No abstract

The progress in solution of problems involving non-relativistic fast ion-atom collisions with two actively participating electrons has been reviewed. Leading quantum mechanical methods have been analyzed in the framework of four-body scattering theory. A simple formalism has been described on the basis of the Dodd-Greider integral equations for a four-particle system, which were used to analyze the two-electron charge-exchange process at medium and high velocities of relative motion of particles. An important feature of the developed four-particle continuum distorted waves (CDW) method is the consistent preservation of the proper asymptotic limits of the wave functions of a colliding system in the entrance and exit channels of the reaction, which takes into account the long-range nature of Coulomb interactions. The amplitude of the two-electron charge-exchange reaction has been calculated in the approximation of the mechanism of simultaneous capture by an incident particle of two target electrons. The calculations using the presented theory have been made on the example of a two-electron capture reaction in high-energy He 2+ +He collisions.

The problem of interaction of two quasimolecular electrons located at an arbitrary distance from each other and near different atoms (nuclei) is solved. The interaction is considered as a second-order effect of quantum electrodynamics in the coordinate representation. It is shown that a consistent account for the natural condition of the interaction symmetry with respect to both electrons leads to an additional contribution to the relativistic interaction of the two quasimolecular electrons compared with both the standard Breit operator and the generalized Breit operator known previously. The generalized Breit–Pauli operator and the operator of electric dipole–dipole interaction of two quasimolecular electrons located at an arbitrary distance from each other are obtained. Modern methods of accounting for the relativistic and correlative effects in the problem of ion–atom interactions are discussed.

Purpose. As a standard model for describing the processes of a resonant transmission of quantum information on arbitrary distances is the system of two identical two-level atoms, one of which is under radiation of the field of real photons. Such a system can serve as a basis for the construction of an element basis of quantum computers. The purpose of this paper is to study the different modes of dynamics of a system of two identical two-level atoms when they interacts with the field of real photons. Methods. In this paper, we propose a general approach to the description of the processes for the transfer of quantum information from one atom-qubit to another on the arbitrary interatomic distances, which includes two types of new physical effects: the attenuation of quantum states and the retardation of the dipole-dipole interaction. Results. The optical properties of a system of two identical two-level atoms in collective (symmetric Ψ s and antisymmetric Ψ a) Bell states at arbitrary interatomic distances are investigated. The closed analytical expressions for the shifts and widths of the considered collective states are considered, taking into account the retarded dipole-dipole interaction of atoms. In calculation of the radial matrix elements of the dipole-dipole interaction, the wave functions of the model Fues potential are used. Conclusions. A detailed study of the mechanisms of resonant transmission of the excitation energy at arbitrary distances between the two-element atoms has an important practical significance for the physical realization of the logical operator CNOT.