300 research outputs found
Simulation of the elementary evolution operator with the motional states of an ion in an anharmonic trap
Following a recent proposal of L. Wang and D. Babikov, J. Chem. Phys. 137,
064301 (2012), we theoretically illustrate the possibility of using the
motional states of a ion trapped in a slightly anharmonic potential to
simulate the single-particle time-dependent Schr\"odinger equation. The
simulated wave packet is discretized on a spatial grid and the grid points are
mapped on the ion motional states which define the qubit network. The
localization probability at each grid point is obtained from the population in
the corresponding motional state. The quantum gate is the elementary evolution
operator corresponding to the time-dependent Schr\"odinger equation of the
simulated system. The corresponding matrix can be estimated by any numerical
algorithm. The radio-frequency field able to drive this unitary transformation
among the qubit states of the ion is obtained by multi-target optimal control
theory. The ion is assumed to be cooled in the ground motional state and the
preliminary step consists in initializing the qubits with the amplitudes of the
initial simulated wave packet. The time evolution of the localization
probability at the grids points is then obtained by successive applications of
the gate and reading out the motional state population. The gate field is
always identical for a given simulated potential, only the field preparing the
initial wave packet has to be optimized for different simulations. We check the
stability of the simulation against decoherence due to fluctuating electric
fields in the trap electrodes by applying dissipative Lindblad dynamics.Comment: 31 pages, 8 figures. Revised version. New title, new figure and new
reference
Ab initio calculation of H + He charge transfer cross sections for plasma physics
The charge transfer in low energy (0.25 to 150 eV/amu) H() + He
collisions is investigated using a quasi-molecular approach for the as
well as the first two singlet states. The diabatic potential energy
curves of the HeH molecular ion are obtained from the adiabatic potential
energy curves and the non-adiabatic radial coupling matrix elements using a
two-by-two diabatization method, and a time-dependent wave-packet approach is
used to calculate the state-to-state cross sections. We find a strong
dependence of the charge transfer cross section in the principal and orbital
quantum numbers and of the initial or final state. We estimate the
effect of the non-adiabatic rotational couplings, which is found to be
important even at energies below 1 eV/amu. However, the effect is small on the
total cross sections at energies below 10 eV/amu. We observe that to calculate
charge transfer cross sections in a manifold, it is only necessary to
include states with , and we discuss the limitations of our
approach as the number of states increases.Comment: 14 pages, 10 figure
Cold collisions of C anions with Li and Rb atoms in hybrid traps
We present a theoretical investigation of reactive and non-reactive
collisions of Li and Rb atoms with C molecular anions at low
temperatures in the context of sympathetic cooling in hybrid trap experiments.
Based on recently reported accurate potential energy surfaces for the singlet
and triplet states of the Li-C and Rb-C systems, we show
that the associative electronic detachment reaction is slow if the colliding
partners are in their ground state, but fast if they are excited. The results
are expected to be representative of the alkali-metal series. We also
investigate rotationally inelastic collisions in order to explore the cooling
of the translational and rotational degrees of freedom of C in hybrid
ion-atom traps. The effect of micromotion is taken into account by considering
Tsallis distributions of collision energies. We show that the translational
cooling occurs much more rapidly than rotational cooling and that the presence
of excited atoms leads to losses of anions on a timescale comparable to that of
rotational cooling.Comment: ICPEAC 2019 conferenc
Evidence for two-electron processes in the mutual neutralization of O- with O+ and N+ at Subthermal Collision Energies
We have measured total absolute cross sections for the Mutual Neutralization
(MN) of O- with O+/N+. A fine resolution (of about 50 meV) in the kinetic
energy spectra of the product neutral atoms allows unique identification of the
atomic states participating in the mutual neutralization process. Cross
sections and branching ratios have also been calculated down to 1 meV
center-of-mass collision energy for these two systems with a multi-channel
Landau-Zener model and an asymptotic method for the ionic-covalent coupling
matrix elements. The importance of two-electron processes in one-electron
transfer is demonstrated by the dominant contribution of a core-excited
configuration of the nitrogen atom in N+ + O- collisions. This effect is
partially accounted for by introducing configuration mixing in the evaluation
of coupling matrix elements.Comment: 5 pages, 4 figure
Ab initio calculation of the 66 low lying electronic states of HeH: adiabatic and diabatic representations
We present an ab initio study of the HeH molecule. Using the quantum
chemistry package MOLPRO and a large adapted basis set, we have calculated the
adiabatic potential energy curves of the first 20 , 19
, 12 , 9 , 4 and 2 electronic
states of the ion in CASSCF and CI approaches. The results are compared with
previous works. The radial and rotational non-adiabatic coupling matrix
elements as well as the dipole moments are also calculated. The asymptotic
behaviour of the potential energy curves and of the various couplings between
the states is also studied. Using the radial couplings, the diabatic
representation is defined and we present an example of our diabatization
procedure on the states.Comment: v2. Minor text changes. 28 pages, 18 figures. accepted in J. Phys.
Static secondary ion mass spectrometry (S-SIMS) analysis of atmospheric plasma treated polypropylene films
Combined CI+MBPT calculations of energy levels and transition amplitudes in Be, Mg, Ca, and Sr
Configuration interaction (CI) calculations in atoms with two valence
electrons, carried out in the V(N-2) Hartree-Fock potential of the core, are
corrected for core-valence interactions using many-body perturbation theory
(MBPT). Two variants of the mixed CI+MBPT theory are described and applied to
obtain energy levels and transition amplitudes for Be, Mg, Ca, and Sr
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