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Physical Review A

Observation and analysis of the hyperfine structure of near-dissociation levels of the NaCs cΣ+3 state below the dissociation limit 3S1/2+6P3/2

Wenliang Liu, Jizhou Wu, Jie Ma, Peng Li, V. B. Sovkov, Liantuan Xiao, Suotang Jia

Published Sep 30, 2016• 22 citations
Publisher

Abstract

We report photoassociation (PA) of ultracold Na and Cs atoms in a dual-species magneto-optical trap. Trap loss spectroscopy of the ultracold polar NaCs molecules formed by PA, which carries information about relative PA transition strengths, has been experimentally obtained by using highly sensitive modulation spectroscopy technique. The fine and hyperfine effects at near-dissociation levels of NaCs molecular $c\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}^{+}$ state are observed and modeled. The interaction Hamiltonian is described in terms of the Hund's case ($a$) coupling scheme. The molecular hyperfine structure of near-dissociation levels is simulated within a simplified model of four interacting vibrational levels belonging to different initially unperturbed electronic states. The results of the simulation infer that the interaction parameters of the observed near-dissociation levels are close to the asymptotic parameters of the pair of atoms. The coupling of the electronic states is essential for forming the hyperfine structure.

DOI
10.1103/physreva.94.032518

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We report photoassociation (PA) of ultracold Na and Cs atoms in a dual-species magneto-optical trap. Trap loss spectroscopy of the ultracold polar NaCs molecules formed by PA, which carries information about relative PA transition strengths, has been experimentally obtained by using highly sensitive modulation spectroscopy technique. The fine and hyperfine effects at near-dissociation levels of NaCs molecular c3\ensuremathΣ+c\phantom{\rule{0.16em}{0ex}}^{3}\mathrm{\ensuremath{\Sigma}}^{+}c3\ensuremathΣ+ state are observed and modeled. The interaction Hamiltonian is described in terms of the Hund's case (aaa) coupling scheme. The molecular hyperfine structure of near-dissociation levels is simulated within a simplified model of four interacting vibrational levels belonging to different initially unperturbed electronic states. The results of the simulation infer that the interaction parameters of the observed near-dissociation levels are close to the asymptotic parameters of the pair of atoms. The coupling of the electronic states is essential for forming the hyperfine structure.
We report on the production of ultracold heteronuclear NaCs* molecules in a dual-species magneto-optical trap through photoassociation. The electronically excited molecules are formed below the Na (3S1/2) + Cs (6P1/2) dissociation limit. 12 resonance lines are detected using trap-loss spectroscopy based on a highly sensitive modulation technique. The highest observed rovibrational level exhibits clear hyperfine structure, which is detected for the first time. This structure is simulated within a simplified model consisting of 4 coupled levels belonging to the initially unperturbed Hund’s case “a” electronic states, which have been explored in our previous work that dealt with the Na (3S1/2) + Cs (6P3/2) asymptote [W. Liu et al., Phys. Rev. A 94, 032518 (2016)].
We present photoassociation spectroscopy of ultracold NaCs molecules formed in a dual-species magneto-optical trap. Excited-state molecules are formed in states correlating to the Na(3S 1/2 )+Cs(6P 3/2 ) asymptote. We assign the most prominent observed vibrational progression to the Ω=2 long range state based on a comparison with ab initio potentials. Molecules are secondarily excited before decaying to deeply bound levels of the electronic ground X 1 Σ + state where they are ionized and detected by time-of-flight mass spectroscopy.
We report on new observations of the photoassociation spectroscopy of ultracold cesium molecules using a highly sensitive detection technique and a combined analysis with all observed electronic states. The technique is achieved by directly modulating the frequency of the trapping lasers of a magneto-optical trap. New observations of the Cs2 0g(-), 0u(+), and 1g states at the asymptotes 6S1/2 + 6P1/2 and 6S1/2 + 6P3/2 are reported. The spectral range is extended to the red detuning of 112 cm(-1) below the 6S1/2 + 6P3/2 dissociation limit. Dozens of vibrational levels of the ultracold Cs2 0g(-), 0u(+), and 1g states are observed for the first time. The available experimental binding energies of these states are analyzed simultaneously in a framework of the generalized LeRoy-Bernstein theory and the almost degenerate perturbation theory by Marinescu and Dalgarno [Phys. Rev. A: At., Mol., Opt. Phys. 52, 311 (1995)]. The unique atomic-related parameter c3 governing the dispersion forces of all the molecular states is estimated as (10.29 ± 0.05) a.u.
