Gated Mode Superconducting Nanowire Single Photon Detectors

Single Photon Detectors (SPD) are fundamental to quantum optics and quantum information. Superconducting Nanowire SPDs (SNSPD) [1] provide high performance in terms of quantum efficiency (QE), dark count rate (DCR) and timing jitter [2], but have limited maximum count rate (MCR) when operated as a free-running mode (FM) detector [3, 4]. However, high count rates are needed for many applications like quantum computing [5] and communication [6], and laser ranging [7]. Here we report the first operation of SNSPDs in a gated mode (GM) that exploits a single photon triggered latching phenomenon to detect photons. We demonstrate operation of a large active area single element GM-SNSPD at 625MHz, one order of magnitude faster than its FM counterpart. Contrary to FM-SNSPDs, the MCR in GM can be pushed to GHz range without a compromise on the active area or QE, while reducing the DCR

Свойства матрицы относительных летучестей многокомпонентных зеотропных и азеотропных смесей

Using definitions, concepts and the mathematical apparatus of linear algebra the basic regularities including the condition of azeotropy for the matrix of relative volatilities are considered in the paper.Ппривлечением понятий, определений и математического аппарата линейной алгебры рассмотрены основные свойства, в том числе условие азеотропии для матрицы относительных летучестей многокомпонентных смесей различной физико-химической природы

Spectral dependency of superconducting single photon detectors

International audienceWe investigate the effect of varying both incoming optical wavelength and width of NbN nanowires on the superconducting single photondetectors (SSPD) detection efficiency. The SSPD are current biased close to critical value and temperature fixed at 4.2 K, far from transition. The experimental results are found to verify with a good accuracy predictions based on the "hot spot model," whose size scales with the absorbed photon energy. With larger optical power inducing multiphoton detection regime, the same scaling law remains valid, up to the three-photon regime. We demonstrate the validity of applying a limited number of measurements and using such a simple model to reasonably predict any SSPD behavior among a collection of nanowire device widths at different photon wavelengths. These results set the basis for designing efficient single photondetectors operating in the infrared (2-5 μm range)

Диаграммы единичных α-линий в трехкомпонентных зеотропных и азеотропных смесях

Different properties and types of α-1-lines for ternary zeotropic mixtures and ternary mixtures with one binary azeotrope are presented in a brief literature review.Представлен обзор по вопросам, касающимся свойств, количества, типов и видов диаграмм единичных α-линий для трехкомпонентных зеотропных смесей и тройных смесей с одним бинарным азеотропом

Основные закономерности ректификации многокомпонентных смесей в режиме первого класса фракционирования

The basic regularities and some peculiarities of multicomponent mixtures rectification in the mode of the first class fractionalization are considered. Rectification trajectories are presented for ternary zeotropic mixtures for the case when the composition of initial mixture belongs to the α=1 manifold.Рассмотрены основные закономерности и некоторые особенности режима первого класса фракционирования при ректификации многокомпонентных смесей. Для случаев трех-компонентных зеотропных смесей приведены полные фазовые портреты траекторий ректификации первого класса фракционирования, когда состав исходной смеси принадлежит единичному α-многообразию

Эффективность массопереноса в процессе ректификации бинарных и многокомпонентных смесей

Different values describing both the efficiency of rectification column and the efficiency of mass-transfer are represented in the brief literature review. It is also showed that the approach used for the calculation of mass-transfer efficiency characteristics in binary mixtures is not very acceptable for multi-component mixtures.Представлен краткий литературный обзор, в котором описаны различные величины, характеризующие как эффективность работы ректификационной колонны, так и эффективность процесса массопереноса. Также показана ограниченность применения к многокомпонентным смесям подхода для расчета характеристик эффективности массопереноса, используемого для бинарных смесей

COMPARISON OF SOLVING A STIFF EQUATION ON A SPHERE BY THE MULTI-LAYER METHOD AND METHOD OF CONTINUING AT THE BEST PARAMETER

A stiff equation, linked with the solution of singularly perturbed differential equations with the use of standard methods of numeral solutions of simple differential equations often lead to major difficulties. First difficulty is the loss of stability of the counting process, when small errors on separate steps lead to an increase in the systematic errors in general. Another difficulty is, directly linked with the first one, consists of the need of decreasing the integrating step by a lot, which leads to a major decrease in the time taken for the calculations. On an example of a boundary value problem for a differential equation of second power on a sphere, comparison of our two approaches of constructing approximate values are held. The first approach is connected with the construction of an approximate multi-layer solution of the problem and is based on the use of recurrent equalities, that come out from classical numeral methods to the interval of a non-constant length. As a result, a numeral, approximated solution is replaced with an approximate solution in form of a function, which is easier to use for adaptation, building a graph and other needs. The second approach is linked with the continuation of the solutions by the best parameter. This method allows us to decrease majorly the number of steps and increase the stability of the computing process compared to standard methods

NUMERICAL METHODS FOR SOLVING PROBLEMS WITH CONTRAST STRUCTURES

In this paper, we investigate the features of the numerical solution of Cauchy problems for nonlinear differential equations with contrast structures (interior layers). Similar problems arise in the modeling of certain problems of hydrodynamics, chemical kinetics, combustion theory, computational geometry. Analytical solution of problems with contrast structures can be obtained only in particular cases. The numerical solution is also difficult to obtain. This is due to the ill conditionality of the equations in the neighborhood of the interior and boundary layers. To achieve an acceptable accuracy of the numerical solution, it is necessary to significantly reduce the step size, which leads to an increase of a computational complexity. The disadvantages of using the traditional explicit Euler method and fourth-order Runge-Kutta method, as well as the implicit Euler method with constant and variable step sizes are shown on the example of one test problem with two boundaries and one interior layers. Two approaches have been proposed to eliminate the computational disadvantages of traditional methods. As the first method, the best parametrization is applied. This method consists in passing to a new argument measured in the tangent direction along the integral curve of the considered Cauchy problem. The best parametrization allows obtaining the best conditioned Cauchy problem and eliminating the computational difficulties arising in the neighborhood of the interior and boundary layers. The second approach for solving the Cauchy problem is a semi-analytical method developed in the works of Alexander N. Vasilyev and Dmitry A. Tarkhov their apprentice and followers. This method allows obtaining a multilayered functional solution, which can be considered as a type of nonlinear asymptotic. Even at high rigidity, a semi-analytical method allows obtaining acceptable accuracy solution of problems with contrast structures. The analysis of the methods used is carried out. The obtained results are compared with the analytical solution of the considered test problem, as well as with the results of other authors