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arXiv:1309.5870 · Physical Review A

High-resolution photoassociation spectroscopy of the 6 Li 2 A(11Σu+) state

Will Gunton, Mariusz Semczuk, Nikesh S. Dattani, Kirk W. Madison

Published Dec 12, 2013• 13 citations
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Abstract

We present spectroscopic measurements of seven vibrational levels $v=29--35$ of the $A({1}^{1}{\ensuremath{\Sigma}}_{u}^{+})$ excited state of Li${}_{2}$ molecules by the photoassociation of a degenerate Fermi gas of ${}^{6}$Li atoms. The absolute uncertainty of our measurements is $\ifmmode\pm\else\textpm\fi{}0.000\phantom{\rule{0.16em}{0ex}}02$ cm${}^{\ensuremath{-}1}$ ($\ifmmode\pm\else\textpm\fi{}600$ kHz) and we use these new data to further refine an analytic potential for this state. This work provides high accuracy photoassociation resonance locations essential for the eventual high-resolution mapping of the $X({1}^{1}{\ensuremath{\Sigma}}_{g}^{+})$ state enabling further improvements to the $s$-wave scattering length determination of Li and enabling the eventual creation of ultracold ground-state ${}^{6}$Li${}_{2}$ molecules.

DOI
10.1103/physreva.88.062510

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We present spectroscopic measurements of seven vibrational levels v=29−−35v=29--35v=29−−35 of the A(11\ensuremathΣu+)A({1}^{1}{\ensuremath{\Sigma}}_{u}^{+})A(11\ensuremathΣu+​) excited state of Li2{}_{2}2​ molecules by the photoassociation of a degenerate Fermi gas of 6{}^{6}6Li atoms. The absolute uncertainty of our measurements is \ifmmode±\else\textpm\fi0.00002\ifmmode\pm\else\textpm\fi{}0.000\phantom{\rule{0.16em}{0ex}}02\ifmmode±\else\textpm\fi0.00002 cm\ensuremath−1{}^{\ensuremath{-}1}\ensuremath−1 (\ifmmode±\else\textpm\fi600\ifmmode\pm\else\textpm\fi{}600\ifmmode±\else\textpm\fi600 kHz) and we use these new data to further refine an analytic potential for this state. This work provides high accuracy photoassociation resonance locations essential for the eventual high-resolution mapping of the X(11\ensuremathΣg+)X({1}^{1}{\ensuremath{\Sigma}}_{g}^{+})X(11\ensuremathΣg+​) state enabling further improvements to the sss-wave scattering length determination of Li and enabling the eventual creation of ultracold ground-state 6{}^{6}6Li2{}_{2}2​ molecules.
We present experimental observations of seven vibrational levels, ${v}^{\ensuremath{'}}=20$--26, of the ${1}^{3}{\ensuremath{\Sigma}}_{g}^{+}$ excited state of Li2{}_{2}2​ molecules by the photoassociation (PA) of a degenerate Fermi gas of 6{}^{6}6Li atoms. For each vibrational level, we resolve the rotational structure using a Feshbach resonance to enhance the PA rates from ppp-wave collisions. We also determine the spin-spin and spin-rotation interaction constants for this state. The absolute uncertainty of our measurements is $\ifmmode\pm\else\textpm\fi{}0.00002$ cm${}^{\ensuremath{-}1}$ ($\ifmmode\pm\else\textpm\fi{}600$ kHz). We use this data to further refine an analytic potential for this state.
We present an accurate potential energy curve of the B (1)Pi state in the LiCs molecule for which vibrational levels between v(') = 0 and v(') = 35 (bound by 11.4 GHz) were measured by photoassociation spectroscopy in an ultracold ensemble of (7)Li and (133)Cs atoms. By the combination of conventional spectroscopic data of the B-X system and the new photoassociation measurements a very precise value of the dissociation energy of the ground state X (1)Sigma(+) of LiCs was determined to be D(0) = 5783.495(5) cm(-1).
Ultracold collisional interactions are crucial to both the dynamical evolution and the steady-state behavior of systems designed to observe Bose-Einstein condensation, and are relevant to the advances in high precision measurements, and the creation of more highly accurate atomic clocks based on laser-cooled neutral atoms. An important parameter for understanding these collisions is the s-wave scattering length {alpha}, which can be determined from accurate knowledge of the two-body interaction potential. Photoassociation of ultracold lithium atoms into bound vibrational levels of the A{sup 1}{Sigma}{sub u}{sup +} excited state is used to probe the X{sup 1}{Sigma}{sub g}{sup +} ground state interaction potential of {sup 6}Li{sub 2} and {sup 7}Li{sub 2}. It had been predicted that the s-wave photoassociation signal strength would pass through a minimum as a function of vibrational level for positive scattering length. The authors present the observation of this novel effect, and use the location of the minimum to precisely determine the singlet s-wave scattering length for both isotopes. The sensitivity of this technique is demonstrated by distinguishing the scattering lengths for collisions involving {sup 7}Li atoms in different hyperfine states.
