Entangling neutral atoms for quantum information processing

Abstract

We review recent proposals for performing entanglement manipulation via cold collisions between neutral atoms. State-dependent, time-varying trapping potentials allow one to control the interaction between atoms, so that conditional phase shifts realizing a universal quantum gate can be obtained with high fidelity. We discuss possible physical implementations with existing experimental techniques, for example optical lattices and magnetic micro-traps.     

Photoionization of atoms and ions

Calculations of subshell photoionization processes are performed for various atoms (neon, argon, iron and uranium), for various degrees of ionization, within the independent-particle approximation. We discuss the asymptotic behavior and the high-energy features of these cross sections, focusing on subshell cross-section ratio functions. Near threshold, a modified Dirac-Fock theory is used to study core relaxation effects on photoabsorption for argon. Finally we examine the ionic neon total photoabsorption cross section as a function of degree of ionization.     

Tripartite entanglement generation using cavity-QED and its dynamics in dissipative environments

We investigate the generation of tripartite field states inside the high-Q cavities using the cavity QED. The main goal is to successfully generate the entanglement in tripartite systems by passing two-level atoms through three identical high-Q cavities. Our scheme gives the successful generation of entangled tripartite W and GHZ states for pre-determined interaction times of atoms with the cavity fields. The dynamics of initial entangled states is studied as the system evolves in the dissipative environments.     

Generation processes of super-high-energy atoms and ions in magnetron sputtering plasma

Energy distribution function (EDF) of ion species (Ar⁺, Kr⁺, Xe⁺) in a rare gas magnetron plasma is measured at a substrate position, 0.1 m away from the target surface, by energy-resolved mass spectrometry. The measured ion EDF contains, besides a bulk low-energy part (<10 eV), a tail part of super-high energy on an order of 100 eV, depending on the mass ratio of ion species to target material (tungsten, permalloy (80% Ni, 20% Fe)). A weak electric field in a diffusion region of magnetron plasma cannot accelerate slow bulk ions of ∼0.2 eV to such high energies. Origin of large kinetic energies is attributed to the backscattering process on the target surface where, e.g., Ar⁺ ions impinging on the target are neutralized and reflected as fast Ar atoms of the kinetic energy approximately given by a two-body collision model. Subsequently, a part of fast atoms may be converted to fast ions in three possible collision processes in the diffusion region: (i) electron impact ionization (ii) resonant charge exchange, and (iii) ionization of slow atoms by fast atoms. Among them, the third process is found to be dominant from Monte Carlo simulations where the backscattering process is evaluated by the TRIM code. Furthermore, when the target mass is larger than the bombarding ion mass, the substrate is bombarded by the super-high-energy atoms having a flux 2-4 orders of magnitude larger than the fast-ion flux.     

Dechanneling of ions on atoms incorporated into carbon nanotubes

Dechanneling of accelerated ions as a result of interaction with atoms incorporated into the cavities of carbon nanotubes (CNTs) is considered. The Chapman-Kolmogorov kinetic equation describing this process is constructed and solved, and analytical formulas for the length of particle dechanneling from CNTs are obtained. It is shown that these lengths strongly depend on the positions of atoms inside CNT channels and, in contrast to the case of dechanneling on electrons, increase as √E with increasing ion energy E.     

Fragmentation of protonated peptide ions via interaction with metastable atoms

Fragmentation of protonated peptide ions via interaction with low kinetic energy electronicallyexcited metastable argon atoms was studied in a linear trap-time-of-flight mass spectrometer. Metastable argon atoms were generated using a glow discharge-type source. Protonated peptide ions of substance P, bradykinin, fibrinopetide A, and insulin oxidized chain B were produced by electrospray ionization and trapped in a quadrupole ion guide for 100-400 ms. Intensive series of c- and z-ions were observed in all cases. The kinetic measurements of the fragmentation rates are consistent with calculations of the reaction cross section based on the Landau-Zener approximation.     

Harmonic generation in laser-produced plasmas containing atoms,ions and clusters: a review

A review of studies of the high-order harmonic generation of laser radiation in laser-produced plasma revealed recent developments in this field. These include new approaches in application of two-colour pumps, generation of extremely broadened harmonics, further developments in harmonic generation in clusters (fullerenes, carbon nanotubes), destructive interference of harmonics from different emitters, new approaches in resonance-induced enhancement of harmonics, applications of high pulse repetition rate lasers for the enhancement of average power of generating harmonics and observation of quantum path signatures, etc. We show that this method of frequency conversion of laser radiation towards the extreme ultraviolet range became mature during multiple sets of studies carried out in many laboratories worldwide and demonstrated new approaches in the generation of strong coherent short-wavelength radiation for various applications.     

The effective stopping of relativistic structural heavy ions colliding with atoms

A nonperturbative method is developed for calculating the energy losses upon collisions of relativistic structural large-Z ions with atoms. By structural ions are implied those containing partly occupied electron shells. Usually possessing a large charge, such projectiles (e.g., fully or partly stripped uranium ions) are frequently employed in the experiments on modern heavy-particle accelerators.     

