134 research outputs found
On the long-range and short-range behavior of potentials from reproducing kernel Hilbert space interpolation
The short-range and long-range asymptotic behavior of potential functions obtained from the reciprocal power reproducing kernel Hilbert spaceinterpolation procedure [Ho and Rabitz, J. Chem. Phys. 104, 2584 (1996)] is analyzed. In the short-range region, the potential functions are polynomial in form: the method should not be used for extrapolation in this region. General formulae for the short-range and long-range expansion coefficients are presented. Potentials for He-Ar+ are discussed as examples
Spectroscopy of Na<sup>+</sup>·Rg and transport coefficients of Na<sup>+</sup> in Rg (Rg=He-Rn)
High-level ab initio calculations are used to obtain accurate potential energy curves for Na+·Kr, Na+·Xe, and Na+·Rn. These data are used to calculate spectroscopic parameters for these three species, and the data for the whole Na+·Rg series (Rg=He-Rn) are compared. Potentials for the whole series are then used to calculate both mobilities and diffusion coefficients for Na+ moving through a bath of each of the six rare gases, under conditions that match previous experimental determinations. Different available potentials and experimental data are then statistically compared. It is concluded that the present potentials are very accurate. The potential and other data for Na+·Rn appear to be the first such reported
Ab initio investigation of intermolecular interactions in solid benzene
A computational strategy for the evaluation of the crystal lattice constants
and cohesive energy of the weakly bound molecular solids is proposed. The
strategy is based on the high level ab initio coupled-cluster determination of
the pairwise additive contribution to the interaction energy. The
zero-point-energy correction and non-additive contributions to the interaction
energy are treated using density functional methods. The experimental crystal
lattice constants of the solid benzene are reproduced, and the value of 480
meV/molecule is calculated for its cohesive energy
Structure and potential energy surface for Na⁺.N₂
Version of RecordPublishe
Spectroscopy of Na⁺.Rg and transport coefficients of Na⁺ in Rg(Rg=He ―Rn)
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Cold collisions of OH and Rb. I: the free collision
We have calculated elastic and state-resolved inelastic cross sections for
cold and ultracold collisions in the Rb() + OH() system,
including fine-structure and hyperfine effects. We have developed a new set of
five potential energy surfaces for Rb-OH() from high-level {\em ab
initio} electronic structure calculations, which exhibit conical intersections
between covalent and ion-pair states. The surfaces are transformed to a
quasidiabatic representation. The collision problem is expanded in a set of
channels suitable for handling the system in the presence of electric and/or
magnetic fields, although we consider the zero-field limit in this work.
Because of the large number of scattering channels involved, we propose and
make use of suitable approximations. To account for the hyperfine structure of
both collision partners in the short-range region we develop a
frame-transformation procedure which includes most of the hyperfine
Hamiltonian. Scattering cross sections on the order of cm are
predicted for temperatures typical of Stark decelerators. We also conclude that
spin orientation of the partners is completely disrupted during the collision.
Implications for both sympathetic cooling of OH molecules in an environment of
ultracold Rb atoms and experimental observability of the collisions are
discussed.Comment: 20 pages, 16 figure
Three-body non-additive forces between spin-polarized alkali atoms
Three-body non-additive forces in systems of three spin-polarized alkali
atoms (Li, Na, K, Rb and Cs) are investigated using high-level ab initio
calculations. The non-additive forces are found to be large, especially near
the equilateral equilibrium geometries. For Li, they increase the three-atom
potential well depth by a factor of 4 and reduce the equilibrium interatomic
distance by 0.9 A. The non-additive forces originate principally from chemical
bonding arising from sp mixing effects.Comment: 4 pages, 3 figures (in 5 files
Creation of ultracold molecules from a Fermi gas of atoms
Since the realization of Bose-Einstein condensates (BEC) in atomic gases an
experimental challenge has been the production of molecular gases in the
quantum regime. A promising approach is to create the molecular gas directly
from an ultracold atomic gas; for example, atoms in a BEC have been coupled to
electronic ground-state molecules through photoassociation as well as through a
magnetic-field Feshbach resonance. The availability of atomic Fermi gases
provides the exciting prospect of coupling fermionic atoms to bosonic
molecules, and thus altering the quantum statistics of the system. This
Fermi-Bose coupling is closely related to the pairing mechanism for a novel
fermionic superfluid proposed to occur near a Feshbach resonance. Here we
report the creation and quantitative characterization of exotic, ultracold
K molecules. Starting with a quantum degenerate Fermi gas of atoms
at T < 150 nanoKelvin we scan over a Feshbach resonance to adiabatically create
over a quarter million trapped molecules, which we can convert back to atoms by
reversing the scan. The small binding energy of the molecules is controlled by
detuning from the Feshbach resonance and can be varied over a wide range. We
directly detect these weakly bound molecules through rf photodissociation
spectra that probe the molecular wavefunction and yield binding energies that
are consistent with theory
A trapped single ion inside a Bose-Einstein condensate
Improved control of the motional and internal quantum states of ultracold
neutral atoms and ions has opened intriguing possibilities for quantum
simulation and quantum computation. Many-body effects have been explored with
hundreds of thousands of quantum-degenerate neutral atoms and coherent
light-matter interfaces have been built. Systems of single or a few trapped
ions have been used to demonstrate universal quantum computing algorithms and
to detect variations of fundamental constants in precision atomic clocks. Until
now, atomic quantum gases and single trapped ions have been treated separately
in experiments. Here we investigate whether they can be advantageously combined
into one hybrid system, by exploring the immersion of a single trapped ion into
a Bose-Einstein condensate of neutral atoms. We demonstrate independent control
over the two components within the hybrid system, study the fundamental
interaction processes and observe sympathetic cooling of the single ion by the
condensate. Our experiment calls for further research into the possibility of
using this technique for the continuous cooling of quantum computers. We also
anticipate that it will lead to explorations of entanglement in hybrid quantum
systems and to fundamental studies of the decoherence of a single, locally
controlled impurity particle coupled to a quantum environment
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