Quantum gates between capacitively coupled double quantum dot two-spin qubits

We study the two-qubit controlled-not gate operating on qubits encoded in the spin state of a pair of electrons in a double quantum dot. We assume that the electrons can tunnel between the two quantum dots encoding a single qubit, while tunneling between the quantum dots that belong to different qubits is forbidden. Therefore, the two qubits interact exclusively through the direct Coulomb repulsion of the electrons. We find that entangling two-qubit gates can be performed by the electrical biasing of quantum dots and/or tuning of the tunneling matrix elements between the quantum dots within the qubits. The entangling interaction can be controlled by tuning the bias through the resonance between the singly-occupied and doubly-occupied singlet ground states of a double quantum dot.Comment: 12 pages, 7 figure

Kohn anomalies in momentum dependence of magnetic susceptibility of some three-dimensional systems

We study a question of presence of Kohn points, yielding at low temperatures non-analytic momentum dependence of magnetic susceptibility near its maximum, in electronic spectum of some three-dimensional systems. In particular, we consider one-band model on face centered cubic lattice with hopping between nearest and next-nearest neighbors, which models some aspects of the dispersion of ZrZn$_2$, and the two-band model on body centered cubic lattice, modeling the dispersion of chromium. For the former model it is shown that Kohn points yielding maxima of susceptibility exist in a certain (sufficiently wide) region of electronic concentrations; the dependence of the wave vectors, corresponding to the maxima, on the chemical potential is investigated. For the two-band model we show existence of the lines of Kohn points, yielding maximum of the susceptibility, which position agrees with the results of band structure calculations and experimental data on the wave vector of antiferromagnetism of chromium.Comment: 13 pages, 9 figures. JETP, in press (2017

To the iconography of the saint warrior horseman in the Byzantine sphragistics of the 12th - 13th centuries. Saint demetrios of Thessalonika

Introduction. The images of holy warriors were extremely popular in the art of Byzantium and the countries of the Byzantine cultural circle of the 11th - 14th centuries. They are known for numerous images in iconography, monumental painting, applied art. They are numerous in sphragistics. The image of a warrior horseman best known for the early 13th century monuments is the rarest and most recent formation. Introducing new sigilographic monuments into the scientific circulation and determining the time of appearance of this iconographic type on their basis are among the main goals of the proposed research. Methods. The methodological basis of the study is an interdisciplinary integrated approach that involves using methods of the comparative analysis of sfragistics, numismatic and other categories of monuments. Analysis. Two seals are kept in the State Hermitage Museum collection. Both sides of the first seal (M-12374) have the depiction of Saint Demetrios of Thessaloniki as a horseman triumphant. On the left, under the cloak, there is the inscription ΟΔΗ. that, apparently, can be revealed as FÏ (Rγιος) Δη(μήτριος). On the other side of the seal there is a full-length image of Saint Stephanos with a censer and pyxis in his hands. On the front side of the second seal (M-3751) there is the same image of Saint Demetrios of Thessaloniki with a similar inscription. On the reverse side of the seal there is the inscription “Defender, look at me, your slave Christopher”. Results. The images of Saint Demetrios of Thessaloniki on both seals are almost identical, which implies the existence of a common prototype, most likely an honored icon. We can assume that it was in Thessaloniki in the Basilica of Saint Demetrios. Probably, the image of the warrior triumphant is the latest version of the iconography of saint warrior and it is known for the few monuments of the late 11th - 12th centuries. As a result, both seals can be dated to the same time. © 2019 Volgograd State University. All rights reserved

