H-theorem and Maxwell Demon in Quantum Physics

The Second Law of Thermodynamics states that temporal evolution of an isolated system occurs with non-diminishing entropy. In quantum realm, this holds for energy-isolated systems the evolution of which is described by the so-called unital quantum channel. The entropy of a system evolving in a non-unital quantum channel can, in principle, decrease. We formulate a general criterion of unitality for the evolution of a quantum system, enabling a simple and rigorous approach for finding and identifying the processes accompanied by decreasing entropy in energy-isolated systems. We discuss two examples illustrating our findings, the quantum Maxwell demon and heating-cooling process within a two-qubit system.Comment: 7 pages, 2 figures, IV International Conference on Quantum Technologie

Mathematical Modeling of a Solar Arrays Deploying Process at Ground Tests

This paper focuses on the creating of a mathematical model of a solar array deploying process during ground tests. Lagrange equation was used to obtain the math model. The distinctive feature of this mathematical model is the possibility of taking into account the gravity compensation system influence on the construction in the deploying process and the aerodynamic resistance during ground tests

Experimental demonstration of scalable quantum key distribution over a thousand kilometers

Secure communication over long distances is one of the major problems of modern informatics. Classical transmissions are recognized to be vulnerable to quantum computer attacks. Remarkably, the same quantum mechanics that engenders quantum computers offers guaranteed protection against such attacks via quantum key distribution (QKD). Yet, long-distance transmission is problematic since the essential signal decay in optical channels occurs at a distance of about a hundred kilometers. We propose to resolve this problem by a QKD protocol, further referred to as the Terra Quantum QKD protocol (TQ-QKD protocol). In our protocol, we use semiclassical pulses containing enough photons for random bit encoding and exploiting erbium amplifiers to retranslate photon pulses and, at the same time, ensuring that at the chosen pulse intensity only a few photons could go outside the channel even at distances of about a hundred meters. As a result, an eavesdropper will not be able to efficiently utilize the lost part of the signal. The central component of the TQ-QKD protocol is the end-to-end loss control of the fiber-optic communication line since optical losses can in principle be used by the eavesdropper to obtain the transmitted information. However, our control precision is such that if the degree of the leak is below the detectable level, then the leaking states are quantum since they contain only a few photons. Therefore, available to the eavesdropper parts of the bit encoding states representing `0' and `1' are nearly indistinguishable. Our work presents the experimental demonstration of the TQ-QKD protocol allowing quantum key distribution over 1079 kilometers. Further refining the quality of the scheme's components will expand the attainable transmission distances. This paves the way for creating a secure global QKD network in the upcoming years.Comment: 23 pages (main text: 15 pages, supplement: 8 pages), 21 figures (main text: 7 figures, supplement: 14 figures

Development of the fully Geant4 compatible package for the simulation of Dark Matter in fixed target experiments

The search for new comparably light (well below the electroweak scale) feebly interacting particles is an exciting possibility to explain some mysterious phenomena in physics, among them the origin of Dark Matter. The sensitivity study through detailed simulation of projected experiments is a key point in estimating their potential for discovery. Several years ago we created the DMG4 package for the simulation of DM (Dark Matter) particles in fixed target experiments. The natural approach is to integrate this simulation into the same program that performs the full simulation of particles in the experiment setup. The Geant4 toolkit framework was chosen as the most popular and versatile solution nowadays. The simulation of DM particles production by this package accommodates several possible scenarios, employing electron, muon or photon beams and involving various mediators, such as vector, axial vector, scalar, pseudoscalar, or spin 2 particles. The bremsstrahlung, annihilation or Primakoff processes can be simulated. The package DMG4 contains a subpackage DarkMatter with cross section methods weakly connected to Geant4. It can be used in different frameworks. In this paper, we present the latest developments of the package, such as extending the list of possible mediator particle types, refining formulas for the simulation and extending the mediator mass range. The user interface is also made more flexible and convenient. In this work, we also demonstrate the usage of the package, the improvements in the simulation accuracy and some cross check validations.Comment: 17 pages, 11 figures, 1 tabl

Separation of signals from neutrons and gamma quanta by the method of normalized signals

The solution of the problem how to register fast neutrons in the presence of intense gamma radiation is required when solving such fundamental and applied problems as registration of the neutron and gamma background in underground low-background experiments (the low background detectors of the neutrino and dark matter); beam diagnostic at particle accelerators; radiation monitoring at nuclear facilities, nuclear medicine; environmental monitoring. To separate signals from neutrons and gamma quanta, scintillation detectors with organic scintillators are used. The best scintillators are organic crystals of stilbene and p-terpheny