Temperature dependence of coherent oscillations in Josephson phase qubits

We experimentally investigate the temperature dependence of Rabi oscillations and Ramsey fringes in superconducting phase qubits. In a wide range of temperatures, we find that both the decay time and the amplitude of these coherent oscillations remain nearly unaffected by thermal fluctuations. In the two-level limit, coherent qubit response rapidly vanishes as soon as the energy of thermal fluctuations k(B)T becomes larger than the energy level spacing variant Planck's over h omega of the qubit. In contrast, a sample of much shorter coherence times displayed semiclassical oscillations very similar to Rabi oscillation, but showing a qualitatively different temperature dependence. Our observations shed new light on the origin of decoherence in superconducting qubits. The experimental data suggest that, without degrading already achieved coherence times, phase qubits can be operated at temperatures much higher than those reported till now.     

Microwave Giant Magnetoresistance and Ferromagnetic and Spin-Wave Resonances in (CoFe)/Cu Nanostructures

Journal of Experimental and Theoretical Physics - The microwave phenomena that occur in magnetic multilayer (CoFe)/Cu nanostructures, which have a giant magnetoresistance, are studied. The...     

Ion solvation of aqueous solutions of alkali, alkaline earth, and transition metal halides

The published data on the density and velocity of ultrasound are used to determine the ion solvation parameters of sodium, magnesium, and cobalt chlorides. It is shown that the solvation of typical coordination compounds, such as cobalt chloride, is determined by the same underlying systems and interactions as that of electrolytes with ions of alkali and alkaline earth metals.     

Subterahertz superlattice parametric oscillator

We report a superlattice parametric oscillator (SPO), with a GaAs/AlAs superlattice as the active element. The SPO was pumped by a microwave field (power 4 mW) and produced third harmonic radiation at subterahertz frequencies (near 300 GHz; 0.1 mW). We attribute the parametric gain to the nonlinearity of the miniband transport.     

Hall effect in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>x</Subscript>MnO<Subscript>3</Subscript> crystals

A study of the temperature dependences of the ordinary and anomalous Hall coefficients and of the Hall mobility of carriers in single crystals of the ferromagnetic manganites La_1?xSr_xMnO₃ (x=0.15, 0.20, 0.25) was carried out in the temperature interval from 85 to 400 K. The nature of the carriers and the conduction mechanisms in these compounds are discussed.     

Considerable increase in thermal conductivity of a polycrystalline CVD diamond upon isotope enrichment

We measured the temperature dependence of thermal conductivity of a polycrystalline CVD diamond with natural isotope composition and an isotope enriched (99.96% ¹²C) sample at temperatures from 5 to 420 K. The isotope enriched diamond demonstrates a considerable growth of thermal conductivity at temperatures above 80 K compared to the diamond with natural composition of isotopes. At room temperature the thermal conductivity reaches 24.3 W·cm^?1K^?1, and the isotope effect makes up not less than 34%.     

Emission of terahertz radiation from GaAsN/GaAs heterostructures in an electric field

Emission of terahertz radiation from strained Be-doped GaAsN layers has been revealed at 4.2 K in postbreakdown electric fields. Heavy and light hole subbands are split in strained layers, and, along with localized acceptor states, resonant states arise. The spectrum of terahertz radiation has been obtained, the current-voltage characteristics of the samples were investigated, and the energy spectra of acceptors were calculated. Peaks in the spontaneous emission spectrum correlate well with the results of the energy spectrum calculations. The transitions between the resonant and localized states of the acceptors make the main contribution to the terahertz radiation intensity.     

Methods of analysing ropes. The extension–torsion method

Two new approaches are used for calculating the stress–strain state of a rope and its stiffnesses. The first approach relies on the theory of fibrous composites and Saint-Venant's solution for a cylinder with helical anisotropy. The second approach is based on the solution by the finite element method of the three-dimensional problem of elasticity theory for a solid inhomogeneous cylinder formed by a finite number of elastic fibres arranged in helical lines and connected by a weak filler (in the sense that its Young's modulus is several orders of magnitude less than the Young's modulus of the fibre). The behaviour of the stiffness when the modulus of elasticity of the filler tends to zero is analysed, and the results of the limiting transition are discussed. The numerical results obtained are compared with calculations by other well-known applied theories.     

Statistical interpretation of the Dubinin-Radushkevich equation

A statistical approach was applied to describe the model of a homogeneous microporous adsorbent and obtain the dependences of the thermodynamic functions on the number of molecules and the temperature for molecular aggregates in discrete micropores over a wide region of fillings that lead to the Dubinin—Radushkevich equation. The energy nonuniformity of the adsorption space is the fundamental property of carbon adsorbents. In the region of small fillings, the statistical approach leads to Henry's law and the finite value of the initial differential energy of adsorption. The value of sorption corresponding to the saturated vapor pressure decreases with increasing temperature, but the decrease is considerably less than for the density of the corresponding liquid. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 261–265, February, 1999.