Quasi-BIC Resonant Enhancement of Second-Harmonic Generation in WS2 Monolayers.

Atomically thin monolayers of transition metal dichalcogenides (TMDs) have emerged as a promising class of novel materials for optoelectronics and nonlinear optics. However, the intrinsic nonlinearity of TMD monolayers is weak, limiting their functionalities for nonlinear optical processes such as frequency conversion. Here we boost the effective nonlinear susceptibility of a TMD monolayer by integrating it with a resonant dielectric metasurface that supports pronounced optical resonances with high quality factors: bound states in the continuum (BICs). We demonstrate that a WS2 monolayer combined with a silicon metasurface hosting BICs exhibits enhanced second-harmonic intensity by more than 3 orders of magnitude relative to a WS2 monolayer on top of a flat silicon film of the same thickness. Our work suggests a pathway to employ high-index dielectric metasurfaces as hybrid structures for enhancement of TMD nonlinearities with applications in nonlinear microscopy, optoelectronics, and signal processing

Thermochemiluminescent peroxide crystals

Chemiluminescence, a process of transduction of energy stored within chemical bonds of ground-state reactants into light via high-energy excited intermediates, is known in solution, but has remained undetected in macroscopic crystalline solids. By detecting thermally induced chemiluminescence from centimeter-size crystals of an organic peroxide here we demonstrate direct transduction of heat into light by thermochemiluminescence of bulk crystals. Heating of crystals of lophine hydroperoxide to ~115 °C results in detectable emission of blue-green light with maximum at 530 nm with low chemiluminescent quantum yield [(2.1 ± 0.1) × 10 ‒7 E mol ‒1 ]. Spectral comparison of the thermochemiluminescence in the solid state and in solution revealed that the solid-state thermochemiluminescence of lophine peroxide is due to emission from deprotonated lophine. With selected 1,2-dioxetane, endoperoxide and aroyl peroxide we also establish that the thermochemiluminescence is common for crystalline peroxides, with the color of the emitted light varying from blue to green to red

Quantum walks: a comprehensive review

Quantum walks, the quantum mechanical counterpart of classical random walks, is an advanced tool for building quantum algorithms that has been recently shown to constitute a universal model of quantum computation. Quantum walks is now a solid field of research of quantum computation full of exciting open problems for physicists, computer scientists, mathematicians and engineers. In this paper we review theoretical advances on the foundations of both discrete- and continuous-time quantum walks, together with the role that randomness plays in quantum walks, the connections between the mathematical models of coined discrete quantum walks and continuous quantum walks, the quantumness of quantum walks, a summary of papers published on discrete quantum walks and entanglement as well as a succinct review of experimental proposals and realizations of discrete-time quantum walks. Furthermore, we have reviewed several algorithms based on both discrete- and continuous-time quantum walks as well as a most important result: the computational universality of both continuous- and discrete- time quantum walks.Comment: Paper accepted for publication in Quantum Information Processing Journa

Mesopause region semidiurnal tide over Europe as seen from ground-based wind measurements

Wind measurements carried out at 6 European sites are investigated to set up a climatology of the semidiurnal tide in the mesopause region over Europe for the latitudinal range between 50°N and 56°N. Intercomparison of amplitudes and phases generally shows good agreement of the results from the different measuring systems. The longitudinal variation of the semidiurnal tide is small. The results are compared with an empirical model of the semidiurnal tide

Гидродинамика теплоносителя в активной зоне реактора PWR с ТВС-Квадрат разных конструкций

