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arXiv:1507.06519 · Physical Review A

Model for the hyperfine structure of electronically excited KCs molecules

Andrea Orbán, Romain Véxiau, O. Krieglsteiner, Hanns‐Christoph Nägerl, Olivier Dulieu, A. Crubellier, Nadia Bouloufa-Maafa

Published Sep 21, 2015• 19 citations

Abstract

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 $^{39}\mathrm{KCs}$ and fermionic $^{40}\mathrm{KCs}$ molecules. The hyperfine structure of the potential-energy curves of the states correlated to the $\mathrm{K}(4s\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}{}^{2}{S}_{1/2})+\mathrm{Cs}(6p\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}{}^{2}{P}_{1/2,3/2})$ dissociation limits is described in terms of different coupling schemes depending on the internuclear distance $R$. These results provide a 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.

DOI: 10.1103/physreva.92.032510

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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}\mathrm{KCs}

and fermionic

^{40}\mathrm{KCs}

molecules. The hyperfine structure of the potential-energy curves of the states correlated to the

\mathrm{K}(4s\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}{}^{2}{S}_{1/2})+\mathrm{Cs}(6p\phantom{\rule{0.16em}{0ex}}\phantom{\rule{0.16em}{0ex}}{}^{2}{P}_{1/2,3/2})

dissociation limits is described in terms of different coupling schemes depending on the internuclear distance

R

. These results provide a 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.

Abstract 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 39 K( 4 p 2 P 1 / 2,3 / 2 ) + 133 Cs( 6 s 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 39 K( 4 s 2 S 1 / 2 ) + 133 Cs( 6 p 2 P 1 / 2,3 / 2 ).

We have observed 28 heteronuclear Feshbach resonances in ten spin combinations of the hyperfine ground states of a $^{40}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ mixture. The measurements were performed by observing the loss rates from an atomic mixture at magnetic fields between

0

and

700\phantom{\rule{0.3em}{0ex}}\mathrm{G}

. These data were used to significantly refine an interatomic potential derived from molecular spectroscopy, yielding a highly consistent model of the $^{40}\mathrm{K}\text{\ensuremath{-}}^{87}\mathrm{Rb}$ interaction. Thus, the measured resonances can be assigned to the corresponding molecular states. In addition, this potential allows for an accurate calculation of the energy differences between highly excited levels and the rovibrational ground level. This information is of particular relevance for the formation of deeply bound heteronuclear molecules. Finally, the model is used to predict Feshbach resonances in mixtures of

^{87}\mathrm{Rb}

combined with

^{39}\mathrm{K}

or

^{41}\mathrm{K}

.

We report on the creation of ultracold heteronuclear and electronically excited Rb*Yb molecules in a hybrid conservative trap by photoassociation of ultracold

^{87}\mathrm{Rb}

and

^{176}\mathrm{Yb}

. The molecules are formed below the

{\mathrm{Rb}}_{5\mathit{p}1}(^{2}P_{1/2})+{\mathrm{Yb}}_{6\mathit{s}2}(^{1}S_{0})

dissociation limit and the resonances are detected using trap-loss spectroscopy. By addressing vibrational levels with binding energies down to ${E}_{B}=\ensuremath{-}h\ifmmode\times\else\texttimes\fi{}2.2\phantom{\rule{0.16em}{0ex}}\mathrm{THz}$, we study the change in hyperfine coupling of the diatomic molecule as a function of internuclear separation. We observe a decreasing hyperfine splitting for more tightly bound excited molecular states where the hyperfine splitting is reduced by more than

30%

compared to the atomic value for

^{87}\mathrm{Rb}

.

We explore the electronic structure of ultralong-range penta-atomic Rydberg molecules from a merger of a Rydberg atom and two ground-state heteronuclear diatomic molecules. Our focus is on the interaction of

\mathrm{Rb}(23s

) and

\mathrm{Rb}(n=20

, $l\ensuremath{\ge}3$) Rydberg states with ground and rotationally excited KRb diatomic polar molecules. For symmetric and asymmetric configurations of the penta-atomic Rydberg molecule, we investigate the metamorphosis of the Born-Oppenheimer potential curves, essential for the binding of the molecule, with varying distance from the Rydberg core and analyze the alignment and orientation of the polar diatomic molecules.

We investigate the energy levels of heteronuclear alkali-metal dimers in levels correlating with the lowest rotational level of the ground electronic state, which are important in efforts to produce ground-state ultracold molecules. We use density-functional theory to calculate nuclear quadrupole and magnetic coupling constants for KRb and RbCs and explore the hyperfine structure in the presence of electric and magnetic fields. For nonrotating states, the zero-field splittings are dominated by the electron-mediated part of the nuclear spin-spin coupling. They are a few kilohertz for KRb isotopologs and a few tens of kilohertz for RbCs isotopologs.