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$_2$, 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$_2$, Cs$_2$ and Fr$_2$ 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 $R_e$ scale as $(R_e)^3$, 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