. The paper presents the results of experimental studies of the hydrodynamics of the coolant in the core of the PWR reactor with fuel assemblies “TVS-Kvadrat” of various designs. Experimental studies of hydrodynamics consisted in studying the velocity fields and the process of cross-flow of coolant between adjacent fuel assemblies “TVS-Kvadrat” of various designs in homogeneous and mixed cores on large-scale experimental models, including fragments of two adjacent fuel assemblies “TVS-Kvadrat” and a gap between them. The test models differ in the number of installed grids, this is due to the fact that in a homogeneous core the hydraulic load along the height of the fuel assemblies is identical, and in a mixed core the hydraulic load is uneven due to the different number of installed grids. The hydrodynamics of the coolant has been studied on an aerodynamic open-loop based on the theory of hydrodynamic similarity, using individually calibrated pneumometric sensors. Based on the data obtained, the fields of local axial and transverse velocities in various sections along the length of the studied section of the test models have been constructed. The fields of local dimensionless transverse and axial flow velocities in the fuel bundles and the gap between the fuel assemblies “TVS-Kvadrat” of the PWR reactor core have been studied. Peculiarities of the process of transverse flow between adjacent “TVS-Kvadrat” of a homogeneous and the mixed core of the PWR reactor have been revealed. The results of experimental studies have been transferred to the developer of “TVS-Kvadrat”, that is  JSC “Experimental Design Bureau of Mechanical Engineering named after I. I. Afrikantov”,  for further use in justifying the design and operating modes of a nuclear power plant.  В статье приведены результаты экспериментальных исследований гидродинамики теплоносителя в активной зоне реактора PWR c ТВС-Квадрат разных конструкций. Экспериментальные исследования гидродинамики заключались в изучении полей скоростей и процесса поперечного перетекания теплоносителя между соседними ТВС-Квадрат разных конструкций в однородной и смешанной активных зонах на масштабных экспериментальных моделях, включающих в себя фрагменты двух соседних ТВС-Квадрат и зазор между ними. Экспериментальные модели отличаются количеством установленных решеток. Это обусловлено тем, что в однородной активной зоне гидравлическая нагрузка по высоте ТВС идентична, а в смешанной – неравномерна из-за разного количества установленных решеток. Гидродинамика теплоносителя изучалась на аэродинамическом исследовательском стенде с учетом теории гидродинамического подобия с использованием пневмометрических датчиков с индивидуальной тарировкой. На основании полученных данных построены поля локальных осевых и поперечных скоростей в различных сечениях по длине исследуемого участка экспериментальных моделей. Изучены поля локальных безразмерных поперечных и аксиальных скоростей потока в твэльных пучках и зазоре между ТВС-Квадрат активной зоны реактора PWR. Выявлены особенности процесса поперечного перетекания потока между соседними ТВС-Квадрат однородной и смешанной активной зон реактора PWR. Результаты экспериментальных исследований переданы разработчику ТВС-Квадрат АО «ОКБМ Африкантов» для дальнейшего использования при обосновании конструкции и режимов работы ядерной энергетической установки

Исследование локальной гидродинамики теплоносителя в смешанной активной зоне реактора ВВЭР

