H-+ ion production from collisions between antiprotons and excited positronium: cross sections calculations in the framework of the GBAR experiment:

In the framework of the gravitational behaviour of antihydrogen at rest (GBAR) experiment, cross sections for the successive formation of (p) over bar and H-+ from collisions between positronium (Ps) and antiprotons ((p) over bar) have been computed in the range 0-30 keV (p) over bar energy, using the continuum distorted wave-final state theoretical model in its three-body and four-body formulations. The effect of the electronic correlations in H-+ on the total cross sections of H-+ production has been studied using three different wave functions for H- (the matter equivalent of H-+). Ps excited states up to n(p) = 3, as well as H- excited states up to n(h) = 4, have been investigated. The results suggest that the production of H-+ can be efficiently enhanced by using either a fraction of Ps(2p) and a 2 keV ((p) over bar) beam or a fraction Ps(3d) and antiprotons with kinetic energy below 1 keV

Bose-Einstein condensation of positronium in silica pores

We investigate the possibility to produce a Bose-Einstein condensate made of positronium atoms in a porous silica material containing isolated nanometric cavities. The evolution equation of a weakly interacting positronium system is presented. The model includes the interactions among the atoms in the condensate, the surrounding gas of noncondensed atoms, and the pore surface. The final system is expressed by the Boltzmann evolution equation for noncondensed particles coupled with the Gross-Pitaevskii equation for the condensate. In particular, we focus on the estimation of the time necessary to form a condensate containing a macroscopic fraction of the positronium atoms initially injected in the material. The numerical simulations reveal that the condensation process is compatible with the lifetime of ortho-positronium

Bose-Einstein-condensation dynamics with a quantum-kinetic approach

The evolution equation of a weakly interacting boson system is derived. The model includes the interaction between the atoms in the condensate and the surrounding gas of noncondensed particles. The Bogoliubov transformation is introduced in a full quantum context and the scattering kernel between dressed particles and the condensate phase is obtained. The final system is expressed by the Boltzmann evolution equation for noncondensed particles coupled to the Gross-Pitaevskii equation for the condensate. We consider an out-of-equilibrium situation that induces a fast production of condensed particles. We apply our model to study the condensation dynamics of positronium atoms by evaporation

Quantum-relativistic hydrodynamic model for a spin-polarized electron gas interacting with light

We develop a semirelativistic quantum fluid theory based on the expansion of the Dirac Hamiltonian to second order in 1/c. By making use of the Madelung representation of thewave function, we derive a set of hydrodynamic equations that comprises a continuity equation, an Euler equation for the mean velocity, and an evolution equation for the electron spin density. This hydrodynamic model is then applied to study the dynamics of a dense and weakly relativistic electron plasma. In particular, we investigate the impact of the quantum-relativistic spin effects on the Faraday rotation in a one-dimensional plasma slab irradiated by an x-ray laser source

Autoresonant switching of the magnetization in single-domain nanoparticles: Two-level theory:

The magnetic moment of a single-domain nanoparticle can be effectively switched on an ultrashort time scale by means of oscillating (microwave) magnetic fields. This switching technique can be further improved by using fields with time-dependent frequency (autoresonance). Here, we provide a full theoretical framework for the autoresonant switching technique, by exploiting the analogy between the magnetization state of an isolated nanoparticle and a two-level quantum system, whereby the switching process can be interpreted as a population transfer. We derive analytical expressions for the threshold amplitude of the microwave field, with and without damping, and consider the effect of thermal fluctuations. Comparisons with numerical simulations show excellent agreement

Equivalence between the semirelativistic limit of the Dirac-Maxwell equations and the Breit-Pauli model in the mean-field approximation

We demonstrate the equivalence between (i) the semirelativistic limit (up to second order in the inverse of the speed of light) of the self-consistent Dirac-Maxwell equations and (ii) the Breit-Pauli equations in the mean-field (Hartree-like) approximation. We explain how the charge and current densities that act as sources in the Dirac-Maxwell equations are related to the microscopic two-electron interactions of the Breit-Pauli model (spin orbit, spin-other-orbit, and spin-spin). The key role played by the second-order corrections to the charge density is clarified

High-harmonic generation by nonlinear resonant excitation of surface plasmon modes in metallic nanoparticles

The nonlinear electron dynamics in metallic nanoparticles is studied using a hydrodynamic model that incorporates most quantum many-body features, including spill-out and nonlocal effects as well as electron exchange and correlations. We show that, by irradiating the nanoparticle with a chirped laser pulse of modest intensity (autoresonance), it is possible to drive the electron dynamics far into the nonlinear regime, leading to enhanced energy absorption and complete ionization of the nanoparticle on a time scale of the order of 100 fs. The accompanying radiated power spectrum is rich in high-order harmonics

Magnetization reversal in isolated and interacting single-domain nanoparticles

Computational and experimental results of thermally induced magnetization reversal in single-domain magnetic nanoparticles are reported. The simulations are based on direct integration of the Fokker-Planck equation that governs the dynamics of the magnetic moment associated with the nanoparticles. A mean-field approximation is used to account for the influence of the dipolar interaction between nanoparticles. It is shown that the interactions can either speed up or slow down the reversal process, depending on the angle between the external magnetic field and the axis of easymagnetization. The numerical results are in good agreement with experimental measurements of cobalt-platinum nanoparticles

Exact treatment of planar two-electron quantum dots: Effects of anharmonicity on the complexity:

The static properties of an anharmonic potential model for planar two-electron quantum dots are investigated using a method that allows for the exact representation of the matrix elements, including the full Coulombic electron-electron interaction. A quartic perturbation of the harmonic confining potential in combination with the interparticle Coulomb interaction affects the spectral properties of the system considerably as it implies total loss of separability in the dynamics. Consequently, the classical phase space is mixed regular-chaotic and standard spectral measures of quantum chaos indicate an intermediate degree of complexity. Apart from the prompt transition from a regular to a moderately chaotic regime for weak quartic perturbation, the complexity of the system appears to be insensitive to the strength of the quartic potential. DOI: 10.1103/PhysRevB.87.15541

Lagrangian approach to the semirelativistic electron dynamics in the mean-field approximation

We derive a mean-field model that is based on a two-component Pauli-like equation and incorporates quantum, spin, and relativistic effects up to second order in 1/c. Using a Lagrangian approach, we obtain the self-consistent charge and current densities that act as sources in the Maxwell equations. A physical interpretation is provided for the second-order corrections to the sources. The Maxwell equations are also expanded to the same order. The resulting self-consistent model constitutes a suitable semirelativistic approximation to the full Dirac-Maxwell equations