Effects of positron phonon interaction in metals

We investigate the importance of positron phonon interaction for the many body effects observed in positron annihilation in metals. The interaction is formulated as the screened Coulomb interaction of the positron with the polarization charge of the metal produced by lattice vibrations. The phonon contribution to the effective mass is found negligibly small. Due to the interaction with phonons the equilibrium positron momentum distribution deviates from a Boltzmann distribution leading to a larger thermal smearing of the annihilation curves than expected from the rather small effective mass. The positron energy loss in the thermalization process due to phonon excitation is discussed and found comparable to the energy loss due to the excitation of electron hole pairs in the experimentally interesting temperature range.     

Simultaneously phase-matched parametric processes in a single-pass interaction for efficient visible generation

We demonstrate simultaneously phase-matched cascaded optical parametric amplification (OPA) and sum-frequency generation (SFG) processes in a single-pass interaction in a BBO crystal, where the seed pulse is produced through the self-induced superfluorescence generation. Tunable femtosecond pulses in the blue-green spectral range are produced through the single-pass SFG interaction with a maximum conversion efficiency of about 12%.     

Resonant tunneling of ultracold atoms through vacuum induced potentials

We demonstrate resonant tunneling of ultracold atoms through potentials produced by the interaction of atoms with the vacuum field of a system of cavities. We show the close connection of the transmission characteristics to the resonant states in vacuum induced potentials. Transmission of cold atoms, though sharing some features with tunneling in finite semiconductor superlattices, is strongly dependent on the coherent addition of amplitudes from various wells and barriers.     

Systematic analysis of pT -distributions in p + p collisions

A systematic analysis of transverse momentum distribution of hadrons produced in ultra-relativistic p + p collisions is presented. We investigate the effective temperature and the entropic index from the non-extensive thermodynamic theory of strong interaction. We conclude that the existence of a limiting effective temperature and of a limiting entropic index is in accordance with experimental data.     

Time-odd correlation in a neutron reflectometry experiment

We find that neutron transmission of magnetic systems with the noncollinear magnetization contains a time-odd correlation. The neutron reflection from such a system violates detailed balance. Time-odd correlation is shown to violate T-invariance even in the presence of an irreversibly produced by losses and described by the imaginary part in the neutron-matter interaction.     

Quantum-mechanical expressions for the current electric dipole and quadrupole moments and the current electrostatic contact interaction

We derive quantum-mechanical expressions for the current electric dipole and quadrupole moments produced by motion of a particle with a magnetic moment. We show that there exists a current electrostatic contact interaction. We also show that the Dirac and anomalous magnetic moments appear with different coefficients in the expressions for the current electric moments and the current electrostatic interaction.Scientific—Research Institute of Nuclear Problems, Belorussian State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 66–71, April, 1995.     

Subsystem purity as an enforcer of entanglement

We show that entanglement can always arise in the interaction of an arbitrarily large system in any mixed state with a single qubit in a pure state. This small initial purity is enough to enforce entanglement even when the total entropy is close to maximum. We demonstrate this feature using the Jaynes-Cummings interaction of a two-level atom in a pure state with a field in a thermal state at an arbitrarily high temperature. We find the time and temperature variation of a lower bound on the amount of entanglement produced and study the classical correlations quantified by the mutual information.     

Incoherent light-induced self-organization of molecules

Although coherent light is usually required for the self-organization of regular spatial patterns from optical beams, we show that peculiar light-matter interaction can break this evidence. In the traditional method of recording laser-induced periodic surface structures, a light intensity distribution is produced at the surface of a polymer film by an interference between two coherent optical beams. We report on the self-organization followed by propagation of a surface relief pattern. It is induced in a polymer film by using a low-power and small-size coherent beam assisted by a high-power and large-size incoherent and unpolarized beam. We demonstrate that we can obtain large size and well-organized patterns starting from a dissipative interaction. Our experiments open new directions to improving optical processing systems.     

