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arXiv:1009.2075 · Physical Review A

Hyperfine, rotational, and vibrational structure of the a3Σu+ state of Rb87 2

Christoph Strauß, T. Takekoshi, Florian J. W. Lang, Klaus Winkler, Rudolf Grimm, Johannes Hecker Denschlag, E. Tiemann

Published Nov 19, 2010• 124 citations
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Abstract

We have performed high-resolution two-photon dark-state spectroscopy of an ultracold gas of $^{87}\mathrm{Rb}$${}_{2}$ molecules in the ${a}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ state at a magnetic field of about 1000 G. The vibrational ladder as well as the hyperfine and low-lying rotational structure are mapped out. Energy shifts in the spectrum are observed due to singlet-triplet mixing at binding energies as deep as a few hundred $\text{GHz}\ifmmode\times\else\texttimes\fi{}h$. This information, together with data from other sources, is used to optimize the potentials of the ${a}^{3}{\ensuremath{\Sigma}}_{u}^{+}$ and ${X}^{1}{\ensuremath{\Sigma}}_{g}^{+}$ states in a coupled-channel model. We find that the hyperfine structure depends weakly on the vibrational level. This provides a possible explanation for inaccuracies in recent Feshbach resonance calculations.

DOI
10.1103/physreva.82.052514

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We have performed high-resolution two-photon dark-state spectroscopy of an ultracold gas of ^{87}\mathrm{Rb}$${}_{2} molecules in the a3\ensuremathΣu+{a}^{3}{\ensuremath{\Sigma}}_{u}^{+}a3\ensuremathΣu+​ state at a magnetic field of about 1000 G. The vibrational ladder as well as the hyperfine and low-lying rotational structure are mapped out. Energy shifts in the spectrum are observed due to singlet-triplet mixing at binding energies as deep as a few hundred GHz\ifmmode×\else\texttimes\fih\text{GHz}\ifmmode\times\else\texttimes\fi{}hGHz\ifmmode×\else\texttimes\fih. This information, together with data from other sources, is used to optimize the potentials of the a3\ensuremathΣu+{a}^{3}{\ensuremath{\Sigma}}_{u}^{+}a3\ensuremathΣu+​ and X1\ensuremathΣg+{X}^{1}{\ensuremath{\Sigma}}_{g}^{+}X1\ensuremathΣg+​ states in a coupled-channel model. We find that the hyperfine structure depends weakly on the vibrational level. This provides a possible explanation for inaccuracies in recent Feshbach resonance calculations.
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We present the results of an experimental and theoretical study of the electronically excited $(1){}^{3}{\ensuremath{\Sigma}}_{\mathrm{g}}^{+}$ state of 87Rb^{87}\mathrm{Rb}87Rb2{}_{2}2​ molecules. The vibrational energies are measured for deeply bound states from the bottom up to ${v}^{\ensuremath{'}}=15$ using laser spectroscopy of ultracold Rb2{}_{2}2​ Feshbach molecules. The spectrum of each vibrational state is dominated by a 47-GHz splitting into ${0}_{\mathrm{g}}^{\ensuremath{-}}$ and 1g{1}_{\mathrm{g}}1g​ components caused mainly by a strong second-order spin-orbit interaction. Our spectroscopy fully resolves the rotational, hyperfine, and Zeeman structure of the spectrum. We are able to describe this structure to the first order using a simplified effective Hamiltonian.
We create atom-molecule dark states in a degenerate Fermi gas of 6Li^{6}\mathrm{Li}6Li in both weakly and strongly interacting regimes using two-photon Raman scattering to couple fermion pairs to bound molecular states in the ground singlet and triplet potential. Near the unitarity point in the BEC-BCS crossover regime, the atom number revival height associated with the dark state abruptly and unexpectedly decreases and remains low for magnetic fields below the Feshbach resonance center at 832.2 G. With a weakly interacting Fermi gas at 0 G, we perform precision dark-state spectroscopy of the least-bound vibrational levels of the lowest singlet and triplet potentials. From these spectra, we obtain binding energies of the ${v}^{\ensuremath{'}\ensuremath{'}}=9$, ${N}^{\ensuremath{'}\ensuremath{'}}=0$ level of the $a({1}^{3}{\mathrm{\ensuremath{\Sigma}}}_{u}^{+})$ potential and the ${v}^{\ensuremath{'}\ensuremath{'}}=38$, ${N}^{\ensuremath{'}\ensuremath{'}}=0$ level of the $X({1}^{1}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+})$ potential with absolute uncertainty as low as 20 kHz. For the triplet potential, we resolve the molecular hyperfine structure.
Mixing of 0+{0}^{+}0+ and 0−{0}^{-}0− observed in the hyperfine and Zeeman structure of ultracold Rb2{\mathrm{Rb}}_{2}Rb2​ molecules
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