This thesis describes a suite of experimental tools and spectroscopic measurements performed on ultracold ⁶Li molecules. The aim is to create the necessary ingredients for the coherent transfer of the population of ultracold, weakly bound, Feshbach molecules of ⁶Li to deeply bound ro-vibrational levels, making the eventual creation of a Bose-Einstein condensate (BEC) of ground state lithium dimers a reality at the University of British Columbia. Some of the technological milestones include the development of a unique laser system consisting of two Ti:Sapphire lasers frequency stabilized to a femtosecond frequency comb as well as the demonstration of the first in Canada BEC of Feshbach molecules. To determine a suitable path for the coherent transfer using stimulated Raman adiabatic passage (STIRAP) we measure the binding energies of the vibrational levels v''=20-26 of the c(1³Ʃ+g) and v''=29-35 of the A(1¹Ʃ+u) excited states of lithium dimers by the photoassociation of a degenerate Fermi gas of 6Li atoms, achieving accuracy of 600 kHz. For each vibrational level of the triplet potential, we resolve the rotational structure using a Feshbach resonance to enhance the photoassociation rates from p-wave collisions. We also, for the first time, determine the spin-spin and spin-rotation interaction constants for this state. Finally, we are the first to demonstrate exotic dark states in quantum gases of fermionic lithium where atom-molecule coherence is produced between a deeply bound singlet (or triplet) molecular level and atomic pairs in a weakly interacting Fermi gas at zero gauss or in the BEC-BCS crossover regime (i.e. Feshbach molecules or BCS-like pairs). We observe an abrupt and unanticipated change of the classic EIT signature (Electromagnetically Induced Transparency) of the dark-state (i.e. the suppression of single photon absorption to the excited state) in the vicinity of the broad Feshbach resonance at 832.2 gauss potentially indicating new physics not previously considered.
The spectra of the high-lying vibrational levels of the Asp1Sigmasbspu+A\\sp1\\Sigma\\sbsp{u}{+}Asp1Sigmasbspu+ and 1sp3Sigmasbspg+1\\sp3\\Sigma\\sbsp{g}{+}1sp3Sigmasbspg+ singly excited states of both sp6rmLisb2\\sp6\\rm Li\\sb2sp6rmLisb2 and sp7rmLisb2\\sp7\\rm Li\\sb2sp7rmLisb2 are obtained via photoassociation of colliding ultracold atoms confined in a magneto-optical trap. The least bound state of the asp3Sigmasbspu+a\\sp3\\Sigma\\sbsp{u}{+}asp3Sigmasbspu+ ground state potential, obtained by two-photon photoassociative spectroscopy, is also presented for both sp7rmLisb2\\sp7\\rm Li\\sb2sp7rmLisb2 and sp6rmLisb2\\sp6\\rm Li\\sb2sp6rmLisb2. The vibrational levels have resolved hyperfine structure, whose relative energy splittings and transition strengths are accurately modeled. The photoassociative spectra are used to precisely determine both the singlet and triplet s-wave scattering lengths for both isotopes, which are important parameters in systems designed to observe quantum degenerate effects and Bose-Einstein condensation.
Photoassociation of ultracold lithium atoms into bound vibrational levels of the $A^{1}\ensuremath{\Sigma}_{u}^{+}$ excited state is used to probe the $X^{1}\ensuremath{\Sigma}_{g}^{+}$ ground-state interaction potential of 6Li2^{6}\mathrm{Li}_{2}6Li2​ and 7Li2^{7}\mathrm{Li}_{2}7Li2​. It had been predicted that the sss-wave photoassociation signal strength would pass through a minimum as a function of vibrational level for positive sss-wave scattering length. We report the observation of this novel effect, and use the location of the minimum to precisely determine the singlet sss-wave scattering length for both isotopes. The sensitivity of this technique is demonstrated by distinguishing the minima for collisions involving 7Li^{7}\mathrm{Li}7Li atoms in different hyperfine states.