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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Ultracold Heteronuclear Molecules created from Quantum Gases

C. Ospelkaus, Silke Ospelkaus, Leif Humbert, Philipp T. Ernst, K. Sengstock, Kai Bongs, F. Deuretzbacher, K. Plassmeier, Daniela Pfannkuche

Published Jun 1, 2007• 0 citations
Publisher

Abstract

This work discusses the first creation of long-lived heteronuclear molecules made from fermionic40K and bosonic87Rb atoms. A suppression of collisions is achieved by the creation and storage of individual molecules in separate wells of an optical lattice. In particular, a quantum degenerate Fermi-Bose mixture in a 3D optical lattice is obtained, the magnetic field close to an interspecies Feshbach resonance is tuned, and the rf association of the atoms is performed.

DOI
10.1109/cleoe-iqec.2007.4386709

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This work discusses the first creation of long-lived heteronuclear molecules made from fermionic40K and bosonic87Rb atoms. A suppression of collisions is achieved by the creation and storage of individual molecules in separate wells of an optical lattice. In particular, a quantum degenerate Fermi-Bose mixture in a 3D optical lattice is obtained, the magnetic field close to an interspecies Feshbach resonance is tuned, and the rf association of the atoms is performed.
This PhD tutorial article is a review of our experiments on heteronuclear quantum gas mixtures at the University of Hamburg. We introduce basic properties of trapped Fermi-Bose mixtures and demonstrate the achievement of large quantum degenerate mixtures of 40K and 87Rb. Using heteronuclear Feshbach resonances, we show how the heteronuclear interaction can be tuned, allowing us to induce phase separation and collapse for large repulsive and attractive interactions, respectively. We realize Fermi-Bose mixtures in 3D optical lattices as a novel quantum many-body system and study coherence properties of the mixture. Combining our experiments on lattices and Feshbach resonances, we present the first realization of ultracold heteronuclear Feshbach molecules. The molecules are created at individual sites of a 3D optical lattice. We discuss lifetime, binding energy and rf association efficiency in terms of a universal model and give an outlook for possible future developments.
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.
This thesis reports on experiments with quantum degenerate atomic mixtures and molecular gases at ultracold temperatures.The work describes the first realization of a quantum degenerate Fermi-Fermi mixture of two different species with unequal masses.In addition, the first quantum degenerate three-species mixture is realized.Furthermore, the first heteronuclear bosonic molecules with temperatures close to quantum degeneracy are created from a two-species mixture.Within this work a new and very versatile experimental platform to study quantum degenerate two-species Fermi mixtures is presented.The experimental concept relies on sympathetic cooling of two fermionic species ( 40 K and 6 Li) by a large bosonic gas ( 87 Rb).It is shown that large atom numbers and reliable operation are guaranteed by careful choice of the experimental components and parameters, which is essential to deal with the complexity of such an experimental platform with three atomic species.The first important milestone towards quantum degeneracy is realized by simultaneous trapping 87 Rb, 40 K and 6 Li in a magneto-optical trap.This marks the first realization of magneto-optical trapping of two fermionic species and also of three species.To achieve quantum degeneracy, different experimental challenges and difficulties of the three species with very different initial temperatures, scattering cross sections and masses were overcome.A combined compressed MOT and temporal dark MOT phase, a careful state cleaning process during the cooling process, species selective evaporative cooling of rubidium and removing of high energetic lithium atoms turn out to be essential for the successful realization of a quantum degenerate Fermi-Fermi-Bose mixture.Furthermore, at the end of the sympathetic cooling process, the cooling efficiency of lithium is improved by catalytic cooling through potassium.A quantum degenerate Fermi-Fermi mixture can be realized in the strongly interacting regime at a s-wave Feshbach resonance.By an adiabatic magnetic field sweep across the Feshbach resonance ultracold bosonic heteronuclear molecules are created with high efficiencies of up to 50 %.The associated number of molecules are up to 4 × 10 4 molecules, which is the largest number of heteronuclear molecules produced so far.Furthermore, close to resonance an increased molecular lifetime of more than 100 ms is observed.Therefore, this is the first system that may be used to explore many-body physics of a heteronuclear mixture in the strongly interacting regime across a Feshbach resonance.The heteronuclear Fermi mixture adds the mass ratio and the different internal structure as new parameters to quantum degenerate Fermi gases.The molecular cloud being close to quantum degeneracy marks the first starting point for the realization of a heteronuclear molecular BEC and to investigate the BEC-BCS crossover with unequal masses.Moreover, the molecules can be transferred into the rovibrational ground state to create a polar BEC with an anisotropic, long-range interaction.
We report on the observation of ultracold heteronuclear Feshbach molecules. Starting with a 87Rb^{87}\mathrm{Rb}87Rb Bose-Einstein condensate and a cold atomic gas of 85Rb^{85}\mathrm{Rb}85Rb, we utilize previously unobserved interspecies Feshbach resonances to create up to 25 000 molecules. Even though the 85Rb^{85}\mathrm{Rb}85Rb gas is nondegenerate, we observe a large molecular conversion efficiency due to the presence of a quantum degenerate 87Rb^{87}\mathrm{Rb}87Rb 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.