Towards local oscillators based on arrays of niobium Josephson junctions
Various applications in the field of terahertz technology are in urgent need of compact, wide-tunable solid-state continuous wave radiation sources with a moderate power. However, satisfactory solutions for the THz frequency range are scarce yet. Here we report on coherent radiation from a large planar array of Josephson junctions (JJs) in the frequency range between 0.1 and 0.3 THz. The external resonator providing the synchronization of JJ array is identified as a straight fragment of a single-strip-line containing the junctions themselves. We demonstrate a prototype of the quasioptical heterodyne receiver with the JJ array as a local oscillator and a hot-electron bolometer mixer.
It is well known that new effects appear in superconductors with the reduction of their size. Among them one is the most interesting – phenomenon of changing of critical temperature. It can be both decrease and increase in different metals, however, despite the number of existing works, there is still no generally accepted conception of what is exactly the origin of this effect. At the moment it is more or less clear, that this is a rather complicated mechanism, which is influenced by many factors, particularly connected with the sample’s manufacturing. Nevertheless, we suppose even after minimization of all impacts, the temperature of superconducting transition shifts anyway because of quantum size effect. We present here the results of the investigation of high-quality polycrystalline aluminum films and demonstrate the presence of quantum-confinement process that was not considered earlier. © 2019 International Institute of Refrigeration. All rights reserved.
These notes have appeared as a result of a one-term course in superfluidity and superconductivity given by the author to fourth-year undergraduate students and first-year graduate students of the Department of Physics, Moscow State University of Education. The goal was not to give a detailed picture of these two macroscopic quantum phenomena with an extensive coverage of the experimental background and all the modern developments, but rather to show how the knowledge of undergraduate quantum mechanics and statistical physics could be used to discuss the basic concepts and simple problems, and draw parallels between superconductivity and superfluidity.
Superconductivity and superfluidity are two phenomena where quantum mechanics, typically constrained to the microscopic realm, shows itself on the macroscopic level. Conceptually and mathematically, these phenomena are related very closely, and some results obtained for one can, with a few modifications, be immediately carried over to the other. However, the student of these notes should be aware of important differences between superconductivity and superfluidity that stem mainly from two facts: (1) electrons in a superconductor carry a charge, therefore one has to take into account interaction with electromagnetic radiation; (2) electrons move in a lattice, therefore phonons play a role not only a mediators of attractive interaction between pairs of electrons, but also as scatterers of charge carriers.
Although these are notes on superfluidity and superconductivity, and there are a few cross-references, the two subjects can be studied independently with, perhaps, a little extra work by the student to fill in the gaps resulting from such study. The material of Chapter 1 introduces the method of second quantisation that is commonly used to discuss systems with many interacting particles. It is then applied in Chaper 2 to treat the uniform weakly interacting Bose gas within the approach by N. Bogoliubov, and in Chapter 4 to formulate the theory of the uniform superconducting state put forth by J. Bardeen, L. Cooper and R. Schrieffer. Chapter 3 presents the theory proposed independently by E. Gross and L. Pitaevskii of a non-uniform weakly interacting Bose gas, with a discussion of vortices, rotation of the condensate, and the Bogoliubov equations. In Chapter 5 we discuss the Ginzburd-Landau theory of a non-uniform superconductor near the critical temperature and apply it to a few simple problems such as the surface energy of the boundary between a normal metal and a superconductor, critical current and critical magnetic field, and vortices.
Recently bright-light control of the SSPD has been demonstrated. This attack employed a "backdoor" in the detector biasing scheme. Under bright-light illumination, SSPD becomes resistive and remains "latched" in the resistive state even when the light is switched off. While the SSPD is latched, Eve can simulate SSPD single-photon response by sending strong light pulses, thus deceiving Bob. We developed the experimental setup for investigation of a dependence on latching threshold of SSPD on optical pulse length and peak power. By knowing latching threshold it is possible to understand essential requirements for development countermeasures against blinding attack on quantum key distribution system with SSPDs.
We demonstrate evidence of coherent magnetic flux tunneling through superconducting nanowires patterned in a thin highly disordered NbN film. The phenomenon is revealed as a superposition of flux states in a fully metallic superconducting loop with the nanowire acting as an effective tunnel barrier for the magnetic flux, and reproducibly observed in different wires. The flux superposition achieved in the fully metallic NbN rings proves the universality of the phenomenon previously reported for InOx .We perform microwave spectroscopy and study the tunneling amplitude as a function of the wire width, compare the experimental results with theories, and estimate the parameters for existing theoretical models.
