Abstract We spectroscopically investigate a pathway for the conversion of 23Na39K Feshbach molecules into rovibronic ground state molecules via stimulated Raman adiabatic passage. Using photoassociation spectroscopy from the diatomic scattering threshold in the a 3Σ+ potential, we locate the resonantly mixed electronically excited intermediate states ∣ B 1 Π , v = 8 〉 and ∣ c 3 Σ + , v = 30 〉 which, due to their singlet–triplet admixture, serve as an ideal bridge between predominantly a 3Σ+ Feshbach molecules and pure X 1Σ+ ground state molecules. We investigate their hyperfine structure and present a simple model to determine the singlet–triplet coupling of these states. Using Autler–Townes spectroscopy, we locate the rovibronic ground state of the 23Na39K molecule ( ∣ X 1 Σ + , v = 0 , N = 0 〉 ) and the second rotationally excited state N = 2 to unambiguously identify the ground state. We also extract the effective transition dipole moment from the excited to the ground state. Our investigations result in a fully characterized scheme for the creation of ultracold bosonic 23Na39K ground state molecules.
We report on photoassociation spectroscopy probing the ${c}^{3}{\mathrm{\ensuremath{\Sigma}}}_{1}^{+}$ potential of the bialkali NaCs molecule, identifying 11 vibrational lines between ${v}^{\ensuremath{'}}=0$ and ${v}^{\ensuremath{'}}=25$ of the excited ${c}^{3}{\mathrm{\ensuremath{\Sigma}}}_{1}^{+}$ potential and fitting their rotational and hyperfine structure. The observed lines are assigned by fitting to an effective Hamiltonian model of the excited-state structure with rotational and hyperfine constants as free parameters. We discuss unexpected broadening of select vibrational lines and its possible link to strong spin-orbit coupling of the ${c}^{3}{\mathrm{\ensuremath{\Sigma}}}_{1}^{+}$ potential with the nearby ${b}^{3}{\mathrm{\ensuremath{\Pi}}}_{1}$ and ${B}^{1}{\mathrm{\ensuremath{\Pi}}}_{1}$ manifolds. Finally, we report use of the ${v}^{\ensuremath{'}}=22$ line as an intermediate state for two-photon transfer of weakly bound Feshbach molecules to the rovibrational ground state of the ${X}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ manifold.
We spectroscopically investigate the hyperfine, rotational, and Zeeman structure of the vibrational levels ${v}^{\ensuremath{'}}=0,7,13$ within the electronically excited $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ state of
87Rb2 for magnetic fields of up to
1000G. As spectroscopic methods we use short-range photoassociation of ultracold Rb atoms as well as photoexcitation of ultracold molecules which have been previously prepared in several well-defined quantum states of the $a{\phantom{\rule{0.222222em}{0ex}}}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$ potential. As a by-product, we present optical two-photon transfer of weakly bound Feshbach molecules into $a{\phantom{\rule{0.222222em}{0ex}}}^{3}\mathrm{\ensuremath{\Sigma}}{}_{u}^{+}$,
v=0 levels featuring different nuclear spin quantum numbers. A simple model reproduces well the molecular level structures of the $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ vibrational states and provides a consistent assignment of the measured resonance lines. Furthermore, the model can be used to predict the relative transition strengths of the lines. From fits to the data we extract for each vibrational level the rotational constant, the effective spin-spin interaction constant, as well as the Fermi contact parameter and the anisotropic hyperfine constant. In an alternative approach, we perform coupled-channel calculations where we fit the relevant potential energy curves, spin-orbit interactions, and hyperfine functions. The calculations reproduce the measured hyperfine level term frequencies with an average uncertainty of $\ifmmode\pm\else\textpm\fi{}9\phantom{\rule{0.28em}{0ex}}\mathrm{MHz}$, similar as for the simple model. From these fits we obtain a section of the potential energy curve for the $c{\phantom{\rule{0.222222em}{0ex}}}^{3}{\mathrm{\ensuremath{\Sigma}}}_{g}{}^{+}$ state which can be used for predicting the level structure for the vibrational manifold ${v}^{\ensuremath{'}}=0$ to 13 of this electronic state.