[en] We focus on the theoretical modelling of the dynamics of ion-neutral systems at ultracold temperatures (<< 1K) in order to design ways for their full quantum control. Our aims are connected to experimental investigations of alkaline earth ion - alkali atom systems with hybrid traps. Due to the laser cooling scheme a metastable d-level of the alkaline-earth ion is considerably populated in these experiments, e.g. in case of 88Sr+ ion embedded in the cloud of ultracold 87Rb atoms [1] or 138Ba+ in 6Li cloud [2]. The large internal energy of the ion induces several inelastic processes like charge-exchange, spin-orbit change collisions or electronic excitation exchange. We compute cross sections and rate coefficients for these processes within the framework of the quantum coupled-channel model considering the fine-structure of the colliding partners and the rotational coupling. Our calculations involve potential energy curves including the determination of R-dependent spin-orbit couplings (see Figs. 1, 2) following a diabatization approach [3]. Fig.1: Selected Hund's case (a) LiBa+ potential energy curves in the molecular frame. The red shadow shows the location of an avoided crossing of 21 Σ and 31 Σ responsible of the non-radiative charge exchange (NRCE) process (red arrow): Li(2s)+Ba+(5d) → Li++Ba(6s2,1S) . Fig.2: The R-dependent spin-orbit couplings of the first 3 dissociation limits, based on Ω=0+/-, 1, 2, 3 the projection of the total angular momentum on molecular axis. [1] R. Ben-Shlomi, R. Vexiau, Z. Meir, T. Sikorsky, N. Akerman, M. Pinkas, O. Dulieu, R. Ozeri, Phys. Rev. A 102 ,031301(R) [2] P. Weckesser, F. Thielemann, D. Wiater, A. Wojciechowska, L. Karpa, K.Jachymski, M. Tomza, T. Walker, T. Schaetz, Nature 600, 429 (2021) [3] X. Xing, R. Vexiau, N. Bouloufa, O. Dulieu et al, in preparation. We acknowledge support from the CRNS International Emerging Action (IEA) - ELKH, 2023-2024; Program Hubert Curien ”BALATON” (CampusFranceGrantNo.49848TC)–NKFIHTE ́T-FR(2023-2024)

[en] Heteronuclear alkali-metal dimers represent the class of molecules of choice for creating samples of ultracold molecules exhibiting an intrinsic large permanent electric dipole moment. Among them, the KCs molecule, with a permanent dipole moment of 1.92 Debye still remains to be observed in ultracold conditions. Based on spectroscopic studies available in the literature completed by accurate quantum chemistry calculations, we propose several optical coherent schemes to create ultracold bosonic and fermionic KCs molecules in their absolute rovibrational ground level, starting from a weakly bound level of their electronic ground state manifold. The processes rely on the existence of convenient electronically excited states allowing an efficient stimulated Raman adiabatic transfer of the level population. (paper)

[en] We have calculated the isotropic C₆ 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 X¹Σ⁺. We consider the ten species made up of ⁷Li, ²³Na, ³⁹K, ⁸⁷Rb, and ¹³³Cs. Following our previous work [Lepers et al., Phys. Rev. A 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

[en] The possibility to shield short-range dynamics between colliding particles of an ultracold gas with an optical field is controlled by the details of their long-range interactions. Using an asymptotic model presented in a previous work (Orbán et al 2015 Phys. Rev. A 92 032510), we determine the long-range interaction between an excited and a ground-state alkali-metal atom, including their hyperfine structure. As an example we focus on the bosonic pair ³⁹K($4p{}^2{P}_{1/2,3/2}$) + ¹³³Cs($6s{}^2{S}_{1/2}$), which corresponds to the second dissociation limit of the KCs molecule above the ground state. Several excited electronic states are found repulsive at large interatomic distances, being thus promising candidates for optical shielding. The results reveal that the hyperfine coupling scheme is essentially different from the one described in (Orbán et al 2015 Phys. Rev. A 92 032510) for the states correlated to the ³⁹K($4s{}^2{S}_{1/2}$) + ¹³³Cs($6p{}^2{P}_{1/2,3/2}$). (paper)

[en] 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 Cs₂, showing that the photoassociation is probably efficient for any Cs₂ rotational energy.

[en] The present paper aims at finding optimal parameters for trapping of Cs₂ molecules in optical lattices, with the perspective of creating a quantum degenerate gas of ground-state molecules. We have calculated dynamic polarizabilities of Cs₂ 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.