AA VASILYEV ABOUT CRIMEAN GOTHIA OF THE SECOND HALF OF THE 10th-THE BEGINNING OF THE 11th CENTURY

Introduction. In the national historiography there is an opinion that the work of A.A. Vasilyev The Goths in the Crimea still remains the most authoritative, if not the only research on this problem. However, the reference to the sources used by him gives grounds to assume that a certain part of the facts given by him is not based on the data of these sources, being a consequence of the logical constructions of the researcher. As a result, the author’s methodology as well as his conclusions need a more critical approach. The purpose of this article is based on an existing source base to determine the significance of the reconstruction of the A. A. Vasilyev history of the Crimean Gothia in the second half of the 10th – beginning of the 11th century in general and its relations with Byzantium and Rus in this period in particular. Methods. The methodological basis of the work is determined by the interdisciplinary approach, which provides, along with historical analysis, the use of methods of analysis of data of narrative sources, prosopography, sphragistics, epigraphy. The sources on the topic are few. This are Povest vremennykh let, History by Leo Diacon, the seals of Byzantine functionaries in the Crimea, the epigraphic and the archaeological sources. There is no special work on the problem of the article. Until now, the conclusions of A.A. Vasilyev were considered to be the ultimate truth and references to them were present in most of the works on the history of the Crimea of the middle Byzantine period. Analysis and results. The scheme of relations between Crimean Gothia, Kievan Rus and Byzantium proposed by A. A. Vasilyev in the second half of the 10th century is purely speculative and does not rely on facts. In fact, he needed to fill a gap in the history of Gothia which he did. At the same time, the Russian historiography of the Soviet period and later the influence of Russia in the Northern Black sea is excessively exaggerated and based on the writings of predecessors for more than very limited information of Russian chronicle

Динаміка біопродуктивності лісів Київської області

The urgency of research on bioproductivity of plantings by phytomass components has long gone beyond the regional problem and acquired a global character. It is believed that due to the improvement of forest reproduction and optimization of the age structure of plantations, additional afforestation of areas it will be possible to move part of CO2 from the atmosphere to the phytomass. In order to obtain comprehensive results that reflect the estimation of bioproductivity by components of phytomass of the main forest species of the Kyiv region, methodological principles are used as the basis for the conducted researches. The results of simulation of components of phytomass of main forest species of the Kiev region are presented. It has been established that the principle of constructing models for assessing the bioproductivity of forest stands of the main forest species in the region based on the components of the above-ground phytomass, which consists in establishing their multifactorial dependencies, depends on the main taxing attributes of plantations, which are indicated in the forest cadastre data. Regression analysis has shown that the most suitable in terms of accuracy and practicality is a two-factor model of the dependence of the main components of phytomass planting, in which the factors involved planting age and bonion class. Plants of the Kiev region are located in two forest areas. During the analysis, the positive dynamics of quantitative indicators of increasing the density of phytomass and carbon in plantations of the Kiev region was determined, which increased by 8.4‑4.2 kg·(m2)-1, respectively. During the study period there was an increase in phytomass in 1,6 times. Accordingly, in the forest areas Polissya and Forest-steppe in 1.4‑2.1 times. Forest plantations have a great influence on the formation of the environment and can affect factors such as temperature and humidity of the planet. The role of the forest can not be assessed as something unambiguous, since this resource is used in a variety of industries. Therefore, the plantations of the Kyiv region have important economic, ecological and social significance, perform important protective and protective functions and are highly productive.Наведено результати моделювання компонентів фітомаси головних лісотвірних порід Київської обл. Встановлено, що від основних таксаційних ознак насаджень, які вказують у даних лісового кадастру, залежить принцип побудови моделей оцінки біопродуктивності деревостанів головних лісотвірних порід області за компонентами надземної фітомаси, який полягав у встановленні їх багатофакторних залежностей. Регресійний аналіз засвідчив, що найпридатніша з точки зору точності та практичності застосування є двофакторна модель залежності основних компонентів фітомаси насадження, в якій як фактори задіяні вік насадження та клас бонітету. Насадження Київської обл. розташовані у двох лісорослинних зонах. Під час аналізу визначено позитивну динаміку кількісних показників збільшення щільності фітомаси та вуглецю в насадженнях Київської обл., яка зросла відповідно на 8,4–4,2 кг·(м2)-1. За досліджуваний період відбулося збільшення фітомаси в 1,6 раза. Відповідно в лісорослинних зонах Полісся та Лісостепу в 1,4–2,1 раза. Лісові насадження мають великий вплив на формування навколишнього середовища і здатні впливати на такі фактори, як температура і вологість повітря на планеті. Роль лісу неможливо оцінити як щось однозначне, оскільки цей ресурс використовують у різноманітних галузях виробництва. Тому насадження Київської обл. мають важливе економічне, екологічне та соціальне значення, виконують важливі захисні та охоронні функції і є високопродуктивними