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arXiv:0712.3889 · Physical Review A

Heteronuclear molecules in an optical dipole trap

J. J. Zirbel, Kang-Kuen Ni, Silke Ospelkaus, Travis Nicholson, M. L. Olsen, Paul S. Julienne, Carl Wieman, Jun Ye, D. S. Jin

Published Jul 23, 2008• 120 citations

Abstract

We report on the creation and characterization of heteronuclear $^{40}\text{K}^{87}\text{R}\text{b}$ Feshbach molecules in an optical dipole trap. Starting from an ultracold gas mixture of $^{40}\text{K}$ and $^{87}\text{R}\text{b}$ atoms, we create as many as 25 000 molecules at 300 nK by rf association. Optimizing the association process, we achieve a conversion efficiency of 25%. We measure the temperature dependence of the rf association process and find good agreement with a phenomenological model that has previously been applied to Feshbach molecule creation by slow magnetic-field sweeps. We also present a measurement of the binding energy of the heteronuclear molecules in the vicinity of the Feshbach resonance and provide evidence for Feshbach molecules as deeply bound as 26 MHz.

DOI: 10.1103/physreva.78.013416

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We report on the creation and characterization of heteronuclear

^{40}\text{K}^{87}\text{R}\text{b}

Feshbach molecules in an optical dipole trap. Starting from an ultracold gas mixture of

^{40}\text{K}

and

^{87}\text{R}\text{b}

atoms, we create as many as 25 000 molecules at 300 nK by rf association. Optimizing the association process, we achieve a conversion efficiency of 25%. We measure the temperature dependence of the rf association process and find good agreement with a phenomenological model that has previously been applied to Feshbach molecule creation by slow magnetic-field sweeps. We also present a measurement of the binding energy of the heteronuclear molecules in the vicinity of the Feshbach resonance and provide evidence for Feshbach molecules as deeply bound as 26 MHz.

We report on the creation of ultracold heteronuclear molecules assembled from fermionic 40K and bosonic 87Rb atoms in a 3D optical lattice. Molecules are produced at a heteronuclear Feshbach resonance on both the attractive and the repulsive sides of the resonance. We precisely determine the binding energy of the heteronuclear molecules from rf spectroscopy across the Feshbach resonance. We characterize the lifetime of the molecular sample as a function of magnetic field and measure lifetimes between 20 and 120 ms. The efficiency of molecule creation via rf association is measured and is found to decrease as expected for more deeply bound molecules.

We report on the observation of ultracold heteronuclear Feshbach molecules. Starting with a

^{87}\mathrm{Rb}

Bose-Einstein condensate and a cold atomic gas of

^{85}\mathrm{Rb}

, we utilize previously unobserved interspecies Feshbach resonances to create up to 25 000 molecules. Even though the

^{85}\mathrm{Rb}

gas is nondegenerate, we observe a large molecular conversion efficiency due to the presence of a quantum degenerate

^{87}\mathrm{Rb}

gas; this represents a key feature of our system. We compare the molecule creation at two different Feshbach resonances with different magnetic-field widths. The two Feshbach resonances are located at $265.44\ifmmode\pm\else\textpm\fi{}0.15\text{ }\mathrm{G}$ and $372.4\ifmmode\pm\else\textpm\fi{}1.3\text{ }\text{ }\mathrm{G}$. We also directly measure the small binding energy of the molecules through resonant magnetic-field association.

We present a detailed analysis of the production efficiency of weakly bound heteronuclear

^{40}\mathrm{K}^{87}\mathrm{Rb}

Feshbach molecules using radio-frequency association in a harmonic trap. The efficiency was measured in a wide range of temperatures, binding energies, and radio frequencies. A comprehensive analytical model is presented, explaining the observed asymmetric spectra and achieving good quantitative agreement with the measured production rates. This model provides a deep understanding of the molecule association process and paves the way for future experiments which rely on Feshbach molecules, e.g., for the production of deeply bound molecules.

We report the first creation of a bulk sample of ultracold heteronuclear p-wave Feshbach molecules in an optically trapped Bose-Bose mixture of 23Na and 87Rb atoms. Using loss spectroscopy and binding energy measurements, we systematically characterize the interspecies p-wave Feshbach resonances near 284 G. Leveraging this understanding, we use magneto-association to form p-wave NaRb Feshbach molecules, producing both pure samples and mixtures of molecules in different p-wave orbitals. We further measure the molecular lifetime and identify atom-molecule and molecule-molecule collisions as the dominant loss mechanisms. This work establishes a previously unavailable ultracold molecule platform that combines orbital anisotropy with heteronuclear constituents, represents a significant step toward realizing tunable p-wave interactions in Bose-Bose mixtures, and provides a foundation for exploring non-zero angular momentum molecules.