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Journal of Physics B Atomic Molecular and Optical Physics

Hyperfine structure of electronically-excited states of the 39 K 133 Cs molecule

Andrea Orbán, Ting Xie, Romain Véxiau, Olivier Dulieu, Nadia Bouloufa-Maafa

Published Apr 29, 2019• 8 citations
Publisher

Abstract

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 ).

DOI
10.1088/1361-6455/ab1d94

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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 ).
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 39KCs^{39}\mathrm{KCs}39KCs and fermionic 40KCs^{40}\mathrm{KCs}40KCs molecules. The hyperfine structure of the potential-energy curves of the states correlated to the K(4s2S1/2)+Cs(6p2P1/2,3/2)\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})K(4s2S1/2​)+Cs(6p2P1/2,3/2​) dissociation limits is described in terms of different coupling schemes depending on the internuclear distance RRR. 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.
This thesis is concerned with long range behavior of the interaction potential of two neutral atoms.Two aspects are of special interest: First, how the long range behavior changes if one of the atoms is replaced by another isotope.Second, how to model the influence of a laser field on long range interaction.Several high precision spectroscopy experiments on particle beams are carried out.The transition frequencies of the D lines of 39,40,41 K are measured with frequency comb generated by a self-referenced femtosecond laser, which is locked to a Cs-clock.Discrepancies in the literature are removed and new values for the hyperfine structures of the 4p 1/2 and 4p 3/2 state and the isotope shift of both D lines are derive.On a beam of potassium dimers the A 1 Σ + u state of K 2 is studied up to the dissociation limit complementing and extending photoassociation spectroscopy of ultracold ensembles.Local perturbation due to the spin-orbit coupling with the b 3 Π u state are identified.Molecular hyperfine structure of levels close to the asymptote is observed and modeled by atomic parameter only.Improved values of the atomic radiative lifetime of the states 4p 1/2 and 4p 3/2 are derived from the long range parameter C 3 of the molecule.Also, an improved value for the dissociation energy of the X 1 Σ + g ground state is obtained and recipes for the investigation of cold collision via spectroscopy of the molecular structure at the ground state asymptotes are derived.For the first time asymptotic levels of two isotopomers of K 2 are studied and a comparison of asymptotic spectra of two isotopomers 39 K 2 and 39 K 41 K shows that corrections to the Born-Oppenheimer potential are needed.Optical coupling between asymptotic ground state levels and long range levels of an excited state has been suggested as tool for influencing cold collisions.Here, we model lineshapes for an experiment which investigates such a coupling systematically in Na 2 by laser spectroscopy in a beam.A fit program for the lineshape is used to compare experimental and theoretical values and to check the validity of the applied model from multichannel quantum defect theory.The dependency on the detuning of the coupling laser is reproduced but other details failed.To allow similar studies are reported for alkali metals on the simpler quantum system from alkali earth elements the development of an oven for a continuous beam of Ca 2 for Doppler-free spectroscopy is discussed including a major change of design and first experiences are reported.The heating of the oven is, unlike those for the beams applied above, outside the vacuum tank because of the high temperatures needed for the oven.
The K and Cs atom pair and its $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\ensuremath{\Sigma}}^{+}$ and $a{\phantom{\rule{0.16em}{0ex}}}^{3}{\ensuremath{\Sigma}}^{+}$ electronic molecular states are studied by Fourier-transform spectroscopy with special emphasis on bound states close to the ground state asymptote (4s)K+(6s)Cs(4s)\text{K}+(6s)\text{Cs}(4s)K+(6s)Cs. Significant vibrational mixing due to hyperfine coupling was observed leading to improved potential energy curves for both states. The observed intensity pattern of the hyperfine structure for the last vibrational levels of $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\ensuremath{\Sigma}}^{+}$ and $a{\phantom{\rule{0.16em}{0ex}}}^{3}{\ensuremath{\Sigma}}^{+}$ reveals deep insight into the multicomponent wave function of such levels with its influence for modeling the asymptotic behavior of the excited electronic states involved in the reported observations. Examples of derived properties of cold collisions are given and the importance of the present results for efficient production schemes for ultracold KCs is discussed.
Research focusing on the formation of ultracold atomic and molecular quantum gases is a continuously expanding field due to its envisioned applications such as quantum-controlled chemistry or quantum simulation. The aim of our theoretical work is to find ways to suppress inelastic or reactive processes between colliding particles in ultracold quantum gases. Using a laser field detuned to the blue of a relevant transition, we propose to couple the initial colliding particle state to a repulsive excited one, thus preventing the particles to come close to each other. This "blueshielding" technique is applied for ultracold quantum gases, close to quantum degeneracy. We investigate the optical shielding in ultracold39K-Cs collision by using close-coupling channel method. As the (3)3Σ+and (2)3Π+molecular states are repulsive in long range[1], one verified effective optical shielding can be realized via driving the transition from the ground α3Σ+state to these excited states in the presence of linear-polarized light. We demonstrate that a strong field with a small blue detuning to the atomic transition is to the benefit of shielding since the Condon point is farther away from the inner region of ground triplet state. The spontaneous emission effect is taken into account by considering excited optical potentials with the modified formula of shielding rate [2]. We expect the shielding efficiency could be improved by using circular-polarized light [3].
Collisions with chemically inert atoms or molecules change the hyperfine coupling $A\phantom{\rule{0.16em}{0ex}}\mathbf{I}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{S}$ of an alkali-metal atom through the hyperfine-shift interaction $\ensuremath{\delta}A\phantom{\rule{0.16em}{0ex}}\mathbf{I}\ifmmode\cdot\else\textperiodcentered\fi{}\mathbf{S}$. This interaction is responsible for the pressure shifts of the microwave resonances of alkali-metal atoms in buffer gases, is an important spin interaction in alkali-metal--noble-gas van der Waals molecules, and is anticipated to enable the magnetoassociation of ultracold molecules such as RbSr. An improved estimate is presented for the long-range asymptote of this interaction for Na, K, Rb, and Cs. To test the results, the change in hyperfine coupling due to a static electric field is estimated and reasonable agreement is found.
Abstract Ultracold temperatures in dilute quantum gases opened the way to an exquisite control of matter at the quantum level. Here we focus on the control of ultracold atomic collisions using a laser to engineer their interactions at large interatomic distances. We show that the entrance channel of two colliding ultracold atoms can be coupled to a repulsive collisional channel by the laser light so that the overall interaction between the two atoms becomes repulsive: this prevents them to come close together and to undergo inelastic processes, thus protecting the atomic gases from unwanted losses. We illustrate such an optical shielding (OS) mechanism with 39 K and 133 Cs atoms colliding at ultracold temperature (<1 μK). The process is described in the framework of the dressed-state picture and we then solve the resulting stationary coupled Schrödinger equations. The role of spontaneous emission and photoinduced inelastic scattering is also investigated as possible limitations of the shielding efficiency. We predict an almost complete suppression of inelastic collisions over a broad range of Rabi frequencies and detunings from the 39 K D2 line of the OS laser, both within the [0, 200 MHz] interval. We found that the polarization of the shielding laser has a minor influence on this efficiency. This proposal could easily be formulated for other bialkali-metal pairs as their long-range interaction are all very similar to each other.