Noncommutative tori and universal sets of non-binary quantum gates

A problem of universality in simulation of evolution of quantum system and in theory of quantum computations is related with the possibility of expression or approximation of arbitrary unitary transformation by composition of specific unitary transformations (quantum gates) from given set. In an earlier paper (quant-ph/0010071) application of Clifford algebras to constructions of universal sets of binary quantum gates $U_k \in U(2^n)$ was shown. For application of a similar approach to non-binary quantum gates $U_k \in U(l^n)$ in present work is used rational noncommutative torus ${\Bbb T}^{2n}_{1/l}$. A set of universal non-binary two-gates is presented here as one example.Comment: 5 pages, REVTeX3.1, v2: spelling and misprints, 4 new ref

Mapping the optical properties of slab-type two-dimensional photonic crystal waveguides

We report on systematic experimental mapping of the transmission properties of two-dimensional silicon-on-insulator photonic crystal waveguides for a broad range of hole radii, slab thicknesses and waveguide lengths for both TE and TM polarizations. Detailed analysis of numerous spectral features allows a direct comparison of experimental data with 3D plane wave and finite-difference time-domain calculations. We find, counter-intuitively, that the bandwidth for low-loss propagation completely vanishes for structural parameters where the photonic band gap is maximized. Our results demonstrate that, in order to maximize the bandwidth of low-loss waveguiding, the hole radius must be significantly reduced. While the photonic band gap considerably narrows, the bandwidth of low-loss propagation in PhC waveguides is increased up to 125nm with losses as low as 8$\pm$2dB/cm.Comment: 10 pages, 8 figure

Interaction between superconducting vortices and Bloch wall in ferrite garnet film

Interaction between a Bloch wall in a ferrite-garnet film and a vortex in a superconductor is analyzed in the London approximation. Equilibrium distribution of vortices formed around the Bloch wall is calculated. The results agree quantitatively with magneto-optical experiment where an in-plane magnetized ferrite-garnet film placed on top of NbSe2 superconductor allows observation of individual vortices. In particular, our model can reproduce a counter-intuitive attraction observed between vortices and a Bloch wall having the opposite polarity. It is explained by magnetic charges appearing due to discontinuity of the in-plane magnetization across the wall.Comment: 4 pages, 5 figure

Finger patterns produced by thermomagnetic instability in superconductors

A linear analysis of thermal diffusion and Maxwell equations is applied to study the thermomagnetic instability in a type-II superconducting slab. It is shown that the instability can lead to formation of spatially nonuniform distributions of magnetic field and temperature. The distributions acquire a finger structure with fingers perpendicular to the screening current direction. We derive the criterion for the instability, and estimate its build-up time and characteristic finger width. The fingering instability emerges when the background electric field is larger than a threshold field, $E>E_c$, and the applied magnetic field exceeds a value $H_fing \propto 1/\sqrt{E}$. Numerical simulations support the analytical results, and allow to follow the development of the fingering instability beyond the linear regime. The fingering instability may be responsible for the nucleation of dendritic flux patterns observed in superconducting films using magneto-optical imaging.Comment: 8 pages, 6 figures, accepted to Phys. Rev. B; (new version: minor changes

Hydrodynamic Instability of the Flux-antiflux Interface in Type-II Superconductors

The macroturbulence instability observed in fluxline systems during remagnetization of superconductors is explained. It is shown that when a region with flux is invaded by antiflux the interface can become unstable if there is a relative tangential flux motion. This condition occurs at the interface when the viscosity is anisotropic, e.g., due to flux guiding by twin boundaries in crystals. The phenomenon is similar to the instability of the tangential discontinuity in classical hydrodynamics. The obtained results are supported by magneto-optical observations of flux distribution on the surface of a YBCO single crystal with twins.Comment: 12 pages, 3 figures, submitted to Physical Review Letter

Effect of iron doping on the properties of nanopowders and coatings on the basis of Al2O3 produced by pulsed electron beam evaporation

