No abstract available

[en] We derive the equilibrium conditions for a thermal atom-molecule mixture near a Feshbach resonance. Under the assumption of low collisional loss, thermodynamical properties are calculated and compared to the measurements of a recent experiment on thermal fermionic lithium atoms. We discuss and evaluate possible collision mechanisms which can lead to atom-molecule conversion. Finally, we propose a novel evaporative cooling scheme to efficiently cool the molecules toward Bose-Einstein condensation

[en] We study three-body recombination in an optically trapped ultracold gas of cesium atoms with precise magnetic control of the s-wave scattering length a. At large positive values of a, we measure the dependence of the rate coefficient on a and confirm the theoretically predicted scaling proportional to a⁴. Evidence of recombination heating indicates the formation of very weakly bound molecules in the last bound energy level

[en] In the year 2005, we obtained first evidence for the existence of weakly bound quantum states of three resonantly interacting particles, as predicted 35 years earlier by Vitaly Efimov. In our laboratory, the striking signature of an Efimov state was a giant three-body loss resonance observed in a gas of cesium atoms that was evaporatively cooled to temperatures of about 10 nano kelvin. Here, I will give a short personal account on what prepared the ground for this observation, on how things finally happened in our laboratory, and on how our experiments then developed further. (author)

No abstract available

[en] We report on measurements of three-body recombination at negative scattering lengths in an ultracold cesium gas. Magnetic tuning of the scattering length by means of a Feshbach resonance is used to investigate a strong loss peak resulting from an Efimov resonance. The position of maximum loss shifts significantly when the temperature of the gas is varied, providing quantitative insight into the evolution of an Efimov state into a triatomic continuum resonance. We compare our measurements with several calculations that extend the theory of three-body recombination to non-zero collision energies. In our apparatus we prepare an ultracold gas of cesium atoms in an optical surface trap. The main part is a glass cell with an integrated prism, providing good optical access and accurate and fast control of the magnetic field. The atoms are located a few micrometers above the dielectric prism surface. Raman sideband and Sisyphus cooling are applied to reach temperatures of a few μK. We further reduce the temperature below 100 nK via evaporative cooling. We then apply different magnetic fields and measure the rate of three-body recombination

[en] We report on measurements of three-body recombination at negative scattering lengths in an ultracold cesium gas. Magnetic tuning of the scattering length by means of a Feshbach resonance is used to investigate a strong loss peak resulting from an Efimov resonance. The position of maximum loss shifts significantly when the temperature of the gas is varied, providing quantitative insight into the evolution of an Efimov state into a triatomic continuum resonance. We compare our measurements with several calculations that extend the theory of three-body recombination to non-zero collision energies. In our apparatus we prepare an ultracold gas of cesium atoms in an optical surface trap. The main part is a glass cell with an integrated prism, providing good optical access and accurate and fast control of the magnetic field. The atoms are located a few micrometers above the dielectric prism surface. Raman sideband and Sisyphus cooling are applied to reach temperatures of a few μK. We further reduce the temperature below 100 nK via evaporative cooling. We then apply different magnetic fields and measure the rate of three-body recombination

[en] Ultracold atomic gases are versatile systems to study few-body physics because of full control over the external and internal degrees of freedom and the magnetic tunability of the scattering properties using Feshbach resonances. Here we experimentally study three- and four-body physics by investigating ultracold (30-250 nK) atom-dimer and dimer-dimer collisions with Cs Feshbach molecules in various molecular states and Cs atoms in different hyperfine states. Resonant enhancement of the atom-dimer relaxation rate is observed in a system of three identical bosons and interpreted as being induced by a trimer state, possibly an Efimov state. A strong magnetic field dependence of the relaxation rate is also observed when the atoms are transferred to a different hyperfine sublevel. For dimer-dimer collisions we have observed an unexpected temperature dependence and a suppression of the collisional loss rate

[en] We present our recent work on ultracold cesium Feshbach molecules in an optical dipole trap. We have implemented a new crossed-beam laser trap, which traps atoms and molecules simultaneously. By scanning one laser beam the ellipticity can be dynamically tuned for an optimal trap configuration. We routinely prepare ultracold mixed atomic and molecular or pure molecular samples at temperatures down to 30 nK. We selectively populate Feshbach molecules in various s-, d-, g- and even l-wave states. We have experimentally demonstrated that the l-wave dimers can be stable against spontaneous decay on the timescale of one second well above the dissociation threshold. We have recently implemented the technique of resonantly modulated magnetic field spectroscopy. Transitions between the atomic continuum and dimer states, and vice versa, as well as dimer-dimer transitions can be driven. Our main motivation is to apply this technique to search for trimer and tetramer states, whose presence has been indicated by resonances in collisional loss measurements

[en] In the last few years there has been a growing interest in the in the area of heteronuclear ultracold quantum gases and the production of heteronuclear molecules via Feshbach resonances. We present the first observation of heteronuclear Feshbach resonances in a mixture of ultracold ⁸⁷Rb and ¹³³Cs. We give an overview about our experimental setup and the procedure of sample preparation. One of the key ingredients to reach the ultracold limit is the implementation of simultaneous degenerate Raman sideband cooling on both species. This cooling technique allows us to get around 10⁸ atoms, fully polarized in the lowest magnetic sublevel at a temperature of ∝1μK in a crossed dipole trap. We discuss the next steps towards double degeneracy and present our approach to produce ground state RbCs molecules starting from weakly bound Feshbach molecules