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arXiv:1710.04883 · Physical Review A

High-resolution molecular spectroscopy for producing ultracold absolute-ground-state Na23Rb87 molecules

Mingyang Guo, Romain Véxiau, Bing Zhu, Bo Lü, Nadia Bouloufa-Maafa, Olivier Dulieu, Dajun Wang

Published Nov 14, 2017• 24 citations
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Abstract

We report a detailed molecular spectroscopy study of the lowest excited electronic states of $^{23}\mathrm{Na}\phantom{\rule{0.16em}{0ex}}^{87}\mathrm{Rb}$ for producing ultracold $^{23}\mathrm{Na}\phantom{\rule{0.16em}{0ex}}^{87}\mathrm{Rb}$ molecules in the electronic, rovibrational, and hyperfine ground state. Starting from weakly bound Feshbach molecules, a series of vibrational levels of the $A{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}\text{\ensuremath{-}}b{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$ coupled excited states is investigated. After resolving, modeling, and interpreting the hyperfine structure of several lines, we successfully identify a long-lived level resulting from the accidental hyperfine coupling between the ${0}^{+}$ and ${0}^{\ensuremath{-}}$ components of the $b{\phantom{\rule{0.16em}{0ex}}}^{3}\mathrm{\ensuremath{\Pi}}$ state, satisfying all the requirements for the population transfer toward the lowest rovibrational level of the $X{\phantom{\rule{0.16em}{0ex}}}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state. Using two-photon spectroscopy, its binding energy is measured to be 4977.308(3) ${\mathrm{cm}}^{\ensuremath{-}1}$. We calibrate all the transition strengths carefully and also demonstrate Raman transfer of Feshbach molecules to the absolute ground state.

DOI
10.1103/physreva.96.052505

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We report the successful production of an ultracold sample of absolute ground-state ^{23}Na^{87}Rb molecules. Starting from weakly bound Feshbach molecules formed via magnetoassociation, the lowest rovibrational and hyperfine level of the electronic ground state is populated following a high-efficiency and high-resolution two-photon Raman process. The high-purity absolute ground-state samples have up to 8000 molecules and densities of over 10^{11} cm^{-3}. By measuring the Stark shifts induced by external electric fields, we determined the permanent electric dipole moment of the absolute ground-state ^{23}Na^{87}Rb and demonstrated the capability of inducing an effective dipole moment over 1 D. Bimolecular reaction between ground-state ^{23}Na^{87}Rb molecules is endothermic, but we still observed a rather fast decay of the molecular sample. Our results pave the way toward investigation of ultracold molecular collisions in a fully controlled manner and possibly to quantum gases of ultracold bosonic molecules with strong dipolar interactions.
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We report on high-resolution spectroscopy of ultracold fermionic 23 Na 40 K Feshbach molecules, and identify a two-photon pathway to the rovibrational singlet ground state via a resonantly mixed B 1 Π ∼ c 3 Σ + intermediate state.Photoassociation in a 23 Na-40 K atomic mixture and one-photon spectroscopy on 23 Na 40 K Feshbach molecules reveal about 20 vibrational levels of the electronically excited c 3 Σ + state.Two of these levels are found to be strongly perturbed by nearby B 1 Π levels via spinorbit coupling, resulting in additional lines of dominant singlet character in the perturbed complex. The dominantly singlet level is used to locate the absolute rovibrational singlet ground state v J X 0, 0via Autler-Townes spectroscopy.We demonstrate coherent two-photon coupling via dark state spectroscopy between the predominantly triplet Feshbach molecular state and the singlet ground state.Its binding energy is measured to be 5212.0447(1)cm -1 , a thousand-fold improvement in accuracy compared to previous determinations.In their absolute singlet ground state, 23 Na 40 K molecules are chemically stable under binary collisions and possess a large electric dipole moment of 2.72 Debye.Our work thus paves the way towards the creation of strongly dipolar Fermi gases of NaK molecules.
Creation of a strongly dipolar gas of ultracold ground-state 23Na87Rb^{23}\rm{Na}^{87}\rm{Rb}23Na87Rb molecules
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One possibility for the creation of ultracold, high phase space density quantum gases of molecules in the rovibronic ground state relies on first associating weakly-bound molecules from quantum-degenerate atomic gases on a Feshbach resonance and then transferring the molecules via several steps of coherent two-photon stimulated Raman adiabatic passage (STIRAP) into the rovibronic ground state. Here, in ultracold samples of Cs2 Feshbach molecules produced out of ultracold samples of Cs atoms, we observe several optical transitions to deeply-bound rovibrational levels of the excited 0(u)+ molecular potentials with high resolution. At least one of these transitions, although rather weak, allows efficient STIRAP transfer into the deeply-bound vibrational level (see text for symbols)v = 73 > of the singlet X1 sigma(g)+ ground state potential, as recently demonstrated (J. G. Danzl, E. Haller, M. Gustavsson, M. J. Mark, R. Hart, N. Bouloufa, O. Dulieu, H. Ritsch, and H.-C. Nägerl, Science, 2008, 321, 1062). From this level, the rovibrational ground state (see text for symbols)v = 0, J = 0 > can be reached with one more transfer step. In total, our results show that coherent ground state transfer for Cs2 is possible using a maximum of two successive two-photon STIRAP processes or one single four-photon STIRAP process.
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