75 research outputs found
Calculations of static dipole polarizabilities of alkali dimers. Prospects for alignment of ultracold molecules
The rapid development of experimental techniques to produce ultracold alkali
molecules opens the ways to manipulate them and to control their dynamics using
external electric fields. A prerequisite quantity for such studies is the
knowledge of their static dipole polarizabilities. In this paper, we computed
the variations with internuclear distance and with vibrational index of the
static dipole polarizability components of all homonuclear alkali dimers
including Fr, and of all heteronuclear alkali dimers involving Li to Cs, in
their electronic ground state and in their lowest triplet state. We use the
same quantum chemistry approach than in our work on dipole moments (M. Aymar
and O. Dulieu, J. Chem. Phys. 122, 204302 (2005)), based on pseudopotentials
for atomic core representation, Gaussian basis sets, and effective potentials
for core polarization. Polarizabilities are extracted from electronic energies
using the finite-field method. For the heaviest species Rb, Cs and
Fr and for all heteronuclear alkali dimers, such results are presented for
the first time. The accuracy of our results on atomic and molecular static
dipole polarizabilities is discussed by comparing our values with the few
available experimental data and elaborate calculations. We found that for all
alkali pairs, the parallel and perpendicular components of the ground state
polarizabilities at the equilibrium distance scale as , which
can be related to a simple electrostatic model of an ellipsoidal charge
distribution. Prospects for possible alignment and orientation effects with
these molecules in forthcoming experiments are discussed.Comment: Accepted for publication in J Chem Phy
Modeling many-particle mechanical effects of an interacting Rydberg gas
In a recent work [Phys. Rev. Lett. 98, 023004 (2007)] we have investigated
the influence of attractive van der Waals interaction on the pair distribution
and Penning ionization dynamics of ultracold Rydberg gases. Here we extend this
description to atoms initially prepared in Rydberg states exhibiting repulsive
interaction. We present calculations based on a Monte Carlo algorithm to
simulate the dynamics of many atoms under the influence of both repulsive and
attractive longrange interatomic forces. Redistribution to nearby states
induced by black body radiation is taken into account, changing the effective
interaction potentials. The model agrees with experimental observations, where
the ionization rate is found to increase when the excitation laser is
blue-detuned from the atomic resonance
Suppression of Excitation and Spectral Broadening Induced by Interactions in a Cold Gas of Rydberg Atoms
We report on the observation of ultralong range interactions in a gas of cold
Rubidium Rydberg atoms. The van-der-Waals interaction between a pair of Rydberg
atoms separated as far as 100,000 Bohr radii features two important effects:
Spectral broadening of the resonance lines and suppression of excitation with
increasing density. The density dependence of these effects is investigated in
detail for the S- and P- Rydberg states with main quantum numbers n ~ 60 and n
~ 80 excited by narrow-band continuous-wave laser light. The density-dependent
suppression of excitation can be interpreted as the onset of an
interaction-induced local blockade
Sub-Poissonian statistics of Rydberg-interacting dark-state polaritons
Interfacing light and matter at the quantum level is at the heart of modern
atomic and optical physics and enables new quantum technologies involving the
manipulation of single photons and atoms. A prototypical atom-light interface
is electromagnetically induced transparency, in which quantum interference
gives rise to hybrid states of photons and atoms called dark-state polaritons.
We have observed individual dark-state polaritons as they propagate through an
ultracold atomic gas involving Rydberg states. Strong long-range interactions
between Rydberg atoms give rise to an effective interaction blockade for
dark-state polaritons, which results in large optical nonlinearities and
modified polariton number statistics. The observed statistical fluctuations
drop well below the quantum noise limit indicating that photon correlations
modified by the strong interactions have a significant back-action on the
Rydberg atom statistics.Comment: 7 pages, 4 figure
- …