The motion of particle spin in a nonuniform electromagnetic field

We have applied the Foldy-Wouthuysen transformation to spin-1 particles interacting with a nonuniform electromagnetic field. This allowed us to simultaneously confirm that the Pomeransky-Khriplovich-Sen’kov theory is valid and that the interaction of spin 1-particles with a weak field is properly described by the Corben-Schwinger equation. We analyzed the possibilities for experimentally testing theoretical conclusions by observing spin oscillations for the planar channeling of particles or nuclei in straight crystals. By carrying out such experiments, we can also detect the spin oscillations produced by electromagnetic interaction and measure the quadrupole moments of short-lived nuclei.     

Damping and frequency shift in the oscillations of two colliding Bose-Einstein condensates

We have investigated the center-of-mass oscillations of a ⁸⁷Rb Bose-Einstein condensate in an elongated magneto-static trap. We start from a trapped condensate and we transfer part of the atoms to another trapped level, by applying a radio-frequency pulse. The new condensate is produced far from its equilibrium position in the magnetic potential, and periodically collides with the parent condensate. We discuss how both the damping and the frequency shift of the oscillations are affected by the mutual interaction between the two condensates, in a wide range of trapping frequencies. The experimental data are compared with the prediction of a mean-field model. Received 28 May 2001     

Rb Bose-Einstein condensate with tunable interaction: A quantum many body approach

We present a quantum many body approach with van der Waal type of interaction to achieve ⁸⁵Rb Bose-Einstein condensate with tunable interaction which has been produced by magnetic field induced Feshbach resonance in the JILA experiment.     

Study of emission characteristics of the projectile fragments produced in the interaction of 84Kr36 with nuclear emulsion detector at 1 GeV

This article is focused on the characteristics of the projectile fragments of charge 1 ≤ Z ≤ 10 produced in the interaction of the ⁸⁴Kr₃₆ with nuclear emulsion detector at 1 GeV per nucleon. We have studied the average charge distribution and multiplicity distribution of the projectile fragments having charge 1 ≤ Z ≤ 10. We have also studied the emission behavior of various projectile fragments produced from the interaction with different target groups of nuclear emulsion detector. From this study we have observed that the emission of projectile fragments is strongly dependent on the interaction with different type of the target groups of nuclear emulsion detector as well as on the mass of the projectile beam. The results are compared with other experimental observations carried out at relativistic energy and found to be consistent.     

Observation of fine structures in laser-driven electron beams using coherent transition radiation

We have measured the coherent optical transition radiation emitted by an electron beam from laser-plasma interaction. The measurement of the spectrum of the radiation reveals fine structures of the electron beam in the range 400-1000 nm. These structures are reproduced using an electron distribution from a 3D particle-in-cell simulation and are attributed to microbunching of the electron bunch due to its interaction with the laser field. When the radiator is placed closer to the interaction point, spectral oscillations have also been recorded, signature of the interference of the radiation produced by two electron bunches delayed by 74 fs. The second electron bunch duration is shown to be ultrashort to match the intensity level of the radiation. Whereas transition radiation was used at longer wavelengths in order to estimate the electron bunch length, this study focuses on the ultrashort structures of the electron beam.     

Transverse momentum distribution of vector mesons produced in ultraperipheral relativistic heavy ion collisions

We study the transverse momentum distribution of vector mesons produced in ultraperipheral relativistic heavy ion collisions (UPCs). In UPCs there is no strong interaction between the nuclei, and the vector mesons are produced in photon-nucleus collisions where the (quasireal) photon is emitted from the other nucleus. Exchanging the role of both ions leads to interference effects. A detailed study of the transverse momentum distribution, which is determined by the transverse momentum of the emitted photon, the production process on the target, and the interference effect, is done. We study the unrestricted cross section and the one with an additional electromagnetic excitation of one or both ions; in the latter case small impact parameters are emphasized.     