We developed the model of the internal phonon bottleneck to describe the energy exchange between the acoustically soft ultrathin metal film and acoustically rigid substrate. Discriminating phonons in the film into two groups, escaping and nonescaping, we show that electrons and nonescaping phonons may form a unified subsystem, which is cooled down only due to interactions with escaping phonons, either due to direct phonon conversion or indirect sequential interaction with an electronic system. Using an amplitude-modulated absorption of the sub-THz radiation technique,we studied electron-phonon relaxation in ultrathin disordered films of tungsten silicide.We found an experimental proof of the internal phonon bottleneck. The experiment and simulation based on the proposed model agree well, resulting in τe−ph ∼ 140–190 ps at TC = 3.4K, supporting the results of earlier measurements by independent techniques.
The thermodynamical potential of a superconducting quantum cylinder is calculated. The dependence of the critical temperature and the heat capacity of a superconducting system of the surface concentration of electrons and on the radius of the nanotube is studied.
Overview This book concisely presents the latest trends in the physics of superconductivity and superfluidity and magnetismin novel systems, as well as the problem of BCS-BEC crossover in ultracold quantum gases and high-Tc superconductors. It further illuminates the intensive exchange of ideas between these closely related fields of condensed matter physics over the last 30 years of their dynamic development. The content is based on the author’s original findings obtained at the Kapitza Institute, as well as advanced lecture courses he held at the Moscow Engineering Physical Institute, Amsterdam University, Loughborough University and LPTMS Orsay between 1994 and 2011. In addition to the findings of his group, the author discusses the most recent concepts in these fields, obtained both in Russia and in the West. The book consists of 16 chapters which are divided into four parts. The first part describes recent developments in superfluid hydrodynamics of quantum fluids and solids, including the fashionable subject of possible supersolidity in quantum crystals of 4He, while the second describes BCS-BEC crossover in quantum Fermi-Bose gases and mixtures, as well as in the underdoped states of cuprates. The third part is devoted to non-phonon mechanisms of superconductivity in unconventional (anomalous) superconductors, including some important aspects of the theory of high-Tc superconductivity. |The last part considers the anomalous normal state of novel superconductive materials and materials with colossal magnetoresistance (CMR). The book offers a valuable guide for senior-level undergraduate students and graduate students, postdoctoral and other researchers specializing in solid-state and low-temperature physics.
The article considers the Views of L. N. Tolstoy not only as a representative, but also as a accomplisher of the Enlightenment. A comparison of his philosophy with the ideas of Spinoza and Diderot made it possible to clarify some aspects of the transition to the unique Tolstoy’s religious and philosophical doctrine. The comparison of General and specific features of the three philosophers was subjected to a special analysis. Special attention is paid to the way of thinking, the relation to science and the specifics of the worldview by Tolstoy and Diderot. An important aspect is researched the contradiction between the way of thinking and the way of life of the three philosophers.
Tolstoy's transition from rational perception of life to its religious and existential bases is shown. Tolstoy gradually moves away from the idea of a natural man to the idea of a man, who living the commandments of Christ. Starting from the educational worldview, Tolstoy ended by creation of religious and philosophical doctrine, which were relevant for the 20th century.
This important new book offers the first full-length interpretation of the thought of Martin Heidegger with respect to irony. In a radical reading of Heidegger's major works (from Being and Time through the ‘Rector's Address' and the ‘Letter on Humanism' to ‘The Origin of the Work of Art' and the Spiegel interview), Andrew Haas does not claim that Heidegger is simply being ironic. Rather he argues that Heidegger's writings make such an interpretation possible - perhaps even necessary.
Heidegger begins Being and Time with a quote from Plato, a thinker famous for his insistence upon Socratic irony. The Irony of Heidegger takes seriously the apparently curious decision to introduce the threat of irony even as philosophy begins in earnest to raise the question of the meaning of being. Through a detailed and thorough reading of Heidegger's major texts and the fundamental questions they raise, Haas reveals that one of the most important philosophers of the 20th century can be read with as much irony as earnestness. The Irony of Heidegger attempts to show that the essence of this irony lies in uncertainty, and that the entire project of onto-heno-chrono-phenomenology, therefore needs to be called into question.
The article is concerned with the notions of technology in essays of Ernst and Friedrich Georg Jünger. The special problem of the connection between technology and freedom is discussed in the broader context of the criticism of culture and technocracy discussion in the German intellectual history of the first half of the 20th century.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.