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PHOTOASSOCIATION SPECTROSCOPY OF ${^{85}}Rb_{2}$ NEAR ITS DISSOCIATION LIMIT

R. S. Freeland, Ph. W. Courteille, Chin‐Chun Tsai, Daniel J. Heinzen, J. M. M. J. Vogels, Frank A. van Abeelen, BOUDEWIJN J. VERHAAR

Published Jan 1, 1998• 0 citations
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Abstract

We present results which probe the structure of ${^{85}}Rb_{2}$ very near its lowest dissociation limit. To obtain these results, we used two different variations of photoassociation spectroscopy of laser-cooled and trapped ${^{85}}Rb$ atoms. First, we have determined the positions of twelve of the highest vibrational levels of ${^{85}}Rb_{2}$, all bound by less than $0.7 cm^{-1}$, with two-color (free-bound-bound) photoassociation spectroscopy. The levels lie in an energy range for which singlet and triplet states are strongly mixed by the hyperfine interaction. We found that we could accurately describe these states with a novel coupled-channels inverse perturbation analysis. In a second experiment, we have carried out Zeeman-resolved photoassociation spectroscopy. This technique allowed us to probe the energy range in the lowest part of the electronic ground state continuum, which lies between the dissociation limits corresponding to different hyperfine states of the separated atoms. With this method, we have observed a Feshbach scattering resonance in the continuum for the first time, which we find can be tuned to zero energy with a magnetic field.

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PHOTOASSOCIATION SPECTROSCOPY OF 85Rb2{^{85}}Rb_{2}85Rb2​ NEAR ITS DISSOCIATION LIMIT
We present results which probe the structure of 85Rb2{^{85}}Rb_{2}85Rb2​ very near its lowest dissociation limit. To obtain these results, we used two different variations of photoassociation spectroscopy of laser-cooled and trapped 85Rb{^{85}}Rb85Rb atoms. First, we have determined the positions of twelve of the highest vibrational levels of 85Rb2{^{85}}Rb_{2}85Rb2​, all bound by less than 0.7cm−10.7 cm^{-1}0.7cm−1, with two-color (free-bound-bound) photoassociation spectroscopy. The levels lie in an energy range for which singlet and triplet states are strongly mixed by the hyperfine interaction. We found that we could accurately describe these states with a novel coupled-channels inverse perturbation analysis. In a second experiment, we have carried out Zeeman-resolved photoassociation spectroscopy. This technique allowed us to probe the energy range in the lowest part of the electronic ground state continuum, which lies between the dissociation limits corresponding to different hyperfine states of the separated atoms. With this method, we have observed a Feshbach scattering resonance in the continuum for the first time, which we find can be tuned to zero energy with a magnetic field.
We determine the energies of twelve vibrational levels lying within 20 GHz of the lowest dissociation limit of 85Rb2{}^{85}{\mathrm{Rb}}_{2}85Rb2​ with two-color photoassociation spectroscopy of ultracold 85Rb{}^{85}\mathrm{Rb}85Rb atoms. The levels lie in an energy range for which singlet and triplet states are mixed by the hyperfine interaction. We carry out a coupled channels bound state analysis of the level energies, and derive accurate values for 85Rb2{}^{85}{\mathrm{Rb}}_{2}85Rb2​ interaction parameters. The information obtained is sufficient to allow for quantitative calculations of arbitrary Rb ultracold collision properties.
We report the first observation of the highest lying bound levels of the ground electronic state of ^85Rb2 by means of optical double resonance (free-bound-bound) photoassociation spectroscopy of colliding, laser-cooled ^85Rb atoms. Twelve levels with binding energies from 0.13 to 20 Ghz are observed. We carry out an inverse perturbation analysis of these levels that takes full account of the hyperfine-induced singlet-triplet mixing with a coupled channels approach. This analysis yields previously undetermined atomic interaction parameters that are crucial for the understanding of Rb ultracold collisions and Bose-Einstein condensates. Complete consistency is obtained with all previously measured cold collision properties of Rb. We gratefully acknowledge the support at Texas of the R. A. Welch Foundation, the NSF, and the Microgravity Science and Applications Division of NASA.
We probe sss-wave collisions of laser-cooled ${}^{85}\mathrm{Rb}({f\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2,m}_{f}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}2)$ atoms with Zeeman-resolved photoassociation spectroscopy. We observe that these collisions exhibit a magnetically tunable Feshbach resonance, and determine that this resonance tunes to zero energy at a magnetic field of $164\ifmmode\pm\else\textpm\fi{}7\mathrm{G}$. This result indicates that the self-interaction energy of an 85Rb{}^{85}\mathrm{Rb}85Rb Bose-Einstein condensate can be magnetically tuned. We also demonstrate that Zeeman-resolved photoassociation spectroscopy provides a useful new tool for the study of ultracold atomic collisions.
We study the photoassociative collisional loss of laser-cooled Rb atoms from a far-off resonance optical dipole force atom trap. We obtain a well-resolved photoassociation spectrum from 50 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ to 980 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ below the first excited dissociation limit of the Rb2{\mathrm{Rb}}_{2}Rb2​ molecule. Two vibrational series associated with excited Rb2{\mathrm{Rb}}_{2}Rb2​ $^{3}\mathrm{\ensuremath{\Sigma}}_{\mathit{g}}^{+}$ states are clearly visible. Oscillations in the associated Franck-Condon factors reflect the structure of the triplet ground state wave function. Our results clearly demonstrate the potential of photoassociation spectroscopy as a new probe of molecular structure.
We study the states of Rb2{\mathrm{Rb}}_{2}Rb2​ that lie within 35 ${\mathrm{cm}}^{\ensuremath{-}1}$ of the 52S12+52P32{5}^{2}{S}_{\frac{1}{2}}+{5}^{2}{P}_{\frac{3}{2}}52S21​​+52P23​​ dissociation limit with photoassociation spectroscopy of laser-cooled Rb atoms. We observe the rotationally resolved bound levels of the novel ${0}_{g}^{\ensuremath{-}}$ "pure long-range" state, which has an inner turning point beyond 25 bohrs. We also identify levels belonging to 1g{1}_{g}1g​ and ${0}_{\ensuremath{\mu}}^{+}$ states and find that the ${0}_{\ensuremath{\mu}}^{+}$ levels are broadened by predissociation. With our new method, excited molecular states with a binding energy from less than 0.3 to more than 1000 ${\mathrm{cm}}^{\ensuremath{-}1}$ can be studied with a resolution better than 0.002 ${\mathrm{cm}}^{\ensuremath{-}1}$.
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.