Linear versus nonlinear coupling effects in single- and multiphonon atom-surface scattering

We present a comparative assessment of the features of inelastic atom-surface scattering spectra that are produced by different forms of linear and nonlinear phonon coupling to the projectile atom. Starting from a simple theoretical model of atom-surface scattering and employing recently developed exact numerical and approximate analytical methods we calculate and compare the scattering probabilities ensuing from each form of interaction. This enables us to demonstrate that in the regime of thermal energy atom scattering from surfaces the dominant contributions to the zero-, one-, and multiphonon excitation probabilities arise from linear coupling treated to all orders in the interaction.     

Generation of Multiple-Photon GHZ State via Cavity-Assisted Interaction

We propose a scheme for preparing multiple-photon GHZ state via cavity-assisted interaction. There are n-pair single-photon pulses successively injected and reflected from two sides of the cavity, which traps one atom. After the atomic state is measured, a 2n-photon GHZ state is produced. In the ideal case, the successful probability of the scheme is close to unity.     

Resonant multiphoton ionization of Li

We present calculations of three photon ionization of Li produced by 3-ps laser pulses within a single electron local model potential using the dressed state picture. The laser frequency ranges from 15 000 to 18 400 cm⁻¹. We have found that the measured ionization signal as a function of photon frequency results from ionization processes in a region where the laser intensity is not homogeneous. We assume a Gaussian shape for the light pulse in the interaction volume. Our results are shown to be in good agreement with experiment. We propose that free electrons are submitted to a ponderomotif potential to interpret experimental results. This revised version was published online in August 2006 with corrections to the Cover Date.     

Fast-field-cycling NMR study of magnetomechanically induced relaxation enhancement in ferrogelatine

We describe a field-cycling magnetic resonance experiment aimed to study the nuclear spinlattice relaxation in the simultaneous presence of an oscillating magnetic field and a magnetomechanically induced perturbation across the sample volume. The studied system is a gelatine doped with surfacted nanosize ferromagnetic particles. The spin system relaxes in coexistence with the magnetic interaction between the dopants and a weak external alternating magnetic field. Due to the interaction between the alternating field and the high magnetic moment of the dopants, a mechanical shaking of the particles becomes effective at low evolution fields. In this way, the particles act as local sonic sources, thus transmitting the vibrations to the gelic matrix where they are trapped. The impact produced on the molecular dynamics is observed through a magnetic resonance relaxation experiment. Saturation of the proton magnetization produced by the alternating magnetic field is also discussed. Results are compared with the direct effects produced by a pure sonic perturbation at the same frequency, introduced by coupling a piezoelectric transducer in direct contact with the sample.     

Detection of atomic oxygen by laser-induced fluorescence spectroscopy at 130 nm

VUV radiation generated by stimulated Raman scattering from H₂ and tunable around 130 nm is applied to the detection of atomic oxygen produced in a flow-tube. Concentrations in the range to the detection of atomic oxygen produced in a flow-tube. Concentrations in the range of 10¹⁰ to 10¹¹ O-atoms per cm³ lead to fluorescence signals that can easily be detected on a nanosecond timescale. We deduce that oxygen impurities generated by plasma-wall interaction in present-day tokamak experiments should be measurable with spatial and temporal resolution applying this vuv source.     

Amplitude scaling behavior of band center states of Frenkel exciton chains with correlated off-diagonal disorder

We report the amplitude scaling behavior of Frenkel exciton chains with nearest-neighbor correlated off-diagonal random interactions. The band center spectrum and its localization properties are investigated through the integrated density of states and the inverse localization length. The correlated random interactions are produced through a binary sequence similar to the interactions in spin glass chains. We produced sets of data with different interaction strength and “wrong” sign concentrations that collapsed after scaling to the predictions of a theory developed earlier for Dirac fermions with random-varying mass. We found good agreement as the energy approaches the band center for a wide range of concentrations. We have also established the concentration dependence of the lowest order expansion coefficient of the scaling amplitudes for the correlated case. The correlation causes unusual behavior of the spectra, i.e., deviations from the Dyson-type singularity.