предложений для снижения порога заболеваемости пищеварительными патологиями

Chirality of nanophotonic waveguide with embedded quantum emitter for unidirectional spin transfer

Scalable quantum technologies may be achieved by faithful conversion between matter qubits and photonic qubits in integrated circuit geometries. Within this context, quantum dots possess well-defined spin states (matter qubits), which couple efficiently to photons. By embedding them in nanophotonic waveguides, they provide a promising platform for quantum technology implementations. In this paper, we demonstrate that the naturally occurring electromagnetic field chirality that arises in nanobeam waveguides leads to unidirectional photon emission from quantum dot spin states, with resultant in-plane transfer of matter-qubit information. The chiral behaviour occurs despite the non-chiral geometry and material of the waveguides. Using dot registration techniques, we achieve a quantum emitter deterministically positioned at a chiral point and realize spin-path conversion by design. We further show that the chiral phenomena are much more tolerant to dot position than in standard photonic crystal waveguides, exhibit spin-path readout up to 95±5% and have potential to serve as the basis of spin-logic and network implementations

Reinforcement Learning with Neural Networks for Quantum Feedback

Artificial neural networks are revolutionizing science. While the most prevalent technique involves supervised training on queries with a known correct answer, more advanced challenges often require discovering answers autonomously. In reinforcement learning, control strategies are improved according to a reward function. The power of this approach has been highlighted by spectactular recent successes, such as playing Go. So far, it has remained an open question whether neural-network-based reinforcement learning can be successfully applied in physics. Here, we show how to use this method for finding quantum feedback schemes, where a network-based "agent" interacts with and occasionally decides to measure a quantum system. We illustrate the utility by finding gate sequences that preserve the quantum information stored in a small collection of qubits against noise. This specific application will help to find hardware-adapted feedback schemes for small quantum modules while demonstrating more generally the promise of neural-network based reinforcement learning in physics