Multiphase nanopowders (NPs) and amorphous/amorphous-nanocrystalline coatings (A-NC) have been prepared by the evaporation of ceramic targets of Al2O3-Fe2O3 (0.1, 3, 5 Fe2O3 mass %) by a pulsed electron beam in vacuum. The specific surface area of NP Al2O3-Fe2O3 reached 277 m2/g. The α and γ phases Al2O3 and other nonidentified phases have been found in the composition of NP Al2O3-Fe2O3. All coatings contained an insignificant fraction of the crystalline γ phase. No secondary phases on the basis of iron have been revealed. According to transmission electron microscopy, the fine fraction of NP Al2O3-Fe2O3 consists of amorphous nanoparticles of an irregular and quasispherical shape no more than 10 nm in size which form agglomerates reaching 1.5 μm. A large fraction of NPs consists of crystal spherical nanoparticles with preferential sizes of about 10-20 nm. All NP Al2O3-Fe2O3 showed ferromagnetic behavior at room temperature. The maximum magnetic response has been established in NPs with a minimum iron content (1.1 mass %). The pulsed cathode luminescence spectra of coatings and NP Al2O3-Fe2O3 have been presented by a wide band in the wavelength range of 300-900 nm regardless of their phase composition. Phase transformations into NP AL2O3-1.1% Fe and coatings from undoped Al2O3 heated to 1400°C occur according to the following scheme: amorphous phase → γ → δ → θ → α, regardless of their initial phase composition. The threshold of thermal stability of the Γ phase in NPs and the coating of undoped Al2O3 does not exceed 830°C. For the first time, the increased thermo and optically stimulated luminescent response comparable with the response of the leading TLD-500K thermoluminescent dosimeter has been reached in A-NC coatings of undoped Al2O3. © 2013 Pleiades Publishing, Ltd

Mass for the graviton

Can we give the graviton a mass? Does it even make sense to speak of a massive graviton? In this essay I shall answer these questions in the affirmative. I shall outline an alternative to Einstein Gravity that satisfies the Equivalence Principle and automatically passes all classical weak-field tests (GM/r approx 10^{-6}). It also passes medium-field tests (GM/r approx 1/5), but exhibits radically different strong-field behaviour (GM/r approx 1). Black holes in the usual sense do not exist in this theory, and large-scale cosmology is divorced from the distribution of matter. To do all this we have to sacrifice something: the theory exhibits {*prior geometry*}, and depends on a non-dynamical background metric.Comment: 12 pages, plain LaTeX. Major revisions: (1) Inconsistency in equations of motion fixed. (2) More discussion of the problems associated with quantization. (3) Many more references adde

Luminescent and dosimetric properties of thin nanostructured layers of aluminum oxide obtained using evaporation of a target by a pulsed electron beam

Results of a study of optically and thermally stimulated luminescence (OSL and TL) of thin nanostructured aluminum oxide coatings obtained with evaporation of the target by a pulsed electron beam and deposited on quartz glass, Al, steel, Cu, Ta, and graphite wafers are presented. It follows from data of X-ray phase analysis that the obtained Al2O3 layers have an amorphous nanocrystal structure with different contents of the γ phase depending on the geometry of the wafer location on evaporation and annealing temperature of the samples. It is established that the material of the wafer and the ratio of the amorphous and γ phase in Al2O3 layers affect the yields of OSL and TL. Annealing at up to 970 K results in an increase of γ-phase concentration and OSL and TL responses. It was found that the yields of OSL and TL for the most emission-effective coating samples are comparable with those for the detectors on the basis of anion-defective corundum. The dose-dependence for β radiation, which was linear in the range 20-5000 mGy, was investigated. © 2013 Pleiades Publishing, Ltd

Electron-ion-plasma modification of the structure and properties of commercial steels

The work is devoted to the structural-phase analysis of steels of the austenitic and martensitic grade, irradiated with a high-intensity pulsed electron beam of the submillisecond duration of exposure in the mode of the surface layer melting. A thermodynamic analysis of phase transformations occurring during heat treatment in alloys of the composition Fe-Cr-C and Fe-Cr-Ni-C, which are the basis of steels 20X13 and 12X18H10T, is carried out. It is shown that formation of solid solutions on the basis of [alpha]-iron (BCC crystalline lattice) and [gamma]- iron (FCC crystalline lattice) as well as the entire range of carbide phases of a complex elemental composition (M[23]C[6], M[7]C[3] и M[3]C, where symbol M refers to atoms of metallic elements Fe, Cr, and Ni) is possible in equilibrium conditions in given materials. The irradiation of steels 12X18H10T and 20X13 with a high-intensity pulsed electron beam of the submillisecond duration of exposure is carried out. It is shown that the electron-beam processing of steel in the melting mode and the subsequent rapid crystallization is accompanied by a significant transformation of the surface layer structure, consisting in complete dissolution of original carbide phase particles; in formation of dendritic crystallization cells of submicron sizes; in occurrence of martensitic [gamma]->[alpha] and [gamma]->[epsilon] transformation; in re-allocation of nanosized particles of carbide and intermetallic phases