Radiophysics and Quantum Electronics最新文献

We analyze electron–nucleus collisions in a strongly magnetized ideal plasma with a low temperature at which the Coulomb interaction energy of particles at a distance of the order of the electron Larmor radius exceeds their thermal energy. In this limit, the motion of the electron in close collisions becomes quasibound. Analytical expressions for the spectral power of bremsstrahlung in the continuum at frequencies where quasibound motion makes a decisive contribution to the emission have been obtained. The proposed quantum approach is valid both in the limit of such a low energy of an electron that the latter can occupy only a fundamental Landau level before and after the collision and in the limit of classical particle motion. In the classical regime, the radiation losses approximately preserve the trajectory of the particle: the emission of a photon just changes the phase incursion of the electron wave function by the same amount within the cross section of a beam of rays approximating the state of the particle. A condition is formulated under which spontaneous emission puts the particle into a superposition of states essentially differing from the initial state by the probability for the electron to occupy different Landau levels after the collision. This emission regime takes place in the low-temperature plasma of the photosphere of a white dwarf in the infrared continuum.

We study the effectiveness of spatial signal processing at the apertures of the vertical and horizontal antenna arrays for acoustic waveguides with irregular free boundaries. The main attention is paid to a joint use of statistical models of signal and noise, which is generated near the waveguide boundary by dipole sources, and optimal algorithms for processing of partially coherent signals. The proposed signal and noise models allow for the effects of multiple scattering of acoustic modes. On the basis of the obtained theoretical results, we perform computations of the gain of the antenna arrays of various orientations for an oceanic waveguide with a wavy surface and regular parameters, which are typical of shallow sea. The dependences of the antenna-array gain on the distance and wind velocity are analyzed for various spatial-processing algorithms. The influence of the intermode signal correlations and the statistical model of noise on these results is discussed.

Superconducting circuits are among the most promising platforms for quantum computing. The milestone experiments demonstrating quantum advantage and suppression of quantum errors have already been performed on a simple and reliable transmon qubit. However, a transmon has a number of structural and technological features which limit the fidelity of basic operations required for a high-performance quantum computing device. Therefore, alternative superconducting qubits with a better protection from external noise are of growing interest. A fluxonium, which is characterized by significant anharmonicity and a large coherence time, is one of the most promising qubits. In this work, we describe the first experiments with an elementary unit cell of a quantum processor with planar fluxonium qubits. Methods of individual initialization and dispersive readout of qubits are demonstrated; single-qubit gates with a fidelity exceeding 99.96% and a two-qubit CZ gate with a fidelity of 99.22% are realized.

We consider superconducting single-photon detectors, which are the key element of quantum optical technologies due to their unique characteristics not available in other technologies today. Since the first demonstration in Russia in 2001, such detectors have evolved significantly, and their waveguide-based versions are ready for scaling both in the fields of classical technologies (attenuated light) and of quantum optical applications (non-classical light). The paper studies the operating principle of such detectors and their main characteristics, analyzes superconducting materials and dielectric waveguide platforms, highlights the design principles, considers various levels of integration of on-chip waveguide superconductor detectors, and presents important new areas of application towards the implementation of photonic and ion quantum processors, as well as energy-efficient neuromorphic computing.

This paper is devoted to the use of quantum integrated circuits based on superconducting artificial atoms to solve quantum machine learning problems. The process of designing such chips is de- scribed in detail, including the selection of the most important geometric parameters of the device, as well as numerical calculations of electromagnetic characteristics. The process of controlling a quantum integrated circuit is described. Much attention is paid to the implementation of single- and two-qubit operations. The qubit state readout procedure is also described. A brief introduction into the field of quantum machine learning is given. An algorithm that makes it possible to solve multilabel classification problems using quantum integrated circuits is described. The selection of optimal quantum circuits for the implementation of this algorithm is made using numerical simulations. The operation of the algorithm is demonstrated by the example of standard datasets. Obtained experimental results are compared with the results of theoretical calculations.

We present the results of direct measurement of vibrations of the drill-string bottom structures in the drilling process. Special attention during the measurements is paid to the high-frequency part of the vibration spectrum. The vibrations were recorded using a specially manufactured downhole noise recorder with an integrated three-component accelerometer and the temperature and externalpressure sensors. This recorder was adapted for embedding directly into the drill string in the bottomhole assembly area. Vibration signals were recorded in a frequency interval of up to 25 kHz. The full-scale measurements were performed for all possible borehole operations carried out for both controlled (horizontal) and vertical drilling. This work presents the distribution functions and power spectral densities of vibration noise for various drilling operations and conditions.

We consider the influence of the temperature, at which a cyclic deformation takes place, on the elastic properties of chromium-nickel austenitic steels with different susceptibilities to deformation-induced martensite transformation. Specific features are revealed in variations of the acoustic and elastic parameters depending on the loading temperature and the chemical composition of various steels.

We consider the problems of developing the systems for gauging and diagnostics of the technical condition of the shaft lines of the steam-turbine generator sets of nuclear and thermal power plants using torsional vibrations. The requirements for full-time systems of diagnostic monitoring of torsional vibrations are formulated. The measuring schemes and methods to measure torsional vibrations of rotary machines by the time-interval measurement method are analyzed. Their advantages and disadvantages are shown. The reasons causing errors when measuring torsional vibrations are described. A method for measuring torsional vibrations of rotary machines by the time-interval method has been developed, which can serve as an arbitration technique, since it allows for the influence of the largest number of spurious factors and provides the most accurate measurement of torsional vibrations. The reasons for exciting torsional vibrations of the shaft lines of the gas turbine generator sets and the methods of their identification, ways to solve the problem of assessing the stress-strain state of the shaft line in dynamics, and early detection of the shaft line integrity defects during operation are considered.

We describe the principle of operation of the radio interferometer, which is used to detect the displacement and determine the velocity of the free surface of a sample in the plane-wave experiment. Several measurement schemes are compared experimentally. For some of them, good agreement of the results with the data of the independent measurements is revealed, which demonstrates the possibility of measuring the free-surface velocity with a time resolution of about 0.1 μs and a margin of error of about 10 m/s.

We consider the dynamic behavior of a beam with a moving load resting on a deformable base and characterized by two bed coefficients with allowance for dissipative losses. A self-consistent boundary-value problem has been formulated which correctly takes into account the interaction forces in a moving contact. The features of the bending-wave generation by a zero-frequency oscillation source are studied. The critical velocities of the source motion are determined. In the case of low viscosity, the critical velocities do not depend on dissipative losses in the base and are determined by the physical and mechanical properties of the beam and the bed coefficients. An expression for the force due to the wave pressure (the force of resistance to motion) is obtained. The dependence of the constant component of this force on the object velocity and elastic and viscous parameters of the base is studied. The calculation of the energy consumption of the source, which ensures the object motion at a constant velocity, is carried out. When the load moves at a velocity not exceeding the minimum phase velocity of the bending-wave propagation in the beam, the motion-resistance force and the energy consumption are zero and differ from zero in the presence of dissipative losses in the deformable base. A comparison with the results obtained for the one-parameter elastic base of the Fuss-Winkler model is given.