The article presents the results of experimental studies of the local hydrodynamics of the coolant flow in the mixed core of the VVER reactor, consisting of the TVSA-T and TVSA-T mod.2 fuel assemblies. Modeling of the flow of the coolant flow in the fuel rod bundle was carried out on an aerodynamic test stand. The research was carried out on a model of a fragment of a mixed core of a VVER reactor consisting of one TVSA-T segment and two segments of the TVSA-T.mod2. The flow pressure fields were measured with a five-channel pneumometric probe. The flow pressure field was converted to the direction and value of the coolant velocity vector according to the dependencies obtained during calibration. To obtain a detailed data of the flow, a characteristic cross-section area of the model was selected, including the space cross flow between fuel assemblies and four rows of fuel rods of each of the TVSA fuel assemblies. In the framework of this study the analysis of the spatial distribution of the projections of the velocity of the coolant flow was fulfilled that has made it possible to pinpoint regularities that are intrinsic to the coolant flowing around spacing, mixing and combined spacing grates of the TVSA. Also, the values of the transverse flow of the coolant caused by the flow along hydraulically nonidentical grates were determined and their localization in the longitudinal and cross sections of the experimental model was revealed. Besides, the effect of accumulation of hydrodynamic flow disturbances in the longitudinal and cross sections of the model caused by the staggered arrangement of hydraulically non-identical grates was determined. The results of the study of the coolant cross flow between fuel assemblies interaction, i.e. between the adjacent TVSA-T and TVSA-T mod.2 fuel assemblies were adopted for practical use in the JSC of “Afrikantov OKB Mechanical Engineering” for assessing the heat engineering reliability of VVER reactor cores; also, they were included in the database for verification of computational hydrodynamics programs (CFD codes) and for detailed cell-based calculation of the reactor core.В статье представлены результаты экспериментальных исследований локальной гидродинамики потока теплоносителя в смешанной активной зоне реактора ВВЭР, состоящей из ТВСА-Т и ТВСА-Т.mod.2. Моделирование процессов течения потока теплоносителя в пучке твэлов проводилось на аэродинамическом стенде. Исследования осуществлялись на модели фрагмента смешанной активной зоны реактора ВВЭР, состоящей из одного сегмента ТВСА-Т и двух ТВСА-Т.mod.2. Поля давлений потока измеряли пятиканальным пневмометрическим зондом. Поле давлений потока согласно зависимостям, полученным при тарировке, пересчитывалось в направление и величину вектора скорости теплоносителя. Для создания детальной картины течения потока была выделена характерная область поперечного сечения модели, включающая межкассетное пространство и четыре ряда твэлов каждой из топливных сборок ТВСА. В рамках реализации данного исследования проведен анализ пространственного распределения проекций скорости потока теплоносителя, который позволил выявить закономерности обтекания теплоносителем дистанционирующих, перемешивающих и комбинированных дистанционирующих решеток ТВСА, определены величины поперечных потоков теплоносителя, вызванных обтеканием гидравлически неидентичных решеток, установлена их локализация в продольном и поперечном сечениях экспериментальной модели. Кроме того, выявлен эффект накопления гидродинамических возмущений потока в продольном и поперечном сечениях модели, вызванный шахматным расположением гидравлически неидентичных решеток. Результаты исследования межкассетного взаимодействия теплоносителя между соседними ТВСА-Т и ТВСА-Т.mod.2 приняты для практического использования в АО «ОКБМ Африкантов» при оценке теплотехнической надежности активных зон реакторов ВВЭР и включены в базу данных для верификации программ вычислительной гидродинамики (CFD-кодов) и детального поячеечного расчета активной зоны реакторов

On-chip generation of high-dimensional entangled quantum states and their coherent control

Optical quantum states based on entangled photons are essential for solving questions in fundamental physics and are at the heart of quantum information science1. Specifically, the realization of high-dimensional states (D-level quantum systems, that is, qudits, with D > 2) and their control are necessary for fundamental investigations of quantum mechanics2, for increasing the sensitivity of quantum imaging schemes3, for improving the robustness and key rate of quantum communication protocols4, for enabling a richer variety of quantum simulations5, and for achieving more efficient and error-tolerant quantum computation6. Integrated photonics has recently become a leading platform for the compact, cost-efficient, and stable generation and processing of non-classical optical states7. However, so far, integrated entangled quantum sources have been limited to qubits (D = 2)8, 9, 10, 11. Here we demonstrate on-chip generation of entangled qudit states, where the photons are created in a coherent superposition of multiple high-purity frequency modes. In particular, we confirm the realization of a quantum system with at least one hundred dimensions, formed by two entangled qudits with D = 10. Furthermore, using state-of-the-art, yet off-the-shelf telecommunications components, we introduce a coherent manipulation platform with which to control frequency-entangled states, capable of performing deterministic high-dimensional gate operations. We validate this platform by measuring Bell inequality violations and performing quantum state tomography. Our work enables the generation and processing of high-dimensional quantum states in a single spatial mode