Long-range interactions between polar bialkali ground-state molecules in arbitrary vibrational levels

We have calculated the isotropic $C\_6$ coefficients characterizing the long-range van der Waals interaction between two identical heteronuclear alkali-metal diatomic molecules in the same arbitrary vibrational level of their ground electronic state $X^1\Sigma^+$. We consider the ten species made up of $^7$Li, $^{23}$Na, $^{39}$K, $^{87}$Rb and $^{133}$Cs. Following our previous work [M.~Lepers \textit{et.~al.}, Phys.~Rev.~A \textbf{88}, 032709 (2013)] we use the sum-over-state formula inherent to the second-order perturbation theory, composed of the contributions from the transitions within the ground state levels, from the transition between ground-state and excited state levels, and from a crossed term. These calculations involve a combination of experimental and quantum-chemical data for potential energy curves and transition dipole moments. We also investigate the case where the two molecules are in different vibrational levels and we show that the Moelwyn-Hughes approximation is valid provided that it is applied for each of the three contributions to the sum-over-state formula. Our results are particularly relevant in the context of inelastic and reactive collisions between ultracold bialkali molecules, in deeply bound or in Feshbach levels

Model for the hyperfine structure of electronically-excited KCs{\rm KCs} molecules

A model for determining the hyperfine structure of the excited electronic states of diatomic bialkali heteronuclear molecules is formulated from the atomic hyperfine interactions, and is applied to the case of bosonic $^{39}$KCs and fermionic $^{40}$KCs molecules. The hyperfine structure of the potential energy curves of the states correlated to the K(4s\,^2S_{1/2})+Cs(6p\,^2P_{1/2,3/2}) dissociation limits is described in terms of different coupling schemes depending on the internuclear distance $R$. These results provide the first step in the calculation of the hyperfine structure of rovibrational levels of these excited molecular states in the perspective of the identification of efficient paths for creating ultracold ground-state KCs molecules.Comment: 12 pages, 15 figure

Photoassociative creation of ultracold heteronuclear 6Li40K* molecules

We investigate the formation of weakly bound, electronically excited, heteronuclear 6Li40K* molecules by single-photon photoassociation in a magneto-optical trap. We performed trap loss spectroscopy within a range of 325 GHz below the Li(2S_(1/2))+K(4P_(3/2)) and Li(2S_(1/2))+K(4P_(1/2)) asymptotic states and observed more than 60 resonances, which we identify as rovibrational levels of 7 of 8 attractive long-range molecular potentials. The long-range dispersion coefficients and rotational constants are derived. We find large molecule formation rates of up to ~3.5x10^7s^(-1), which are shown to be comparable to those for homonuclear 40K_2*. Using a theoretical model we infer decay rates to the deeply bound electronic ground-state vibrational level X^1\Sigma^+(v'=3) of ~5x10^4s^(-1). Our results pave the way for the production of ultracold bosonic ground-state 6Li40K molecules which exhibit a large intrinsic permanent electric dipole moment.Comment: 6 pages, 4 figures, submitted to EP

Photoassociation of a cold-atom-molecule pair. II. Second-order perturbation approach

The electrostatic interaction between an excited atom and a diatomic ground-state molecule in an arbitrary rovibrational level at large mutual separations is investigated with a general second-order perturbation theory, in the perspective of modeling the photoassociation between cold atoms and molecules. We find that the combination of quadrupole-quadrupole and van der Waals interactions competes with the rotational energy of the dimer, limiting the range of validity of the perturbative approach to distances larger than 100 Bohr radii. Numerical results are given for the long-range interaction between Cs and Cs-2, showing that the photoassociation is probably efficient for any Cs-2 rotational energy

Formation of ultracold RbCs molecules by photoassociation

The formation of ultracold metastable RbCs molecules is observed in a double species magneto-optical trap through photoassociation below the ^85Rb(5S_1/2)+^133Cs(6P_3/2) dissociation limit followed by spontaneous emission. The molecules are detected by resonance enhanced two-photon ionization. Using accurate quantum chemistry calculations of the potential energy curves and transition dipole moment, we interpret the observed photoassociation process as occurring at short internuclear distance, in contrast with most previous cold atom photoassociation studies. The vibrational levels excited by photoassociation belong to the 5th 0^+ or the 4th 0^- electronic states correlated to the Rb(5P_1/2,3/2)+Cs(6S_1/2) dissociation limit. The computed vibrational distribution of the produced molecules shows that they are stabilized in deeply bound vibrational states of the lowest triplet state. We also predict that a noticeable fraction of molecules is produced in the lowest level of the electronic ground state

Influence of a Feshbach resonance on the photoassociation of LiCs

We analyse the formation of ultracold 7Li133Cs molecules in the rovibrational ground state through photoassociation into the B1Pi state, which has recently been reported [J. Deiglmayr et al., Phys. Rev. Lett. 101, 133004 (2008)]. Absolute rate constants for photoassociation at large detunings from the atomic asymptote are determined and are found to be surprisingly large. The photoassociation process is modeled using a full coupled-channel calculation for the continuum state, taking all relevant hyperfine states into account. The enhancement of the photoassociation rate is found to be caused by an `echo' of the triplet component in the singlet component of the scattering wave function at the inner turning point of the lowest triplet a3Sigma+ potential. This perturbation can be ascribed to the existence of a broad Feshbach resonance at low scattering energies. Our results elucidate the important role of couplings in the scattering wave function for the formation of deeply bound ground state molecules via photoassociation.Comment: Added Erratum, 20 pages, 9 figure

Global analysis of data on the spin-orbit coupled A1Σu+A^{1}\Sigma_{u}^{+} and b3Πub^{3}\Pi_{u} states of Cs2

We present experimentally derived potential curves and spin-orbit interaction functions for the strongly perturbed $A^{1}\Sigma_{u}^{+}$ and $b^{3}\Pi_{u}$ states of the cesium dimer. The results are based on data from several sources. Laser-induced fluorescence Fourier transform spectroscopy (LIF FTS) was used some time ago in the Laboratoire Aim\'{e} Cotton primarily to study the $X ^{1}\Sigma_{g}^{+}$ state. More recent work at Tsinghua University provides information from moderate resolution spectroscopy on the lowest levels of the $b^{3}\Pi_{0u}^{\pm}$ states as well as additional high resolution data. From Innsbruck University, we have precision data obtained with cold Cs$_{2}$ molecules. Recent data from Temple University was obtained using the optical-optical double resonance polarization spectroscopy technique, and finally, a group at the University of Latvia has added additional LIF FTS data. In the Hamiltonian matrix, we have used analytic potentials (the Expanded Morse Oscillator form) with both finite-difference (FD) coupled-channels and discrete variable representation (DVR) calculations of the term values. Fitted diagonal and off-diagonal spin-orbit functions are obtained and compared with {\it ab initio} results from Temple and Moscow State universities

Optimal trapping wavelengths of Cs2_2 molecules in an optical lattice

The present paper aims at finding optimal parameters for trapping of Cs$_2$ molecules in optical lattices, with the perspective of creating a quantum degenerate gas of ground-state molecules. We have calculated dynamic polarizabilities of Cs$_2$ molecules subject to an oscillating electric field, using accurate potential curves and electronic transition dipole moments. We show that for some particular wavelengths of the optical lattice, called "magic wavelengths", the polarizability of the ground-state molecules is equal to the one of a Feshbach molecule. As the creation of the sample of ground-state molecules relies on an adiabatic population transfer from weakly-bound molecules created on a Feshbach resonance, such a coincidence ensures that both the initial and final states are favorably trapped by the lattice light, allowing optimized transfer in agreement with the experimental observation