We investigate the effects of a static electric field on the rovibrational spectra of several alkali polar dimers in their electronic ground state, and on their formation via stimulated emission from ultracold ground state atoms.
The formation of heteronuclear molecules in their electronic ground states from a mixture of two ultracold atomic species via a one-photon stimulated emission process is investigated. The presence of an additional external homogeneous and static electric field is shown to severely influence the induced emission process. Using the LiCs molecule as a prototype, we study the corresponding cross section and its dependence on the continuum energy, final rovibrational state, and static electric field strength. The possibility of controlling the single-photon association process via an additional static electric field is demonstrated.
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 polarizability. 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 as in our work on dipole moments [Aymar and 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.
The formation of ultracold molecules via stimulated emission followed by a radiative de-excitation cascade in the presence of a static electric field is investigated. By analyzing the corresponding cross-sections, we demonstrate the possibility to populate the lowest rotational excitations via photoassociation. The modification of the radiative cascade due to the electric field leads to narrow rotational state distributions in the vibrational ground state. External fields might therefore represent an additional valuable tool towards the ultimate goal of quantum state preparation of molecules.
In recent years there has been a great deal of progress towards cooling heteronuclear alkali metal dimer molecules to quantum degeneracy in their absolute ground state [1]. Ultracold polar molecules such as these are of great interest in many fields ranging from precision science and metrology to manybody physics [2]. Of particular interest to many-body physics is the fact that heteronuclear molecules have permanent electric dipole moments which give rise to long-range interactions in a DC electric field. Also, because of a nuclear quadrupole coupling, this dipole moment can also be used to access the many internal hyperfine states in a controlled way. This paves the way to rich, complex dynamics, such as the many-body dephasing of Rabi flopping between two internal states as shown in Fig. 1.
In this thesis properties of ultracold alkali dimers are studied both theoretically and experimentally. In the first, theoretical, part, the prospects for the formation of ultracold LiCs dimers in deeply bound vibrational levels using photoassociation (PA) are investigated. Furthermore a previous systematic investigation of the structure of all alkali dimers is extended by the ab initio calculation of static dipole polarizabilities. An extensive comparison with other published results supports the reliability of the chosen method. Based on these results an experimental scheme for the creation of an sample of oriented ultracold dipolar molecules is developed. In the second, experimental part the formation of LiCs ground state molecules by PA is investigated. PA spectroscopy is used to improve the accuracy of the potential energy curve for the B1P and the value of the dissociation energy of the X1S+ state significantly. The rovibrational distribution of ground state molecules is probed in a combination of resonance-enhanced multi-photon ionization and depletion spectroscopy. A simple scheme is found to form ultracold polar LiCs molecules in the absolute ground state X1S+,v''=0,J''=0. In a quasi-electrostatic trap created by a CO2 laser, LiCs molecules are formed and stored. A lifetime of 24(3)s, limited by collisions with background gas, is observed and rate coefficients for inelastic collisions between LiCs in high vibrational states and Cs atoms are determined. The long storage time facilitates the observation of radiative decay of polar molecules towards lower vibrational levels.