Electron stripping cross section from multiply charged ions by neutral atoms

Electron stripping cross sections for energetic highly charged C and Ne ions are calculated using the method based on the binary encounter approximation. Electrons of the ion are considered to be stripped by collision with the target nucleus, i.e. the electron screening is ignored. The cross section is written in terms of relative velocity between each electron and the target nucleus. The velocity distribution of electrons of the ions is obtained by the Thomas-Fermi statistical model for the purpose of obtaining the general behavior of projectile and target atomic number dependences. The effect of shell-structure on the cross section is taken into account by considering the average binding energies of electrons that are supposed to exist in each shell.     

Potential sputtering of hydrogen atoms on various surfaces with slow highly-charged ions

Several recent findings on a new sputtering mechanism of hydrogen with slow highly-charged ions are discussed. The sputtering yields of protons were proportional to q^∼5 for q≲10 independent of the surface condition for both untreated and well-defined surfaces, where q is the charge state of the ion. This q^∼5 dependence started to level off for q≲10. The yield for the Si(100)1×1–H surface was ten times larger than that for the Si(100)2×1–H surface although the stoichiometric hydrogen abundance of the former is only twice that of the latter. The key quantity to govern the yield is proposed to be surface roughness, which also influences the energy distribution of sputtered protons. These findings were consistently explained with a pair-wise potential sputtering model involving two successive electron transfers which follow the classical over barrier mechanism.     

Single and double ionization cross sections of atoms colliding with relativistic structural heavy ions

The single and double ionization cross sections of hydrogen and helium atoms colliding with relativistic structural heavy ions are calculated within the framework of the eikonal approximation. By structural ions are implied those containing partly occupied electron shells. It is shown that an allowance for the finite size of charged ions leads to significant changes in the ionization cross sections as compared to those determined for the point ions possessing the same charges and energies.     

Analytic model for the lowering of the ionization potentials of atoms and ions in a collisional plasma

A model admitting of an analytic solution is developed for the calculation of the level shift and the reduction of the ionization potentials of atoms and ions due to screening in a collisional plasma. The application of the derived equations to the plasmas of aluminum, gold, copper and cesium shows the greatest reduction in the ionization potential occurs for cesium. Pis’ma Zh. Tekh. Fiz. 23, 44–49 (June 26, 1997)     

Experimental setup for X-ray spectroscopy of muonic atoms formed from implanted ions in solid hydrogen

An experimental setup comprising of a cryogenic target and an ion implantation system has been constructed to perform muonic X-ray spectroscopy with muonic atoms formed from implanted ions in solid hydrogen films. Gaseous mixtures of hydrogen (H₂) and deuterium (D₂) have been frozen onto a thin 60-mm diameter silver foil, and then irradiated with charged particles of energies up to 33 keV/q. Already, solid films of H₂ and D₂ mixtures with implanted helium ions have been successfully used in muon catalyzed fusion related experiments at RIKEN-RAL Muon Facility. This new method allows studies of the nuclear charge distribution of unstable atoms by means of the muonic X-ray method at facilities where both negative muon and radioactive nuclear beams would be available.     

Self-deflection of dissipative holographic screening-photovoltaic solitons in a biased dissipative photovoltaic-photorefractive crystal

The self-deflection of dissipative holographic screening-photovoltaic (DHSP) solitons has been investigated in the dissipative system, which consists of a biased dissipative photovoltaic-photorefractive (PV-PR) crystal and two coherently coupled beams; the signal beam (self-trapping beam) gets the energy gain from the pump beam via the two-beam coupling process. The analytical results are in good agreement with the numerical ones. Both predict that the centre of the solitary beam moves on a parabolic trajectory. Moreover, the central spatial-frequency component shifts linearly with the propagation distance. The DHSP soliton has the fixed self-deflection that is completely determined by the system parameters, its self-deflection is slight under small-signal condition, which will bring little influence on the formation of DHSP solitons. Furthermore, the relevant properties on the behaviour of bright DHSP soliton are discussed in detail.     

Energy flux in dissipative media

Summary Energy flux density in dissipative solids and fluids is investigated. First it is emphasized that inescapably ambiguities arise about the expression of the energy flux if the identification is merely based on possible splittings of the terms occurring in the energy equation. Then the energy flux density is determined for inhomogeneous waves in solids and fluids. New terms for solids are found in connection with transverse waves due to the complex-valuedness of the amplitude. The results for fluids are new and turn out to be qualitatively similar to those for solids.     

Pinning and dissipative effects in Bi-Pb-Sr-Ca-CuO superconductor

Pinning and dissipative effects have been investigated in Bi-Pb-Sr-Ca-CuO sintered compounds by means of DC magnetization and magnetic relaxation measurements. Hysteresis cycles have been performed up to 5 T from 18 to 50 K, and the time decay of the zero field cooled magnetization (M _zfc) has been recorded both as a function of field and temperature. The observed temperature dependence of the reduced pinning force and the crossover from a logarithmic to a nonlogarithmic time decay ofM _zfc (forT>50 K), are discussed in relation to the collective pinning and the related extensions to flux creep.