The production and research of ultracold heteronuclear molecules have aroused the great interest recently. On the one hand, these molecules are extremely popular in experiments for exploring the collision dynamic behaviors in threshold, photoassociative spectrum and strong dipole-dipole interactions. On the other hand, ultracold polar molecules populated at deeply bound levels in the singlet ground state are the right candidates to investigate quantum memories for quantum simulation, and to study strongly interacting quantum degenerate gases. The precise knowledge of cold collision processes between two different types of alkali atoms is necessary for understanding and utilizing ultracold heteronuclear molecules, sympathetic cooling, and thus formation of two species BEC. The goal of the present investigation is to study the collisions between ultracold sodium atoms and cesium atoms. We systematically demonstrate simultaneously trapping ultracold sodium and cesium atoms in a dual-species magneto-optical trap (MOT). The sodium atom trap loss rate coefficient Na-Cs is measured as a function of Na trapping laser intensity. At low intensities, the trap loss is dominated by ground-state hyperfine-changing collisions, while at high intensities, collisions involving excited atoms are more important. A strong interspecies collision-induced loss for Na atoms in the MOT is observed. In order to obtain the trap loss coefficient Na-Cs, we proceed in two steps. First, the Cs repumping laser is blocked to avoid the formation of ultraold Cs atoms. The loading process of Na atoms is recorded when the Cs trapping laser is on. Second, the loading curves of the Na atoms are obtained as Cs atoms are present with the repumping laser beams. The total losses PNa and PNa' are acquired by fitting the two loading curves of trapped Na atoms. Thus, the trap loss coefficient Na-Cs can be derived from the difference between total losses PNa and PNa' divided by the density of the Cs atoms. The coefficient Na-Cs decreases in a range of 5-10mW/cm2, which originates from the hyperfine-state changing (HFC) collision. A Doppler model is used to calculate the Na atom trap depth, in that the atom trap depth and exoergic energy determine the behavior of the collisional trap loss rate coefficient. The three corresponding calculated critical intensities of Na trapping laser are 7.98, 14.82, 16.2 mW/cm2 respectively in the Na-Cs HFC collision process. The first calculated critical intensity value agrees well with the experimental result. Our work provides a valuable insight into HFC collision between Na and Cs atoms and also paves the way for the production of ultracold NaCs molecules using Photoassociation (PA) technology. Furthermore, the experimental results lay a great basis for the obtainments of high sensitive heteronuclear NaCs molecular PA spectrum and the creation of deeply bound ground state molecules.
We present high-precision trap loss spectroscopy of excited molecules obtained by the photoassociation of ultracold sodium atoms. Near the dissociation limit, hyperfine and rotational (Coriolis-type) interactions cause significant mixing of states of different nominal Hund's case (c) symmetry resulting in a complex pattern of spectral lines. We construct a theoretical model of the large, slowly rotating molecule starting from a long-range, atomic viewpoint. Interaction potentials are derived from the known long-range resonant dipole and van der Waals forces between atoms, supplemented at short range by the results of electronic-structure calculations. Spin-dependent interactions coupling the various angular momenta---nuclear spin, electron spin, electron orbit, and the mechanical rotation of the molecule as a whole---are derived from known atomic parameters. We avoid imposing approximate symmetries or coupling schemes and consequently include all nonadiabatic mixing of different degrees of freedom. Quantitative agreement between experiment and theory for both line positions and intensities is found. Specifically, we observe and calculate mixing of levels of , , and symmetry bound by below the asymptote.