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arXiv:cond-mat/0312613

Ultracold Cs$_2$ Feshbach Spectroscopy

Cheng Chin, Vladan Vuletić, Andrew J. Kerman, Steven Chu, Eite Tiesinga, Paul J. Leo, Carl J. Williams

Published Dec 23, 2003• 0 citations
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Abstract

We have observed and located more than 60 magnetic field-induced Feshbach resonances in ultracold collisions of ground-state $^{133}$Cs atoms. These resonances are associated with molecular states with up to four units of rotational angular momentum, and are detected through variations in the elastic, inelastic, and radiative collision cross sections. These observations allow us to greatly improve upon the interaction potentials between two cesium atoms and to reproduce the positions of most resonances to accuracies better than 0.5%. Based on the relevant coupling scheme between the electron spin, nuclear spin, and orbital angular momenta of the nuclei, quantum numbers and energy structure of the molecular states beneath the dissociation continuum are revealed. Finally, we predict the relevant collision properties for cesium Bose-Einstein condensation experiments.

DOI
10.48550/arxiv.cond-mat/0312613

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Ultracold Cs2_22​ Feshbach Spectroscopy
We have observed and located more than 60 magnetic field-induced Feshbach resonances in ultracold collisions of ground-state 133^{133}133Cs atoms. These resonances are associated with molecular states with up to four units of rotational angular momentum, and are detected through variations in the elastic, inelastic, and radiative collision cross sections. These observations allow us to greatly improve upon the interaction potentials between two cesium atoms and to reproduce the positions of most resonances to accuracies better than 0.5%. Based on the relevant coupling scheme between the electron spin, nuclear spin, and orbital angular momenta of the nuclei, quantum numbers and energy structure of the molecular states beneath the dissociation continuum are revealed. Finally, we predict the relevant collision properties for cesium Bose-Einstein condensation experiments.
We have observed and located more than 60 magnetic field-induced Feshbach resonances in ultracold collisions of ground-state 133Cs^{133}\mathrm{Cs}133Cs atoms. Multiple extremely weak Feshbach resonances associated with ggg-wave molecular states are detected through variations in the radiative collision cross sections. The Feshbach spectroscopy allows us to determine the interactions between ultracold cesium atoms and the molecular energy structure near the dissociation continuum with unprecedented precision. Our work not only represents a very successful collaboration of experimental and theoretical efforts, but also provides essential information for cesium Bose-Einstein condensation, Cs2{\mathrm{Cs}}_{2}Cs2​ molecules, and atomic clock experiments.
Abstract : We measure high-resolution Feshbach resonance spectra for ultracold desium atoms colliding in different hyperfine and magnetic sublevels. More than 25 Feshback resonances are observed for magnetic fields below 230 G in the elastic and inelastic ground state collision cross sections, as well as in the cross section for light-assisted collisions. From thes spectra a consistent set of ground state molecular interaction parameters for desium is extracted, including singlet and triplet scattering lengths of As=(280 +/- 10)a) and At=(2400 +/- 100)a), a van der Waals coefficient C6=(6890 +/- 35) a.u., as well as the strength of the indirect spin-spin coupling. This set of parameters allows for the first time a complet characterisation of cesium's ultra-cold collision properties.
We measure high-resolution Feshbach resonance spectra for ultracold cesium atoms colliding in different hyperfine and magnetic sublevels. More than 25 resonances are observed for magnetic fields up to 230 G and their positions are measured with an accuracy down to 0.03 G. From these spectra several ground-state molecular interaction parameters can be extracted with sufficient accuracy to permit for the first time an unambiguous and accurate determination of cesium's ultracold collision properties [P. J. Leo, C. J. Williams, and P. S. Julienne, following Letter, Phys. Rev. Lett. 85, 2721 (2000)].
We observe several Feshbach resonances in magnetic fields below 40 G for Cs atoms trapped in a 1D optical lattice. One resonance occurs in the lowest-energy ground state F=3F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3F=3, mF=3{m}_{F}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3mF​=3 which is stable against inelastic binary collisions. This opens new possibilities for Bose condensation of Cs. When the elastic collision rate far exceeds the radial vibration frequency, we enter a 2D hydrodynamic regime where the thermalization rate is independent of density and temperature. Other resonances are also observed in the F=3F\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3F=3, ${m}_{F}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\ensuremath{-}3$ state through a dramatic increase in the dipolar relaxation rate.
We explore the rich internal structure of Cs2{\text{Cs}}_{2}Cs2​ Feshbach molecules. Pure ultracold molecular samples are prepared in a CO2{\text{CO}}_{2}CO2​-laser trap, and a multitude of weakly bound states is populated by elaborate magnetic-field ramping techniques. Our methods use different Feshbach resonances as input ports and various internal level crossings for controlled state transfer. We populate higher partial-wave states of up to eight units of rotational angular momentum (lll-wave states). We investigate the molecular structure by measurements of the magnetic moments for various states. Avoided level crossings between different molecular states are characterized through the changes in magnetic moment and by a Landau-Zener tunneling method. Based on microwave spectroscopy, we present a precise measurement of the magnetic-field-dependent binding energy of the weakly bound sss-wave state that is responsible for the large background scattering length of Cs. This state is of particular interest because of its quantum-halo character.
We investigate quantum-mechanical interactions between ultracold rubidium and cesium in an optical trap at temperatures of a few microkelvin. Our results provide, on the one hand, an experimental key to understand the collisional properties and, on the other hand, a tool to control the interspecies interactions. By performing loss measurements we locate several Feshbach resonances, which provide insight into the energy structure of weakly bound RbCs molecules near the dissociation threshold and allow for the production of such heteronuclear Feshbach molecules. In the future we will transfer these loosely-bound molecules into the absolute internal ground state. The availability of ultracold heteronuclear ground state molecules will open the door to investigate phenomena associated with ultracold polar quantum gases. In our new experimental set-up we are able to trap and cool rubidium and cesium atoms in their lowest internal states. First we load both species into a two-color magneto-optical trap, having full control over the single-species atom number. We extend the technique of degenerate Raman-sideband cooling to a two-color version, which is able to simultaneously cool and polarize both rubidium and cesium. Thereafter we load the atoms into a levitated crossed optical dipole trap. Because of the presence of the gradient magnetic field the trap is highly state selective and consequently provides perfect spin-polarization of the sample. Furthermore, a coincidence of the magnetic-moment-to-mass ratios of the two species allows for simultaneous levitation of both, which assures an almost perfect spatial overlap between the species. We perform Feshbach spectroscopy in two different spin channels of the mixture within a magnetic field ranging from 20 to 300G. In the lowest spin combination of the species we locate 23 interspecies Feshbach resonances, while in a higher spin mixture we find 2 resonances. The high number of resonances found within this range of magnetic field is unusual for alkali mixtures. The presence of many resonances points to scattering properties of the mixture, which include higher-order coupling mechanisms. The obtained data on the Feshbach spectroscopy provide, on one hand, fundamental experimental input to characterize the Rb-Cs scattering properties and, on the other hand, identification of possible starting points for the association of ultracold heteronuclear RbCs molecules. In addition we show preliminary results on spectroscopy of the binding energy of RbCs dimers, based on a modulation of the magnetic field. The recently obtained Bose-Einstein condensate of Cs atoms, which represents a benchmark for the performance of the present apparatus, will be discussed as well as the potential pathways towards a double-degenerate mixture. We follow two main goals, first the production of a double Bose-Einstein condensate and, second, the transfer of shallow bound Feshbach molecules to the absolute internal ground state. The production of heteronuclear ground state molecules allows to enter the world of ultracold polar quantum systems.