Biomedical subjects

K Bongs

Publications and source records attributed to K Bongs.

8 recordsLinked to original sources

PubMed2006

Ultracold heteronuclear molecules in a 3D optical lattice.

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.

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PubMed2006

Tuning of heteronuclear interactions in a degenerate Fermi-Bose mixture.

We demonstrate tuning of interactions between fermionic 40K and bosonic 87Rb atoms by Feshbach resonances and access the complete phase diagram of the harmonically trapped mixture from phase separation to collapse. On the attractive side of the resonance, we observe a strongly enhanced mean-field energy of the condensate due to the mutual mean-field confinement, predicted by a Thomas-Fermi model. As we increase heteronuclear interactions beyond a threshold, we observe an induced collapse of the mixture. On the repulsive side of the resonance, we observe vertical phase separation of the mixture in the presence of the gravitational force, thus entering a completely unexplored part of the phase diagram of the mixture. In addition, we identify the 515 G resonance as p wave by its characteristic doublet structure.

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PubMed2006

Magnetically tuned spin dynamics resonance.

We present the experimental observation of a magnetically tuned resonance phenomenon in the spin mixing dynamics of ultracold atomic gases. In particular, we study the magnetic field dependence of spin conversion in F=2 (87)Rb spinor condensates in the crossover from interaction dominated to quadratic Zeeman dominated dynamics. We discuss the observations in the framework of spin dynamics as well as matter wave four wave mixing. Furthermore, we show that the validity range of the single mode approximation for spin dynamics is significantly extended at high magnetic field.

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PubMed2006

Localization of bosonic atoms by fermionic impurities in a three-dimensional optical lattice.

We observe a localized phase of ultracold bosonic quantum gases in a 3-dimensional optical lattice induced by a small contribution of fermionic atoms acting as impurities in a Fermi-Bose quantum gas mixture. In particular, we study the dependence of this transition on the fermionic (40)K impurity concentration by a comparison to the corresponding superfluid to Mott-insulator transition in a pure bosonic (87)Rb gas and find a significant shift in the transition parameter. The observed shift is larger than expected based on a simple mean-field argument, which indicates that disorder-related effects play a significant role.

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PubMed2006

Interaction-driven dynamics of 40K- 87Rb Fermion-Boson gas mixtures in the large-particle-number limit.

We have studied effects of interspecies attraction in a Fermi-Bose mixture over a large regime of particle numbers in the 40K-87Rb system. We report on the observation of a mean-field driven collapse at critical particle numbers of 1.2 x 10(6) 87Rb atoms in the condensate and 7.5 x 10(5) 40K atoms consistent with mean-field theory for a scattering length of aFB = -284a(0). For large overcritical particle numbers, we see evidence for revivals of the collapse. Part of our detailed study of the decay dynamics and mechanisms is a measurement of the (87Rb- 87Rb- 40K) three-body loss coefficient K3 = (2.8 +/- 1.1) x 10(-28) cm6/s, which is an important parameter for dynamical studies of the system.

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PubMed2004

Soliton trains in Bose-Fermi mixtures.

We theoretically consider the formation of bright solitons in a mixture of Bose and Fermi degenerate gases. While we assume the forces between atoms in a pure Bose component to be effectively repulsive, their character can be changed from repulsive to attractive in the presence of fermions provided the Bose and Fermi gases attract each other strongly enough. In such a regime the Bose component becomes a gas of effectively attractive atoms. Hence, generating bright solitons in the bosonic gas is possible. Indeed, after a sudden increase of the strength of attraction between bosons and fermions (realized by using a Feshbach resonance technique or by firm radial squeezing of both samples) soliton trains appear in the Bose-Fermi mixture.

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PubMed2004

Dynamics of F=2 spinor Bose-Einstein condensates.

We experimentally investigate and analyze the rich dynamics in F=2 spinor Bose-Einstein condensates of 87Rb. An interplay between mean-field driven spin dynamics and hyperfine-changing losses in addition to interactions with the thermal component is observed. In particular, we measure conversion rates in the range of 10(-12) cm(3) s(-1) for spin-changing collisions within the F=2 manifold and spin-dependent loss rates in the range of 10(-13) cm(3) s(-1) for hyperfine-changing collisions. We observe polar behavior in the F=2 ground state of 87Rb, while we find the F=1 ground state to be ferromagnetic. We further see a magnetization for condensates prepared with nonzero total spin.

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PubMed2002

Bose-Einstein condensation in dilute atomic gases.

Bose-Einstein condensation is one of the most curious and fascinating phenomena in physics. It lies at the heart of such intriguing processes as superfluidity and superconductivity. However, in most cases, only a small part of the sample is Bose-condensed and strong interactions are present. A weakly interacting, pure Bose-Einstein condensate (BEC) has therefore been called the "holy grail of atomic physics". In 1995 this grail was found by producing almost pure BECs in dilute atomic gases. We review the experimental development that led to the realization of BEC in these systems and explain how BECs are now routinely produced in about 25 laboratories worldwide. The tremendous experimental progress of the past few years is outlined and a number of recent experiments show the current status of the field. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00114-001-0277-8.

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